ALBERT

Description: The health of Corymbia calophylla (marri), a keystone tree species in the native forests of southwest Western Australia, has been in decline for the past few decades. Phytophthora root disease and waterlogging have often been cited as contributing to this decline. Traditional methods (i.e., field surveys and sampling) of mapping Phytophthora root infection in the field are time-consuming and expensive; thus, the potential of reflectance spectroscopy to characterize marri response to Phytophthora and waterlogging stress was investigated. Twelve-month old marri plants were infected with either P. cinnamomi or P. multivora in two glasshouse trials and waterlogged for 24 h each fortnight. Spectral measurements with a portable high-resolution spectroradiometer were taken weekly. Plant biophysical measurements were taken at harvest time. Normalized difference spectral index (NDSI) was calculated for every combination of reflectance values between 400 and 2500 nm for all time points, correlated with the treatment effects and displayed as heat maps. Narrowband vegetation indices (VIs), utilizing different wavelengths of the electromagnetic spectrum, were also calculated from the spectral data. The Phytophthora treatments did not cause significant differences with the biophysical measurements in both trials. In the second trial, the waterlogging treatment significantly lowered plant top dry weight (P = 0.016) and diameter (P = 0.044). Reflectance values plotted against wavelength displayed differences between treatments as well as a seasonal trend. The NDSI heat maps indicated that the Phytophthora and waterlogging treatment effects were strongest correlated with bandwidths in the visible and near-infrared portions of the electromagnetic spectrum (538–558 nm and 701–709 nm). Six of the VIs (normalized difference nitrogen index 2, anthocyanin reflectance index 1, photochemical reflectance index, Carter index 1, Vogelman index 3 and water band index) were able to track the biochemical changes in the leaves over the 10 weeks, confirming the seasonal trend. The interaction effect between P. cinnamomi, waterlogging and elapsed time in the first trial was significant for water band index (P = 0.010). This study demonstrates that reflectance spectroscopy holds promise for characterizing marri response but more work needs to be done to identify the optimum wavelengths for identifying Phytophthora and waterlogging stress with marri.

Description: Methods for the three-dimensional (3D) reconstruction of forest trees have been suggested for data from active and passive sensors. Laser scanner technologies have become popular in the last few years, despite their high costs. Since the improvements in photogrammetric algorithms (e.g. structure from motion—SfM), photographs have become a new low-cost source of 3D point clouds. In this study, we use images captured by a smartphone camera to calculate dense point clouds of a forest plot using SfM. Eighteen point clouds were produced by changing the densification parameters (Image scale, Point density, Minimum number of matches) in order to investigate their influence on the quality of the point clouds produced. In order to estimate diameter at breast height (d.b.h.) and stem volumes, we developed an automatic method that extracts the stems from the point cloud and then models them with cylinders. The results show that Image scale is the most influential parameter in terms of identifying and extracting trees from the point clouds. The best performance with cylinder modelling from point clouds compared to field data had an RMSE of 1.9 cm and 0.094 m3, for d.b.h. and volume, respectively. Thus, for forest management and planning purposes, it is possible to use our photogrammetric and modelling methods to measure d.b.h., stem volume and possibly other forest inventory metrics, rapidly and without felling trees. The proposed methodology significantly reduces working time in the field, using ‘non-professional’ instruments and automating estimates of dendrometric parameters.

Description: Emerald ash borer (EAB), an invasive forest insect from Asia, has impacted vast areas in the United States and European Russia. To proactively understand the social impact of an EAB invasion in Europe and the USA, this study analyzed visitors’ preferences and preference heterogeneity for EAB-impacted forest scenarios in Vienna, Austria (n = 510) and Minneapolis, USA (n = 307). An image-based discrete choice experiment with latent-class analysis among on-site completed questionnaires in Vienna indicated four different visitor segments based on trade-offs among biophysical, social and viewscape elements. Within the forested environment, two segments placed greater importance on (bio)physical attributes and two on social aspects. Although all segments preferred a non-impacted ash forest, only one of the four identified the attribute describing EAB impacts and forest management as the most important attribute. Rather, visitor numbers and background viewscapes were more important than EAB impact and management to differentiate landscape preferences for three of the four segments. Differences in preferences were found between the Vienna and Minneapolis samples. Vienna respondents showed a higher preference for more natural conditions, disliked more the initial stage of EAB impact and placed more importance on background viewscapes and visitor numbers. Forest managers and greenspace planners need to consider the entirety of the forested condition, social and visual, for effective management and address that visitors differ in their preferences for all of these conditions.

Description: Collaboration has been the key to success for urban forest management in Colorado, not only collaboration amongst agencies at all levels of government but also in engaging industry allies, coordinating education and outreach efforts and in fostering community support. A unique interagency team, the Emerging Pests in Colorado (EPIC) Workgroup, was formed in 2009 to address the immediate threat from Thousand Cankers Disease (TCD) of walnut and to plan for the arrival of other invasive urban forest pests to Colorado. When the emerald ash borer (Agrilus planipennis Fairmaire) (EAB) was detected in Boulder, Colorado in 2013, it marked the westernmost occurrence of EAB in the US, threatening millions of planted and naturalized ash trees representing over 25 percent of the tree canopy throughout Colorado’s urban and riparian forests. The detection in Boulder prompted the development of a second multi-agency group, the Colorado EAB Response Team (CORT). The preparedness and established working relationships between stakeholders and responsible authorities allowed for a quick, decisive and unified response. We review as a case study: (1) the formation and history of collaborative interagency groups in Colorado; (2) how the interagency collaborative planning and post-detection EAB response have supported community forestry programmes throughout the state; (3) development of the post-detection EAB management plan and economics behind the strategy in Boulder, Colorado; and (4) the proactive EAB planning and outreach efforts underway in Denver, Colorado.

Description: Harvesting practices in temperate mixedwoods of eastern North America have a history of diameter-limit cuts, which have often resulted in degraded residual stands. In this study, we examined the factors influencing stand basal area (BA) and tree diameter growth in previously high-graded mixedwood forests, to understand which stands are more likely to recover from high-grading. Over 15 years, we monitored tree growth, recruitment and stem quality of 532 sample plots that were located in high-graded stands of Quebec’s mixedwood forest. We found that diameter growth rates were positively correlated with precipitation-related variables for balsam fir (Abies balsamea) and for yellow birch (Betulla alleghaniensis) but opposing trends for temperature-related variables were found. Conversely to balsam fir, yellow birch growth was positively correlated to temperature variables. Our results also show that BA growth was greater for plots with a larger acceptable growing stock (AGS: trees with potential sawlog production) and that the increase in AGS was greater for plots with larger amount of conifer BA. These result highlights the importance to maintain a proportion of conifer trees in these mixed stands. Moreover, the significant effect of asymmetric competition in our study underscores the relevance of considering the spatial distribution when choosing crop trees.

Description: European ash (Fraxinus excelsior L.) is a highly valued native species in the UK and elsewhere. The rapid spread and predicted impact of ash dieback (caused by Hymenoscyphus fraxineus), has led researchers to explore a range of responses from introducing non-native ash to use of Genetic Modification (GM) technologies to develop disease resistance. To support decisions over which approaches should receive further investment to encourage adoption, it is necessary to understand what is acceptable to forest practitioners. Interviews with 22 forest advisors and managers revealed ash is highly valued for the multiple benefits it provides but past experiences with pest and diseases have encouraged a more cautious (‘wait and see’) attitude to approaches for dealing with ash dieback. These practitioners showed a strong interest in the concept of resistant ash but emphasized that any ‘new’ varieties should have similar characteristics, retain genetic diversity and be able to withstand future pests. There was limited support for planting non-native ash and use of GM methods and greater support for traditional breeding, though views varied dependent upon objectives and could evolve with experience countering the disease. There were concerns about the time required to produce resistant varieties and more information was needed about the costs, benefits and impacts of the different approaches. These findings point to the need for continued communication and engagement with stakeholders in the refinement of responses to dieback and any development of resistant ash.

Description: In this study, we investigate the relationship between the mean wind-induced load on an open-grown oak tree and the mean wind speed. The estimation of the wind load is based on bending moment observations on the stem, using strain gauges installed close to the base of the tree. The measurement campaign included periods where the crown was both with and without foliage. A new post-processing method to compensate for time- and temperature-dependent drifts of long-term strain gauge measurements is presented. The time-scale, at which the method is applied, is determined from the observed high coherence between the wind speed and the induced bending moments. The analysis shows that the wind load on the tree is proportional to the wind speed raised to an exponent of 1.60–1.68 and 1.90–2.01 in the case of a crown with and without leaves, respectively. The results indicate that the presence of foliage increases the wind-induced load by a factor of 2–3. The impact of the wind speed range on these results is discussed and compared to the measured wind deficit in the lee of the tree. The application of this method can potentially be extended to other tree mounted sensors.

Description: Mixed mountain forests of European beech (Fagus sylvatica L.), Norway spruce (Picea abies (L.) Karst), and silver fir (Abies alba Mill.) cover a total area of more than 10 million hectares in Europe. Due to altitudinal zoning, these forests are particularly vulnerable to climate change. However, as little is known about the long-term development of the productivity and the adaptation and mitigation potential of these forest systems in Europe, reliable information on productivity is required for sustainable forest management. Using generalized additive mixed models this study investigated 60 long-term experimental plots and provides information about the productivity of mixed mountain forests across a variety of European mountain areas in a standardized way for the first time. The average periodic annual volume increment (PAI) of these forests amounts to 9.3 m3ha−1y−1. Despite a significant increase in annual mean temperature the PAI has not changed significantly over the last 30 years. However, at the species level, we found significant changes in the growth dynamics. While beech had a PAI of 8.2 m3ha−1y−1 over the entire period (1980–2010), the PAI of spruce dropped significantly from 14.2 to 10.8 m3ha−1y−1, and the PAI of fir rose significantly from 7.2 to 11.3 m3ha−1y−1. Consequently, we observed stable stand volume increments in relation to climate change.

