A generalized,lumped-parameter model of photosynthesis,evapotranspiration and net primary production in temperate and boreal forest ecosystems

Summary PnET is a simple, lumped-parameter, monthlytime-step model of carbon and water balances of forests built on two principal relationships: 1) maximum photosynthetic rate is a function of foliar nitrogen concentration, and 2) stomatal conductance is a function of realized photosynthetic rate. Monthyly leaf area display and carbon and water balances are predicted by combining these with standard equations describing light attenuation in canopies and photosynthetic response to diminishing radiation intensity, along with effects of soil water stress and vapor pressure deficit (VPD). PnET has been validated against field data from 10 well-studied temperate and boreal forest ecosystems, supporting our central hypothesis that aggregation of climatic data to the monthly scale and biological data such as foliar characteristics to the ecosystem level does not cause a significant loss of information relative to long-term, mean ecosystem responses. Sensitivity analyses reveal a diversity of responses among systems to identical alterations in climatic drivers. This suggests that great care should be used in developing generalizations as to how forests will respond to a changing climate. Also critical is the degree to which the temperature responses of photosynthesis and respiration might acclimate to changes in mean temperatures at decadal time scales. An extreme climate change simulation (+3° C maximum temperature, –25% precipitation with no change in minimum temperature or radiation, direct effects of increased atmospheric CO₂ ignored) suggests that major increases in water stress, and reductions in biomass production (net carbon gain) and water yield would follow such a change.     

Inter‐specific Variation in Foliar Nutrients and Resorption of Nine Canopy‐tree Species in a Secondary Neotropical Rain Forest

The influence of environmental gradients on the foliar nutrient economy of forests has been well documented; however, we have little understanding of what drives variability among individuals within a single forest stand, especially tropical forests. We evaluated inter‐ and intra‐specific variation in nutrient resorption, foliar nutrient concentrations and physical leaf traits of nine canopy tree species within a 1‐ha secondary tropical rain forest in northeastern Costa Rica. Both nitrogen (N) and phosphorus (P) resorption efficiency (RE) and proficiency of the nine tree species varied significantly among species, but not within. Both N and P RE were significantly negatively related to leaf specific strength. Green leaf N and P concentrations were strongly negatively related to leaf mass per area, and senesced leaf nutrient concentrations were significantly positively related to green leaf nutrient concentrations. This study reveals a strong influence of physical leaf traits on foliar nutrient and resorption traits of co‐occurring species in a secondary wet tropical forest stand.     

Imaging spectroscopy reveals the effects of topography and logging on the leaf chemistry of tropical forest canopy trees

Logging, pervasive across the lowland tropics, affects millions of hectares of forest, yet its influence on nutrient cycling remains poorly understood. One hypothesis is that logging influences phosphorus (P) cycling, because this scarce nutrient is removed in extracted timber and eroded soil, leading to shifts in ecosystem functioning and community composition. However, testing this is challenging because P varies within landscapes as a function of geology, topography and climate. Superimposed upon these trends are compositional changes in logged forests, with species with more acquisitive traits, characterized by higher foliar P concentrations, more dominant. It is difficult to resolve these patterns using traditional field approaches alone. Here, we use airborne light detection and ranging‐guided hyperspectral imagery to map foliar nutrient (i.e. P, nitrogen [N]) concentrations, calibrated using field measured traits, over 400 km² of northeastern Borneo, including a landscape‐level disturbance gradient spanning old‐growth to repeatedly logged forests. The maps reveal that canopy foliar P and N concentrations decrease with elevation. These relationships were not identified using traditional field measurements of leaf and soil nutrients. After controlling for topography, canopy foliar nutrient concentrations were lower in logged forest than in old‐growth areas, reflecting decreased nutrient availability. However, foliar nutrient concentrations and specific leaf area were greatest in relatively short patches in logged areas, reflecting a shift in composition to pioneer species with acquisitive traits. N:P ratio increased in logged forest, suggesting reduced soil P availability through disturbance. Through the first landscape scale assessment of how functional leaf traits change in response to logging, we find that differences from old‐growth forest become more pronounced as logged forests increase in stature over time, suggesting exacerbated phosphorus limitation as forests recover.     

