Biology subjects

Bauhus, J.

Publications and source records attributed to Bauhus, J..

7 recordsLinked to original sources

bioRxiv2025

Resource economics of tree communities control soil food web multifunctionality in European forests

Plants affect terrestrial ecosystem functioning by performing the primary production that energetically sustains heterotrophic organisms1, and by shaping the microenvironment2. However, the influence of plant diversity and community composition on ecosystem functioning through their effects on energy flow into food webs has been little studied3,4, especially for soil food webs that channel most of the plant-derived energy1,5. Applying a food web energetics approach6,7, we show that the resource economics of dominant tree species control soil food web multifunctionality across European forests. Specifically, tree communities dominated by resource acquisitive species promoted faster rates of multiple soil trophic functions simultaneously than did those dominated by resource conservative species. This was primarily driven by their production of plant litter with higher nutritional quality and their warmer forest microclimate, leading to a higher metabolic activity of soil organisms8. Tree species mixing had rather weak and negative effects on soil food web multifunctionality, mostly due to a shift in the resource-based energy channeling from living plant fine roots to litter and a cooling effect on the forest microclimate. Tree diversity effects were largely outweighed by community compositional effects, which were of similar magnitude to the effects of biogeographic differences among locations. Our findings emphasize the importance of plant functional traits related to resource economics as drivers of plant community effects on soil food web functioning5,9 and highlight the consequences that climate-driven shifts in tree community composition could have for forest soil functioning.

ecology↗

bioRxiv2024

Multi-year drought strengthens positive and negative functional diversity effects on tree growth response

O_LIMixed-species forests are proposed as strategy to increase the resistance and resilience of forests to drought stress. However, evidence suggest that increasing tree species richness does not consistently enhance tree growth responses to drought. Moreover, tree diversity effects under unprecedented multiyear droughts remain uncertain, calling for a better understanding of the underlying processes. C_LIO_LIHere, we used a network of planted tree diversity experiments to investigate how drought-induced growth responses of individual trees are influenced by neighborhood tree diversity and the functional traits of the focal tree species. We analyzed tree cores (948 trees across 16 species) from nine experiments across Europe featuring gradients of tree species richness (1-6 species), which experienced severe droughts in recent years. Radial growth response to drought was quantified as tree-ring biomass increment using X-ray computed tomography. We applied hydraulic trait-based growth models to analyze single-year drought responses across all sites and site-specific responses during consecutive drought years for six sites as a function of neighborhood tree diversity. C_LIO_LIThe large variability in tree growth responses to a single-year drought was partially explained by the focal species hydraulic safety margin (representing species drought tolerance) and drought intensity, but independent of neighborhood species richness or functional trait diversity. However, tree diversity effects on growth responses strengthened during consecutive drought years and were site-specific, with contrasting direction (both positive and negative). This indicated opposing pathways of diversity effects under consecutive drought events, possibly resulting from competitive release or greater water consumption in diverse mixtures. C_LIO_LIWe conclude that tree diversity effects on growth responses to single-year droughts may differ considerably from responses to consecutive drought years. Our study highlights the need to consider trait-based approaches (specifically, hydraulic traits) and tree neighborhood scale processes to understand the multifaceted growth responses of tree mixtures under prolonged drought stress. C_LI

ecology↗

bioRxiv2022

Neighbourhood species richness and drought-tolerance traits modulate tree growth and δ13C responses to drought

O_LIMixed-species forests are promoted as a forest management strategy for climate change adaptation, but whether they are more resistant to drought than monospecific forests remains contested. Particularly, the trait-based mechanisms driving the role of tree diversity under drought remain elusive. C_LIO_LIUsing tree cores from a large-scale biodiversity experiment, we investigated tree growth and physiological stress responses (i.e. increase in wood carbon isotopic ratio; {delta}13C) to changes in climate-induced water availability (wet to dry years) along gradients in neighbourhood tree species richness and drought-tolerance traits. We hypothesized that neighbourhood species richness increases growth and decreases {delta}13C and that these relationships are modulated by the abiotic (i.e. climatic conditions) and the biotic context. We characterized the biotic context using drought-tolerance traits of focal trees and their neighbours. These traits are related to cavitation resistance vs resource acquisition and stomatal control. C_LIO_LITree growth increased with neighbourhood species richness. However, we did not observe a universal relief of water stress in species-rich neighbourhoods. Neighbourhood species richness effects on growth and {delta}13C did not strengthen from wet to dry years. Instead, richness-growth and richness-{delta}13C relationships were modulated by climatic conditions and the traits of trees and their neighbours. At either end of each drought-tolerance gradient, species responded in opposing directions during drought and non-drought years. C_LIO_LIWe show that species drought-tolerance traits can explain the strength and nature of biodiversity-ecosystem functioning relationships in experimental tree communities experiencing drought. Mixing tree species can increase growth but may not universally relieve drought stress. C_LI One-sentence summaryThe drought-tolerance traits of trees and their neighbours determine biodiversity-ecosystem functioning relationships in experimental tree communities.