Description: A wealth of recent research has improved our understanding of the structure, growth and yield of mixed-species stands. However, appropriate quantitative concepts for their silvicultural regulation remain scarce. Due to the species-specific stand densities, growing area requirements and potential over-density, the density and mixing regulation in mixed stands is much more intricate than in monospecific stands. Here, we introduce the species-specific coefficients: density equivalence coefficients (DEC), for density equivalence; and density modification coefficient (DMC), for density modification in mixed species stands. DEC is suitable for the conversion of the stand density and growing area requirement of one species into that of another species. DMC estimates the modification of maximum stand density by tree species mixing using as reference the maximum stand density of one of the species. First, we introduce the theoretical concept of these coefficients. Second, we derive the mean values of these coefficients based on long-term experiments using different mixtures of European beech. Third, we apply DEC and DMC for flexible regulation of the stand density and mixing proportion. Thus, silvicultural regulation of monospecific stands and mixed-species stands forms a continuum, where monospecific stands represent an extreme case of mixed-species stands. Lastly, we discuss the advantages and limitations of these concepts. Future directions comprise the inclusion of additional species, their integration in guidelines and simulation models, and their establishment for the quantitative regulation of experimental plots and the practical implementation in forest stands.

Description: Tree growth is expected to be responsive to climatic drivers across a spectrum of temporal scales, ranging from yearly growth to daily water use and photosynthesis. Automatic dendrometers offer the potential to provide continuous high-resolution measurements of tree radius changes. The signal recorded contains three components: (1) a long-term seasonal growth component, (2) a mid-term component representing swelling after rainfall and subsequent drying and (3) daily cycles of water-uptake related to tree transpiration. For 91 trees at 4 sites (Picea abies: 58, Pinus cembra: 17, Fagus sylvatica: 14, Pinus sylvestris: 2) monitored in Austria between 2012 and 2015, we simultaneously modelled these three processes using a hierarchical nonlinear mixed-effects model represented by two logistic growth curves. The focus was on the mid-term and daily component, and therefore long-term growth that is typically modelled by including tree size, competition or site variables was represented by random effects only. Both mid-term and short-term components were species-specific. In general, P. cembra and F. sylvatica were less sensitive to climate variables than P. abies. For all species, the mid-term component was best represented using a 14-day moving average difference between rainfall and potential evapotranspiration, a 24-h moving average of precipitation and its 1–3 days lags, a 24-h moving average temperature and its 1–3 days lags. The daily cycles of water uptake were best related to hourly humidity and its 3-h lag, and interactions with the 14-day moving average difference between rainfall and potential evapotranspiration accounted for attenuating cycles after rainy events and increasing cycles in dry periods.

Description: This paper presents a spatially explicit methodology for integrated forest management and wood supply chain optimization over time in the context of a Finnish forest strategy anticipating new investments and renewal of business in the wood processing industry. The Finnish MELA simulator was used to generate multiple treatment schedules over time at the management unit level – each treatment schedule providing unique estimates of extracted wood volumes by different assortment categories for each time period. The J linear programming (LP) software was used to analyse different regional forest strategies in terms of wood supply and transportation costs to multiple market destinations. The analysis revealed clear differences both in wood flows and forest resources between strategies maximizing wood supply or optimizing wood supply to market destinations. In addition, the wood flows appeared responsive to new mill and increased demand. Further, the changes in factory price had a heavier impact on pulpwood supply than on sawlog supply. The same methodology can be applied for analysing the impact of new factories on wood flows from forest to factories and between factories or to support forest enterprises in planning their wood supply over multiple time periods and multiple destinations.

Description: The Asian chestnut gall wasp (ACGW), Dryocosmus kuriphilus (Hymenoptera: Cynipidae), is an invasive pest that affects chestnut trees. The first record of this pest in Spain was in 2012, in Catalonia, and it is now distributed in virtually every chestnut growing area in the country. In this study, we present an overview of parasitoid recruitment by ACGW in Catalonia over a 4-year period (2013–2016) comparing parasitoid communities attacking galls on oak and chestnut trees at the same sites. A total of 22 species of native parasitoids that normally attack oak cynipids emerged from ACGW galls, together with the non-native Torymus sinensis. The most abundant species were Bootanomyia dorsalis, Torymus flavipes, Ormyrus pomaceus and Eupelmus urozonus. The study also found that 20 of the 22 native parasitoids in ACGW galls were also reared from galls of 13 species of oak gall inducer (12 Cynipidae, 1 Cecidomyiidae).

Description: This study addresses the use of multiple sources of auxiliary data from unmanned aerial vehicles (UAVs) and airborne laser scanning (ALS) data for inference on key biophysical parameters in small forest properties (5–300 ha). We compared the precision of the estimates using plot data alone under a design-based inference with model-based estimates that include plot data and the following four types of auxiliary data: (1) terrain-independent variables from UAV photogrammetric data (UAV-SfM); (2) variables obtained from UAV photogrammetric data normalized using external terrain data (UAV-SfMDTM); (3) UAV-LS and (4) ALS data. The inclusion of remotely sensed data increased the precision of DB estimates by factors of 1.5–2.2. The optimal data sources for top height, stem density, basal area and total stem volume were: UAV-LS, UAV-SfM, UAV-SfMDTM and UAV-SfMDTM. We conclude that the use of UAV data can increase the precision of stand-level estimates even under intensive field sampling conditions.

Description: We present a recruitment model for pure and mixed beech and oak stands in Belgium, the first empirical model for this forest type in this geographical area. Data from the Wallonia National Forest Inventory were used to fit the model. We adopted a zero-inflated formulation where model parameters governing species’ behaviour were simultaneously fitted. Plot random effects specific to each species were included, the simultaneous fit allowing them to correlate. Model predictions proved accurate and corresponded to current ecological knowledge about the regeneration dynamics of this kind of mixture. While our model could potentially be used to complement the existing beech and oak growth models for this region of Europe, our results also show that beech recruits tend to dominate regardless of the oak share in the overstorey composition and the stand stocking. This confirms that the beech–oak mixture may not be stable under the conditions of the study area and current management aimed at promoting continuous forest cover.

Description: Loblolly pine (Pinus taeda L.) is one of the most widely planted tree species globally. As the reliability of estimating forest characteristics such as volume, biomass and carbon becomes more important, the necessary resources available for assessment are often insufficient to meet desired confidence levels. Small area estimation (SAE) methods were investigated for their potential to improve the precision of volume estimates in loblolly pine plantations aged 9–43. Area-level SAE models that included lidar height percentiles and stand thinning status as auxiliary information were developed to test whether precision gains could be achieved. Models that utilized both forms of auxiliary data provided larger gains in precision compared to using lidar alone. Unit-level SAE models were found to offer additional gains compared with area-level models in some cases; however, area-level models that incorporated both lidar and thinning status performed nearly as well or better. Despite their potential gains in precision, unit-level models are more difficult to apply in practice due to the need for highly accurate, spatially defined sample units and the inability to incorporate certain area-level covariates. The results of this study are of interest to those looking to reduce the uncertainty of stand parameter estimates. With improved estimate precision, managers, stakeholders and policy makers can have more confidence in resource assessments for informed decisions.

Description: The southernmost portion of the Andes in South America hosts Nothofagaceae forests that form ectomycorrhizal (EcM) associations. We compiled all the published reports of EcM taxa from these woodlands, based on fruit-body collections and molecularly identified root tips. This resulted in 87 peer-reviewed research papers dealing with EcM associations from Nothofagaceae forests published over the past 62 years. Based on these papers the EcM richness and its association with Nothofagaceae species was analyzed. Represented by 45 genera (34 Basidiomycetes and 11 Ascomycetes), 479 EcM taxa have been recorded, plus an additional 46 EcM taxa which are potentially EcM. Cortinarius was the most frequent and diverse genus, with 64.9% of total species. Nothofagus dombeyi had the highest number of unique EcM species, followed by N. pumilio, N. antarctica and Lophozonia obliqua. The EcM community associated with Nothofagus species, except N. nitida, showed higher similarities among themselves, than with Lophozonia and Fuscospora species. Beta diversity indexes showed EcM Nothofagus species have 29–42% niche overlap, while Nothofagus—Lophozonia only had 1–16%. The assessment of the accuracy of the EcM diversity, host specificity and community structure deserve further studies combining phylogenetic analysis based on broad ecological surveys. On the basis of pre-selected criteria Austropaxillus statuum, Cortinarius fragilis, Cortinarius xiphidipus and Hallingea purpurea are proposed as candidates for nursery spore inoculations, and should be subject to scientific evaluation to determine costs and benefits.

Description: Modern silviculture is based on simulating natural disturbance regimes on the one side and reducing their impact on the other side. Disturbances modify light regimes of forests along complex spatial patterns, and species participating in the ecosystem tend to have unique adaptations to the multitude of light conditions found in forests. We studied the height growth reaction of saplings from eight native North American tree species to different light availabilities in a Sierra Nevada mixed conifer forest. Large height growth differences occurred between species. Height growth increased for most species with increasing light availability. However, black oak but also incense cedar and tanoak reached an optimal value or saturation point of light availability at intermediate light levels, above which their growth stayed the same or slightly declined on average. A variety of stand conditions, representing the range from early to late successional stages, are beneficial to maintain tree species diversity across stands. Such a gradient of conditions can be achieved by diversifying silvicultural regimes and using regeneration approaches that mimic a range of disturbance intensities. The results add to knowledge on the species’ ecology by specifying their height growth in dependence of a quantified light environment. The quantification of the light environment can directly be linked to % canopy cover and a range of regeneration methods, respectively. With this, the results may help achieve a more precise and target-oriented management of Sierra Nevada mixed conifer forests.

Description: Knowledge of the spatial distribution of aboveground biomass (AGB) is crucial to guide forest conservation and management to maintain carbon stocks. LiDAR has been highly successful for this purpose, but has limited availability. Very-high resolution (

Description: The critically endangered Brazilian pine, also called araucaria, (Araucaria angustifolia (Bertol.) Kuntze) is a key species of the Araucaria moist forest (AMF, Mixed Ombrophilous Forest). Illegal timber extraction, agricultural conversion and severe degradation have reduced the AMF to only 13 per cent of its original cover, with climate change imposing additional challenges for cold adapted species such as araucaria. Previous studies have assessed climate change impacts on A. angustifolia, but have been limited by analysis constraints. Here, we used a machine learning technique to understand how land use and climate change might affect the distribution of A. angustifolia, and to evaluate the effectiveness of existing protected areas (PAs) to conserve this species. Our results demonstrated that despite the recent efforts to conserve the Atlantic Forest, conversion of natural habitats into forest plantation still occurs within araucaria’s distribution range. Our model predicted a drastic reduction in environmentally suitable areas for this species of up to 77 per cent in the coming decades. Also, the existing PAs show low efficacy to protect suitable areas in the future. Combined, these results suggest that A. angustifolia will be under great threat within the next few decades and the development of conservation strategies to save this species is essential. Ideally, the conservation programs should integrate in situ and on farm approaches, including forest management strategies. Although in situ strategies play an important role as gene banks, on-farm strategies can be used to promote the restoration and expansion of A. angustifolia populations in the areas predicted as suitable.