Foliar production and decomposition rates in urban forests invaded by the exotic invasive shrub, <Emphasis Type="Italic">Lonicera maackii</Emphasis>

Exotic invasive shrubs can form dense monocultures in forest understories, which can have cascading effects on ecosystem structure and function. Amur honeysuckle, an exotic shrub that forms dense canopies in eastern forests, has the potential to alter plant community structure and ecosystem functions, such as primary production and decomposition. The goal of this study was to examine foliar productivity and leaf litter decomposition in forests invaded by Amur honeysuckle (Lonicera maackii) and to determine the extent to which the presence of this dominant exotic species may alter ecosystem function in these forests. We found that forests invaded by Amur honeysuckle had 16 times greater honeysuckle foliar biomass and 1.5 times lower total foliar biomass than forests of equivalent tree basal area, but having few honeysuckle shrubs. This suggests that productivity of native tree and shrub species may be reduced where honeysuckle density is high. Additionally, honeysuckle litter decayed four times faster and released nitrogen more rapidly than sugar maple litter, and sugar maple litter decayed 19% faster in forests invaded by Amur honeysuckle. These findings suggest that forests invaded by Amur honeysuckle may exhibit lower rates of organic matter accrual and less nitrogen retention in the forest floor. Since honeysuckle leaves develop in early spring before those of other shrubs or trees in the area, the rapid release of nitrogen from honeysuckle litter that we measured in early spring is timed to benefit this invasive species. The temporally coincident phenologies of nitrogen release during decomposition with the foliar growth needs of this shrub indicates that a potential positive feedback loop may exist between these processes that promotes continued growth and dominance of honeysuckle shrubs in these forested systems.     

Liana optical traits increase tropical forest albedo and reduce ecosystem productivity

Lianas are a key growth form in tropical forests. Their lack of self-supporting tissues and their vertical position on top of the canopy make them strong competitors of resources. A few pioneer studies have shown that liana optical traits differ on average from those of colocated trees. Those trait discrepancies were hypothesized to be responsible for the competitive advantage of lianas over trees. Yet, in the absence of reliable modelling tools, it is impossible to unravel their impact on the forest energy balance, light competition, and on the liana success in Neotropical forests. To bridge this gap, we performed a meta-analysis of the literature to gather all published liana leaf optical spectra, as well as all canopy spectra measured over different levels of liana infestation. We then used a Bayesian data assimilation framework applied to two radiative transfer models (RTMs) covering the leaf and canopy scales to derive tropical tree and liana trait distributions, which finally informed a full dynamic vegetation model. According to the RTMs inversion, lianas grew thinner, more horizontal leaves with lower pigment concentrations. Those traits made the lianas very efficient at light interception and significantly modified the forest energy balance and its carbon cycle. While forest albedo increased by 14% in the shortwave, light availability was reduced in the understorey (?30% of the PAR radiation) and soil temperature decreased by 0.5°C. Those liana-specific traits were also responsible for a significant reduction of tree (?19%) and ecosystem (?7%) gross primary productivity (GPP) while lianas benefited from them (their GPP increased by +27%). This study provides a novel mechanistic explanation to the increase in liana abundance, new evidence of the impact of lianas on forest functioning, and paves the way for the evaluation of the large-scale impacts of lianas on forest biogeochemical cycles.     

