Influence of slope and aspect on long‐term vegetation change in British chalk grasslands

Abstract

Summary 1The species composition of fragmented semi-natural grasslands may change over time due to stochastic local extinction and colonization events, successional change and/or as a response to changing management or abiotic conditions. The resistance of vegetation to change may be mediated through the effects of topography (slope and aspect) on soils and microclimate. 2 To assess long-term vegetation change in British chalk grasslands, 92 plots first surveyed by F. H. Perring in 1952-53, and distributed across four climatic regions, were re-surveyed during 2001-03. Changes in vegetation since the original survey were assessed by comparing local colonization and extinction rates at the plot scale, and changes in species frequency at the subplot scale. Vegetation change was quantified using indirect ordination (Detrended Correspondence Analysis; DCA) and Ellenberg indicator values. 3 Across all four regions, there was a significant decrease in species number and a marked decline in stress-tolerant species typical of species-rich calcareous grasslands, both in terms of decreased plot occupancy and decreased frequency within occupied plots. More competitive species typical of mesotrophic grasslands had colonized plots they had not previously occupied, but had not increased significantly in frequency within occupied plots. 4 A significant increase in Ellenberg fertility values, which was highly correlated with the first DCA axis, was found across all regions. The magnitude of change of fertility and moisture values was found to decrease with angle of slope and with a topographic solar radiation index derived from slope and aspect. 5 The observed shift from calcareous grassland towards more mesotrophic grassland communities is consistent with the predicted effects of both habitat fragmentation and nutrient enrichment. It is hypothesized that chalk grassland swards on steeply sloping ground are more resistant to invasion by competitive grass species than those on flatter sites due to phosphorus limitation in shallow minerogenic rendzina soils, and that those with a southerly aspect are more resistant due to increased magnitude and frequency of drought events.

Long-term changes in lowland calcareous grassland plots using Tephroseris integrifolia subsp. integrifolia as an indicator species

“…Our re-visitation study appears to support the observations of Bennie et al (2006) with regard to the relative resilience of vegetation on steep south-facing turf over shallow rendzina soils, with little change overall in species richness noted across our study sites. Furthermore, we detected no significant temporal or spatial change in evenness or diversity, and these results do not appear to have been affected to any great extent by pseudo-turnover.…”

“…Van den Berg et al (2011) re-surveyed permanent quadrat data from the early 1990s to understand better the effects of atmospheric nitrogen (N) deposition on species-rich calcareous grassland sites, finding significant associations with high deposition and changes in Shannon diversity, evenness and a decline in the frequency of characteristic species. Bennie et al (2006) re-visited calcareous grassland plots first surveyed in the early 1950s, finding that although there was a general reduction in species richness and a shift to more mesotrophic vegetation, plots located on steep, south-facing slopes with shallow rendzina soils were more resilient to the spread of competitive species compared with communities of deeper soils, due to phosphorus limitation and an increased frequency and magnitude of drought events. Pykälä et al (2005) reported similar results, with greater species richness maintained on sites with greater solar radiation.…”

Site selection of European ground squirrels (Spermophilus citellus) in Eastern Romania and how they are influenced by climate, relief, and vegetation

“…A southern and eastern facing slope (more open to sunlight and warm winds) will be warmer and dryer due to higher levels of evapotranspiration than a north-facing slope (Bennie et al, 2006). Because of this microclimate, southern and eastern slopes positively influence the density of the European ground squirrel colonies from Eastern Romania.…”

The influence of sample plot size on evaluations with Ellenberg indicator values

“…In addition, EIV are absolutely irreplaceable where temporal changes of ecological factors are inferred from historical data that lack environmental measurements. Major environmental factors, that have caused long-term changes in various types of vegetation, have been traced from the floristic composition of historical and recent data sets in forest vegetation (Wittig et al 1985;Hédl 2004), meadows (Knollová 2004;Bennie et al 2006) and weeds (Ejrnaes et al 2003;Lososová et al 2004). EIV can also be used to research appropriate management techniques (Decocq et al 2004) or for interpretation of patterns of species diversity (Cornwell & Grubb 2003;Ewald 2003a).…”