Description: Emerald ash borer (EAB) (Agrilus planipennis Fairmaire), discovered in southeastern Michigan, USA in 2002, has become the most destructive and costly invasive forest insect in North America. This phloem-boring beetle has also invaded Moscow, Russia and continued spread of EAB potentially threatens European ash (Fraxinus spp.) species. This review summarizes EAB life history, including interspecific variation in host preference, invasion impacts and challenges of detecting new infestations and provides an overview of available management tactics. Advances in systemic insecticides, particularly emamectin benzoate products applied via trunk injection, have yielded effective and practical options both to protect individual trees and to slow EAB population growth and ash decline on an area-wide basis without disrupting natural enemies. Economic costs of treating ash are substantially lower than removal costs, retain ecosystem services provided by the trees, reduce sociocultural impacts and conserve genetic diversity in areas invaded by EAB. Girdled ash trees are highly attractive to EAB adults in low-density populations and debarking small girdled trees to locate larval galleries is the most effective EAB detection method. An array of woodpeckers, native larval parasitoids and introduced parasitoids attack EAB life stages but mortality is highly variable. Area-wide management strategies that integrate insecticide-treated trees, girdled ash trap trees and biological control can be adapted for local conditions to slow and reduce EAB impacts.

Description: The proportion of mixed-species forests is presently increasing since they are commonly seen as providing a higher level of many ecosystem goods and services than monospecific stands. This may be due to a more complex three-dimensional distribution pattern of plant elements, which has often been noted, but to date rarely been quantified. In the present study, we used terrestrial laser scanning data to analyze the relationship between tree species mixing and stand structural complexity in three regions of Germany. We examined 60 forest plots representing commercially important and typical species combinations for Central Europe. The results showed an increasing but saturating relationship between stand structural complexity and tree species diversity. Moreover, we found that as the proportion of broadleaved trees increased, the stand structural complexity of coniferous stands also increased. Our study provides evidence that the conversion of monospecific conifer stands into mixed forests with broadleaved tree species as well as mixing tree species with interspecific differences in physiological and morphological traits can promote the development of structurally more complex stand structures.

Description: Spatially explicit information about stand-level Time Since the last stand-replacing Disturbance (TSD) is fundamental for modelling many forest ecosystem processes, but most of the current satellite remote sensing mapping approaches are based on change detection and time series analysis, and can detect only disturbances that have occurred since the start of the optical satellite data record. The spatial legacy of stand-replacing disturbances can however persist on the landscape for several decades to centuries, in the form of distinct horizontal and vertical stand structure features. We propose a new approach to reconstruct the long-term disturbance history of a forest, estimating TSD through stand-level analysis of LiDAR data, which are highly sensitive to the three-dimensional forest canopy structure. The study area is in the Nez Perce-Clearwater National Forest in north-central Idaho, where airborne LiDAR covering about 52,000 ha and ancillary TSD reference data for a period of more than 140 years were available. The root mean square difference (RSMD) between predicted and reference TSD was 17.5 years with a BIAS of 0.8 years; and on 72.8% of the stands the predicted TSD was less than 10 years apart from the reference TSD (78.2% of the stands when considering only disturbances occurred in the last 100 years). The results demonstrate that airborne LiDAR-derived data have enough explanatory power to reconstruct the long-term, stand-replacing disturbance history of temperate forested areas at regional scales.

Description: One of the main aims of EPPO is to help its member countries to prevent entry or spread of dangerous pests (plant quarantine). The Organization has therefore been given the task of identifying pests which may present a risk (early warning/horizon scanning), evaluating their risk for the region and making proposals on the phytosanitary measures which can be taken against them (Pest Risk Analysis). Standards are also developed, including standards on how to eradicate and control pests. In addition to the development of Standards, activities on communication and citizen science (development of guidelines on raising public awareness and the production of toolkits to use in raising awareness campaigns) have also recently been started. The EPPO Secretariat was alerted by the National Plant Protection Organization (NPPO) of Sweden in 2003, and Norway in 2010, to two potential new pests, Emerald ash borer (EAB), Agrilus planipennis (Fairmaire) and Bronze birch borer, Agrilus anxius (Gory) respectively. Because of the importance of these two pests for forest species in the EPPO region, member countries agreed that EPPO recommendations should be prepared. The different EPPO activities relevant to A. planipennis and A. anxius are presented, highlighting the challenges they currently pose to the region.

Description: We examined typhoon windthrow patterns in stand-scale permanent plots within three natural forests and the long-term dynamics of surviving trees in two of these plots. The aim was to verify whether pre-disturbance composition and structure affected windthrow damage and stand recovery. The stands, which were in Hokkaido, the northernmost main island of Japan, differed in pre-disturbance composition (coniferous, mixed and broadleaved stands) and structure, and the basal area losses by the windthrow event were 81–93 per cent. Tree mortality was significantly related to tree size (diameter at breast height) and species. The windthrow patterns differed among the three stands; and, windthrow severity was affected by the pre-disturbance composition and structure. The mortality of trees that survived the windthrow event was ~60 per cent in the two plots. The surviving trees comprised a majority of the canopy layer in the secondary stands. The relative basal area of surviving trees decreased rapidly with increasing tree density in the stand initiation stage but differed between plots. Consequently, the pre-disturbance composition and structure influenced windthrow severity, stand recovery and secondary succession in the recovered stands.

Description: About 70 million m3 was damaged by the storm Gudrun that hit southern Sweden in January 2005, i.e. almost as much as the normal annual cut for the whole country. To establish any differences in forest state and forest management before and after the storm, measures such as growing stock, annual growth, age-class distribution, choice of species in regeneration and cleaning and thinning activities were studied for the area affected and the area unaffected by the storm. For all analyses, sample plots from the Swedish National Forest Inventory were used. Results based on mean values for the periods 2000–2004/2006–2010/2012–2016 showed that the total growing stock for the damaged area decreased significantly by ~30 million m3 directly after the storm but has now recovered to the same level as before the storm. Therefore, it seems clear that forest owners and forest managers made rational choices when aiming to restore the forest area. As expected , the annually cleaned area and the area in immediate need of cleaning increased significantly in the Gudrun area after the storm. No other significant changes in behaviour to reduce future storm damage risk could be detected.

Description: The mechanical response of a well-instrumented Norway spruce (Picea abies L.) tree under controlled winch loading was monitored. The main aims of this study were to understand the tree-root-soil response to lateral pull loads, to examine the applicability of simple engineering principles to the tree-root-soil response and to introduce a soil component into the tree stability analysis. The stem response was recorded with tilt sensors at three different heights; two sensors at each height tracked the response in transverse directions. These data were used to derive deflection and bending moment profiles of the stem for different lateral loads. A root on the windward side and one on the leeward side were instrumented using strain gauges. The tree was winched to failure and the data were collected from the strain gauges during winching. Using the data obtained from strain gauges on the roots, strain, bending moment, shear force and deflection profiles the roots with increasing load were calculated. Using the soil reaction force-deflection profiles of the roots, equivalent spring stiffness constants were determined. An estimate of the anchorage strength and moment–rotation relationship was made using a simple characteristic curve equation normalized by the failure moment and rotation that can be modified for different soil conditions.

Description: This study investigated the influence of spacing, parental genotype and harvesting cycle on woody biomass production in open-pollinated families of the locally selected black locust (Robinia pseudoacacia L.) clones ‘Tsarevets’ and ‘Srebarna’ at specific site conditions. A Nelder experiment with 16, varying along the spokes, nearly-square spacings and two black locust families arranged in alternating sectors, was established in North Central Bulgaria. Alternative harvesting options (‘harvesting cycles’), consisting of one, two or three successive coppicings, were applied and the amounts of dry shoot dendromass collected per plant were accumulated to calculate and analyse the total yield of woody biomass, achievable within 2-, 3- and 4-year periods (‘production period’). The one-coppicing cycle proved superior for both families, regardless of the length of the production period. Biomass yield in the family of ‘Srebarna’ exceeded that of ‘Tsarevets’ at the wider spacings, when 1 and 2 year-old shoots were harvested, while dendromass production of ‘Tsarevets’ was substantially higher in the 4-year-old shoots. The woody biomass yield per plant increased with spacing, and growth tended to saturation at the lowest densities, enabling derivation of optimal planting densities. The total dendromass yield per hectare was maximized at growing space of around 0.5 m2 per plant for the 2-year production period, while spacing of 1.2–2 m2 was required for production periods of 3 and 4 years. If the results from this experiment can be reliably scaled up in practice then short rotation crops of ‘Srebarna’ and ‘Tsarevets’ families at comparable site conditions should be able to produce annual biomass yields of 9–11 Mg.ha−1.year−1 within a 4-year period, given the optimal planting densities and harvesting regimes prescribed.

Description: Fast-growing tree species will be an important tool in the future production of renewables and in substituting non-renewable fossil energy sources. Sweden, like other countries around the Baltic Sea, has large areas of abandoned farmland usable for biomass production, but knowledge of growth performance of tree species candidates is insufficient. An experiment was initiated where six potentially high-producing tree species were compared. The best available plant material for each species was used on five sites over latitudes 56–64°N in Sweden. Results from the first 8–9 years are reported. Short rotation coppice willow (Salix schwerinii Wolf × S. viminalis L., clone ‘Tora’) had the fastest initial growth and production in southern Sweden. Hybrid aspen (Populus tremula L. × P. tremuloides Michx.) and poplar (Populus spp., section Tacamahaca), grown as short rotation forest, grew well over all sites and showed the highest productivity at the two northern sites. Hybrid larch (Larix ×eurolepis Henry) displayed a high potential at the two most southerly sites, whilst silver birch (Betula pendula Roth) was a medium-producing species at all sites. Norway spruce (Picea abies (L.) Karst.) started slowly, and Siberian larch (L. sukaczewii Dylis) produced poorly at the two northern sites in the initial stage. All tree species followed existing height development curves for the respective species on a high site quality level. Currently, well-growing clones of Populus spp. indicated that a wider selection of tree species can be used at high latitudes under climate change. The study showed a high growth potential for most species on former agricultural lands. However, measures to reduce climate and biological damage must be included in future efforts.

