Floristic composition in relation to environmental gradients across KwaZulu‐Natal,South Africa

Conservation planning in the face of global change is still in its infancy. A suggested approach is to incorporate environmental gradients into conservation planning as they reflect the ecological and evolutionary processes generating and maintaining diversity. Our study provides a framework to identify the dominant environmental gradients determining floristic composition and pattern. Nonmetric multidimensional scaling was used on 2155 sampling plots in savanna and grassland habitat located across the province of KwaZulu‐Natal, South Africa (94 697 km²), a floristically rich region having steep environmental gradients, to determine the dominant gradients. Hierarchical cluster analysis was used to group similar plots which were then used in a Classification and Regression Tree analysis to determine the environmental delimiters of the identified vegetation clusters. Temperature‐related variables were the strongest delimiters of floristic composition across the province, in particular mean annual temperature. Frost duration was the primary variable in the Classification and Regression Tree analysis with important implications for savanna/grassland dynamics. Soil properties (base, pH status) and moisture variables accounted for most of the variation for the second and third axes of floristic variation. Given that climatic and edaphic variables were well correlated with floristic composition, it is anticipated that a changing climate will have a marked influence on floristic composition. We predict warmer temperatures may facilitate the spread of frost sensitive savanna species into previously cooler, grassland areas. Species associated with specific soil types will not easily be able to move up the altitudinal gradient to cooler climes because geology is aligned in an approximately north‐south direction compared with increasing altitude from east‐west. Future conservation planning should take cognisance of these gradients which are surrogates for ecological and evolutionary processes promoting persistence.     

Environmental filters and patterns of tree regeneration in high altitude sub-tropical Quercus-dominated forests

We investigated how environmental variables explain patterns of tree regeneration in high altitude sub-tropical Quercus-dominated forests by: (1) determining whether the seedling and sapling communities show non-random spatial patterns of floristic composition; (2) identifying which environmental variables explain the observed patterns of floristic composition; (3) examining if similarity in floristic composition is related to similarity in environmental variables. We used data gathered in permanent plots established across 10 km in high altitude sub-tropical Quercus-dominated forests. Our analyses consisted of unconstrained ordination analyses (Non-metric Multidimensional Scaling) to characterize the spatial patterns of floristic composition; constrained ordination analyses (Canonical correspondence analysis) to assess the contribution of environmental variables in explaining patterns of floristic composition and, the simple and partial Mantel test to correlate the floristic composition similarity to environmental similarity. Our results provided evidence of non-random spatial patterns of floristic distribution due to structured environmental filters such as canopy-related variables, litter, grazing and aspect. Floristic compositional similarity did not depend on geographical distance between sites or on differences in their environment; therefore a number of plots were similar in floristic composition, in both seedlings and saplings, but have no environmental similarity.     

Plant composition associated with environmental gradients in tropical montane forests (Cueva de Los Guacharos National Park,Huila, Colombia)

Niche differentiation among tropical forest plants can generate species turnover along gradients of soil, topography, climate, and land use history. In this study we explore the relative importance of these variables as drivers of floristic composition in Cueva de Los Guacharos National Park. We established twenty 0.1‐ha plots, within which trees, lianas, and shrubs (diameter ≥ 2.5 cm) were censused. We selected plot locations in primary and disturbed forests, and we measured topography and soil variables. Despite their structural similarity, primary and disturbed forests differed floristically, and also differed in environmental variables measured. A NMDS ordination showed that variation in the floristic composition across plots is highly correlated to the exchangeable acidity, elevation, temperature, and magnesium availability. Variance partitioning analysis shows that together spatial and environmental variables explain 24.2 percent of the variation in species composition. ‘Pure environmental’ variables were more important in explaining compositional variability than ‘pure spatial’ processes (9.8% and 1.4%, respectively). Residual variance may be attributed to stochastic process or non‐measured biotic effects.     

