ALBERT

Description: Question Analysing taxonomic, phylogenetic and functional species distribution across a metacommunity allows understanding of how landscape dynamics may influence forest expansion over grassland. In this context, climbing plants are particularly interesting vegetation components, since they actively prospect the best sunlight position, altering forest structure. We investigated if forest structure differentiation along a patch size/isolation gradient would determine the distribution of phylogenetic clades, dispersal and/or establishment-related traits in climbing plant assemblages. We hypothesized that taxonomic, phylogenetic and functional species diversities would show a nested pattern along the gradient of increasing vegetation complexity. Furthermore, less mobile diaspores, as well as climbing mechanisms independent of support limitations, and deeper phylogenetic clades characterized by shade-tolerant species would be associated with more developed and less isolated patches. Location Subtropical grassland surrounded by Araucaria forest, southern Brazil. Method We recorded the composition and abundance of climbing plant species along a gradient of forest patches increasing in size and isolation from the surrounding continuous forest. We performed an analysis of principal coordinates of phylogenetic structure (PCPS) to investigate the distribution of phylogenetic clades across sites, tested its relationship with patch area and isolation using linear models, and for the correlation to species dispersal traits and climbing mechanisms. We employed the treeNODF (Nestedness based on Overlap and Decreasing Fill) method to estimate if there was a phylogenetic, compositional and/or functional nested pattern of the metacommunity structure during forest expansion over grassland. Results We found that species composition distribution was explained by patch size and isolation, but not by phylogeny. Dispersal traits were more structured along the gradient compared to climbing mechanisms. We also found a nested pattern of combined species and phylogenetic/functional diversities, where smaller patches are subsets of larger patches and of continuous forest sites. Conclusion Patch area, isolation and dispersal traits play significant roles in the distribution of climbing plants during the process of forest advance over grassland, independently of phylogenetic relatedness among species. The nested pattern indicated that continuous forest and larger patches provide all the diaspores that colonize the smaller patches in this process, making them important targets for conservation. We analyzed a climbing plant metacommunity along a gradient of forest patches in the process of forest advance over grassland. Patch size and isolation determined species composition but not phylogenetic clades distribution. Phylogenetic and functional diversities were nested throughout the increasing patch size, indicating that larger areas provide most diaspores that colonize smaller patches, making them important targets for conservation.

Description: Questions (1) Which disturbances (harvesting, browsing, drought and fire) are important for tree mortality in a tropical dry forest (TDF)? And do these change with size class (juvenile, sapling, adult)? (2) How is mortality and recruitment in a TDF related to soil moisture content (SMC) and does the relationship change for different size classes? (3) Is disturbance-related mortality selectively removing particular species from the TDFs? Location Sonebhadra and Mirzapur districts of Uttar Pradesh, India. Methods We analysed the structure of a TDF in central India in terms of the tree composition of juveniles, saplings and adults at five distinct sites located along a gradient of SMC, and recorded the numbers of individuals in each size class killed by the four disturbance types over two years. We also recorded total stem density and recruitment at each site. We compared annual mortality index (AMI) and its four disturbance components (harvesting, browsing, drought, fire) and annual recruitment index (ARI), against the mean SMC of each site using generalized linear mixed models. Results The impact of all disturbances on total AMI decreased as SMC increased whereas ARI increased as SMC increased. Mortality due to harvesting was substantially greater than other disturbances for adult and sapling trees whereas both harvesting and browsing were important drivers of mortality for juveniles. There was little evidence that particular species were being deliberately selected for harvesting across sites. Conclusion Tree saplings and adults in this TDF were mainly killed by harvesting, indicating that anthropogenic impacts on tree mortality are more important than non-anthropogenic impacts in the TDF, and impacts of all disturbances are more severe with increasing water stress. Thus changes in TDF structure due to harvesting are likely to be more rapid in more arid environments. This article is protected by copyright. All rights reserved.

