What determines disturbance‐productivity‐diversity relationships? The effect of scale, species and environment on richness patterns in an Australian woodland

Abstract

2003. What determines disturbance-productivity-diversity relationships? The effect of scale, species and environment on richness patterns in an Australian Woodland. -Oikos 102: 173-185.Much of the observed variation in relationships between diversity and disturbance or productivity may be attributed to scale, species characteristics, or environment. We used exclusion fences to create gradients of grazing (by native and introduced herbivores), cover, and standing crop in temperate Eucalypt woodlands. We investigated patterns of native, exotic, and total plant species richness at two scales (1 m 2 and 625 m 2 ). Richness patterns were similar at both scales, though species richness at 1m 2 was more strongly affected by our grazing treatments. Season and rainfall explained more variation in richness than did surrogate measures of productivity or disturbance by herbivores. The richness-herbivory relationship depended strongly on rainfall, season, and species origin, and altering these factors produced the entire range of observed diversity-disturbance relationships. Richness-biomass and richnesscover relationships were consistently hump-shaped, and related to species origin with native richness negatively related and exotic richness positively related. The ability of weedy annuals to pre-empt space after death may have contributed to the observed unimodal responses.

Survival, growth, and escape from herbivory are determined by habitat and herbivore species for three Australian woodland plants

“…We included biomass estimates from spring of 1998 as a predictor variable in statistical analyses of transplant survival because target seedlings were small enough at this time to experience severe competition for light and space with rapidly growing herbaceous plants. Changes in species composition in the experimental plots during this period were described by Allcock and Hik (2003).…”

“…woodlands of New South Wales and Victoria, grazing by a variety of herbivores is a major threat to native plant communities (Prober and Thiele 1995;Sivertsen and Clarke 2000). Remnants are usually grazed by sheep and cattle, and are often partially cleared to increase pasture productivity (which may also increase exotic species and decrease native species: Allcock and Hik 2003). Feral rabbits (Oryctolagus cuniculus) and native macropods are common.…”

Determinants of Species Richness in the Park Grass Experiment

“…Several recent studies report a hump in the species richness-biomass relationship (Pollock et al 1998;Mittelbach et al 2001;Venterink et al 2001;Allcock and Hik 2003), and while most studies are restricted to aboveground biomass, the humped relationship held when belowground biomass was included (Liira and Zobel 2000). On a regional scale in central Europe, there was a hump-shaped relationship between soil nutrient supply and plant species richness within a given biome, but the location of the peak in species richness occurred in different places in different communities; for grasslands and wetlands, the peak was on nutrient-poor soils, but for forests, the peak was on nutrient-rich soils (Cornwell and Grubb 2003).…”

Productivity and species richness in an arid ecosystem: a long-term perspective

“…Moreover, examination of the relationship reveals that variation in species richness is not consistent across all levels of productivity, a condition that indicates other, unmeasured predictor variables are partly responsible for determining species richness (Cade et al 2005). For example, Allcock and Hik (2003) found rainfall to be more important than productivity in predicting species richness. In fact, primary productivity is itself an integrative measure of a variety of important environmental constraints (e.g., nutrient availability, light, water), each interacting in possibly complex ways.…”