Relative importance of climate vs local factors in shaping the regional patterns of forest plant richness across northeast China

Northeast (NE) China covers three climatic zones and contains all the major forest types of NE Asia. We sampled 108 forest plots in six nature reserves across NE China to examine the influence of climate and local factors (canopy seasonality, successional stage, topography and forest structure) on geographic patterns of plant richness. We analyzed the relative effects of different factors at two spatial scales: the regional scale (across both latitude and altitude) and the local scale (along the altitudinal gradient within site). Our results showed that the relative importance of climate vs local factors differed remarkably depending on scale and functional group. While total and tree species richness were mainly limited by climate, herb and shrub richness was more related to local factors (especially at the local scale). In the climatic factors, heat sum was the major correlate of tree, shrub and total species richness, while herb richness was more associated with winter coldness. Precipitation was not a limiting factor for forest plant richness in NE China. Climate accounted for 34–76% of variation in richness at the regional scale, but explained only 0–44% at the local scale. Among the local factors, shrub species richness was sensitive to seasonal canopy openness, with higher richness in deciduous forests than in the evergreen needle-leaf forest. On the other hand, herb richness was sensitive to forest successional stage, with higher richness in middle- successional forests than in the early and late-sucessional forests. Local topography (aspect and position on slope) and forest structure (tree density) also showed remarkable influence on species richness. Our results suggest the importance of including local factors when examining large scale diversity gradient (especially for understory species), and the necessity of comparing diversity patterns among functional groups at different spatial scales.     

河北小五台山国家级自然保护区森林群落与环境的关系

植物与环境之间的关系是一个复杂的演变过程,运用数量生态学方法探讨森林群落的物种组成、种群的生态特征、不同植物群落与环境之间的关系,有助于保护该区森林群落的稳定性和生物多样性。根据148个森林群落样方数据,选用双向指示种分析(TWINSPAN)和典范对应分析(CCA)方法,对河北小五台山国家级自然保护区森林群落进行分类和排序研究。结果表明:(1)TWINSPAN将该区的森林群落分为20个类型;(2)CCA排序结果较好地反映出群落分布格局与环境梯度的关系,各个森林群落类型在前两轴分异明显,在11个环境因子中,海拔、坡位、凋落层厚度、土壤导电率、土壤温度、土壤湿度、土壤厚度和干扰程度这8个环境因子对森林群落的分布起较大的作用,影响森林群落的分布格局,形成不同的植被类型。(3)乔木层优势种的CCA二维排序图所揭示的环境梯度与群落类型的分布有很大的相似性;t值双序图阐明了海拔、凋落层厚度、土壤温度、干扰程度等环境因子对森林群落乔木层优势种有着重要影响。采用TWINSPAN分类与CCA排序的方法,较好地解释了森林群落与环境因子的关系,为小五台山地区森林生态系统的科学管理和保护提供了理论依据,研究结果也为同类地区森林生态系统研究及保护提供参考和借鉴。     

应用排序分析藓类植物分类群分布与气候因素的关系

以我国21个山地藓类植物区系和气象资料为基础,应用典范对应分析(CCA)和除趋势典范对应分析(DCCA),比较了21个山地中藓类植物61个科,曲尾藓科(Dicranaceae)23个属、曲柄藓属(Campylopus)17种及曲尾藓属(Dicranum)35种分布与年均温度、>10℃积温、1月均温、7月均温、年均相对湿度、年均降雨量、年有雾天数、年有霜天数和年日照时数的关系,通过排序进行了直观的展示;同时还应用典范对应分析直观地反映了包括长白山在内的我国9个山地苔藓植物地理成分组成上的相似性及它们与气候因素间的关系.本文研究表明将DCCA和CCA应用到植物区系地理学研究上是可行的.     