Inquiring into the causes of depressed folivory in a fragmented temperate forest

Folivory is lower in forest fragments of the Maulino forest than in continuous stands. We experimentally assessed whether depressed folivory is related to a reduction in foliar palatability caused by the more xeric microclimate of forest fragments. We compared leaf anatomy at fragments and continuous forest for four tree species (Aristotelia chilensis, Cryptocarya alba, Nothofagus glauca and Gevuina avellana), and evaluated consumption of leaves of the two different habitats by insect species (Sericoides viridis and Ormiscodes rufosignata).Anatomy of leaves of fragments differs from that from continuous forest in at least one of the traits, for all the plant species. However, not all species exhibit more sclerophyllous traits in forest fragments. A. chilensis exhibits the greatest number of changes, being more sclerophyllous in fragments. In palatability trials, there were no differences in the consumption of leaves of fragments versus leaves of continuous forest. Therefore, depressed folivory levels in forest remnants of the Maulino forest do not seem to be attributable to reduced foliar palatability, suggesting that changes in the insect assemblage, and not palatability, account for reduced herbivory in fragmented forests.     

The incidence and implications of clouds for cloud forest plant water relations

Although clouds are the most recognisable and defining feature of tropical montane cloud forests, little research has focussed on how clouds affect plant functioning. We used satellite and ground‐based observations to study cloud and leaf wetting patterns in contrasting tropical montane and pre‐montane cloud forests. We then studied the consequences of leaf wetting for the direct uptake of water accumulated on leaf surfaces into the leaves themselves. During the dry season, the montane forest experienced higher precipitation, cloud cover and leaf wetting events of longer duration than the pre‐montane forest. Leaf wetting events resulted in foliar water uptake in all species studied. The capacity for foliar water uptake differed significantly between the montane and pre‐montane forest plant communities, as well as among species within a forest. Our results indicate that foliar water uptake is common in these forest plants and improves plant water status during the dry season.     

山东滨海盐碱地11个造林树种叶解剖特征对土壤条件的响应

叶片作为植物与大气环境连接的重要纽带, 对逆境具有强烈的响应。基于叶性状探讨植物对环境的适应机制对盐碱地植物群落构建具有指导意义。该研究以山东省滨海盐碱地3种不同土壤条件下的11个造林树种为对象, 通过对各树种叶解剖性状的测定分析, 阐明叶片功能性状与盐碱地土壤环境的关系, 以期为盐碱地植被修复与群落构建提供科学依据。主要研究结果: (1) 11个树种的叶片厚度较大, 栅栏组织发达, 紧密排列在叶肉近轴面, 呈3-5层。各树种叶片的栅栏组织与海绵组织厚度比值(PT/ST)普遍较高但差异较大, 可指示叶解剖特征在树种间的差异性。(2)不同树种的叶解剖结构在立地环境间具有显著差异, PT/ST可作为指示指标。(3)相关分析和冗余分析表明, 树种叶片解剖结构与立地土壤条件具有密切联系。PT/ST与土壤理化性质相关程度高, 且与土壤pH以及土壤电导率(25 ℃)均呈显著正相关关系, 与土壤硝态氮含量呈显著负相关关系。叶片特征和叶脉特征可解释叶性状随环境变异约84%的信息量。综上所述,叶解剖结构与盐碱地土壤条件存在密切关系, 基于叶解剖特征可进一步分析树种对盐碱环境的适应性, 并为盐碱地植物群落构建的树种选择提供科学依据。     

Seasonal patterns of herbivory,leaf traits and productivity consumption in dry and wet Patagonian forests

1. Endemic herbivory can influence forest ecosystem function, but how annual productivity consumption relates to seasonal resource utilisation by folivore guilds remains poorly understood. 2. Monthly changes in leaf damage and foliage traits were monitored in ‘dry’ and ‘wet’Nothofagus pumilio (Fagales: Nothofagaceae) deciduous forests in northern Patagonia, Argentina. Herbivore‐induced leaf abscission was assessed and foliar productivity consumption was measured in the canopy and in litterfall harvests. 3. Seasonal damage ranged from 8% to 32% in dry forest, but remained below 5% in wet forest although foliar quality was higher in the latter. In dry forest, dominant guilds were temporally separated; leaf miners consumed younger foliage in spring to early summer, whereas leaf tiers prevailed in late summer to autumn. In wet forest, damage created by external chewers was concentrated in early summer. 4. Insect damage induced premature leaf abscission, especially in dry forest. Although foliar production in wet forest doubled that in dry forest, the percentage of productivity lost to folivores was higher in dry (14–20%) than in wet (1.2–1.8%) forest. 5. The overall greater impact of herbivory in dry forest canopies countered the expectation that consumption would increase with plant productivity and nutritional quality. Lower temperatures and a shorter growing season are likely to constrain folivory in wet forest stands.     

