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: Bottomland hardwoods forests (BLHW) are increasingly subject to active management for water quality improvement, streambank stabilization, to mitigate for urban expansion and to improve habitat for wildlife. Since the majority of remaining BLHW are degraded, restoration attempts are becoming commonplace within the Western Gulf Coastal Plain (WGCP) of the US. However, restoration success in terms of obtaining high stem densities of desirable species has been mixed, with managers observing survival rates

Description: Productive Norway spruce forests in mountainous growing areas are expected to be affected by increasing climate-driven disturbances, which will most likely result in a reduction of their economic performance. This study seeks to compare the potential of currently discussed management options aiming to maintain the economic performance on typical sites of spruce under a changing climate. For this purpose, we used a combined approach of tree mortality simulation and portfolio optimization to assess the management options: (1) including a deciduous species, (2) establishing mixed stands, (3) shortening the rotation periods, (4) forest protection measures focusing on bark beetles and (5) introducing another highly productive species. As a novel feature, we also compared the effect of combined management strategies on the return and risk of stand management. In our simulation and optimization approach, the inclusion of an alternative, highly productive tree species, such as Douglas fir, into the tree species portfolio outcompeted the forest protection measure of intensive bark beetle monitoring with timely sanitation fellings in terms of balancing risks and returns. The adaptation gain of introducing Douglas fir was further enhanced when combined with additional management options such as adapted rotation periods. The resulting synergies were able to overcompensate for the adverse economic effects of climate change. On the contrary, including beech did not only reduce the risks but also the return in a magnitude which was clearly outcompeted by Douglas fir, even with the assumption of high mortality risks for Douglas fir. These results prove the importance of a proactive tree species selection in relation to more reactive forest protection measures for climate change adaptation. They also advise a careful consideration of expected market demands when selecting an additional species for the portfolio.

Description: A prerequisite for successful afforestation and reforestation is understanding the quality of a site before establishing a specific tree species. Ecograms have been widely applied to determine the suitability of different sites for different species by a simple assessment of nutrient and water availability. Their graphical representation of suitability into classes allows ecograms to be easily understood. However, ecograms have generally been mapped for small areas only and their validity has rarely been documented. The aim of this study is to map ecograms for five tree species across Denmark and validate the maps using forest stand production data. For this purpose, we classified the landscape into six nutrient classes and nine water classes based on four variables to generate the ecogram maps. Based on these classes, the generated maps depict if a tree species is unsuitable, suitable or optimal for a specific site. The absolute average misclassification for nutrient and water supply was 1 and 2 classes, respectively. Stepwise linear regression was implemented to determine if the four variables used to create the ecograms were able to predict production as observed from forest experiment and management planning data obtained from across the country. All five species used the full model to explain variation in production. However, the average production values per ecogram growing condition were not significantly different for all species. The range of $R$2 for the five species was 0.05–0.32, indicating that one ecogram template might not work for all species. The high-resolution national ecogram maps incorporate large-scale variables important for tree growth and will be beneficial when selecting new land for afforestation. The simplicity of ecograms allows for easy interpretation, meaning that foresters can quickly determine which regions of a landscape are suitable, saving time and resources.

Description: We tested the efficacy of a range of herbicides to see if they might be potential substitutes for the use of propyzamide or glyphosate to control grass weed species that, if left unchecked, often outcompete recently planted trees in UK forests. Applications of 0.45kg a.i. ha−1 cycloxydim in late April–early May gave good control of wood small reed (Calamagrostis epigejos (L.) Roth), Yorkshire fog (Holcus lanatus L.), and wavy hair grass (Deschampsia flexuosa (L.) Trin.)) for at least 12 weeks after application. When coupled with a sequential application of 0.15kg a.i. ha−1 propaquizafop made 5 weeks later, purple moor grass (Molinia caerulea (L.) Moench) was controlled for at least 21 weeks. Sequential applications of 0.45 kg a.i. ha−1 cycloxydim in October, then 0.45 kg a.i. ha−1 cycloxydim in late April, was the most effective treatment for minimizing competition from purple moor grass, wood small reed or wavy hair grass and equally effective as propyzamide on Yorkshire fog. The herbicides carbetamide, clethodim, clodinafop-propargyl and fenoxaprop-p-ethyl were not as effective as cycloxydim. We conclude that cycloxydim is effective on a broader range of grass weeds than previously thought. Cycloxydim and propaquizafop are both highly selective and unlike the broad-spectrum herbicide glyphosate will not harm young trees, even if they are oversprayed when in active growth. If applied at the correct time of year, cycloxydim is likely to be as effective as glyphosate on most grasses, and for wood small reed, purple moor grass and wavy hair grass considerably more effective than propyzamide. A sequential application of cycloxydim or possibly propaquizafop in the autumn, followed by a second spray in late April of the following spring, is likely to be the most effective means of maximizing tree growth and survival in grass dominated new planting or restock sites in UK forests.