Land-use history affects understorey plant species distributions in a large temperate-forest complex,Denmark

In Europe, forests have been strongly influenced by human land-use for millennia. Here, we studied the importance of anthropogenic historical factors as determinants of understorey species distributions in a 967 ha Danish forest complex using 156 randomly placed 100-m² plots, 15 environmental, 9 spatial, and 5 historical variables, and principal components analysis (PCA), redundancy analysis (RDA) as well as indicator species analysis. The historical variables were status as ancient (1805 AD) high forest, reclaimed bogs, ≤100 m from Bronze Age burial mounds, or former conifer plantation, and stand age. The PCA results showed that the main gradients in species composition were strongly related to the explanatory variables. Forward variable selection and variation partitioning using RDA showed that although modern environment was the dominant driver of species composition, anthropogenic historical factors were also important. The pure historical variation fraction constituted 13% of the variation explained. The RDA results showed that ancient-forest status and, secondarily, reclaimed bog status were the only significant historical variables. Many typical forest interior species, with poor dispersal and a strong literature record as ancient-forest species, were still concentrated in areas that were high forest in 1805. Among the younger forests, there were clear floristic differences between those on reclaimed bogs and those not. Apparently remnant populations of wet-soil plants were still present in the reclaimed bog areas. Our results emphasize the importance of historical factors for understanding modern vegetation patterns in forested landscapes.     

Impacts of local and regional factors on vegetation of boreal semi-natural grasslands

Using data from 46 sites in southern Finland and ordination methods, we examined plant-environment relationships in boreal mesic semi-natural grasslands at two spatial scales (grain sizes), using plots of 0.25 ha and 1 × 1 m. We applied the variation partitioning approach to determine the pure fractions of environmental variable groups and their joint effects on plant species compositional variation in the studied grasslands. The variables related to land-use intensity and high nutrient level (especially phosphorus) had a major role in explaining the species composition at both scales, although soil heterogeneity and habitat characteristics also accounted for a notable amount of the species compositional variation at the 0.25 ha grain size. At the 1 × 1 m grain size, the majority of the species compositional variation was related to the “pure” spatial differences between the studied grasslands (i.e. the site identity (dummy 0/1) variable), whereas the impacts of within-site variation of local environmental factors were considerably smaller. High nutrient levels and variables related to low land-use intensity, e.g. litter accumulation, were also significantly correlated with floristic variation at the 1 × 1 m grain size. Rare and declining grassland species are associated with low-nutrient grassland sites and patches. The main recommendation for the management planning of boreal semi-natural grasslands is that the first restoration attempts should be targeted to areas where nutrient levels, particularly that of phosphorus, are relatively low. Soil properties and plant species composition can provide useful guidelines for defining the correct management procedures for different sites.     

Structure, floristic composition, and vegetation forming factors of three vegetation types in Senegal

Six 1 ha plots were established in a coastal savanna, called Fathala Forest, in Delta du Saloum National Park, Senegal. Two plots were placed in woodland, two in wooded grassland, and two in transition woodland in order to describe structure and floristic composition of the vegetation. All trees ≥ 5 cm dbh were sampled. The three selected vegetation types showed distinct differences in structure as well as in species composition. Woodland had high density (440–449 individuals per ha), many small trees, and high basal area (13.4 m²per ha). Transition woodland was characterised by low density (54–118 individuals per ha) but many large trees and a relatively large basal area (8.6–12.8 m² per ha). Wooded grassland was characterised by medium sized trees, it had low density (86–102 individuals per ha) and low basal area (3.8–5.7 m² per ha). Species richness ranged between 17 and 27 species per ha in the six plots. Only two species were found in all plots, Daniellia oliveri (Caesalpiniaceae) and Prosopis africana (Mimosaceae). Legumes dominated all plots. Wooded grassland and transition woodland had many characteristics of fire-affected vegetation in contrast to woodland. Today wooded grassland encroaches on woodland and transition woodland. Management of the latter two vegetation types should be given priority as they maintain structural and floristic characteristics that are essential to conserve biodiversity and original features of the vegetation, and they are also important for local people who are allowed to make sustainable use of the vegetation.     