Drivers of within-tree leaf trait variation in a tropical planted forest varying in tree species richness

In plant ecology, community-weighted trait means are often used as predictors for ecosystem functions. More recently, also within-species trait variation has been confirmed to contribute to ecosystem functioning. We here go even further and assess within-individual trait variation, assuming that every leaf in a plant individually adjusts to its micro-environment. Using forest plots varying in tree species richness (Sardinilla experiment, Panama), we analysed how leaf traits within individual trees vary along the vertical crown gradient. Furthermore, we tested whether niche partitioning in mixed stands results in a decrease of within-species leaf trait variation and whether niche partitioning can be also observed at the level of individual trees. We focused on leaf traits that describe the growth strategy along the conservative-acquisitive spectrum of growth. We found a decrease in within-species variation of specific leaf area (SLA) with increasing neighbourhood species richness. Both sampling height and local neighbourhood richness contributed to explaining within-species leaf trait variation, which however, varied in importance among different species and traits. With increasing sampling height, leaf dry matter content (LDMC), carbon to nitrogen ratio and lignin content increased, while leaf nitrogen concentration (leaf N), SLA, cellulose and hemicellulose decreased. Variation in leaf N decreased with increasing neighbourhood species richness, while the magnitude of within-individual variation of most traits was unaffected by neighbourhood species richness. Our results suggest an increased niche partitioning with increasing species richness both in a plant community and at the level of individual plants. Our findings highlight the importance of including within-individual trait variation to understand biodiversity-ecosystem functioning relationships.     

Reprint of: Drivers of within-tree leaf trait variation in a tropical planted forest varying in tree species richness

In plant ecology, community-weighted trait means are often used as predictors for ecosystem functions. More recently, also within-species trait variation has been confirmed to contribute to ecosystem functioning. We here go even further and assess within-individual trait variation, assuming that every leaf in a plant individually adjusts to its micro-environment. Using forest plots varying in tree species richness (Sardinilla experiment, Panama), we analysed how leaf traits within individual trees vary along the vertical crown gradient. Furthermore, we tested whether niche partitioning in mixed stands results in a decrease of within-species leaf trait variation and whether niche partitioning can be also observed at the level of individual trees. We focused on leaf traits that describe the growth strategy along the conservative-acquisitive spectrum of growth. We found a decrease in within-species variation of specific leaf area (SLA) with increasing neighbourhood species richness. Both sampling height and local neighbourhood richness contributed to explaining within-species leaf trait variation, which however, varied in importance among different species and traits. With increasing sampling height, leaf dry matter content (LDMC), carbon to nitrogen ratio and lignin content increased, while leaf nitrogen concentration (leaf N), SLA, cellulose and hemicellulose decreased. Variation in leaf N decreased with increasing neighbourhood species richness, while the magnitude of within-individual variation of most traits was unaffected by neighbourhood species richness. Our results suggest an increased niche partitioning with increasing species richness both in a plant community and at the level of individual plants. Our findings highlight the importance of including within-individual trait variation to understand biodiversity-ecosystem functioning relationships.     

