No generality in biodiversity-productivity relationships along elevation in temperate and subtropical forest landscapes

An improved understanding of biodiversity-productivity relationships(BPRs)along environmental gradients is crucial for effective ecosystem management and biodiversity conservation.The stress-gradient hypothesis suggests that BPRs are stronger in stressful environments compared to more favorable conditions.However,there is limited knowledge regarding the variation of BPRs along elevational gradients and their generality across different landscapes.To study how BPRs change with elevation,we harnessed inventory data on 6,431 trees from152 plots surveyed twice in eight to ten year intervals in mountain forests of temperate Europe and subtropical Asia.We quantified the relationship between aboveground productivity and different biodiversity measures,including taxonomic,functional,and phylogenetic diversity.To elucidate the processes underlying BPRs,we studied the variation of different functional traits along elevation across landscapes.We found no general pattern of BPRs across landscapes and elevations.Relationships were neutral for all biodiversity measures in temperate forests,and negative for taxonomic and functional diversity in subtropical forests.BPRs were largely congruent between taxonomic,functional and phylogenetic diversity.We found only weak support for the stress-gradient hypothesis,with BPRs turning from negative to positive(effect not significant)close to the tree line in subtropical forests.In temperate forests,however,elevation patterns were strongly modulated by species identity effects as influenced by specific traits.The effect of traits such as community-weighted mean of maximum plant height and wood density on productivity was congruent across landscapes.Our study highlights the context-dependence of BPRs across elevation gradients and landscapes.Species traits are key modulating factors of BPRs and should be considered more explicitly in studies of the functional role of biodiversity.Furthermore,our findings highlight that potential trade-offs between conserving biodiversity and fostering ecosystem productivity exist,which require more attention in policy and management.

Species-specific effects of genetic diversity and species diversity of experimental communities on early tree performance

Aims Changing biodiversity can affect ecosystem functioning.However,the role of genetic diversity within species,relative to the one of species diversity,has hardly been addressed.Methods To address the effects of both genetic diversity and species diversity during the important stage of early tree life,we used eight seed families(SF)taken from each of 12 evergreen and deciduous tree species of subtropical forest to perform a factorial experiment.We established 264 communities of 16 trees each.Each community had a species diversity of either one or four species and a genetic diversity of either one,two or four SF per species.We measured plant survival,growth rate,final biomass and herbivory 20 months after sowing.Important Findings Species differed from each other in biomass,growth rate,herbivory and survival(P<0.001).Deciduous species tended to have much higher biomass(P<0.1)and experienced higher herbivory(P<0.05)than evergreen species.Species diversity affected the performance of different species differently(species diversity by species interaction,P<0.001 for all variables but survival).Biomass differed between SF and increasing genetic diversity from one to two,and from two to four,SF per species increased biomass for some species and decreased it for others(P<0.001).Our study showed pronounced species-specific responses of early tree performance to species diversity and less pronounced responses to genetic diversity.These species-specific responses suggest feedbacks of species diversity and genetic diversity on future species composition.

Impact of tree diversity and environmental conditions on the survival of shrub species in a forest biodiversity experiment in subtropical China

Aims Although shrubs are an important component of forests,their role has not yet been considered in forest biodiversity experiments.In the biodiversity-ecosystem functioning(BEF)experiment with subtropical tree species in south-east China(BEF-China),we factorially combined tree with shrub species-diversity treatments.Here,we tested the hypotheses that shrub survival differs between the 10 planted shrub species,with lower survival rates of late-than early-successional species and is affected by environmental conditions,such as topography and top soil characteristics,as well as by biotic factors,represented by tree,shrub and herb layer characteristics.Methods We analyzed the survival of 42000 shrub individuals in 105 plots varying in tree and shrub species richness of the BEF-China project four years after planting.Shrub survival was analyzed with generalized linear mixed effects models at the level of individuals and with variance partitioning at the plot level.Random intercept and random slope models of different explanatory variables were compared with respect to the Bayesian Information Criterion(BIC).Important Findings Survival rates differed largely between the 10 shrub species,ranging from 26%to 91%for Ardisia crenata and Distylium buxifolium,respectively.Irrespective of species identity,single abiotic factors explained up to 5%of species survival,with a negative effect of altitude and slope inclination and a positive effect of the topsoil carbon to nitrogen ratio,which pointed to drought as the major cause of shrub mortality.In contrast,neither tree nor shrub richness affected shrub survival at this early stage of the experiment.Among the biotic predictors,only herb layer species richness and cover of the dominant fern species(Dicranopteris pedata)affected shrub survival.Overall,our models that included all variables could explain about 65%in shrub survival,with environmental variables being most influential,followed by shrub species identity,while tree species diversity(species richness and identity)and herb layer characteristics contributed much less.Thus,in this early stage of the experiment the biotic interactions among shrubs and between shrubs and trees have not yet overruled the impact of abiotic environmental factors.

No plant functional diversity effects on foliar fungal pathogens in experimental tree communities

Foliar fungal pathogens affect forest ecosystem processes by exerting highly species-specific impacts on growth and survival of trees.As many ecosystem processes in forests depend on functional diversity of specific tree species,a close relationship is expected between this and foliar fungal pathogen infestation.Testing for such a relationship in the German tree diversity experiment BIOTREE(Bechstedt),we hypothesized that pathogen richness and pathogen load decline with increasing functional diversity of tree communities.Using macro-and microscopic analyses,we assessed pathogen richness and load on 16 tree species in plots that,although differing in functional diversity,had the same tree species richness.We found no effects of functional diversity on pathogen richness or load.However,we encountered strong species identity effects in plot species composition,as susceptible tree species contributed positively to each community’s pathogen richness and load.Furthermore,testing for effects of particular leaf traits and geographical range size of host species revealed a significant effect of total leaf phenolics,which was unexpected as pathogen richness increased with increasing content in polyphenolics.Our study showed that at the community level,host species’identity was more important for foliar fungal pathogen richness and load than the functional diversity of host trees.The positive relationship between pathogen richness and phenolics in leaves,along with the finding that pathogen richness is very much conserved in tree species,point to an evolutionary arms race between hosts and fungi resulting from fungi increasing their capacity to infect tree leaves and trees boosting their defences.