Broad Scale Distribution of Ferns and Lycophytes along Environmental Gradients in Central and Northern Amazonia,Brazil

Establishing which factors determine species distributions is of major relevance for practical applications such as conservation planning. The Amazonian lowlands exhibit considerable internal heterogeneity that is not apparent in existing vegetation maps. We used ferns as a model group to study patterns in plant species distributions and community composition at regional and landscape scales. Fern species composition and environmental data were collected in 109 plots of 250 × 2 m distributed among four sites in Brazilian Amazonia. Interplot distances varied from 1 to ca 670 km. When floristically heterogeneous datasets were analyzed, the use of an extended Sørensen dissimilarity index rather than the traditional Sørensen index improved model fit and made interpretation of the results easier. Major factors associated with species composition varied among sites, difference in cation concentration was a strong predictor of floristic dissimilarity in those sites with pronounced heterogeneity in cation concentration. Difference in clay content was the most relevant variable in sites with uniform cation concentrations. In every case, environmental differences were invariably better than geographic distances in predicting species compositional differences. Our results are consistent with the ideas that: (1) the relative predictive capacity of the explanatory variables depend on the relative lengths of the observed gradients; and (2) environmental gradients can be hierarchically structured such that gradients occur inside gradients. Therefore, site‐specific relationships among variables can mask the bigger picture and make it more difficult to unravel the factors structuring plant communities in Amazonia.     

Land‐use legacies in a central Appalachian forest: differential response of trees and herbs to historic agricultural practices

Question: Are contemporary herb and tree patterns explained by historic land use practices? If so, are observed vegetation patterns associated with life‐history characteristics, soil properties, or other environmental variables? Location: Southeastern Ohio, USA. Methods: Using archival records, currently forested sites were identified with distinct land use histories: cultivated, pasture (but not plowed), and reference sites which appear to have never been cleared. Trees were recorded by size and species on twenty 20 m × 20 m plots; percent cover was estimated for each herb species in nested 10 m × 10 m plots. Environmental characteristics were noted, and soil samples analysed for nutrient availability and organic matter. Nonmetric multidimensional scaling ordination was performed separately on both tree and herb datasets to graphically characterize community composition among plots. Life‐history traits were investigated to explain observed compositional differences. Results: Vegetation patterns were explained by current environmental gradients, especially by land‐use history. Cultivated and pasture sites had similar tree composition, distinct from reference sites. Herb composition of pasture and reference sites was similar and distinct from cultivated sites, suggesting the ‘tenacity’ of some forest herbs on formerly cleared sites. Tilling removes rhizomatous species, and disfavors species with unassisted dispersal. These life‐history traits were underrepresented on cultivated sites, although ant‐dispersed species were not. Conclusions: Historic land‐use practices accounted for as much variation in species composition as environmental gradients. Furthermore, trees and herbs responded differently to past land‐use practices. Life‐history traits of individual species interact with the nature of disturbance to influence community composition.     

A numerical analysis of the mesoscale distribution patterns of vascular plants in the subarctic Kevo Nature Reserve, northern Finland

Different numerical techniques were used to detect and describe the major ecological-biogeographical patterns of vascular plant distributions at the meso-scale level in a subarctic region in Finland. The distribution patterns of 231 native taxa in 362 1 km² grid squares of the Kevo Nature Reserve were analysed by two-way indicator species analysis and detrended correspondence analysis, and were subsequently related to twenty-eight geographical, topographical, geological, and vegetational variables using simple discriminant functions and canonical correspondence analysis with associated Monte Carlo permutation tests.
The floristic variation detected reflects variations in environmental factors operative at the regional and local scales. No major broad-scale coherent geographical patterns were detected; instead, the spatial distribution of the grids with a similar floristic composition shows a scattered distribution. All the numerical techniques reveal a major gradient from alpine areas to lowland sites with rivers and rocky outcrops, and the most important explanatory variables for predicting the main floristic variation are all associated with altitude. The floristic patterns represented by the second ordination gradient mainly correlate with the abundance of mires. Partial ordinations indicate that both the geographical and geological variables explain relatively little of the species distributional patterns.
Although the meso-scale approach reveals much about the plant-environment relationships in the study area, the floristic variation appears to be determined mainly by fine-scale factors. In the most heterogeneous grids, the grid size used fails to detect accurately the ecological patterns of the species present.     