Functional diversity of carbon-gain, water-use, and leaf-allocation traits in trees of a threatened lowland dry forest in Hawaii

We examined carbon-gain, water-use, and leaf-allocation traits for six tree species of a Hawaiian dry forest to better understand the functional diversity within this threatened ecosystem. Tropical dry forests are among the most endangered ecosystems on Earth, and in Hawaii, as elsewhere, declining biodiversity threatens ecosystem processes that may depend on forest functional diversity. We found broad variation among species including a two-fold difference for mean photosynthetic rate, a greater than three-fold difference for predawn water potential, and a nearly three-fold difference for leaf life span. Principal component analysis showed a clear separation of species based on carbon-gain vs. water-use related axes, and δ(13)C analysis revealed differing limitations (supply vs. demand) on carbon assimilation. The broad functional variation not only spanned traditional classifications (avoiders vs. tolerators), but also included unusual strategies (e.g., fast growth with drought tolerance). Correlations among traits, including leaf life span, leaf mass per area, and %N, followed typical global patterns, but some exceptions appeared as a result of unique life-history characteristics, such as latex-rich sap and root parasitism. Elucidating functional variation provides important information that can be used to link plant biodiversity with ecosystem processes and also facilitate the management and preservation of tropical dry forests and other threatened communities.     

南亚热带不同海拔常绿阔叶林树种叶性状的比较分析

南亚热带地带性植被是季风常绿阔叶林(海拔300～600 m;简称季风林),在中山地带则分布为山地常绿阔叶林(海拔1 000～1 500 m;简称山地林)。山地林的生态价值日益受到重视,但是对其树种的环境适应性仍缺乏足够了解。该研究基于南亚热带典型山地林(广西大明山)和季风林(广东鼎湖山)的固定样地,共测定57种代表性树种的叶形态解剖特征、机械强度和水力学性状,比较不同海拔常绿阔叶林树种叶性状以及多类性状关联性的差异。结果表明,与季风林树种相比,山地林树种叶较厚、比叶面积较小、机械强度较高,有利于提高对较高海拔山区冬季冰冻的适应能力。在2022年夏季持续高温干旱时期,季风林树种的叶水势和水力安全边界均低于山地林。但是大部分树种水力安全边界为正值且种间变异较大,表明不同海拔常绿阔叶林的水力风险较低。不同海拔常绿阔叶林的叶性状网络不同,山地林树种叶水力安全性和效率性无权衡关系,而季风林树种叶经济学性状(如比叶面积)与其他指标的关联性较弱。基于叶性状的研究揭示了南亚热带不同海拔常绿阔叶林树种适应策略的差异性和多样性。     

Plant functional traits with particular reference to tropical deciduous forests: a review

Functional traits (FTs) integrate the ecological and evolutionary history of a species, and can potentially be used to predict its response as well as its influence on ecosystem functioning. Study of inter-specific variation in the FTs of plants aids in classifying species into plant functional types (PFTs) and provides insights into fundamental patterns and trade-offs in plant form and functioning and the effect of changing species composition on ecosystem functions. Specifically, this paper focuses on those FTs that make a species successful in the dry tropical environment. Following a brief overview, we discuss plant FTs that may be particularly relevant to tropical deciduous forests (TDFs). We consider the traits under the following categories: leaf traits, stem and root traits, reproductive traits, and traits particularly relevant to water availability. We compile quantitative information on functional traits of dry tropical forest species. We also discuss trait-based grouping of plants into PFTs. We recognize that there is incomplete knowledge about many FTs and their effects on TDFs and point out the need for further research on PFTs of TDF species, which can enable prediction of the dynamics of these forests in the face of disturbance and global climate change. Correlations between structural and ecophysiological traits and ecosystem functioning should also be established which could make it possible to generate predictions of changes in ecosystem services from changes in functional composition.     

Light-exposed shoots of seven coexisting deciduous species show common photosynthetic responses to tree height