Description: The aim of this study was to examine how intensified silviculture affects timber production (sawlogs and pulpwood) and its economic profitability (net present value [NPV], with 2 per cent interest rate) based on forest ecosystem model simulations. The study was conducted on Norway spruce and Scots pine stands located on medium-fertile upland forest sites under middle boreal conditions in Finland, under current climate and minor climate change (the RCP2.6 forcing scenario). In intensified silviculture, improved regeneration materials were used, with 10–20 per cent higher growth than the unimproved materials, and/or nitrogen (N) fertilization of 150 kg ha−1, once or twice during a rotation of 50–70 years. Compared to the baseline management regime, the use of improved seedlings, alone or together with N fertilization, increased timber production by up to 26–28 per cent and the NPV by up to 32–60 per cent over rotation lengths of 60–70 years, regardless of tree species (although more in spruce) or climate applied. The use of improved seedlings affected timber yield and NPV more than N fertilization. Minor climate change also increased these outcomes in Scots pine, but not in Norway spruce.

Description: This paper aims to assess the population structure of Pentadesma butyracea Sabine, a local oil tree species and to analyze the occurrence of woody plants in P. butyracea natural stands. Data were collected in 41 plots of 50 × 20 m across natural stands of P. butyracea in two regions of the south-Sudanian phytogeographic zone of Burkina Faso. Stem diameter, total height and tree health were recorded and the woody plant diversity was assessed. Stand data were calculated and the diameter structure was analyzed at the regional level using the Weibull distribution. Significant differences (P 〈 0.05) were found in density and basal area between regions. In both regions, 32 per cent of trees show signs of poor health. The diameter distributions of individuals showed a structure close to a reverse J-shape (c 〈 1). Natural stands of P. butyracea exhibit good natural regeneration, but the large trees in the sampled populations commonly had poor health. The data may indicate early signs of stands of P. butyracea changing into savanna in the Banfora region as a consequence of human activities and climate deterioration. P. butyracea is a dominant species in riparian forest, its conservation has a potential to restore the riparian forest; appropriate management guidance and support that involves local communities is required to ensure sustainable management.

Description: Understanding climatic influences on annual basal area growth (ABAG) rates of individual trees is necessary to predict future stand dynamics. We fitted nonlinear ABAG models for shortleaf pine (Pinus echinata Mill.) with climate variables linearly added to the arguments of logistic and exponential multiplicative functions of climate variables as climate modifiers to incorporate 14 growing seasons and 30 month-specific climate variables including standardized precipitation index. Data were collected from permanently established plots in Arkansas and Oklahoma. Six re-measurement events collected between 1985 and 2014 provided five growth periods (GPs) and ABAG models were fitted using a mixed-effects approach. Model performance was evaluated using likelihood ratio tests and fit statistics. Climate variables from GPs expressed as deviations from long-term means that performed better than other candidate variables included (1) month-specific: June mean maximum air temperature (°C) (DTMAX6), and September precipitation (mm) (DPPT9); and (2) growing seasons: mean maximum air temperature (°C) (DGTMAX) and precipitation (mm) (DGPPT). ABAG models fitted with multiplicative climate modifiers provided improved growth predictions compared with models fitted with climate variables linearly added to the argument of a logistic function. There was positive correlation with DGTMAX and negative correlation with DMPPT. In addition, 1°C increase in mean maximum temperature had a greater cumulative effect on ABAG rates of young versus old trees. Fitting ABAG models with climate modifiers are useful for assessing variations in productivity due to climate change in the future.

Description: The aim of this study was to explore methods to: (1) enhance coarse-scale estimates of wood volume from National Forest Inventories (NFIs) data and (2) map them at finer scales. The ‘standard’ coarse-scale estimation extrapolates wood volume from clusters to the grid cell they represent, using the cluster’s represented forested area (RFA) to predict the cell’s forested area. Data from a subset of Brazil’s NFI clusters were combined with Landsat-8 imagery to explore a new coarse-scale method, where forested area derived from image classification (FADIC) is used instead of RFA. The RFA- and FADIC-derived estimates of total volume were, respectively, 197.4 million m3 and 116.3 million m3. For fine-scale methods, volume was estimated and mapped at pixel level using: (i) surface reflectance-based models (SRMs), and (ii) regression-kriging (RK) and a RK model (RKM) whose inputs were latitude and longitude of pixels. The SRM-based method captured the mean and the general spatial trend of the volume well. The RK-based method also estimated the mean well, but it failed to predict higher and lower volumes. The SRM- and RK-based estimates of total volume were 211.7 million m3 and 203.3 million m3, an overestimate of 7 per cent and 3 per cent, respectively, of the ‘standard’ NFI estimate (197.4 million m3), though both estimates were within the 95 per cent confidence interval, meaning that both fine-scale methods yield total volume statistically similar to the ‘standard’ coarse-scale method.

Description: Glyptostrobus pensilis (Staunt.) Koch is a relict species in the Cupressaceae that previously had a global distribution but is now restricted to Southern China and two disjunct populations along the Annamite ranges in Laos and Vietnam. Using nuclear and chloroplast microsatellite markers (cpSSR and nSSR, respectively), we investigated the genetic diversity and divergence within and between 14 populations representing the entire range. Nuclear EST-SSR markers revealed low genetic diversity (He = 0.272) within populations and strong genetic differentiation (FST = 0.452) among populations. Populations in Laos, which represent the last primary forests of G. pensilis, contain the highest genetic diversity and are of particular conservation importance. The geographic cpSSR variation is consistent with the results from the nSSR analysis. Prolonged geographical isolation is likely to be the main reason for regional genetic patterns. Climatic changes during the Holocene, coupled with anthropogenic impacts, have further reduced its distribution and population size. The clear genetic structure suggests that at least, two refugia existed at different latitudes in Southeast Asia. Preserving and expanding its remaining habitat and increasing population sizes are likely to be the most important measures for the conservation of this species.

Description: Humans act as drivers for the introduction of non-native trees. Some non-native species may become invasive and cause undesirable impacts, thereby motivating targeted decision-making and management actions. Australian acacias (or wattles; genus Acacia subgenus Phyllodineae) have been introduced worldwide, offering both opportunities and risks for local communities. Understanding how stakeholders perceive invasive acacias is paramount to assist effective decision-making. We assessed stakeholders’ perceptions about these non-native acacias, their invasion process, social-ecological impacts and management. We conducted a questionnaire-based survey with experienced managers and decision-makers in Northern Portugal, where acacia invasions are widespread. We found that most stakeholders are not able to recognize non-native species, failing to identify the introduction period, drivers of dispersion and appropriate management methods of Australian acacias. We could also identify different stakeholder perceptions on the benefits and negative impacts provided by these species. We call for the implementation of technical training and information outreach strategies to address stakeholders’ lack of knowledge (and experience) on the recognition and identification of non-native trees, as well as on their introduction and invasion history, drivers of dispersion, costs and benefits, and effective management actions. Stakeholders’ engagement should be promoted in the design and implementation of biosecurity efforts to control (and/or adapt to) invasive acacias at relevant scales of invasion management.

Description: Reliable information concerning stand volume is fundamental to making strategic decisions in sustainable forest management. A variety of remotely sensed data and different inventory methods have been used for the estimation of forest biometric parameters. Particularly, airborne laser scanning (ALS) point clouds are widely used for the estimation of stand volume and forest biomass using an area-based approach (ABA) framework. This method relies on the reference measurements of field plots with the necessary prerequisite of a precise co-registration between ground reference plots and the corresponding ALS samples. In this research, the allometric area-based approach (AABA) is proposed in the context of stand volume estimation of Scots pine (Pinus sylvestris L.) stands. The proposed method does not require detailed information about the coordinates of the field plots. We applied Polish National Forest Inventory data from 9400 circular field plots (400 m2) to develop a plot level stand volume allometric model using two independent variables: top height (TH) and relative spacing index (RSI). The model was developed using the multiple linear regression method with a log–log transformation of variables. The hypothesis was that, the field measurements of TH and RSI could be replaced with corresponding ALS-derived metrics. It was assumed that TH could be represented by the maximum height of the ALS point cloud, while RSI can be calculated based on the number of tree crowns delineated within the ALS-derived canopy height model. Performance of the developed AABA model was compared with the semi-empirical ABASE (with two predictors: TH and RSI) and empirical ABAE (several point cloud metrics as predictors). The models were validated at the plot level using 315 forest management inventory plots (400 m2) and at the stand level using the complete field measurements from 42 Scots pine dominated forest stands in the Milicz forest district (Poland). The AABA model showed a comparable accuracy to the traditional ABA models with relatively high accuracy at the plot (relative root mean square error (RMSE) = 22.8 per cent; R2 = 0.63) and stand levels (RMSE = 17.8 per cent, R2 = 0.65). The proposed novel approach reduces time- and cost-consuming field work required for the classic ABA method, without a significant reduction in the accuracy of stand volume estimations. The AABA is potentially applicable in the context of forest management inventory without the necessity for field measurements at local scale. The transportability of the approach to other species and more complex stands needs to be explored in future studies.

Description: Since its first introduction in the 19th century, Douglas-fir has become the economically most important non-native forest tree species in Central European countries. Many of these planted forests are important seed sources and/or exhibit natural regeneration. Thus, it is important to assess (1) the genetic diversity of the mature stands and (2) if the genetic diversity can be passed on to the next generations. In order to address these issues, we genotyped mature Douglas-fir individuals and natural regeneration from 〉100 native and non-native populations using nuclear microsatellite markers. We compared the genetic diversity of native North American populations with mature Douglas-fir populations in Central Europe. The results show that genetic diversity did not differ significantly between European populations and the assigned native origin. Using a subset of 36 sites from Central Europe, we detected a significant reduction in the genetic diversity of adult versus naturally regenerated juvenile trees, indicating a bottleneck effect in the next generation of European Douglas-fir stands. The main reason may be that the mature European Douglas-fir stands are highly fragmented and thus the stand size is not adequate for transmitting the genetic diversity to the next generation. This should be taken into account for the commercial harvesting of seed stands. Seed orchards may offer a potential alternative in providing high quality and genetically diverse reproductive material.

