Plant communities are generally spatially structured. Therefore, in order to enhance the interpretation of distance-dependent community patterns, spatially explicit measures of β-diversity are needed that, besides simple species turnover, are able to account for the rate at which biological similarity decays with increasing distance. We show that a multivariate semivariogram computed from species presence and absence data can be considered as a space-dependent alternative to existing definitions of β-diversity. To illustrate how the proposed method works, we used a classical data set from a second-growth piedmont hardwood forest.
Authors:Sz. Fóti, J. Balogh, Z. Nagy, Zs. Ürmös, S. Bartha, and Z. Tuba
Remnants of the former semiarid forest-steppe vegetation of Hungary are suspected to undergo degradation processes because of recent land-use changes. Secondary succession towards closing of the vegetation starts with shrub invasion, mainly with species of the shrub layer of loess steppe oak forest. Soil respiration (SR) activity of the intercanopy loess grassland community was followed occasionally along of six years period, as well as the spatial patterns of SR and soil water content (SWC) with three direct measuring campaigns. Dependence of SR on SWC-soil temperature was statistically significant for the six years period, but the rest of the variance should be explained by other factors, as found for normalized difference vegetation index. In the spatial analysis, significant differences were found in the ranges of semivariograms according to the seasonal variation of soil moisture content. Larger scale patches were found under summer water stress (4 m for SR, 2.6 m for SWC) and autumn senescence (3.8 m for SR, 1.3 m for SWC) periods than under well-watered, peak performance summer circumstances (0.8 m for SR, 0.6 m for SWC). This suggests that homogeneity of patterns is typical at good water supply, while coarse-grained patches prevail under drought stress.