Description: Questions How do canopy-understory interactions respond to variation in disturbance severity over extended periods of time? For forests with different disturbance histories, do light availability and understory-cohort densities converge towards a common old-growth structure, or do historical legacies influence populations indefinitely?. Locations Remnants of primary spruce ( Picea abies (L.) Karst.) forests throughout Germany, Slovakia, Ukraine, and Romania. Methods A disturbance history of more than 200 years was reconstructed from 11 278 tree cores collected from forest plots (n = 520). Understory tree densities of two size classes and hemi-photo based light availabilities were inventoried and modelled as functions of the severity of the main disturbance and time since the event. Results Variation in understory tree densities had a hump-shaped distribution through time. Stem densities were approximately static in the least disturbed sites, and they declined in relation to disturbance severity over approximately 100 years. Similar to patterns of stem densities, initially high understory light availability also reached a minimum at 100 years, which indicated crown closure. Following this, light availability and stem densities both increased as stands transitioned from stem exclusion to understory reinitiation. The effect of disturbance severity on understory densities and patchiness in light availability persisted for more than 200 years. Conclusions Long-term trends in canopy-understory interactions validate current conceptual models of forest development. Furthermore, we empirically validate that these conceptual models generalize over gradients in disturbance severity. Higher-disturbance sites exhibited a more even-aged character with more pronounced periods of stem exclusion, canopy closure, and understory reinitiation; forests with low-severity disturbance histories yielded a more stationary uneven-aged structure. The model identified the extent of variation in disturbance severity within which these P . abies forests are able to regenerate and retain their monospecific character, which is increasingly relevant as disturbance regimes continue to shift under global climate change. This article is protected by copyright. All rights reserved.

Description: Questions Forest recovery in Mediterranean environments is influenced by factors such as aridity, herbivory and facilitation by shrubs, as well as by seed limitation in the case of highly fragmented forests. How these various factors interact can determine the direction of secondary succession, yet these interactions are poorly understood. We assessed the relative importance of several factors in forest species recruitment in Retama sphaerocarpa (L.) Boiss (Retama) shrublands at different spatial scales. Location Centre of the Iberian Peninsula. Methods We surveyed mid- and late-successional woody species common in Holm oak forests in 29 Retama shrublands that are distributed along an environmental gradient of increasing aridity and herbivory (regional scale) and are located at various distances from forest patches of different sizes (landscape and local scale). In each Retama shrubland, we analysed the effects of microhabitat (under Retama canopy vs. open gaps); aridity; presence of nurse shrubs; herbivory, based on the density of pellet droppings; and propagule pressure, measured as the ratio between the size of forest patches acting as seed sources and their distance to Retama shrubs. Results Quercus ilex, Asparagus acutifolius and Juniperus oxycedrus were the mid- and late-successional woody species most recruited in Retama shrublands. Their frequency, which increased with precipitation, was greater under Retama canopy than in gaps. Differences in Q. ilex recruitment between Retama canopy or gaps increased with rainfall, suggesting a decrease in Retama facilitation effectivity with increasing aridity. Frequency of recruited oaks increased with the total area of woodland remnants located 〈0.5 km, yet propagule pressure did not modulate the positive effect of Retama and rainfall on recruitment. Forest patches at distances 〉0.5 km did not contribute to recruitment. Conclusions Presence of the shrub Retama sphaerocarpa and dispersal related processes at local scale are main determinants of the colonisation of shrublands by late successional woody species. Preserving Retama shrublands and Q. ilex woodland remnants is therefore crucial for extensive passive restoration of Mediterranean oak forests. However, facilitation by Retama is much weaker when both aridity and herbivory are high, regardless of seed source availability. This article is protected by copyright. All rights reserved.

Description: Aim The European forest-steppe ecotone extends over 6000 km from the Carpathian to the Ural Mountains. It is extensively used for agriculture with very few patches of semi-natural vegetation. Little is known about the history of the forest-steppe ecotone in Eastern Europe and here we examine its Holocene dynamics and stability and investigate when it was transformed to the modern agro-pastoral landscapes. Location Mid-Russian Upland. Methods We summarise the information from five pollen diagrams for the last 7000 years and estimate forest cover using the best modern analogue technique. We use the principal component and principal curve analysis to evaluate compositional changes. Results The pollen data suggest that the east European forest-steppe boundary was located 50-70 km further north-west from the presumed present position during the period 7000–4500 cal yr BP. After 4500 cal yr BP, it moved approximately 100-130 km to the south-east. Since 2000 cal yr BP land-use affected the boundary, while a total forest clearance and transformation to agricultural landscapes took place in the last 400 years. Pollen data indicate a NW – SE direction of the forest-steppe vegetation gradient. Prior to clearance, open lime-pedunculate oak forests existed in the NW, while the south was characterized by pine woodlands with an admixture of oak and lime with 20-40% forest cover. Conclusions The east European forest-steppe ecotone is sensitive to climate change. The Late Holocene expansion of forest cover is in agreement with evidence suggesting an increase in moisture availability during this time. The quick recovery to a similar composition after human disturbance indicates a high resilience of the woodland in the ecotone, which may be connected to a naturally high disturbance regime possibly through fire. The information revealed on the position of the gradient and natural composition of the forest is currently not depicted in maps of the potential natural vegetation. This article is protected by copyright. All rights reserved.