Description: Urban trees are instrumental in providing ecosystem services to urban society. However, they are subject to many pressures linked to harsh site conditions created by the urban environment, climate change, attack by pests and diseases and the political and social influences that control how urban trees are perceived and managed. An ongoing provision of services from all trees within an urban area (known as the urban forest) can only be achieved through high resilience to these pressures. This study aims to examine the current state of composition, condition and structure of 12 urban forests across Great Britain, by reviewing data collected from i-Tree Eco city or town-wide surveys and recommending a framework to rate their sustainability. The study shows that urban forests are hardy to local winter temperatures and in good health, but lack in large size trees and tree species diversity. Also, several urban forests offer small percentage canopy cover. The wider application of this framework and the creation of detailed tree strategies could help local authorities to establish management strategies, set goals and monitor progress towards achieving greater sustainability.

Description: Understanding tree stability under self-weight and applied loads from wind and snow is important when developing management strategies to reduce the risk of damage from these abiotic agents. In this paper, linear buckling analysis was conducted using the finite element method to identify the instability modes of a tree structure under a specified set of loads. A non-prismatic elastic circular column of height H was analysed, taking self-weight into account. Various scenarios were considered: column taper, base rigidity, radial and longitudinal stiffness, ellipticity and crown weight. The effect on the critical buckling height was assessed in each case. Validation against closed form solutions of benchmark problems was conducted satisfactorily. The results indicate that column taper, base rigidity and the stiffness/density ratio are particularly important for this problem. Further comparison was made using data from a 15-year old Pinus radiata stand in New Zealand, which contained both buckled and non-buckled trees. While the model predicted factors of safety against buckling that were close to unity, it was unable to differentiate between buckled and non-buckled trees. Further investigation is needed to examine the reasons why this occurred. Despite this, the current study provides an in-depth numerical investigation, which has aided our understanding of the effects that material properties, geometric properties and boundary conditions have on buckling phenomenon in trees.

Description: Recent research in the central Amazon suggests that wind is a major agent of disturbance, however, a mechanistic understanding of how wind may lead to tree mortality in Amazonian forests remains unclear. Here we estimated wind speeds necessary to topple central Amazon trees by linking both static and dynamic versions of two wind speed estimation methods (four methods total) to field data on tree failure derived from a static winching study. Static versions of these methods assumed invariant wind characteristics as more trees failed, while dynamic versions updated tree spacing, leaf area index and wind profiles progressively after each tree failure. First, we used a profile method which estimates wind force on individual trees by segments. We calculated drag on each segment and converted drag into basal turning moment, and compared the summed turning moments to the critical turning moment measured in the winching study. Estimated critical wind speeds from the static profile method varied greatly, from 10.75 m s−1 to 〉120.0 m s−1 with a mean of 45.70 m s−1. Critical wind speeds estimated with static approaches decreased with tree size but were not significantly different between two focal genera. Primary drivers of variation in critical wind speed were tree height and crown size. Second, we used the turning moment coefficient method of Hale, S.E., Gardiner, B., Peace, A., Nicoll, B., Taylor, P. and Pizzirani, S. 2015 Comparison and validation of three versions of a forest wind risk model. Environ. Model. Softw.68, 27–41. doi:10.1016/j.envsoft.2015.01.016.; the static version of this method yielded less-variable estimates, ranging from 18.98 to 52.01 m s−1, with a mean of 30.88 m s−1. Notably, the two static methods for estimating critical wind speeds differed in the trees they identified as having the highest and lowest critical wind speeds. Dynamic variants of the above two methods produced greatly reduced ranges in CWS estimates for our study trees, because after the early tree failures, remaining trees were subject to greater wind penetration into the stand and thus greater loading for a given above-canopy wind speed. CWS estimated with dynamic approaches differed significantly between the focal taxa. Nevertheless, both estimates suggest that wind speeds commonly observed during Amazon storms are sufficient to produce widespread tree damage and mortality.

Description: Wind is a major force of disturbance in forests throughout the world, causing trees to break or uproot and topple over, depending on tree morphology and growing conditions. Previous research has suggested that trees that are more massive or which have lower height–diameter ratios are less at risk to wind throw, but the influence of crown size and branching architecture has been more difficult to elucidate. In general, there has been more research on coniferous trees, which have more simplified and symmetrical crown structures, relative to broad-leaved, deciduous trees. Here, we modelled the probability of wind throw for American beech (Fagus grandifolia Ehrh.), a broad-leaved, deciduous species common in the eastern USA, for trees covering a broad range of sizes (5.6–79.8 cm, diameter at breast height), in two nearby stands, in an experimental forest in southwestern Michigan, USA, where a wind event occurred. After a major blow-down of more than 200 trees in one of the stands, a subset of trees was destructively sampled after the storm. Analysis of the characteristics of the wind-thrown versus non-wind-thrown, residual trees, indicated that a very large branch fraction of total tree mass was a key factor leading to toppling of the wind-thrown trees. This study provides new empirical data related to the characteristics of wind-thrown American beech trees and suggests a potentially important role for branch to stem mass ratios as a predictor of wind throw risk for this species and possibly other broad-leaved, deciduous tree species, with a deliquescent branching architecture.

Description: In addition to causing large-scale catastrophic damage to forests, wind can also cause damage to individual trees or small groups of trees. Over time, the cumulative effect of this wind-induced attrition can result in a significant reduction in yield in managed forests. Better understanding of the extent of these losses and the factors associated with them can aid better forest management. Information on wind damage attrition is often captured in long-term growth monitoring plots but analysing these large datasets to identify factors associated with the damage can be problematic. Machine learning techniques offer the potential to overcome some of the challenges with analysing these datasets. In this study, we applied two commonly-available machine learning algorithms (Random Forests and Gradient Boosting Trees) to a large, long-term dataset of tree growth for radiata pine (Pinus radiata D. Don) in New Zealand containing more than 157 000 observations. Both algorithms identified stand density and height-to-diameter ratio as being the two most important variables associated with the proportion of basal area lost to wind. The algorithms differed in their ease of parameterization and processing time as well as their overall ability to predict wind damage loss. The Random Forest model was able to predict ~43 per cent of the variation in the proportion of basal area lost to wind damage in the training dataset (a random sample of 80 per cent of the original data) and 45 per cent of the validation dataset (the remaining 20 per cent of the data). Conversely, the Gradient Boosting Tree model was able to predict more than 99 per cent of the variation in wind damage loss in the training dataset, but only ~49 per cent of the variation in the validation dataset, which highlights the potential for overfitting models to specific datasets. When applying these techniques to long-term datasets, it is also important to be aware of potential issues with the underlying data such as missing observations resulting from plots being abandoned without measurement when damage levels have been very high.

Description: Non-native tree species (NNT) that pose risks to biodiversity are classified as ‘invasive’ in some European countries. However, country-specific risk assessment methods may lead to different results for the same NNT between countries of comparable growth conditions, raising doubts about the reliability of risk classifications. Here, we analysed six risk assessment tools used in Germany and adjacent countries for their practical applicability and consistency using four NNT (Fraxinus pennsylvanica Marsh., Paulownia tomentosa (Thunb. ex Murray), Pseudotsuga menziesii (Mirb.) Franco and Quercus rubra L.) as case studies. Using these tools to classify risks for the same NNT and reference area (Germany) yielded inconsistent results for all NNT. The reasons for this were (1) differences in classification and weighting of criteria, (2) a lack of data to quantify invasion risks and (3) uncertainties related to assessment methodologies. Moreover, the tools fail to distinguish between risks posed by NNT in different sites. We suggest that instead the risks should be assessed for different ecosystem types by using site-specific inventory data covering the establishment, spread and potential impact of NNT. Our recommendations provide a foundation for developing a consistent, systematic Pan-European approach to assess invasiveness while addressing both risk and forest management aspects.

Description: In northern temperate forests, ice storms are a common disturbance agent, though climate change may alter their occurrence patterns. Their impact on forest ecosystems is complex, as they influence both structure and processes. In 2014, an ice storm of high intensity and large spatial extent occurred in Slovenia, Central Europe, which enabled a detailed study of ice damage to individual trees across a broader spatial scale. Pre- and post-ice storm measurement data on 11 414 trees on 960 permanent plots were used to examine ice damage patterns on trees in the disturbed forest area (~8700 km2) to determine the predictors of ice damage to trees and to investigate the relative susceptibility of eight groups of tree species in mixed Central European forests. We used a novel approach to modelling ice-storm intensity across the region based on measured data on air temperature, precipitation amount and duration, precipitation intensity and wind speed. The ice storm damaged 31 percent of the analysed trees; high variability in the damage rate was observed across the disturbed area. For the tree species, a susceptibility to ice damage index (SI) ranging between 0 (no damage) and 1 (complete damage) was calculated based on terrestrial assessment of trees. Tree species differed significantly in susceptibility to ice damage: Abies alba (SI = 0.14) and Quercus sp. (SI = 0.11) were rather resistant; Picea abies, Fagus sylvatica and Acer sp. (SI = 0.23–0.28) were moderately to very susceptible; and Pinus sp. (SI = 0.62) was extremely susceptible to ice damage. Eight predictors and three interactions were included in an ordinal logistic regression model of tree damage: ice damage on trees depends mainly on ice-storm intensity, elevation and tree species, whilst tree dbh and social status, tree size and tree species diversity indices and slope were relatively less important. Our study illustrates the complexity of damage patterns on trees due to ice storms and the significance of ice-storm intensity and tree species as predictors when modelling ice damage on individual trees.

Description: Forestry practices such as prescribed fire and wildfire management can modify the nutritional resources of ungulates across broad landscapes. To evaluate the influences of fire and forest management on ungulate nutrition, we measured and compared forage quality and abundance among a range of land cover types and fire histories within 3 elk ranges in Montana. We used historical fire data to assess fire-related variations in elk forage from 1900 to 2015. Fire affected summer forage more strongly than winter forage. Between 1900–1990 and 1990–2015, elk summer range burned by wildfire increased 242–1772 per cent, whereas the area on winter range burned by wildfire was low across all decades. Summer forage quality peaked in recently burned forests and decreased as time since burn increased. Summer forage abundance peaked in dry forests burned 6–15 years prior and mesic forests burned within 5 years. Forests recently burned by wildfire had higher summer forage quality and herbaceous abundance than those recently burned by prescribed fire. These results suggest that the nutritional carrying capacity for elk varies temporally with fire history and management practices. Our methods for characterizing nutritional resources provide a relatively straightforward approach for evaluating nutritional adequacy and tracking changes in forage associated with disturbances such as fire.