ecology↗

bioRxiv2022

Tracing the origin of Oriental beech stands across Western Europe and reporting hybridization with European beech - implications for assisted gene flow

Human-aided translocation of individuals within the species range, assisted gene flow (AGF), has been suggested as a climate change mitigation strategy, especially for foundational species, such as forest trees. The benefits and risks of AGF largely depend on the genetic divergence between host and donor populations, their rate and direction of hybridization, and the climate distance that the transfer involves. In this study, we explored the use of Oriental beech (Fagus sylvatica subsp. orientalis), growing from Iran to the Balkans, for AGF in populations of European beech (F. sylvatica subsp. sylvatica), which grow throughout Europe and are increasingly affected by climate warming. Using 16 microsatellite loci and samples from 13 and 6 natural populations of Oriental and European beech, respectively, we identified 5 distinct genetic clusters in Oriental beech with a divergence (FST) of 0.15 to 0.25 from European beech. Using this knowledge, we tracked the origin of 11 Oriental beech stands in Western Europe, some established in the early 1900s. In two stands of Greater Caucasus origin, we additionally genotyped offspring and found evidence for extensive hybridization, with 41.3% and 17.8% of the offspring having a hybrid status. Further, climate data revealed a higher degree of seasonality across the Oriental beech growing sites than across the planting sites in Western Europe, with some sites additionally having a warmer and drier climate. Accordingly, in one of these stands, we found evidence that bud burst of Oriental beech occurs four days earlier than in European beech. These results suggest that AGF of Oriental beech could increase the genetic diversity of European beech stands and may even help the introgression of variants that are more adapted to future climatic conditions. Our study showcases an evaluation of the benefits and risks of AGF and calls for similar studies on other native tree species.

evolutionary biology↗

bioRxiv2021

Hydraulic diversity stabilizes productivity in a large-scale subtropical tree biodiversity experiment

Extreme climatic events threaten forests and their climate mitigation potential globally. Understanding the drivers promoting ecosystem stability is therefore considered crucial to mitigate adverse climate change effects on forests. Here, we use structural equation models to explain how tree species richness, asynchronous species dynamics and diversity in hydraulic traits affect the stability of forest productivity along an experimentally manipulated biodiversity gradient ranging from 1 to 24 tree species. Tree species richness improved stability by increasing species asynchrony. That is, at higher species richness, inter-annual variation in productivity among tree species buffered the community against stress-related productivity declines. This effect was mediated by the diversity of species hydraulic traits regarding drought tolerance and stomatal control, but not by the community-weighted means of these traits. The identified mechanisms by which tree species richness stabilizes forest productivity emphasize the importance of hydraulically diverse, mixed-species forests to adapt to climate change.

ecology↗

bioRxiv2020

Mutually inclusive mechanisms of drought-induced tree mortality

An extreme summer drought caused unprecedented tree dieback across Central Europe in 2018, highlighting the need for a better mechanistic understanding of drought-induced tree mortality. While numerous physiological risk factors have been identified, the principal mechanisms, hydraulic failure and carbon starvation, are still debated. We studied 9,435 trees from 12 temperate species planted in a diversity experiment in 2013 to assess how hydraulic traits, carbon dynamics, pest infestation, tree height and neighbourhood competition influence individual mortality risk. We observed a reduced mortality risk for trees with wider hydraulic safety margins, while a rising sugar fraction of the non-structural carbohydrate pool and bark beetle infestation were associated with higher risk. Taller trees had a lower mortality risk. The sign and magnitude of neighbourhood effects on mortality risk depended on the species-identity of the involved trees, with most species having beneficial and some having deleterious effects on their neighbours. While severe tissue dehydration causing hydraulic failure precedes drought-induced tree mortality, we show that the probability of this event depends on a series of mutually inclusive processes including pest infestation and starch depletion for osmotic adjustment, and is modulated by the size and species identity of a tree and its neighbours.

ecology↗

bioRxiv2017

Strong positive biodiversity-productivity relationships in a subtropical forest experiment

Forest ecosystems contribute substantially to global terrestrial primary productivity and climate regulation, but, in contrast to grasslands, experimental evidence for a positive biodiversity-productivity relationship in highly diverse forests is still lacking1. Here, we provide such evidence from a large forest biodiversity experiment with a novel design2 in subtropical China. Productivity (stand-level tree basal area, aboveground volume and carbon and their annual increment) increased linearly with the logarithm of tree species richness. Additive partitioning3 showed that increasing positive complementarity effects combined with weakening negative selection effects caused a strengthening of the relationship over time. In 2-species mixed stands, complementary effects increased with functional distance and selection effects with vertical crown dissimilarity between species. Understorey shrubs reduced stand-level tree productivity, but this effect of competition was attenuated by shrub species richness, indicating that a diverse understorey may facilitate overall ecosystem functioning. Identical biodiversity-productivity relationships were found in plots of different size, suggesting that extrapolation to larger scales is possible. Our results highlight the potential of multi-species afforestation strategies to simultaneously contribute to mitigation of climate change and biodiversity restoration.

ecology↗