Description: Questions Do vascular plant species richness and β-diversity differ between managed and structurally complex unmanaged stands? To what extent do species richness and β-diversity relate to forest structural attributes and heterogeneity?. Location Five National Parks in central and southern Italy. Methods We sampled vascular plant species composition and forest structural attributes in eight unmanaged temperate mesic forest stands dominated or co-dominated by beech, and in eight comparison stands managed as high forests with similar environmental features. We compared plant species richness, composition and β-diversity, across pairs of stands (unmanaged vs . managed) using Generalized Linear Mixed (effect) Models (GLMMs). β-diversity was quantified both at the scale of each pair of stands using plot-to-plot dissimilarity matrices (species turnover), and across the whole dataset, considering the distance in the multivariate species space of individual plots from the centroid of the plots within the same stand (compositional heterogeneity). We modelled the relationship between species diversity (richness and β-diversity) and forest structural heterogeneity and individual structural variables using GLMMs and Multiple Regression on Distance Matrices. Results Species composition differed significantly between managed and unmanaged stands, but not richness and β-diversity. We found weak evidence that plant species richness increased with increasing levels of structural heterogeneity and canopy diversification. At the scale of individual stands, species turnover was explained by different variables in distinct stands, with variables related to deadwood quantity and quality being selected most often. Conversely, we did not find support to the hypothesis that compositional heterogeneity varies as a function of forest structural characteristics at the scale of the whole dataset. Conclusions Structurally complex unmanaged stands have a distinct herb-layer species composition from that of mature stands in similar environmental conditions; nevertheless, we did not find significantly higher levels of vascular plant species richness and β-diversity in unmanaged stands. β-diversity was related to patterns of deadwood accumulation, while for species richness the evidence that it increases with increasing levels of canopy diversification was weak. These results suggest that emulating natural disturbance, and favoring deadwood accumulation and canopy diversification may benefit some, but not all facets of plant species diversity in Apennine beech forests. This article is protected by copyright. All rights reserved.

Description: Questions Can shrubs ( Cytisus multiflorus ) and large herbivore exclusion (fence) facilitate seedling survival and growth of marcescent and sclerophyllous oaks ( Quercus pyrenaica vs Q. ilex subsp. ballota ) under a bioclimatic limit in Mediterranean grazed areas? Location Open oak woodlands in central-western Spain (41º13’ N, 6º24’ W). Methods A two-year field experiment was conducted by planting 200 seedlings of each Quercus species under four different treatments combining the influence of nurse shrubs and fencing on Quercus seedling survival and growth. Results C. multiflorus enhanced the poor Quercus seedling survival found in the study area, at least during the first two years after planting and particularly during the first dry season. The improvement in soil organic matter under shrub canopy may have contributed to this positive effect, which was more pronounced on Q. pyrenaica seedlings. Seedling herbivory did not seem to be a limitation to survival. Increase seedling growth in both species was also very low and no growth was recorded two years after planting without shrubs. The positive shrub effect on seedling growth, especially marked in fenced areas, was more important in Q. pyrenaica in the first growing period and in Q. ilex in the second; two years after planting no different shrub effect on growth was found in either Quercus species. Seedling herbivory was a limitation to seedling growth in areas without shrubs, mainly in the case of Q. pyrenaica . Conclusions In Mediterranean grazed areas with important summer drougth and very sandy soils, shrubby Cytisus multiflorus plants have a clear facilitative effect on seedlings of ecologically-contrasted Quercus species. The facilitative effect was found in both marcescent and sclerophyllous oak seedlings, but to a different degree depending on the species considered and the variable measured (survival or growth). In terms of survival, the marcescent species was more favored by shrub cover than the sclerophyllous one, and this effect was accentuated throughout time. However, in terms of growth, although Q. pyrenaica was initially more favored by shrubs, differences between both species were attenuated after two years. Therefore, C. multiflorus can have a key role in the restoration of these oak degraded environments. This article is protected by copyright. All rights reserved.