Different aspects of plant diversity show contrasting patterns in Carpathian forest openings

Abstract

It has long been known that aand bdiversity are driven by different ecological processes. Recently, several theoretical papers have suggested that b-diversity can be expressed in many different ways, and that these measures might have different meanings and behaviours. In terms of ecological understanding, it is important to test how these diversity measures behave in different settings, yet this has been rarely attempted. We investigated this question using forest openings in the Trascȃu Mountains, Romania, which contain species from grasslands of high nature value. The sampling was conducted in 40 openings, using edge-to-interior transects composed of 1-m 2 plots (a-diversity), from which we calculated five b-diversity measures at transect level. As predictor variables, we used canopy openness (from hemispherical photos), tree litter cover, heat load index, altitude, and bedrock type for a-diversity, and the means and ranges of these for b-diversity. Generalized linear mixed models showed that adiversity was mostly explained by the first two variables. Amongst the b-diversity measures, the classical additive and multiplicative measures differed, the latter being similar to the Sørensen-based multiple-site dissimilarity. None of the predictors explained the slope of distance decay or Simpsonbased multiple-site dissimilarity, except when considering ecological subsets of the species. We discuss the possible ecological processes underlying the different results, and the implication of our findings for nature conservation in the region. In conclusion, we support the joint application of different measures of aand bdiversity, as long as their particular properties are taken into account.

Landscape effects on diversity of semi-natural grasslands

“…This approach cannot adequately address the processes controlling diversity patterns in complex landscapes where grassland species occur in a variety of habitats (Schmucki et al, 2012). With few exceptions (Schmucki et al, 2012;Turtureanu and Dengler, 2012), the majority of recent studies focus solely on the pattern of alpha diversity without considering simultaneously the patterns of beta and gamma diversity. Partitioning species diversity into its alpha, beta and gamma components is useful for assessing the spatial structure of diversity patterns.…”

“…Understanding the factors determining each of these components and their interrelationships provide useful insights into the mechanisms that determine plant diversity in heterogeneous landscapes. Since different diversity components are driven by different ecological processes, they also provide important information for nature conservation, as conservation strategies based upon single measurements are not recommended (Turtureanu and Dengler, 2012). Finally, studies, which would confirm the significance of the surrounding landscape structure on a large dataset covering multiple habitats distributed over large areas, are completely missing.…”

Relative Importance of Current and Past Landscape Structure and Local Habitat Conditions for Plant Species Richness in Dry Grassland-Like Forest Openings

“…Moreover, PDSI takes shading by adjacent topography and the surrounding trees into account and is therefore a better predictor of species richness especially at relatively small localities such as in our study system [57]. Moreover, Turtureanu and Dengler [25] observed a close correlation between the heat load index and the locality slope, and the slope was also included in our model. For calculating the TWI, we first calculated the slope (using a local morphometry function with a fit 2 degree polynom) and specific catchment area (using a parallel processing function with multiple flow direction method and number one convergence) according to the digital elevation terrain model (DEM).…”

“…In our analysis the number of plant species was, however, not significantly affected by nutrient availability at the localities (expressed by Ellenberg indicator value for N), but it negatively responded to low light availability at the locality (expressed by an Ellenberg indicator value for L). Similarly, Turtureanu and Dengler [25] observed an important positive effect of canopy openness (and thus light availability) on species diversity in Carpathian forest openings. Nature conservation management should thus balance both mechanisms [47] : hunting of mouflons (it was partly practiced) and removal of young trees and shrubs colonizing grassland areas (this type of management was not practiced).…”

“…The species richness of a habitat patch can also depend on habitat conditions at the sites, such as the type of substrate, type of vegetation, soil depth, slope [23] – [25] , insolation or geology [26] , soil pH [24] , [27] , and, in some cases, the disturbance regime [8] or habitat heterogeneity in terms of land use history [26] , [28] . However, the species richness of a habitat patch can also depend on the habitat diversity in the surrounding landscape [29] , [30] .…”