山西灵空山小蛇沟林下草本层植物群落梯度分析及环境解释

通过对山西灵空山小蛇沟集水区的林下草本层植物群落进行调查和多元分析——TWINSPAN分类、典范对应分析(CCA)与生境、生物因素变量分离, 探讨林分水平上草本层物种分布与环境因子之间的关系。结果如下: 1) TWINSPAN将26个调查样方划分为6种群落类型: 以辽东栎(Quercus wutaishanica)为主的辽东栎-油松(Pinus tabulaeformis)林型、辽东栎杂木林型、辽东栎林型、华北落叶松(Larix principis-rupprechtii)林型、油松林和阔叶油松林型、油松-辽东栎均匀混交林型, 体现了该地区地带性植被类型为暖温带森林的特点。2)群落类型的划分与CCA的结果相吻合, 主要反映了CCA排序第一、二轴的环境梯度, CCA排序轴第一轴突出反映了林分类型与土壤养分梯度, 第二排序轴与坡度、坡位显著相关。Monte Carlo检验结果表明, 林分类型、土壤养分和坡度是影响小蛇沟集水区内林下草本物种分异的最主要的环境因子。3)生境因子与生物因子解释了物种格局变化的42.9%, 其中生境因子占31.8%, 生物因子占7.9%, 生境因子与生物因子交互作用解释部分占3.2%。良好的环境解释反映了调查取样和环境因子选取的合理性。对于50%以上未能被解释的变异部分, 可能归咎于未被选取的因子如干扰或者随机过程。4)在海拔梯度较小的山区, 坡向等小地形因子能较好地指示局部生境的小气候条件, 对林下植物的分布有较好的解释力。     

秦岭山地天然次生林群落MRT数量分类、CCA排序及多样性垂直格局

采用多元回归树(MRT)对秦岭山地天然次生林群落进行数量分类,采用典范对应分析(CCA)进行排序,分析了秦岭山地天然次生林群落物种多样性沿海拔梯度的变化规律。结果表明:(1) 275个样方共有种子植物195种,隶属61科128属。乔、灌、草3个层次物种多样性变化沿海拔梯度的变化趋势基本一致,呈单峰模型;(2)经交叉验证认为秦岭山地天然次生林群落可分为2类,Ⅰ冬瓜杨(Populus purdomii)+陇东海棠(Malus kansuensis)+蛇莓(Duchesnea indica)群落,Ⅱ锐齿槲栎(Quercus aliena var. acuteserrata)+黄栌(Cotinus coggygria)+茜草(Rubia cordifolia)群落;(3) CCA排序结果揭示了群落生境的分布范围,反映出生态轴的排序意义,较好地反映秦岭山地天然次生林群落与环境因子的关系,其结果表明,海拔、坡向、凋落层厚度和干扰情况4个变量对该地区次生林群落的分布有较大的影响。     

Tree species distribution in temperate forests is more influenced by soil than by climate

Knowledge of the ecological requirements determining tree species distributions is a precondition for sustainable forest management. At present, the abiotic requirements and the relative importance of the different abiotic factors are still unclear for many temperate tree species. We therefore investigated the relative importance of climatic and edaphic factors for the abundance of 12 temperate tree species along environmental gradients. Our investigations are based on data from 1,075 forest stands across Switzerland including the cold‐induced tree line of all studied species and the drought‐induced range boundaries of several species. Four climatic and four edaphic predictors represented the important growth factors temperature, water supply, nutrient availability, and soil aeration. The climatic predictors were derived from the meteorological network of MeteoSwiss, and the edaphic predictors were available from soil profiles. Species cover abundances were recorded in field surveys. The explanatory power of the predictors was assessed by variation partitioning analyses with generalized linear models. For six of the 12 species, edaphic predictors were more important than climatic predictors in shaping species distribution. Over all species, abundances depended mainly on nutrient availability, followed by temperature, water supply, and soil aeration. The often co‐occurring species responded similar to these growth factors. Drought turned out to be a determinant of the lower range boundary for some species. We conclude that over all 12 studied tree species, soil properties were more important than climate variables in shaping tree species distribution. The inclusion of appropriate soil variables in species distribution models allowed to better explain species' ecological niches. Moreover, our study revealed that the ecological requirements of tree species assessed in local field studies and in experiments are valid at larger scales across Switzerland.     

中条山混沟地区森林乔木种的数量分类与环境解释

通过对中条山混沟地区森林植被调查资料的多元分析——TWINSPAN分类、CCA排序与环境解释,划分了该地区的植被类型,给出了植被与环境因子的定量关系。结果如下:1)40个样地可划分为青檀林(Form.Pteroceltis tatarinowii)、栾树林(Form. Koelreuteria paniculata)、槲栎林(Form. Quercus aliena)、栓皮栎林(Form. Quercus variabilis)、鹅耳枥+葛萝槭林(Form. Carpinus turczaninowii+Acer grosseri)、元宝槭+千金榆林(Form. Acer truncatum+Carpinus cordata)和辽东栎林(Form. Quercus liaotungensis)7种群落类型,体现了中条山地带性植被类型为暖温带落叶阔叶林的特点。2)群落类型的划分主要反映了CCA排序第一、二轴的环境梯度,CCA排序第一轴突出反映了海拔与土壤养分梯度,第二轴与土壤pH值、湿度指数和坡度显著相关。总体来说,海拔和土壤因子是影响混沟地区乔木物种分布分异的最主要环境因子。3)环境因子和空间因子解释了物种格局变化的46.14%,其中环境因子占30.79%,空间因子占8.48%,空间因子和环境因子交互作用解释的部分占6.87%。良好的环境解释反映了调查取样和环境因子选取的合理性,同时也体现了混沟地区植被的原始性。     