Description: Tree diameter at breast height (D) and tree height (H) are often used as predictors of individual tree biomass. Because D and H are correlated, the combined variable D2H is frequently used in regression models instead of two separate independent variables, to avoid collinearity related issues. The justification for D2H is that aboveground biomass is proportional to the volume of a cylinder of diameter, D, and height, H. However, the D2H predictor constrains the model to produce parameter estimates for D and H that have a fixed ratio, in this case, 2.0. In this paper we investigate the degree to which the D2H predictor reduces prediction accuracy relative to D and H separately and propose a practical measure, Q-ratio, to guide the decision as to whether D and H should or should not be combined into D2H. Using five training biomass datasets and two fitting approaches, weighted nonlinear regression and linear regression following logarithmic transformations, we showed that the D2H predictor becomes less efficient in predicting aboveground biomass as the Q-ratio deviates from 2.0. Because of the model constraint, the D2H-based model performed less well than the separate variable model by as much as 12 per cent with regard to mean absolute percentage residual and as much as 18 per cent with regard to sum of squares of log accuracy ratios. For the analysed datasets, we observed a wide variation in Q-ratios, ranging from 2.5 to 5.1, and a large decrease in efficiency for the combined variable model. Therefore, we recommend using the Q-ratio as a measure to guide the decision as to whether D and H may be combined further into D2H without the adverse effects of loss in biomass prediction accuracy.

Description: We used a gap-type forest ecosystem model to study how even- and uneven-aged management affected the carbon dynamics and timber production in boreal Norway spruce stands. In business-as-usual management, the intensity of thinnings (from below) and single-tree selective cuttings followed those recommended for even-aged (BT) and uneven-aged management (BSC) in practical forestry in Finland. Moreover, higher or lower basal area thresholds, and shorter or longer production cycles, were used in simulations. We found that, the mean annual carbon uptake, volume growth, and carbon stock in trees and harvested timber, were nearly the same under even-aged (BT) and uneven-aged (BSC) management, when assuming full seed crop in latter one. However, the carbon stock in the soil and ecosystem and the mean annual net ecosystem exchange were slightly smaller under BT. The carbon retention time was longer under BSC. The net present value (NPV with interest rate of 3 per cent) of timber production was clearly lower under BT, when the calculation was initiated at planting on clear-cutting area, in opposite to when initiating calculation a few years before the second thinning. Higher basal area thresholds and longer production cycles increased carbon stocks, carbon retention and timber yield, regardless of management system. On the other hand, the results of uneven-aged management (BSC) were very sensitive to the success of natural regeneration and ingrowth of seedlings, as a reduction of the seed crop by 25–75 per cent from the full seed crop decreases the volume growth by 44–74 per cent and timber yield up to 46 per cent.

Description: Measures of species co-occurrence, as a proxy of biotic interactions, may be as important as environmental factors when explaining the distribution of many species. We assessed the relative effect of both species co-occurrence and environmental factors in predicting the occurrence (presence/absence) of woodpeckers and passerines in mature forests of the Northern Iberian Peninsula. We hypothesized that woodpecker occurrence would affect the occurrence of passerines. We calculated the occurrence of woodpecker species using models that included environmental factors aggregated at three spatial scales (200, 500 and 1,000-m2). The occurrence of passerine species was then modelled by using either species co-occurrence (including the occurrence of woodpecker species) or environmental factors at the 200-m2 cell scale. The occurrence of five out of nine passerine species was best explained by the co-occurrence of woodpeckers alone, whereas the occurrence of the remaining passerines was best explained using a combination of species co-occurrence (i.e. woodpeckers and/or other passerines) and environmental factors. In Southern Europe, woodpeckers are expanding their distribution in line with forest maturation, and this could increase the diversity of bird communities in forest systems.

Description: In sustainable forestry, forests should produce multiple ecosystem services for society, such as timber, carbon sequestration and biodiversity. Therefore, in the evaluation of forest management strategies, we have to consider the impacts of management on several ecosystem services. In this study, we compared the effects of five different forest management strategies on timber drain, carbon stocks, carbon balance and biodiversity indicators, while maximizing economic revenues from timber production. The assessment was carried out in a boreal landscape of 43 000 ha over a 100-year calculation period. The five management strategies were rotation forest management (with thinning from below or above), continuous cover forestry, a combination of rotation forest management and continuous cover forestry and any-aged forestry. Rotation forest management with thinning from below was less profitable than the other strategies, which were close to each other in economic profitability. Rotation forest management with thinning from below was also the poorest in terms of carbon stocks, carbon balance and biodiversity indicators. Any-aged and continuous cover forestry were the best in terms of carbon sequestration and biodiversity indicators. In general, management strategies that used thinning from above and that were not restricted to rotation forest management as the only option provided more ecosystem services and were also economically profitable. Such management strategies may help to satisfy the increasing demand for diverse uses of forests.

Description: White spruce breeding has traditionally focused on genetic improvement for high productivity, targeting mostly stem volume. However, new challenges, such as the effects of climate change on individual trees and ecosystems and the changing nature of forest products markets, require action to address these issues while providing improved stock for seed and seedling production. This work aims to define the relative importance of white spruce wood traits for the lumber industry, with the intent of guiding tree breeding programs. This manuscript examines: (1) wood features that are important for lumber, (2) the genetics of wood traits and their improvement and (3) the level of acceptance of raw material with optimal traits, as obtained from a survey conducted with sawmills. Stem diameter at stump height, wood density, bending strength and stiffness were determined as the most important properties for sawmills. Decay proportion, knot diameter, slope of grain and the proportion of compression wood were also determined as important for sawmills, but to a lesser extent. Breeding efforts aiming to produce lumber should focus on stems with improved growth that are capable of sustaining the production of dense wood in greater proportion.

Description: Modelling growth and survival dynamics after partial harvesting must take account of the heterogeneous spatial pattern of residual trees that results from the presence of machinery trails. We used data from 23 permanent sample plots in northern hardwood stands to reconstruct the growing environment of individual trees before and after partial harvesting. We modelled harvest probability, growth response and survival probability using a complementary set of explanatory variables that was assembled to reflect the spatial distribution of trees and skid trails prior to and after harvest. Results showed that the distribution of harvested trees was concentrated in skid trails and in their close vicinity. However, this spatial pattern had no significant effect on either the post-cut basal area increment (BAI) or the survival of residual trees. BAI and survival of individual trees were both mostly related to the competitive environment prior to harvest, while post-cut changes in competitive environment had only a marginal effect on growth and survival dynamics. We conclude that selection cuts did not substantially increase the growth and survival of residual trees, likely because tree removal was mostly concentrated near skid trails, where the negative effects of machinery access were highest.

Description: Overlooking the risk of wind and snow damage in forest planning may lead to suboptimal management prescriptions. In this study, we analysed the optimal management of an even-aged, spruce-dominated stand in Norway under the risk of snow and wind damage. The management aim was to maximize discounted net revenues of timber production. We used a simulation-optimization system based on models for stand dynamics and damage, using either deterministic or stochastic approach to consider risk. The different approaches to simulating damage resulted in 41 optimization cases. The results show that considering risk leads to earlier cuttings, lower growing stock densities towards the end of the rotations and changes in the number and intensity of thinnings. The inclusion of stochastic damage provided a valid approach for considering the uncertainty associated with the risk of damage. Ignoring the effect of wind and snow damage in the calculations resulted in up to 25 per cent overestimation of the revenues. The results from this study will help to integrate the risk of natural disturbances into forestry decision-making, and provide a better understanding of the implications that snow and wind damage have on optimal forest management.

Description: Ailanthus altissima is a common tree species of the European non-native flora. In Eastern Austria, Ailanthus has both a long tradition, dating back to the late 18th century, and a high frequency of occurrence. Here, we apply molecular markers from the nuclear and chloroplast DNA in order to study the origin, as well as the clonal and genetic structure of the species in forest stands of this region. Our results indicate a single area of origin for all our study populations from the north-eastern part of the native range, in agreement with historical reports. Within populations, vegetative reproduction has resulted in extensive clonal structures at some sites. Long presence and repeated vegetative recruitment might have led to expansion of clones in areas of early introduction. In addition, limited mate availability may also have promoted vegetative reproduction. Tests for recent bottlenecks were significant in almost all stands, possibly reflecting founder effects since the introduction of Ailanthus in our study area. Among populations, we found a very pronounced and significant genetic structure, which did not follow a spatial pattern. We argue that founder effects due to population establishment with a low number of propagules – whether naturally or artificially – have caused genetic drift and a structured gene pool. The lack of spatial pattern or isolation-by-distance suggests that seed transfer by humans might have been a major factor shaping the genetic variation of Ailanthus in Eastern Austria.

Description: The risk of extreme events due to weather and climate change, such as winds of unprecedented magnitude, is predicted to increase throughout this century. Artificial ecosystems, such as coniferous plantation forests, can suffer irreversible deterioration due to even a slight change in environmental conditions. However, few studies have examined the effects of converting natural forests to plantations on their vulnerability to catastrophic winds. By modelling the 2004 windthrow event of Typhoon Songda in northern Japan using the random forest machine learning method, we answered two questions: do Abies plantation forests and natural mixed forests differ in their vulnerability to strong winds and how do winds, topography and forest structure affect their vulnerability. Our results show that Abies plantation forests are more vulnerable to catastrophic wind than natural mixed forests under most conditions. However, the windthrow process was common to both types of forests, and the behaviour of wind inside the forests may determine the windthrow probability. Future management options for adapting to climate change were proposed based on these findings, including modifications of plantation forest structure to reduce windthrow risk and reconversion of plantations to natural forests.