Landscape-Scale Environmental and Floristic Variation in Costa Rican Old-Growth Rain Forest Remnants

Studies of tropical rain forest beta-diversity debate environmental determinism versus dispersal limitation as principal mechanisms underlying floristic variation. We examined the relationship between soil characteristics, terrain, climate variation, and rain forest composition across a 3000 km² area in northeastern Costa Rica. Canopy tree and arboreal palm species abundance and soils were measured from 127 0.25-ha plots across Caribbean lowlands and foothills. Plot elevation, slope, temperature, and precipitation variation were taken from digital grids. Ordination of forest data yielded three floristic groups with strong affinities to foothills and differing lowland environments. Variation in floristics, soil texture, and climate conditions showed parallel patterns of significantly positive spatial autocorrelation up to 13 km and significantly negative correlation beyond 40 km. Partial Mantel tests resulted in a significant correlation between floristic distance and terrain, climate and soil textural variables controlling the effect of geographical distance. Separate comparisons for palm species showed significant correlation with Mg and Ca concentrations among other soil factors. Arboreal palm species demonstrated a stronger relationship with soil factors than did canopy trees. Correlation between floristic data and geographical distance, related to seed dispersal or unmeasured variables, was not significant after controlling for soil characteristics and elevation. Canopy trees and palms showed differing relationships to soil and other environmental factors, but lend greater support for a niche-assembly hypothesis than to a major role for dispersal limitation in determining species turnover for this landscape.     

Elevational gradient and vegetation‐environmental relationships in the central Hyrcanian forests of northern Iran

Tertiary‐relict Hyrcanian (Caspian) forest along the shores of the southern Caspian Sea is a center of biodiversity. Still, there is little information on plant diversity patterns in this area. This study evaluated plant diversity, variation in life forms, and geographical distribution of the zonal vegetation types and their relationships with environmental variables, in the educational and experimental forest of Kheyrudkenar, an important protected area in the central Hyrcanian forest of northern Iran. For this purpose, 226 vegetation plots of 400 m² were laid out along two altitudinal transects from the lowlands (100 m a.s.l.) to the timberline (2000 m a.s.l.). Four vegetation types were identified using modified TWINSPAN, indirect and direct gradient analyses. Species‐related (species diversity indices, life form and phytogeographical elements) and environmental variables (climate, topographic and soil variables) were calculated and subjected to one‐way ANOVA among the vegetation types. Both constrained (CCA) and unconstrained (DCA) ordination analyses showed an almost identical variation of the floristic composition along their axes and demonstrated that there are two main gradients in the Hyrcanian forest. Elevation together with annual precipitation and mean annual temperature were the most important factors controlling the floristic composition in the area. Topographic features such as slope inclination and heat index were found to be important within an elevation zone/vegetation type. Soil physical and chemical properties were of secondary importance for the separation of the vegetation types. This knowledge will be useful for forest management and conservation practices in the Hyrcanian area with its distinct and unique flora and vegetation.     