Mountain landscapes offer few opportunities for high‐elevation tree species migration

Climate change is anticipated to alter plant species distributions. Regional context, notably the spatial complexity of climatic gradients, may influence species migration potential. While high‐elevation species may benefit from steep climate gradients in mountain regions, their persistence may be threatened by limited suitable habitat as land area decreases with elevation. To untangle these apparently contradictory predictions for mountainous regions, we evaluated the climatic suitability of four coniferous forest tree species of the western United States based on species distribution modeling (SDM) and examined changes in climatically suitable areas under predicted climate change. We used forest structural information relating to tree species dominance, productivity, and demography from an extensive forest inventory system to assess the strength of inferences made with a SDM approach. We found that tree species dominance, productivity, and recruitment were highest where climatic suitability (i.e., probability of species occurrence under certain climate conditions) was high, supporting the use of predicted climatic suitability in examining species risk to climate change. By predicting changes in climatic suitability over the next century, we found that climatic suitability will likely decline, both in areas currently occupied by each tree species and in nearby unoccupied areas to which species might migrate in the future. These trends were most dramatic for high elevation species. Climatic changes predicted over the next century will dramatically reduce climatically suitable areas for high‐elevation tree species while a lower elevation species, Pinus ponderosa, will be well positioned to shift upslope across the region. Reductions in suitable area for high‐elevation species imply that even unlimited migration would be insufficient to offset predicted habitat loss, underscoring the vulnerability of these high‐elevation species to climatic changes.     

Climate-growth relations of congeneric tree species vary across a tropical vegetation gradient in Brazil

Seasonally dry tropical forests are an important global climatic regulator, a main driver of the global carbon sink dynamics and are predicted to suffer future reductions in their productivity due to climate change. Yet, little is known about how interannual climate variability affects tree growth and how climate-growth responses vary across rainfall gradients in these forests. Here we evaluate changes in climate sensitivity of tree growth along an environmental gradient of seasonally dry tropical vegetation types (evergreen forest – savannah – dry forest) in Northeastern Brazil, using congeneric species of two common neotropical genera: Aspidosperma and Handroanthus. We built tree-ring width chronologies for each species × forest type combinations and explored how growth variability correlated with local (precipitation, temperature) and global (the El Niño Southern Oscillation - ENSO) climatic factors. We also assessed how growth sensitivity to climate and the presence of growth deviations varied along the gradient. Precipitation stimulates tree growth and was the main growth-influencing factor across vegetation types. Trees in the dry forest site showed highest growth sensitivity to interannual variation in precipitation. Temperature and ENSO phenomena correlated negatively with growth and sensitivity to both climatic factors were similar across sites. Negative growth deviations were present and found mostly in the dry-forest species. Our results reveal a dominant effect of precipitation on tree growth in seasonally dry tropical forests and suggest that along the gradient, dry forests are the most sensitivity to drought. These forests may therefore be the most vulnerable to the deleterious effects of future climatic changes. These results highlight the importance of understanding the climatic sensitivity of different tropical forests. This understanding is key to predict the carbon dynamics in tropical regions, and sensitivity differences should be considered when prioritizing conservation measures of seasonally dry topical forests.     

气候变化对阔叶红松林潜在地理分布区的影响

物种地理分布主要取决于它对气候、地形等环境因子的适应性。基于22个环境因子和阔叶红松林的4类主要建群树种——红松、紫椴、水曲柳和蒙古栎的地理分布数据,采用最大熵模型模拟了阔叶红松林的潜在分布区域,并分析决定阔叶红松林地理分布的主要气候和地形因子,最后利用政府间气候变化专门委员会(IPCC)发布的3种排放场景(SRES-A2、SRES-A1B、SRES-B1)下2020、2050、2080年的气候数据预测阔叶红松林的未来潜在分布区。结果表明:各树种的受试者工作特征曲线下面积(AUC值)都大于0.8,说明模型有很好的预测能力;影响阔叶红松林分布的主导环境因子是年降雨量、季节性降雨量、海拔、年平均温度、最湿季度的平均温度。在基准气候条件下,阔叶红松林的高度适宜分布区主要分布在长白山和小兴安岭地区,占研究区总面积的11.69%,低度适宜区面积、不适宜区面积分别占研究区总面积的23%和65.31%。模型预测结果显示,未来在A2、A1B和B1气候情景下,阔叶红松林高度适宜区的南界与北界都向北移动,其面积有缩减的趋势,而低度适宜区的面积有增加的趋势。     

