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Climate warming may enhance the upslope migration of tree species at high elevations. In this context, few studies have analyzed the requirements of tree seedlings with respect to safe sites and soil conditions, particularly in the Alborz Mountains (Iran). We collected regeneration and environmental data focusing on small seedlings and young saplings at the upper limit of tree growth in the Alborz Mountains. For each life stage, we assessed the association of seedlings with safe site conditions (rocks, stones, deadwood, and canopy shade), microhabitat substrates (vegetation, litter, bare soil, and stones), and soil variables along elevational gradients. Our findings revealed strong associations between seedlings and facilitative elements (tree shade, deadwood, rocks, and stones). Fewer associations were observed with microhabitat substrates. These associations differed between the two establishment stages. In addition, seedlings of both life stages exhibited distinct associations with soil variables (total nitrogen, sand, and bulk density). The contrasting relationships between small seedlings and young saplings with safe site conditions, microhabitat substrates, and soil variables suggest that early life stages may have different site requirements compared to later stages. Our results suggest that the potential for upslope migration of tree species may depend on safe site conditions, particularly those provided by tree shade, deadwood, rocks, and stones. [ABSTRACT FROM AUTHOR]

This vegetation–environmental relation study is the first large-scale survey along 34 cross-shore transects in 650 km-coastal dune remnants of the south Caspian Sea, Iran. The five vegetation zones dedicated here seem to be driven by both zonal (climate, distance to the sea and pH) and azonal (salinity) factors. To assess conservation status, different attributes of Hdune diversity index, endemicity index (EI) and Naturalness (N) were estimated based on endemic, alien and total species contributions per plot. Contrary to Hdune index, EI followed a decreasing pattern across the coast–inland gradient, whereas N shows a unimodal pattern of distribution with the highest value at the mobile dune zone. Two main gradients of salinity and alkalinity shaping floristic composition are more prominent than climate, distance to the sea and the anthropogenic factors particularly when a full range of coastal habitats are considered. Human-related factors only partially explain the variability of the vegetation data and negatively affect naturalness and endemicity indices, even though their impact on community composition is aggravated in the western parts of the Caspian coasts. Both N and EI indices can be suggested as bioindicators for proper conservation strategies to preserve the last fragments of sand dunes of the Caspian Sea. [ABSTRACT FROM AUTHOR]

Aim: Species–area relationships (SARs) are among the best investigated patterns in ecology, yet the shape of the function that should describe SARs and the biological meaning of the function parameters are disputed. Elevational gradients offer the opportunity of investigating how biodiversity responds to large variations in environmental characteristics within small geographical areas. We asked which function describes SARs at different elevations and explored how variations in environmental characteristics influence SAR shape. Location: Alborz Mountains (Iran). Taxon: Vascular plants. Methods: We used sets of nested plots (0.001 to 100 m2) placed at 100 m intervals from 2,000 to 4,500 m elevation to construct series of nested SARs as species accumulation curves. Then, we used these curves to assess the appropriateness of different SAR functions at different elevations. We investigated how parameters of the power function varied along the elevational gradient in response to variation in environmental parameters (ruggedness, temperature, precipitation, exposed rock, percentages of soil sand and total nitrogen, and productivity, expressed by the normalized difference vegetation index). Results: The most frequently observed best fit model was the power function, which is controlled by two parameters: z (the velocity in species accumulation with sampled area) and c (the species richness per unit area). z was positively influenced by temperature and soil nitrogen, decreasing with elevation. c was positively influenced by temperature and soil nitrogen, and negatively by rock cover, decreasing with elevation. Main conclusions: The decrease in c‐values with elevation is consistent with the altitudinal decrease in species richness and is explained by the increase in bare rock. By contrast, c was positively influenced by temperature and total nitrogen, which are two factors promoting plant growth. Similarly, z‐values decreased with elevation, thus indicating a decrease in beta diversity. [ABSTRACT FROM AUTHOR]

Climate and environmental heterogeneity are currently discussed as the most important drivers of plant diversity along altitudinal gradients. Compared to functional diversity, taxonomic diversity has received much more attention in research on altitudinal gradients, although functional diversity may provide more information on the ecological mechanisms shaping plant diversity. We assessed the importance of climatic and environmental heterogeneity as drivers of functional diversity in relation to altitude in the central Alborz Mountains, Iran. We sampled 132 vegetation plots along two altitudinal transects. Plant traits including life history, growth form, stem‐leaf ratio, spinescence, hairiness, leaf consistency, dispersal type and plant height were recorded. Functional diversity was measured as functional richness, Rao's quadratic entropy, and their standardized effect sizes (SESs). In general, functional diversity decreased with altitude. The decrease in observed functional diversity was related to the decrease in taxonomic richness. SESs of functional diversity showed contrasting trends, depending on transect and index. At both transects, climatic stress best explained the variation in observed and expected functional diversity. Harsh climatic conditions at higher altitudes decreased the number of species and thus the functional trait space. Environmental heterogeneity played only a minor role for shaping functional diversity. We expect this effect to be due to the length of the sampled altitudinal transects. With increasing length, small‐scale drivers become less effective. The two transects favoured different environmental drivers, meaning that transferability of single studies could be difficult. [ABSTRACT FROM AUTHOR]

Mountains are an excellent system for evaluating ecological and biogeographical patterns. The obvious variations of the environmental factors along the altitude create different zones with adapted plant assemblages. However, few studies make use of plant functional type (PFT) for describing the variation of vegetation along altitudinal gradients. A PFT is a group of taxa with similar traits which respond similarly to the environmental gradients. In this study, we used PFTs as indicators describing five vegetation zones in the western Alborz Mt, Iran from 2000 - 4500 m. The plant trait data presented here covers six plant traits including growth form, stemleaf ratio, spinescence, hairiness, leaf consistency and plant height of 297 species. We considered altitude and soil factors to test the importance of environmental variables. We applied a multivariate analysis of three table ordination, i.e. environmental, species, and traits data to identify the PFTs. We further applied fourth-corner statistic to quantify trait-environment relationships. A constrained hierarchical clustering was used to detect five altitudinal zones and two zones of low and high nitrogen concentration. With regard to altitude we discuss the distribution of species, traits and PFTs. Growth form, plant height and stem-leaf ratio were significantly related to altitude and nitrogen. We identified 19 PFTs from which 18 were significantly associated to one or more altitudinal zones. While the lower altitudinal zones contain a variety of PFTs higher altitudes contain less PFTs with the highest altitude containing only one single PFT, tiny rosette plants with soft mesomorphic leaves. We identified grazing and climatic harshness as well as rockiness as the most important drivers of the distribution of plant functional traits and types across the studied gradient. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]