Floristic variation in ecotonal areas: Patterns,determinants and biogeographic origins of subtropical forests in South America

We present the first quantification of forest community composition and its relationship with environmental factors in South American subtropical Atlantic Forests. In this region, rain, seasonally dry and mixed forests form an ecotonal zone near the parallel of latitude 30°S. To investigate how well current knowledge on climatic effects and biogeographic distribution apply to subtropical ecotones, we tested the following expectations: (i) there is a floristic longitudinal gradient correlated to altitudinal and climatic gradients; (ii) climatic variables are more important than soil factors in shaping floristic composition; and (iii) there are three floristic regions in the southernmost limit of the Atlantic Forest biome that are expected to be distinct in composition, structure and biogeographical origin. We examined floristic composition and its relationship with environmental factors across 52 1‐ha permanent study areas in subtropical Brazil, containing in total 269 tree species ≥ 9.5 dbh (diameter at breast height). Climatic data, related to rainfall seasonality and temperature, as well as soil properties, were compiled from published sources or global data banks. Expectations one and two were confirmed, but expectation three was only partially met. Hierarchical cluster analysis divided the southernmost Atlantic Forests into four major groups (Rain, Seasonally Dry, Western Mixed and Eastern Mixed Forests). Overall, the tested environmental variables differed significantly among the four regions. Using indicator species analysis, we distinguished 46 indicator species, which had significant environmental preferences for one floristic region. These species can be used as indicators of environmental conditions or to determine to which floristic region a certain forest belongs. Biogeographic distributions differed between floristic groups, supporting the interpretation that Eastern Mixed Forests are relict forests of a temperate forest of Andean origin that occurred during colder palaeoclimates. Western Mixed Forests represent the main floristic ecotone between Seasonally dry and Eastern Mixed Forests.     

Effects of Vegetation Traits on Habitat Preferences of Frugivorous Birds in Atlantic Rain Forest

Structural and floristic components of vegetation and fruit production were examined to evaluate the relative importance of each vegetation aspect on patterns of habitat use and to determine whether differences in degree of frugivory would affect sensitivity of birds to vegetation components. Abundances of 12 bird species were quantified in four different habitat types in the Southeastern Atlantic rain forest of Brazil using captures with mist nets. Structural and floristic traits and fruit production were sampled within plots along the mist net lines. Best explanations for the variation in species abundance were obtained by different combinations of the vegetation components (generalized linear models, Akaike information criterion; R ² mean values = 0.48, Δ AIC c = 0). Although each species had a particular preference for some vegetation variables, floristic components stood out in those relationships, generating models with a stronger explanatory capacity ( R ² > 0.40) and higher levels of empirical support (Δ AIC c = minimum values). The variation in bird sensitivities to the floristic component was associated with bird dependence on a fruit diet: there was a correlation between the explanatory capacity of models built with only floristic composition and a species' degree of frugivory (Spearman rank correlation, r = 0.66, P = 0.04), indicating that floristics had a higher effect in more frugivorous birds. For the other vegetation components, there was no clear pattern with statistical support. These results indicate that sensitivities of bird species to vegetation aspects are associated with their dependence on a fruit diet.     

The Role of Urban Structures in the Distribution of Wasteland Flora in the Greater Paris Area,France

Wastelands are likely to host a significant part of urban floristic diversity but have received limited attention because they are not considered interesting green zones. Here, we explore the potential role of wastelands in maintaining urban biodiversity to help define effective urban management plans. We quantified floristic diversity in 98 wasteland sites of Hauts-de-Seine, one of the most densely populated areas in France, and characterized the environmental parameters and spatial distribution of sites to identify some of the factors that influence plant species composition and to explore the impact of urban environment on the floristic interest of wastelands. Their floristic richness represented 58% of the total richness observed in the whole study area. Site richness depended on site area (the largest sites were the richest) and site age, with a maximum in sites of intermediate age (4–13 years). In the largest sites only (>2,500 m²), the floristic distance among sites was positively correlated with geographic distance, which suggests that migration of species among large sites partly controls local floristic composition. In contrast, the environmental distance among sites was not correlated with floristic distance. Finally, we showed that the presence of collective and individual dwellings within 200 m of a wasteland decreased its floristic rarity, whereas the presence of rivers or ponds increased it. We derive several recommendations to optimize the management of wastelands with respect to conservation of urban biodiversity.     