Description: There is increasing interest across Europe in adopting forest management strategies, which promote species and structural diversity through the use of irregular silvicultural systems, an approach often described as continuous cover forestry (CCF). However, there is little information about the proportion of CCF practised across the continent or about the knowledge gaps and other obstacles that limit its use. A survey of respondents in 33 European countries sought to address these issues. The results indicated that the silvicultural systems associated with CCF were single stem, group selection and irregular shelterwood. Rotational forest management (RFM) was more frequent than CCF in about 66 per cent of countries, whereas in 25 per cent the reverse was true. We estimated that between 22 and 30 per cent of European forests are managed through CCF, although good data are lacking. The main knowledge gaps were: uncertainties arising from climate change (e.g. appropriate species choice, carbon storage in CCF), using CCF to increase forest resilience, deployment of mechanized harvesting systems, lack of knowledge about CCF amongst professional foresters and better information on economic implications of this approach. Major obstacles included: little awareness of CCF amongst forest owners, limited competence in CCF within the forestry profession and a scarcity of skilled forest workers to implement this approach, high ungulate populations damaging natural regeneration, a sawmilling sector geared to processing medium-sized logs, subsidy regimes favouring practices associated with RFM and a lack of experience in transforming plantation forests to more diverse structures. Better information on the use of different silvicultural systems is essential to allow policymakers and other stakeholders to monitor progress in diversifying forests. Establishment of a continental network of long-term operational trials (e.g. expanding the existing Association Futaie Irrégulière network) would improve professional understanding of CCF, would demonstrate this approach to forest owners and other stakeholders and could provide a valuable platform for supporting research.

Description: Climate change is predicted to increase temperature and seasonal temperature variance in Great Britain (GB). Sitka spruce (Picea sitchensis (Bong.) Carr) is the most important tree species used in commercial plantations throughout Europe and GB. Frosts that occur outside the winter dormancy period can negatively affect trees, since they happen after dehardening. Damage can be especially severe at bud burst, before emerging needles mature and form protective barriers. Here, we modelled the impact of climate change on frost sensitivity in Sitka spruce with temperature data from five climate projections. The UKCP09 climate model HadRm3 uses emission scenario SRESA1B for the years 2020–2099. The global and downscaled versions of the UKCP18 HadGem3 model use the emissions scenario RCP 8.5. The global model CMCC-CM uses the RCP 4.5 and RCP 8.5 emissions scenarios. The predictions based on these models were compared with results from gridded historical data for the period 1960–2015. Three indicators that assessed the frost sensitivity of Sitka spruce were explored: the total number of frosts between the onset of dehardening and the end of summer, which use three different temperature thresholds (Index 10°C, 1–3°C, 1–5°C); the total number of frosts after bud burst (Index 2); the number of days with minimum temperatures below the resistance level (backlashes) during the hardening–dehardening period (September–August) (Index 3). The indices were validated with historical data for frost damage across GB, and Index 1–3°C, Index 1–5°C and Index 3 were shown to be significantly correlated. The frequency of all frosts and backlashes is expected to decrease with climate change, especially under higher emissions scenarios. Post-bud burst frosts have been historically very rare in GB and remain so with climate change. Downscaled regional climate models detect geographic variability within GB and improve prediction of overall trends in frost damage in comparison to global climate change models for GB.

