Simulating functional diversity of European natural forests along climatic gradients

Aim: We analyse how functional diversity (FD) varies across European natural forests to understand the effects of environmental and competitive filtering on plant trait distribution. Location: Forest ecosystems in Europe from 11°W to 36°E and 29.5°N to 62°N. Taxon: Pinaceae, Fagaceae and Betulaceae, Oleaceae, Tiliaceae, Aceraceae, Leguminosae (unspecific). Methods: We adopted the existing Dynamic Global Vegetation Model Lund-Potsdam- Jena managed Land of flexible individual traits (LPJmL-FIT) for Europe by eliminating both bioclimatic limits of plant functional types (PFTs) and replacing prescribed values of functional traits for PFTs with emergent values under influence of environmental filtering and competition. We quantified functional richness (FR), functional diver- gence (FDv) and functional evenness (FE) in representative selected sites and at Pan- European scale resulting from simulated functional and structural trait combinations of individual trees. While FR quantifies the amount of occupied trait space, FDv and FE describe the distribution and abundance of trait combinations, respectively, in a multidimensional trait space. Results: Lund-Potsdam-Jena managed Land of flexible individual traits reproduces spatial PFTs and local trait distributions and agrees well with observed productivity, biomass and tree height of European natural forests. The observed site-specific trait distributions and spatial gradients of traits of the leaf- and stem-resource economics spectra coincide with environmental filtering and the competition for light and water in environments with strong abiotic stress. Where deciduous and needle-leaved trees co-occur, for example, in boreal and mountainous forests, the potential niche space is wide (high FR), and extreme ends in the niche space are occupied (high FDv). We find high FDv in Mediterranean forests where drought increasingly limits tree growth, thus niche differentiation becomes more important. FDv decreases in temperate for- ests where a cold climate increasingly limits growth efficiency of broad-leaved sum- mer green trees, thus reducing the importance of competitive exclusion. Highest FE was simulated in wet Atlantic and southern Europe which indicated relatively even niche occupation and thus high resource-use efficiency. Main Conclusions: We find FD resulting from both environmental and competitive filtering. Pan-European FR, FDv and FE demonstrate the influence of climate gradi- ents and intra- and inter-PFT competition. The indices underline a generally high FD of natural forests in Europe. Co-existence of functionally diverse trees across PFTs emerges from alternative (life-history) strategies, disturbance and tree demography.

研究目的：本研究分析欧洲天然林的功能多样性（functional diversity, FD）空间变异特征，旨在揭示环境过滤与竞争过滤对植物性状分布的影响机制。
研究区域：欧洲森林生态系统，地理范围介于西经11°至东经36°、北纬29.5°至北纬62°之间。
研究类群：松科（Pinaceae）、壳斗科（Fagaceae）、桦木科（Betulaceae）、木犀科（Oleaceae）、椴树科（Tiliaceae）、槭树科（Aceraceae）、豆科（Leguminosae，未特指具体类群）。
研究方法：本研究采用经调整的动态全球植被模型——隆德-波茨坦-耶拿管理土地灵活个体性状模型（Lund-Potsdam-Jena managed Land of flexible individual traits, LPJmL-FIT）欧洲版本，去除植物功能型（plant functional type, PFT）的生物气候限制，并将PFT预设功能性状值替换为受环境过滤与竞争影响下的涌现值。研究在代表性样点及全欧洲尺度上，量化个体树木功能与结构性状组合所形成的功能丰富度（functional richness, FR）、功能离散度（functional divergence, FDv）及功能均匀度（functional evenness, FE）。其中，FR衡量性状空间的占据量，FDv与FE分别描述多维性状空间中性状组合的分布特征与丰度特征。
研究结果：LPJmL-FIT模型可重现欧洲天然林的植物功能型空间分布及局域性状分布，并与观测到的生产力、生物量及树高数据高度吻合。叶与茎资源经济谱性状的局域分布及空间梯度特征，与强非生物胁迫环境下的环境过滤及光水竞争过程一致。在落叶树与针叶树共存区域（如寒带及山地森林），潜在生态位空间较广（FR较高），且生态位空间的极端端被占据（FDv较高）。地中海森林因干旱加剧限制树木生长，生态位分化更为重要，故FDv较高；温带森林中，寒冷气候限制阔叶夏绿树的生长效率，竞争排斥作用减弱，FDv降低；湿润大西洋区域及南欧模拟出最高的FE值，表明生态位占据相对均匀，资源利用效率较高。
主要结论：欧洲天然林的功能多样性由环境过滤与竞争过滤共同驱动。全欧洲尺度的FR、FDv及FE指标反映了气候梯度及植物功能型内部与种间竞争的影响。这些指标表明欧洲天然林总体功能多样性较高。跨植物功能型的功能多样树木共存现象，源于替代（生活史）策略、干扰及树木种群动态等因素。