山西太岳山脱皮榆群落的生态梯度分析及环境解释

为了解释山西太岳山脱皮榆(Ulmus lamellosa)群落中物种的分布情况与该群落环境因子之间的相互关系,采用TWINSPAN数量分类和典范对应分析(CCA)与环境因子的变量分离进行讨论。结果表明,TWINSPAN将60个调查样方划分为7种群丛类型,体现了该脱皮榆群落主要以乔木脱皮榆和草本披针叶苔草(Carex lanceolata)为优势种。7种群丛类型与CCA排序结果一致,CCA排序第1轴主要体现了坡位和海拔;坡向与第2排序轴存在显著相关性。Monte Carlo检验结果表明,影响脱皮榆群落物种分布最主要的环境因子是海拔。在环境分离变量解释方面,环境因子解释了39.60%,空间因子解释了7.95%,空间因子与环境因子交互作用解释部分占10.89%。而其中不能解释的部分占41.56%。在该研究区,海拔对植物的分布有较好的解释力,其次是坡位和坡向。     

凉水自然保护区阔叶红松林林分空间结构特征及其与影响因子关系简

根据凉水自然保护区28块典型阔叶红松林样地的5个林分空间结构参数和18个影响因子数据,采用典范对应分析（CCA）方法,对凉水自然保护区阔叶红松林林分空间结构与影响因子间关系进行分析。研究结果表明：（1）研究区域阔叶红松林整体具有较好的林分空间结构,其水平分布格局主要表现为随机分布,树木生长整体处于中庸状态,林木的整体混交程度较高;（2）林分空间结构的CCA排序较好的揭示了该区林分空间结构与影响因子的关系;CCA第一排序轴反映了林龄、坡度、阔叶比和坡向的变化,第二排序轴反映了坡向、土壤有机质和平均胸径的变化,上述6因子的组合是决定林分空间结构特征的主要影响因子;（3）影响林分空间结构的变量中,地形、土壤和林分因子共解释了林分空间结构变化的59.20%,其中纯地形因子占30.68%,纯林分因子占19.01%,纯土壤因子占8.21%,未能解释部分为40.80%。     

Relationships between vegetation and climate on the Loess Plateau in China

The Loess Plateau is one of the most environmentally sensitive regions in China. This study addresses the relationships between vegetation and climate of this area quantitatively at a large-scale, in order to determine the factors that control vegetation distribution. The Loess Plateau, located at 101°01′–155°10′ E and 34°02′–40°40′ N, covers an area of 52 million hectares. Vegetation data were collected from the vegetation map (1:500,000) and the Landsat Thematic Mapper scenes of the Loess Plateau. The Loess Plateau was divided into small districts of 30′ latitude by 30′ longitude on the vegetation map. In each district, areas with different vegetation were measured and used as vegetation data. The climatic data were average values of county meteorological records in each district in the past 25 years. GIS, TWINSPAN and canonical correspondence analysis (CCA) were employed for analysis. 257 small districts were clustered into 7 groups using TWINSPAN, representing 7 vegetation regions or subregions. The first three CCA axes had significant correlations with climate. The first CCA axis represented the variation of vegetation and climate along the latitude gradient, while the second CCA axis the variation along the longitude gradient. The distribution pattern of 171 vegetation formations on the CCA plot is identical to that of vegetation regions (districts). The spatial distribution of vegetation is closely related to climate variables on the Loess Plateau. Water variables and temperature are important in both latitude and longitude gradients, while the sunshine hours, accumulated temperature and wind speed are more important than water variables and temperature in longitude gradients.     