Description: Efficient subsampling designs reduce forest inventory costs by focusing sampling efforts on more variable forest attributes. Sector subsampling is an efficient and accurate alternative to big basal area factor (big BAF) sampling to estimate the mean basal area to biomass ratio. In this study, we apply sector subsampling of spherical images to estimate aboveground biomass and compare our image-based estimates with field data collected from three early spacing trials on western Newfoundland Island in eastern Canada. The results show that sector subsampling of spherical images produced increased sampling errors of 0.3–3.4 per cent with only about 60 trees measured across 30 spherical images compared with about 4000 trees measured in the field. Photo-derived basal area was underestimated because of occluded trees; however, we implemented an additional level of subsampling, collecting field-based basal area counts, to correct for bias due to occluded trees. We applied Bruce’s formula for standard error estimation to our three-level hierarchical subsampling scheme and showed that Bruce’s formula is generalizable to any dimension of hierarchical subsampling. Spherical images are easily and quickly captured in the field using a consumer-grade 360° camera and sector subsampling, including all individual tree measurements, were obtained using a custom-developed python software package. The system is an efficient and accurate photo-based alternative to field-based big BAF subsampling.

Description: Quality information on forest resources is fundamental for sustainable forest management. Manual aerial photointerpretation is used as a cost-effective source of data for forest inventories; however, the process of photointerpretation is inherently subjective and is often undertaken by multiple photointerpreters for a given forest management area. In contrast, airborne laser scanning (ALS) data enable characterization of forest structure in a systematic fashion with quantifiable levels of accuracy and precision that often exceed required targets and standards. However, the gains associated with the use of new technologies for forest inventory are difficult to measure because the quality of existing photointepreted inventories have rarely been quantified. Using ALS data as reference, the objective of this study was to quantify the precision of photointerpreted estimates of forest stand height and canopy cover (CC). We examined forest inventories from three study sites in three different forest regions of Canada. Each of the study sites was located within a different provincial jurisdiction with unique photointerpretation standards and forest ecosystems. Stand-level estimates of forest height and cover were compared to reference estimates generated from the ALS data. Overall, our results indicated that precision was greater for photointerpreted estimates of height, with a relative standard deviation ranging from 22 per cent to 29 per cent among our three sites, compared to estimates for CC, with precision ranging from 28 per cent to 59 per cent. While the relationship between photointerpreted estimates of height and ALS estimates of height were generally linear and consistent for all study sites, relationships for CC were non-linear. We found that precision for both stand height and cover varied by dominant species, inventory stand structure, age, and ALS canopy complexity, and that in the majority of cases, the differences between the photointerpreted estimate and the ALS estimate were statistically significant. It is also noted that the variability in photointerpretation precision as a function of the aforementioned factors was not consistent among our three study sites, indicating that site-specific forest conditions and photointerpretation procedures influence the precision of photointerpreted estimates. The influence of local forest conditions and interpretation procedures are therefore important considerations when seeking to quantify the potential relative gains in precision, which may be afforded by technologies such as ALS for forest inventory programs. Moreover, approaches to improve consistency in photointerpreted estimates of cover would be useful for operational inventory programs.

Description: The pattern of change in carbon (C) accumulation with forest ageing can vary greatly amongst different forest types. Documenting how C accumulates in various forest ecosystems in the absence of logging makes it possible to predict what would be the outcome of extending forest rotations or in dedicating more land to conservation on C storage. This study was conducted in boreal balsam fir (Abies balsamea (L.) Mill.) forests of Quebec, in eastern Canada. We compared carbon stocks in forest pools (aboveground (live) biomass, deadwood, FH horizon and mineral soil) of mature (70 years after harvest) vs old-growth stands (stands with no signs or history of human disturbance). Total ecosystem C stocks were not significantly different between mature and old-growth stands. However, as mature stands transition to old-growth stage, there appears to be a shift of C from live biomass pools towards deadwood and soil FH horizons. Coarse woody debris in old-growth stands were also found to be at more advanced stages of decay. The variability of C stocks was also high amongst old-growth stands; however, there was no obvious difference in structural diversity between mature and old-growth stands. Results suggest that ageing balsam fir stands through the lengthening of forest rotations (e.g. past the maturity age of 70 years) or by placing them under conservation, while not creating an important C sink, still contributes to maintain large forest C stocks across landscapes. Preserving or increasing the presence of old-growth forests is an important aspect of ecosystem-based forest management; our study concludes that it could also be compatible with sustainable forest carbon management.