Homogenization of forest plant communities and weakening of species–environment relationships via agricultural land use

Abstract

Summary1 Disturbance may cause community composition across sites to become more or less homogenous, depending on the importance of different processes involved in community assembly. In north-eastern North America and Europe local (alpha) diversity of forest plants is lower in forests growing on former agricultural fields (recent forests) than in older (ancient) forests, but little is known about the influence of land-use history on the degree of compositional differentiation among sites (beta diversity). 2 Here we analyse data from 1446 sites in ancient and recent forests across 11 different landscapes in north-eastern North America and Europe to demonstrate decreases in beta diversity and in the strength of species-environment relationships in recent vs. ancient forests. 3 The magnitude of environmental variability among sites did not differ between the two forest types. This suggests the difference in beta diversity between ancient and recent forests was not due to different degrees of environmental heterogeneity, but rather to dispersal filters that constrain the pool of species initially colonizing recent forests. 4 The observed effects of community homogenization and weakened relationships between species distributions and environmental gradients appear to persist for decades or longer. The legacy of human land-use history in spatial patterns of biodiversity may endure, both within individual sites and across sites, for decades if not centuries.

Non-Native Plants Disrupt Dual Promotion of Native Alpha and Beta Diversity

“…2b)? It seems that high native beta diversity in the presence of non-native species is simply a result of statistical inevitability, where low alpha diversity automatically results in high beta diversity (Koleff et al 2003;Jost 2007;Vellend et al 2007), as supported by our null model analysis (Fig. 3).…”

“…It has been pointed out that beta diversity is often not independent of alpha diversity (Koleff et al 2003;Jost 2007;Vellend et al 2007). For example, if species are randomly distributed in plots from a common pool of potential colonizers, the smaller the number of species that are distributed per plot (i.e., lower alpha diversity), the more variable the set of species will be between plots (i.e., higher beta diversity).…”

“…However, given a fixed regional pool of species from which species immigrate, alpha diversity may be inversely related to beta diversity such that high alpha is automatically linked to low beta (Zobel 1997). This relationship arises because the more species local communities contain, the more similar the communities must be in species composition, particularly if local communities are randomly assembled from the regional pool (Koleff et al 2003;Jost 2007;Vellend et al 2007). Not all local communities are randomly assembled, however (Götzenberger et al 2012;Rajaniemi et al 2012).…”

Deer herbivory affects the functional diversity of forest floor plants via changes in competition‐mediated assembly rules

“…Under the classical paradigm, ecologically dissimilar species can coexist through niche partitioning, which is based on the theory that the coexistence of functionally similar species is limited by interspecific competition (i.e., limiting similarity; MacArthur and Levins 1967;MacArthur 1972;Chesson 2000). These niche differences can rise from speciesspecific interactions with resources, specialist consumers, pathogens, mutualists, or temporal environmental heterogeneity (Tilman 1982(Tilman , 1988Chesson 2000;Sammul et al 2006;Chesson and Kuang 2008), and trait overdispersion is thought to be the consequence of this process. In contrast, shared adaptive characteristics among syntopic species promote the co-existence of species with similar traits.…”

Effects of stand density on ecosystem properties of subalpine forests in the southern Rocky Mountains, USA

“…Humans have altered forest landscapes over millennia, primarily through resource extraction and manipulation of fire (Heckenberger et al, 2003). For example, large-scale clearcutting techniques and a century of fire suppression in the USA have homogenized landscape structure and functioning by removing patch-scale events (Fuller et al, 1998;Vellend et al, 2007). While the creation of even-aged stands may have economic benefits in the short-term (Gilless and Buongiorno, 2003), high stand densities and drought have increased the incidence of crown fire and insect outbreaks while also causing decline of native species (McCullough et al, 1998;National Research Council, 2000;Veblen et al, 2000).…”