Floristic patterns of epiphytes in the Brazilian Atlantic Forest,a biodiversity hotspot

To assess the main factors driving epiphytic angiosperm distribution throughout the Brazilian Atlantic Forest, we compiled 57 floristic surveys and analysed species composition under the influence of environmental variables, space and vegetation type using canonical correspondence analysis (CCA), similarity (Sorensen) and Mantel's tests. The indicator value index (IndVal) was used to find indicator species of each Brazilian Atlantic Forest vegetation type. Group sharpness analysis was performed in order to determine the appropriate group partition level. CCA showed a separation of the epiphytic flora reflecting temperature and rainfall gradients. Mantel's test showed that environment and space were highly correlated with floristic similarity. Cluster analysis, indicating floristic similarity, resolved five groups, mainly grouped by region. Clear differentiation of the Brazilian Atlantic Forest epiphytic flora on a north–south axis with a strong correlation with temperature and rainfall gradients was found. The role of space and environment on species composition varied according to distinct epiphytic species groups. In particular, for Bromeliaceae and Orchidaceae, the main factor associated with floristic similarity was space. Indicator species were found for all vegetation types apart from the Seasonal Semideciduous Forest that seemed to represent a subset of a more humid forest type. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 587–601.     

Role of environmental and spatial processes in structuring anuran communities across a tropical rain forest

This study aimed to evaluate if anuran species distributions in riparian and non‐riparian areas are influenced by environmental factors (i.e. niche) and/or by spatial factors (i.e. dispersal). The environmental variables analysed were altitude, distance from the stream and leaf litter depth. Spatial factors were represented by the eigenvectors extracted from geographical coordinates by eigenfunction analysis. The study was conducted in 24 km² of terra‐firme forest in Central Amazonia, Manaus – Amazonas, Brazil. Between November 2008 and May 2009, three samples were taken from 41 plots, 21 plots being placed at non‐riparian areas and another 20 placed in riparian areas. We submitted the assemblage dataset to a partial redundancy analysis to evaluate the contributions of environmental and spatial variables (selected with a forward selection procedure). In addition, we tested if communities differ from riparian and non‐riparian areas using a db‐MANOVA. Species richness and species composition differed between riparian and non‐riparian plots. Some species were restricted to riparian areas. Altitude was the only significant variable (P = 0.005) explaining 21% of the total variance. When analysing the data from all plots using the partial redundancy analysis, 27% of the variance was explained by spatial and environmental variables. The environmental variables explained exclusively 4% of the variance in assemblage composition, and 13% was explained by environmental variables that were also structured in space (i.e. the shared fraction), while 10% was explained exclusively by spatial variables. In conclusion, our results showed differences between the assemblages of riparian and non‐riparian areas which can be explained by the distribution of anuran species along environmental gradients altitude and distance to streams, with little evidence of dispersal limitation.     

Grazing in remnant woodland vegetation: changes in species composition and life form groups

Abstract. Grazing by domestic livestock in native woodlands can have major effects on ecosystem functioning by the removal of plant species that form important functional groups. This paper documents the changes in floristics in a large group of remnants of native woodland left after agricultural clearing in southwestern Australia. Species richness and diversity were significantly reduced in remnants and the proportion of exotic species increased. Detrended Correspondence Analysis (DCA) was used to identify floristic and environmental patterns among plots and identified two distinct groups based on grazing intensity. This indicated that the significance of the relationship between grazing effects and DCA floristic axes was greater than edaphic characteristics that normally influence floristic patterns. Floristic characteristics of sites that were influencing the position of plots on the ordination diagram included proportion of exotic species and proportion of native perennial shrubs and herbs. Numbers of species of native shrubs and perennial herbs were significantly reduced in grazed plots and numbers of exotic annual grasses and herbs were significantly higher. Other life form groups such as native perennial grasses and geophytes were not significantly affected by grazing. Reproductive strategies of perennial species showed a significant decrease in numbers of resprouters and a significant increase in numbers of facultative seeder/sprouters. Exclosure plots showed increases in number and cover of perennial shrubs and herbs after three years whereas number and cover of exotic species did not change. Time series DCA showed that the floristic composition of exclosure plots in grazed sites became closer to that of the ungrazed sites.     