Description: This paper discusses the advance in our understanding of the interaction between wind and trees over the last 25 years. It does this by comparing papers in this special issue of Forestry and a companion volume in Agricultural and Forest Meteorology, based on work presented at the 8th IUFRO Wind and Trees Conference in 2017, with papers published in book format after the 1st IUFRO Wind and Trees Conference in 1993. The analysis is divided into sections on ‘airflow and tree mechanics’, ‘forest management and ecology’, ‘tree adaptation and acclimation’ and ‘modelling and statistical techniques’. It is clear that in the last 25 years large advances have been made in our understanding of airflow and turbulence within and above forest canopies and the wind flow and wind loading around and on individual trees. There have also been important developments in the mechanistic and statistical modelling of wind damage risk to forests. Much of the progress has been aided by the enormous advances in measurement systems, computer power and modelling techniques. Furthermore, this knowledge is beginning to influence the approach to temperate and boreal forest management and the development of systems to mitigate the risk of wind damage. At the same time there has been a growing awareness of the ecological impact of wind in many forests around the world, including tropical forests. However, other areas of the effect of wind on trees have progressed much less in the last 25 years. This includes the process of fatiguing in the root-soil system, both during individual storms and over longer periods, and which is known to be a critical factor in the process of windthrow. In addition the exact nature of damage propagation within forests during a storm, and then in subsequent storms, has received relatively little attention although new studies using advanced computational methods are making advances. Of particular relevance, and despite the known critical importance of tree acclimation to the wind, there have been very few studies in the last 25 years on wind acclimation in full-size trees. This is an area of enormous importance in understanding how resistance to the wind varies for different species and between areas with different wind climates. In summary, overall much has been learnt since the 1st Wind and Trees conference but there remain many intriguing and exciting challenges ahead for this multi-disciplinary subject.

Description: Wall-to-wall forest management inventories with the area-based method using airborne laser scanner (ALS) data are operational in many countries. With this method, empirical relationships are established between ALS metrics and ground reference observations of forest attributes, and wall-to-wall predictions can be made over large areas. However, the prediction errors may be influenced by terrain slope and aspect because the properties of the ALS point cloud are dependent on these factors. Two datasets covering wide ranges of terrain slope and aspect, collected in the western part of Norway, were analysed. The first dataset represented sample plots from an ordinary operational forest management inventory and the second dataset were collected as an experimental dataset where clusters of sample plots were distributed on slopes with different inclinations. Six forest attributes were predicted using non-linear regression and the prediction errors were analysed using univariate- and multivariate analysis of variance. The results showed that slope and aspect affected the prediction errors, but that the effects were small in magnitude. Thus, the current study concludes that terrain effects seem to be negligible in operational forest inventories.

Description: We investigated the latitudinal variation in radial growth phenology (onset, cessation, and duration of radial growth) of Cryptomeria japonica D. Don trees in Japan. The radial growth was observed using dendrometers in 16 stands at multiple latitudes throughout Japan. The onset of radial growth showed a clear latitudinal gradient: at high-latitude sites, C. japonica growth started later than at low-latitude sites. However, cessation of radial growth was independent of latitude. Consequently, the duration of radial growth (defined based on the onset and cessation dates) showed a weak but significant latitudinal gradient: at high-latitude sites, C. japonica trees grew for a shorter period than trees at low-latitude sites. The onset and duration of growth were respectively strongly and weakly affected by temperature, although growth cessation was not explained by temperature or precipitation. The latitudinal gradient for duration of radial growth weakly but significantly supports the hypothesis that regional variation in growth phenology is a key factor responsible for the regional variation in long-term growth. Furthermore, we found that growth duration was more variable at low latitudes than at high latitudes.

Description: We developed a life-cycle analysis (LCA) system to quantify the carbon dynamics for Canadian-made harvested wood products (HWP). We considered the carbon stocks of HWP in use and in landfills/dumps, emissions reduced by substituting HWP for non-wood construction materials, HWP production emissions and methane emissions from decomposing wood disposed of in landfills. Carbon dynamics analyses were conducted for five HWP production scenarios. Results indicate structural panels have the highest potential in mitigating greenhouse gases (GHG) emissions, followed by lumber and non-structural panels. Net GHG effects of Canadian-made HWP were evaluated by integrating HWP carbon dynamics with forest carbon analysis using four forest management units (a total of 2.21 million ha of forests managed for timber production) from Ontario, Canada, as a case study. If HWP substitution benefits were estimated using the average displacement factor, and the wood obtained by increasing harvesting (relative to the baseline harvest scenario) in these four management units is used for structural panel, lumber, non-structural panel and business as usual HWP production, 0, 21, 39 and 84 years are needed to achieve net emission reductions, respectively; net emission reductions were, respectively, estimated to be 112, 93, 66 and 21 Mt CO 2 -equivalent in 100 years. Our results suggest harvesting sustainably managed forests in Canada to produce long-lived solid HWP can significantly contribute to GHG mitigation.

Description: Bark stripping behaviour of bears, which may significantly reduce the value of timber, has been reported mostly from North America and Japan, but in recent decades also from Europe. We surveyed forest plots in the Bieszczady Mountains of southeast Poland and recorded bark stripping by brown bears. We distinguished two types of tree damage by brown bears – damage to single (since no other damaged trees were found in their vicinity) and groups of trees (when five or more damaged trees were found in a small area). We found that all wound parameters, but especially the wound area and the proportion of the trunk with missing bark, were greater on single damaged trees. Comparison of damaged and control tree plots (1000 m 2 ) revealed that bears foraged in stands where silver firs ( Abies alba Mill.) with larger circumferences were present. Moreover, in stands where damage occurred, bears tended to strip large trees. The preference ratio index clearly showed that bears mostly preferred to forage on firs with circumferences in the 120–180 cm range, even though a wide spectrum of tree circumferences were available. Our results suggest that the brown bear should not be viewed as a pest species in commercial tree stands in Poland. The trees preferred by bears for foraging are large enough for timber production. To minimize economical losses, forestry personnel should regularly monitor tree stands that consist of trees of dimensions preferred by bears.

Description: Ecosystem services (ES) are the benefits that people receive from ecosystems. Understanding the impact of forest management on their supply can inform policy and practice for meeting societal demand. The objectives of this paper are to identify and review the effect of management intensity on priority ES supply and identify synergies and trade-offs among ES of different management approaches. We review seven priority ES identified from UK land and forestry strategy and policy documents: timber/biomass production, carbon storage, biodiversity, health and recreation, water supply and quality and flood protection. We present a synthesis of the impact of management on relative ES supply. It shows that low intensity management is unsuitable for high biomass production, yet provides high or moderately high levels of other services. Higher intensity management impacts negatively on biodiversity, health and recreation and water supply services. Combined objective forestry provides high or moderately high levels for all services except biomass. We recommend that a diversity of management approaches is needed to maintain multiple ecosystem service provision. The ES framework offers opportunities to forest management by revealing areas of conflict or co-production and potential trade-offs that may arise from adjusting management intensity.

Description: Digital hemispherical photography is a valuable method for monitoring changes in the biosphere’s response to climate change. In forests, cameras have often been fitted to existing towers and masts. However, such towers are logistically difficult and expensive to install. Ground-based automatic camera systems offer an alternative that removes the barriers associated with above-canopy photography, but to date there have been few comparisons between upward- and downward-facing images at the same site. This study addresses this issue, by comparing a pair of cameras, one ground-based, one tower-based, viewing the same trees in a deciduous oak ( Quercus robur L.) plantation forest in south-eastern England. Over 6 years, the upward-facing ground-based camera system was able to detect key spring phenological events to the same extent as the more usual downward-facing camera (mean difference of 2 days for green-up date). However, the upward- and downward-facing systems were less well-matched in detecting specific events at the end of the growing season, although both systems displayed similar temporal trends. Upward-facing cameras can therefore act as a reliable and comparable alternative to tower-based phenocam systems, as well as being more suitable for wider spatial coverage without the need for expensive installation infrastructure. In addition to the increased ease of access with upward-facing camera systems, the images from them also allow canopy structural dynamics such as canopy closure to be estimated.

Description: The growth of Sitka spruce ( Picea sitchensis (Bong.) Carr.) on nutrient-poor sites in the British Isles is often improved during the late establishment phase when grown in intimate (‘nursing’) mixture with pioneer species such as pines and larches. However, there is very little information on the longer term effects of such mixtures on stand development and productivity. Therefore, we analysed results from four experiments established in northern Scotland in the 1960s which included nursing mixtures of Sitka spruce with Scots pine ( Pinus sylvestris L.), lodgepole pine ( Pinus contorta Dougl.) or larches ( Larix spp.), as well as plots of pure Sitka spruce given different establishment regimes, sometimes including nitrogen fertilization. At three nutrient-poor sites, spruce in nursing mixture was significantly taller after 15 years than pure spruce without nitrogen. Analysis of foliar nitrogen status showed that pure spruce without nitrogen became deficient by ~8–10 years with no recovery for at least 20 years. Spruce grown in mixture also showed an initial nitrogen deficiency, but with recovery by 10–15 years to optimal or marginal levels. After more than 40 years growth, on the nutrient-poor sites the basal areas in the nursing mixtures were significantly higher than pure spruce without remedial nitrogen and comparable to those of pure spruce given several applications of nitrogen, However, these differences were not evident at the more fertile site. Nearly all mixed plots self-thinned towards dominance by Sitka spruce. The magnitude of this nursing effect is striking and harnessing the mechanisms underpinning this effect could be very important for sustaining productivity of forests on nutrient-poor soils in upland Britain.

Description: The habitat composition of mature non-native plantations may provide a different set of resources to that of native forests, and these differences may influence species communities. We studied a bird community in the northern Iberian Peninsula to understand whether habitat composition in either mature non-native plantations or native forests generated differences in the habitat associations of each bird species as well as the composition of the bird community. We sampled 140 4-ha plots, measuring habitat composition at both the canopy and the understory level using remote sensing data and field surveys, respectively. Using a fixed census in each plot, we also studied the bird species composition and analysed the species-specific associations for various habitat variables at the canopy and understory level. We found that mature plantations differed in understory level from native forest, but these differences in habitat did not translate into differences in bird species composition between forest types. Species–habitat associations were on average stronger at the understory compared to the canopy level, which suggests that a combination of field and remote sensing data might better represent the species-specific response to forest resources when measuring the assembly of bird communities in mature plantations. This work suggests the fact that the combination of different levels of forest resources, such as that provided by mature non-native plantations and native forests, is able to support a rich bird community.