Functional traits of light-exposed leaves have been reported to show tree height-dependent change. However, it remains unknown how plastic response of leaf traits to tree height is linked with shoot-level carbon gain. To answer this question, we examined the photosynthetic properties of fully lit current-year shoots in crown tops with various heights for seven deciduous broad-leaved species dominated in a cool–temperate forest in northern Japan. We measured leaf mass, stomatal conductance, nitrogen content, light-saturated net photosynthetic rate (all per leaf lamina area), foliar stable carbon isotope ratio, and shoot mass allocation to leaf laminae. We employed hierarchical Bayesian models to simultaneously quantify inter-trait relationships for all species. We found that leaf and shoot traits were co-varied in association with height, and that there was no quantitative inter-specific difference in leaf- and shoot-level plastic responses to height. Nitrogen content increased and stomatal conductance decreased with height. Reflecting these antagonistic responses to height, photosynthetic rate was almost unchanged with height. Photosynthetic rate divided by stomatal conductance as a proxy of photosynthetic water use efficiency sufficiently explained the variation of foliar carbon isotope ratio. The increase in mass allocation to leaves in a shoot compensated for the height-dependent decline in photosynthetic rate per leaf lamina mass. Consequently, photosynthetic gain at the scale of current-year shoot mass was kept unchanged with tree height. We suggest that the convergent responses of shoot functional traits across species reflect common requirements for trees coexisting in a forest.     

Experimental warming studies on tree species and forest ecosystems: a literature review

Temperature affects a cascade of ecological processes and functions of forests. With future higher global temperatures being inevitable it is critical to understand and predict how forest ecosystems and tree species will respond. This paper reviews experimental warming studies in boreal and temperate forests or tree species beyond the direct effects of higher temperature on plant ecophysiology by scaling up to forest level responses and considering the indirect effects of higher temperature. In direct response to higher temperature (1) leaves emerged earlier and senesced later, resulting in a longer growing season (2) the abundance of herbivorous insects increased and their performance was enhanced and (3) soil nitrogen mineralization and leaf litter decomposition were accelerated. Besides these generalizations across species, plant ecophysiological traits were highly species-specific. Moreover, we showed that the effect of temperature on photosynthesis is strongly dependent on the position of the leaf or plant within the forest (canopy or understory) and the time of the year. Indirect effects of higher temperature included among others higher carbon storage in trees due to increased soil nitrogen availability and changes in insect performance due to alterations in plant ecophysiological traits. Unfortunately only a few studies extrapolated results to forest ecosystem level and considered the indirect effects of higher temperature. Thus more intensive, long-term studies are needed to further confirm the emerging trends shown in this review. Experimental warming studies provide us with a useful tool to examine the cascade of ecological processes in forest ecosystems that will change with future higher temperature.     

Fungal endophyte communities in two tropical forests of southern India: diversity and host affiliation

Fifteen tree species from a tropical dry thorn forest and fifteen tree species from a tropical dry deciduous forest in the Mudumalai Wildlife Sanctuary, Nilgiri Biosphere Reserve, southern India, were surveyed for their foliar endophyte communities during the dry and wet seasons. Surface sterilized leaf segments of uniform dimension were plated on nutrient agar and culturable endophytes growing from the segments were identified. Endophyte diversity was greater in the dry thorn forest than in the dry deciduous forest in the dry season. Although the isolation frequency of culturable endophytes increased for both forests during the wet season, the assemblages were represented not by any unique fungal species but by the commonly occurring ones. Furthermore, although individual leaves were densely colonized by endophytes, only a few species of endophytes colonized the whole leaves; and, only a few fungal species dominated the foliar endophytic communities and were common for both forests during both dry and wet seasons. Thus, even under wet conditions that favour dispersal and infection by fungi, the endophyte diversity increased only marginally, an indication that certain tropical forests are not hyperdiverse with reference to fungal endophytes. This should be considered when using culturable endophyte diversity as a surrogate for estimating global fungal diversity.     