Diversity and floristic patterns of mediterranean grasslands: the relative influence of environmental and land management factors

Managed grasslands are normally ecosystems with high species diversity. They are associated with traditional extensive livestock grazing. Land-use changes, in particular gradual abandonment or grazing intensification, lead to major changes in floristic patterns of these grasslands, some included in priority habitats of the EU Habitats Directive. In order to analyse these patterns of change, Mediterranean grasslands of eastern areas of mainland Portugal were studied aiming to: (1) establish ecological gradients underlying their floristic patterns; (2) examine the relative importance of both environmental and land-use factors on their floristic composition; (3) assess how floristic composition and species richness are affected by land-use factors. Vegetation sampling was carried out from 2008 to 2009 following phytosociological procedures. Canonical Correspondence Analysis was applied. Variation partitioning was used to assess the relative influence of land-use variables. Richness, legumes cover, endemic species and bryophytes cover were compared in four land-management regimes: unmanaged; extensive grazing by sheep; extensive grazing by cattle and sheep; frequent soil tillage. Significant differences were found in floristic and diversity patterns, revealing the importance of grazing as a management tool for maintaining or improving floristic diversity. From our findings slight extensive grazing can contribute to both maintenance of species diversity and to the increase in legumes cover and thus to palatability and economic value of studied grasslands. Interactions between herbivores and grasslands, considering also their influences on soil properties, have an important role in the equilibrium states which promote biodiversity and conservation of the services of these ecosystems.     

黄土高原腹地人工林下草本层群落构建机制

群落构建机制是生态学研究的核心论题。生态位理论和中性理论是阐明群落构建的两种主要理论, 但这两种理论分别强调的环境过滤和扩散限制对群落构建的影响尚存争议。该研究以黄土高原人工林下草本层群落为研究对象, 将群落物种组成数据与地理空间、气候、地形以及生物因子相结合, 运用随机森林模型(RF)和基于距离矩阵的多元回归方法(MRM), 探究了各个因子的重要性, 并通过邻体主坐标矩阵(PCNM)和基于距离的冗余分析(db-RDA)分别筛选显著的空间结构和环境因子, 最后结合筛选出的PCNM特征值和环境变量进行变差分解。研究结果显示: 1)林下草本层群落组成相似性随地理距离和生境差异的增加而减小。2)地理距离与生境差异共同解释了群落组成相似性变化的47.8%。其中, 空间因子和环境因子的独立解释率分别为14.1%和9.8%, 两者的联合解释率为23.9%。3)地理距离和年降水量是引起研究区内物种组成变化的关键因子, 且地理距离的重要性大于年降水量。在黄土高原腹地, 扩散限制与环境过滤共同主导了人工林下草本层群落的构建过程。     

An ecological approach to the investigation of a beech forest in Vestfold, SE Norway

The vegetation in a beech forest, Fritzøehusparken, is analysed using one hundred sample plots, each 25 m², distributed by a restricted random procedure. Percentage cover and frequency in subplots are used for quantification of species amounts, and their relative performance are evaluated. Advantages of choosing frequency in subplots are discussed. Thirteen environmental variables are measured from each of the sample plots. The vegetation is divided into four topographical/ecological types. This classification served as a reference in the further treatment. Ecological gradients corresponding to the most important vegetational gradients in the beech forest are identified by means of DCA ordination followed by statistical interpretation. Two main complex gradients were recognized; (1) the gradient in nutrient conditions, and (2), the gradient inlitter-wind conditions. The advantages of using DCA and statistical interpretation with integration of ecological measurements are emphasized.