Description: The genus Eucalyptus contains many timber-producing forest species and is extensively planted around the world. The domestication of Eucalyptus has facilitated the global movement of microorganisms associated with this genus. The objective of this study was to characterize the fungal microbes in soil under the economically important tree, Eucalyptus grandis , from Zimbabwe. Soil samples were collected from a 5-year E . grandis plantation and adjacent Miombo woodland, which was treated as the control. The internal transcribed spacer 1 (ITS1) nuclear encoded ribosomal RNA of the fungal communities in the soil was sequenced using the high-throughput Illumina MiSeq technology. Taxonomic composition assessment of reads recovered from soil under E. grandis revealed the dominance of Ascomycota (41.17%), Basidiomycota (20.73%), with very few sequences belonging to Chytridiomycota, Rozellomycota and Zygomycota. Miombo soil was composed of Ascomycota (74.89%) and Basidiomycota (19.08%), also with very few sequences from Chytridiomycota, Rozellomycota and Zygomycota. Fungi belonging to Davidiellaceae, Mycosphaerellaceae and Teratosphaeriaceae, families that are known to be pathogenic to Eucalyptus , were recovered in soil under E . grandis . Ectomycorrhizal fungi classified in the Agaricomycetes were especially abundant in the Eucalyptus soil and were dominated by the genera Pisolithus and Scleroderma , which have been reported as Eucalyptus associates before.

Description: Rapid biodiversity assessment (RBA) methods are regularly applied to assess plant species richness. One approach is developing sampling designs that integrate expert knowledge. 3P sampling does so by selecting samples with probability proportional to prediction (3P). Higher effort is allocated to areas with high species richness based on predictions made on the ground. 3P sampling for RBA was simulated considering two major factors: knowledge of plant species and types of rapid assessment. Two large census forest plots over 25 ha in size were used. Results showed that sampling error of 3P sampling for RBA was relatively low and could be improved by changing methods of prediction. Sampling was more efficient and accurate when predictions were made with knowledge about abundant species instead of random species. When such prediction was made, knowing only three quarters of the total species richness in a forest performed as well as full knowledge. Randomly walking around in an area and predicting also increased efficiency and accuracy compared to standing stationary at an assessment point. This was counterintuitive to the common practices of establishing ground plots for assessment. Our findings propose that 3P sampling for RBA is workable through engaging local communities in an assessment, which could be cost-effective. Finally, the procedure laid out in this study is the first unequal probability sampling design proposed for RBA.

Description: Previous studies suggest that when using natural regeneration of Korean pine ( Pinus koraiensis Sieb. et Zucc.) many seeds do not germinate until the second Spring after dispersal and hence are subject to significant predation pressures. This could be an important factor affecting the restoration of Mixed-broadleaved Korean pine forests in northeast China. This study examined changes of dormancy status under laboratory and field conditions as well as physiological mechanisms involving abscisic acid (ABA), gibberellin acids (GA 1+3 , GA 4+7 ) and the storage reserves of seeds. Our results suggest that seeds of Korean pine have primary dormancy that can be classified as morphophysiological dormancy, i.e. when dispersed they have an underdeveloped embryo with a physiological component of dormancy. A proportion of seeds germinate in the first year after dispersal as the winter chill has broken the physiological dormancy but only when the embryo has had time to elongate in April–June. The remaining seeds germinate in the second Spring after dispersal when embryos are fully developed and the physiological dormancy imposed in the Summer after dispersal has been broken by winter chilling. Thus the seed strategy of Korean pine attempts to reduce risks by providing opportunities for germination in 2 years following dispersal.

Description: This study examines the potential of airborne laser scanning (ALS) to predict diameter distributions in an even-aged plantation of Eucalyptus urograndis in Brazil. The single-species plantation conditions allow different modelling alternatives to be compared without the presence of minor tree species or an understory layer affecting the results. Three modelling alternatives based on the two-parametric Weibull function form; parameter prediction, parameter recovery and distribution matching were tested with a k-nearest neighbour prediction ( k-nn ) method. We also evaluated a parameter prediction alternative, in which the Weibull distribution was predicted using field attributes. The results showed that ALS information can predict diameter distributions with an error margin of slightly more than 10 per cent of the RMSE of the mean of the third power of diameter, and with error index values between 50 and 60. The degree of accuracy was only slightly improved when the Weibull distribution was predicted using field attributes. According to the accuracy metrics, the differences between modelling alternatives were minor but parameter recovery and k-nn seem to be the most favourable ALS-based prediction methods. To conclude, the results showed a strong relationship between ALS information and diameter distributions in a tropical single-species plantation and we discuss how these results could be applied in other types of forests.

Description: Tree height can be a time-consuming measurement to obtain accurately in the field. Thus, height–diameter equations are frequently used to minimize costs associated with inventories and to reduce problems associated with height measurement errors. In this analysis, we compare three methods for estimating height from diameter data for a variety of species: (1) a nonlinear mixed-effects (NLME) model; (2) k nearest neighbour (KNN) imputation; and (3) a copula model. Predicted height values were compared with field height measurements for 922 trees across 24 species using paired point-wise and distribution-based goodness-of-fit criteria. All approaches performed very well, with the NLME and KNN imputation having better point-wise goodness-of-fit measures. Copula models, although generally poorer in terms of the paired point-wise goodness-of-fit, adequately predicted height values, maintained variances observed in field data, and showed the least loss of functionality when applied to species with sparse data or data with atypical parameters. Overall, the copula approach is flexible and may be more appropriate for estimating heights where paired point estimate accuracy is less important such as for tree lists that are subsequently used as inputs into growth and yield models.

Description: Beech bark disease stunts American beech ( Fagus grandifolia Ehrh.) to unmerchantable size, and promotes heavy sprouting that outcompetes more desirable sugar maple ( Acer saccharum Marsh.) and yellow birch ( Betula alleghaniensis Britt.). We investigated whether selection harvest targeting removal of large beech can promote maple and birch regeneration while limiting beech competition. Forty plots were established in 2003 in north-western New Brunswick, Canada, with 26 plots harvested and 14 control plots. Harvested plots were re-measured the year after harvest and both harvested and control plots were re-measured 10 years later. Residual tree diameter increment doubled from 0.24 to 0.51 cm/year for maple, and 0.29 to 0.69 cm/year for birch. Harvest did not alter species composition of regeneration, with seedlings comprised of 88 per cent sugar maple in both treatments, 6 per cent beech in harvested plots vs 3 per cent in control plots, and other species ranging from 1 to 5 per cent. There were four times more beech seedlings/ha in control than in harvested plots, but beech still comprised ~60 per cent of the over 2000 stems/ha of saplings in harvested plots. Rapid growth from beech sprouts provided a strong competitive advantage. Residual tree mortality was negligible. Downed deadwood was 58 per cent greater and standing deadwood basal area 71 per cent lower in harvested plots. The harvest maintained strong overstory growth and survival, and did not benefit beech; however, beech remained a dominant species among the larger regenerating cohort. Our results suggest that similar treatments applied to stands with diseased beech can secure adequate regeneration of maple and birch, but will not control profuse regeneration of beech.

Description: Spruce budworm (SBW; Choristoneura fumiferana [Clem.]) defoliation begins at the top of the crown, and often results in leader death, loss of annual height growth or gradual top dieback, known as topkill. We used regression tree analysis to examine topkill incidences during a severe SBW outbreak in Nova Scotia, Canada in the 1970s–1980s that resulted in 60–100 per cent mortality of merchantable balsam fir ( Abies balsamea (L.) Mill.) volume, and re-examined surviving trees for defects 25 years later. At the study outset in 1979, 4–6 years into the SBW outbreak, stand level topkill ranged from 40 to 88 per cent of trees and mean individual-tree topkill probability was 7, 52, 79 and 87 per cent on trees with ≤25, 26–75, 76–90 and 91–100 per cent total defoliation (all age classes of foliage). By 1987, the SBW outbreak had ended and mortality probability of trees was 12, 59, 85 and 98 per cent for classes of peak total defoliation of ≤25, 26–75, 76–90 or 91–100 per cent. Most mortality occurred following 6–8 years of defoliation, but topkill peaked after 4–6 years, indicating that topkill required less cumulative defoliation than death. When the plots were remeasured in 2012, 25 years later, 90 per cent of the surviving trees with documented topkill during the SBW outbreak had stem defects, of which 26 per cent were crooks, 53 per cent forks and 21 per cent sweeps. From 32 to 88 per cent of stem length was located above the point of the defect, resulting in the long-term downgrading of topkill-damaged logs.

Description: The economic importance of cork in the Mediterranean region demands an accurate assessment of its production. Cork production is currently estimated by aggregating information provided by Regional Forest Services, but this approach results in a lack of robustness at the national level. The objective of the present study is to analyse the role of the Spanish National Forest Inventory (SNFI) as a potential source of data for quantifying cork weight at national level and the scope of National Forest Inventory data to define national trends in cork yield as well as to characterize the main types of cork producing forest stands in Spain. Data from the Second and Third SNFI are used together with the Spanish Forest Map. The results point to the suitability of SNFI to quantify cork production as long as the two main variables defining cork weight, namely cork thickness and debarking height, were correctly recorded in inventories. Although the Second SNFI complied with these requirements, from the Third SNFI the methodology changed, preventing the accurate estimation of cork weight. Based on this study recommendations are made to improve the estimation of cork weight at national level, e.g. to measure cork thickness in all the cork oaks in the plot and to take a sample of cork from the inventoried trees. This information would also make it possible to assess the cork quality in terms of cork thickness growth and to classify cork production in terms of suitability for producing high quality cork products.

Description: A plethora of forest models were developed by transforming the dependent variable, which introduces bias if appropriate corrections are not applied when back-transformed. Many recognized models are still biased and the original data sets are no longer available, which suggests ad hoc bias corrections. The present research presents a procedure for bias correction in the absence of needed information from summary statistics. Additionally, we developed a realistic correction of the square root transformation based on a truncated normal distribution. The transformations considered in this study are the logarithm, the square root and arcsine square root. Using simulated data we found that uncorrected back-transformation created biases by as much as 100 percent. The generated data revealed that depending on available information, that bias can still be present after correction. In addition to generated data we corrected the site index of Douglas-fir and ponderosa pine in Oregon USA, tree volume of 27 species from Romania, stand merchantable volume for longleaf pine in Louisiana and East Texas USA, and canopy fuel weight in Washington USA. Using only the available information, the unbiased back-transformed estimates can change from ≤1 percent (i.e. the site index and canopy fuel weight) to ≥⅓ (tree and stand volume).