Environmental,Spatial and Structural Components in the Composition of Mountain Forest in the Bavarian Alps

A combined systematic and stratified sampling design was conducted in mountain forests of the Bavarian Alps to find the principal dimensions of compositional variation of vegetation and their environmental drivers. In 1,505 plots species composition, forest types and soil profiles were recorded. Data from 14 climate stations were included. As we hypothesized that the tree layer is more influenced by management than the understorey and that the former modifies the habitat of the latter, the two matrices were analysed separately and the species composition of the tree layer was used as a structural predictor variable for the understorey. We applied constrained ordination to reveal the main gradients in floristic composition and variance partitioning to examine the portions of climatic, edaphic, spatial and structural components. Ellenberg indicator values and a generalized linear model were used to test whether a significant spatial gradient exists from east to west, the main spatial extent of the investigation area. Forest types were used as an overlay to assess the underlying environmental factors. It turned out that explained variance of the tree layer was considerably lower than in the understorey. Tree layer composition was more influenced by climatic variables than by soil. In the understorey, edaphic and climatic variables contributed almost equally to explained variance, but the tree layer had an additional explanatory power. No continentality gradient could be detected within the investigation area. Plant communities were well separated along gradients of acidity, moisture, nutrients and climate, which broadly confirms the known gradients for montane and subalpine zonal forests in the region. The study provides a quantitative synthesis of the knowledge on a diverse set of community types, which has so far been subject to disparate and sectorial treatment in the Bavarian Alps.     

中国东北地区12个建群树种对气候变化响应的MaxEnt模型分析

气候变化是当前全球生物多样性面临的最大威胁之一,对物种地理分布格局具有较大影响。东北森林物种丰富度较高,目前尚缺乏基于主要树种、未来不同气候模式的综合研究。基于12种建群树种的分布数据及23个环境变量（19个生物气候因子、土地利用类型、海拔、坡度、坡向）数据,应用MaxEnt模型首次对东北地区乔木树种在3种气候变化情景下（SSP126可持续路径、SSP245中间路径、SSP585化石燃料为主发展路径）的潜在丰富度分布格局、主导环境变量以及树种损失、获得和周转情况进行了预测。结果表明：不同未来气候情景下东北地区各树种的潜在分布变化存在差异,适生区面积减小的树种有：兴安落叶松、山杨、春榆、白桦、水曲柳、胡桃楸、蒙古栎、辽东桤木,减小幅度达到10%-30%;适生区面积变化不大的树种有：红皮云杉、樟子松、黄檗,多数情况下低、中和高适生区面积变化发生了抵消,导致总适生区面积变化不大;适生区增加的树种有：红松,增加幅度达20%左右。环境因素将影响东北地区乔木树种潜在适宜性分布,其中,降水因素对东北地区树种分布格局起关键作用,尤其是降水量季节性变化,是影响东北地区50%左右树种分布格局的主导环境因子。东北地区乔木树种在无迁移和SSP585气候情景下受威胁程度相对较高,而在SSP126气候情景下大多处于低风险状态;物种迁移假设的对物种受威胁程度的影响先于气候变化情景的影响,树种发生适度迁移能够缓解树种受威胁的状况。网格单元中物种损失和周转的预测表明,东北地区树种高周转率主要由树种高损失率造成,损失率较高的地区往往树种周转率也相对较高。预测气候变化对东北地区树木分布格局的影响,有助于制定更有效的气候变化适应策略,以促进东北地区树木的可持续发展。     

Strong effect of climate on ectomycorrhizal fungal composition: evidence from range overlap between two mountains

Separating the effects of environmental factors and spatial distance on microbial composition is difficult when these factors covary. We examined the composition of ectomycorrhizal (EM) fungi along elevation gradients on geographically distant mountains to clarify the effect of climate at the regional scale. Soil cores were collected from various forest types along an elevation gradient in southwestern Japan. Fungal species were identified by the internal transcribed spacer regions of the rDNA using direct sequencing. The occurrence of fungal species in this study was compared with a previous study conducted on a mountain separated by ∼550 km. In total, we recorded 454 EM fungi from 330 of 350 soil cores. Forty-seven fungal species (∼20% of the total excluding singletons) were shared between two mountains, mostly between similar forest types on both mountains. Variation partitioning in redundancy analysis revealed that climate explained the largest variance in EM fungal composition. The similarity of forest tree composition, which is usually determined by climatic conditions, was positively correlated with the similarity of the EM fungal composition. However, the lack of large host effects implied that communities of forest trees and EM fungi may be determined independently by climate. Our data provide important insights that host plants and mutualistic fungi may respond to climate change idiosyncratically, potentially altering carbon and nutrient cycles in relation to the plant–fungus associations.     