Coordinated changes in photosynthesis,water relations and leaf nutritional traits of canopy trees along a precipitation gradient in lowland tropical forest

We investigated leaf physiological traits of dominant canopy trees in four lowland Panamanian forests with contrasting mean annual precipitation (1,800, 2,300, 3,100 and 3,500 mm). There was near complete turn-over of dominant canopy tree species among sites, resulting in greater dominance of evergreen species with long-lived leaves as precipitation increased. Mean structural and physiological traits changed along this gradient as predicted by cost–benefit theories of leaf life span. Nitrogen content per unit mass (N_mass) and light- and CO₂-saturated photosynthetic rates per unit mass (P_mass) of upper canopy leaves decreased with annual precipitation, and these changes were partially explained by increasing leaf thickness and decreasing specific leaf area (SLA). Comparison of 1,800 mm and 3,100 mm sites, where canopy access was available through the use of construction cranes, revealed an association among extended leaf longevity, greater structural defense, higher midday leaf water potential, and lower P_mass, N_mass, and SLA at wetter sites. Shorter leaf life spans and more enriched foliar ¹⁵N values in drier sites suggest greater resorption and re-metabolism of leaf N in drier forest. Greater dominance of short-lived leaves with relatively high P_mass in drier sites reflects a strategy to maximize photosynthesis when water is available and to minimize water loss and respiration costs during rainless periods. Overall, our study links coordinated change in leaf functional traits that affect productivity and nutrient cycling to seasonality in lowland tropical forests.     

Oak trees and soil interactions in Mediterranean forests: a positive feedback model

Questions: What is the spectrum of variability of chemical elements in a Mediterranean forest ecosystem across the different compartments? Do co‐existing tree species with different leaf chemical composition and nutrient cycling distinctly modify soil conditions? Could these species‐specific, tree‐generated soil changes create a potential positive feedback by affecting long‐term species distribution? Location: Mixed oak forests of southern Spain, Los Alcornocales Natural Park. Methods: We sampled and chemically analysed five different ecosystem components: leaves, leaf fall, litter and superficial (0–25 cm) and sub‐superficial (25–50 cm) soil beneath the canopies of evergreen Quercus suber and deciduous Q. canariensis trees. We used multiple co‐inertia analysis (MCoA) to conjointly analyse the patterns of variability and covariation of eight macro‐ and micronutrients determined in each of the sampled ecological materials. We implemented a path analysis to investigate alternative causal models of relationships among the chemical properties of the different ecosystem components. Results: Variability in the concentration of chemical elements was related to the nature of their biogeochemical cycles. However, the rank of element concentration was consistent across ecosystem components. Analysis of co‐inertia (MCoA) revealed that there was a common underlying multivariate pattern of nutrient enrichment in the ecosystem, which supported the hypothesis of a separation in biogeochemical niches between the two co‐existing oak species, with Q. canariensis having richer plant tissues and more fertile soil directly under each tree than Q. suber. The feasibility of a potential tree–soil positive feedback model was the only statistically validated among several alternative (non‐feedback) models tested. Conclusions: In the studied Mediterranean forests, oak species distinctly modify soil fertility conditions through different nutrient return pathways. Further investigation is needed to address whether these tree‐generated soil changes could affect seedling establishment and ultimately influence species distribution.     

Fungal disease incidence along tree diversity gradients depends on latitude in European forests

European forests host a diversity of tree species that are increasingly threatened by fungal pathogens, which may have cascading consequences for forest ecosystems and their functioning. Previous experimental studies suggest that foliar and root pathogen abundance and disease severity decrease with increasing tree species diversity, but evidences from natural forests are rare. Here, we tested whether foliar fungal disease incidence was negatively affected by tree species diversity in different forest types across Europe. We measured the foliar fungal disease incidence on 16 different tree species in 209 plots in six European countries, representing a forest‐type gradient from the Mediterranean to boreal forests. Forest plots of single species (monoculture plots) and those with different combinations of two to five tree species (mixed species plots) were compared. Specifically, we analyzed the influence of tree species richness, functional type (conifer vs. broadleaved) and phylogenetic diversity on overall fungal disease incidence. The effect of tree species richness on disease incidence varied with latitude and functional type. Disease incidence tended to increase with tree diversity, in particular in northern latitudes. Disease incidence decreased with tree species richness in conifers, but not in broadleaved trees. However, for specific damage symptoms, no tree species richness effects were observed. Although the patterns were weak, susceptibility of forests to disease appears to depend on the forest site and tree type.