Local-scale plant species richness and the regional species pool

Plant community structure has been shown to impact ecosystem function. However, these effects vary among ecosystems, data collection techniques, and across spatial and temporal scales. We used identical data collection methods in grazed mesic grassland ecosystems of North America and South Africa to examine the effects of fire and growing season precipitation on large- and small-scale plant species richness and spatial heterogeneity. To explore these dynamics, we used six years of small-scale (4m²) plant species richness data and one year of large-scale (1.5 ha) richness data collected at the Konza Prairie Biological Station (northeastern Kansas) and Kruger National Park (northern South Africa). While these systems are similar in climate and landscape structure, they differ in their evolutionary histories and large ungulate grazer richness. We used these sites and data to address the following questions:

1. Do estimates of the regional species pool vary with sampling technique, site, and fire management;
2. What proportion of the regional species pool is captured by sampling small plots;
3. Does the proportion of local richness relative to regional richness vary with growing season precipitation? Contrary to our predictions, regional richness was found to be higher at Konza Prairie than its counterpart in Kruger National Park (p < 0.001).

At Konza Prairie, fire was found to have a non-significant effect on regional species pool size, while in Kruger National Park, we found a negative relationship between fire frequency and regional species pool size (p = 0.003).  The proportion of local richness relative to regional richness was higher at Konza Prairie, suggesting a more even distribution of species in this North American grassland. Also, this proportion was significantly correlated with growing season precipitation. Overall, our results suggest that community structure and/or richness are likely to be more sensitive to changes in climate and fire management in Kruger National Park (South Africa) than at Konza Prairie (North America).