Patterns and determinants of wood physical and mechanical properties across major tree species in China

The physical and mechanical properties of wood affect the growth and development of trees, and also act as the main criteria when determining wood usage. Our understanding on patterns and controls of wood physical and mechanical properties could provide benefits for forestry management and bases for wood application and forest tree breeding. However, current studies on wood properties mainly focus on wood density and ignore other wood physical properties. In this study, we established a comprehensive database of wood physical properties across major tree species in China. Based on this database, we explored spatial patterns and driving factors of wood properties across major tree species in China. Our results showed that(i) compared with wood density, air-dried density, tangential shrinkage coefficient and resilience provide more accuracy and higher explanation power when used as the evaluation index of wood physical properties.(ii) Among life form, climatic and edaphic variables, life form is the dominant factor shaping spatial patterns of wood physical properties, climatic factors the next, and edaphic factors have the least effects, suggesting that the effects of climatic factors on spatial variations of wood properties are indirectly induced by their effects on species distribution.     

Forest community survey and the structural characteristics of forests in China

Most of the world’s terrestrial biome types can be found in China. To systematically investigate species composition and structure of China’s forest communities, we launched a long‐term project consisting forest vegetation surveys across China’s mountains in the mid 1990s. Over the study period, we have conducted vegetation surveys for 65 mountains and collected vegetation data from about 1500 forest plots, using consistent sampling protocols. In this paper we first introduce the aims, protocols, and major research themes of the project, and then describe the major characteristics of forest communities and their geographic patterns and climatic controls. As latitude increased, diameter at breast height (DBH) and height of trees increased, while individual density of trees and woody species richness decreased. Total basal area (TBA) of trees and species richness of herbs did not vary with latitude. Contemporary climate seems to drive these patterns: temperature was the leading factor for DBH, precipitation was most important for tree height and individual density, actual evapotranspiration (a surrogate of productivity) determined woody (trees and shrubs) species richness, and rainfall was the major controller of the herb species richness. The species–abundance relationship showed that species dominance (measured by the number of individuals per species) declined significantly from boreal forests to evergreen broadleaf forests from north to south. Our results are in line with the idea that productivity drives woody species richness. Similarly, we find that biomass (measured as TBA) is invariant along the environmental gradients. However, individual density varies dramatically, in contrast to the assumptions underlying the metabolic theory of ecology.     

中国主要树种木材物理力学属性的地理格局及其环境控制

木材的物理力学属性制约树木生长发育的重要过程,也是决定木材用途的主要依据.研究木材的物理力学属性及其影响因素,可为合理应用木材、科学开展林木选育、改进林业管理等提供必要参考.目前已有的研究多关注单一的木材密度指标,且缺乏多种影响因子的比较.本研究通过建立中国木材物理力学属性及影响因素综合数据库,对自然状态下我国主要树种木材力学属性的分布格局及其驱动因素进行了探讨.结果表明,选择气干密度、弦向干缩系数和冲击韧性作为评估木材物理力学属性的基础指标,比单一木材密度指标更准确,解释率更高;在选用的生活型、气候和土壤等3类因素中,生活型是影响木材力学物理属性变化的最重要因素,气候因子次之,土壤因子基本可忽略,并且气候和土壤因子的作用被生活型所掩盖,这意味着气候因子对于木材物理力学属性的影响是通过影响物种分布而产生作用的.     

How does forest landscape structure explain tree species richness in a Mediterranean context?

Although the strong relationship between vegetation and climatic factors is widely accepted, other landscape composition and configuration characteristics could be significantly related with vegetation diversity patterns at different scales. Variation partitioning was conducted in order to analyse to what degree forest landscape structure, compared to other spatial and environmental factors, explained forest tree species richness in 278 UTM 10 × 10 km cells in the Mediterranean region of Catalonia (NE Spain). Tree species richness variation was decomposed through linear regression into three groups of explanatory variables: forest landscape (composition and configuration), environmental (topography and climate) and spatial variables. Additionally, the forest landscape characteristics which significantly contributed to explain richness variation were identified through a multiple regression model. About 60% of tree species richness variation was explained by the whole set of variables, while their joint effects explained nearly 28%. Forest landscape variables were those with a greater pure explanatory power for tree species richness (about 15% of total variation), much larger than the pure effect of environmental or spatial variables (about 2% each). Forest canopy cover, forest area and land cover diversity were the most significant composition variables in the regression model. Landscape configuration metrics had a minor effect on forest tree species richness, with the exception of some shape complexity indices, as indicators of land use intensity and edge effects. Our results highlight the importance of considering the forest landscape structure in order to understand the distribution of vegetation diversity in strongly human-modified regions like the Mediterranean.