Productivity and species richness across an environmental gradient in a fire‐dependent ecosystem

Abstract

The fire-dependent longleaf pine-wiregrass (Pinus palustris Mill.-Aristida beyrichiana Trin. & Rupr.) savannas of the southeastern United States provide a unique opportunity to examine the relationship between productivity and species richness in a natural ecosystem because of the extremely high number of species and their range across a wide ecological amplitude (sandhills to edges of wetlands). We used a natural gradient to examine how plant species richness and plant community structure vary with standing crop biomass (which in this system is proportional to annual net productivity) as a function of soil moisture and nitrogen mineralization rates in a frequently burned longleaf pine-wiregrass savanna. Highest ground cover biomass and highest species richness were found at the same position along the gradient, the wet-mesic sites. Relative differences in species richness among site types were independent of scale, ranging from 0.01 m(2) to 100 m(2). Nitrogen availability was negatively correlated with species richness. Dominance of wiregrass (in terms of biomass) was consistent across the gradient and not correlated with species richness. Regardless of site type, the community structure of the savannas was characterized by many perennial species with infrequent occurrences, a factor in the low temporal heterogeneity (percent similarity between seasons and years) and high within-site spatial heterogeneity (percent dissimilarity of vegetation composition). The coexistence of numerous species is likely due to the high frequency of fire that removes competing hardwood vegetation and litter and to the suite of fire-adapted perennial species that, once established, are able to persist. Our results suggest that soil moisture is an important factor regulating both the number of species present and community production within the defined gradient of this study.

Association Between Ants (Hymenoptera: Formicidae) and Habitat Characteristics in Oak-Dominated Mixed Forests

“…Soils from the higher elevations had large stretches of yellow or brownish to white sand underlain at greater depth by relatively solidified dark zones (spodic horizons) (Figure 9). Whereas these (Kirkman et al 2001, Ford et al 2008). Specifically, wet-mesic sites support greater floristic diversity and aboveground biomass than drier, upland sites (Kirkman et al 2001, Ford et al 2008.…”

“…Whereas these (Kirkman et al 2001, Ford et al 2008). Specifically, wet-mesic sites support greater floristic diversity and aboveground biomass than drier, upland sites (Kirkman et al 2001, Ford et al 2008. Ant abundance, however, appears to be highest in the sites near to the water table (lowermedium), but not the shallowest sites ( Figures 3, 4).…”

Regeneration Niche of Whitebark Pine in the Canadian Rocky Mountains: The Basis to Restoring an Endangered Species

“…Basal area was determined by using a basal area prism (BAF 4). From the plant community data, we derived sev-eral variables: total vegetation cover (sum of covers for all species); species richness (number of vascular species per plot to use as a proxy for soil productivity; Kirkman et al, 2001); cover by functional group-trees (cover below 1.4 m in microsite plot of branches and stems of saplings and mature trees), seedlings (all trees <1.4 m in height, other than whitebark pine), graminoids (grass, sedge, and rush species), forbs (herbaceous broadleaf vascular species), prostrate shrubs (woody vascular species <5 cm in height), and upright shrubs (woody vascular species >5 cm height).…”

Carbon Dynamics of Pinus palustris Ecosystems Following Drought

“…Palustris ecosystems have co-evolved with fire and drought. Natural-and now managed-high frequency and low intensity burns have been shown to support the high degree of biodiversity and endemism, and support the intermediate disturbance hypothesis [32]. Hence, one would expect high degrees of biodiversity and associated diversity of plant functions would scale to the ecosystem level and contribute towards resiliency and the ability to recover after disturbance [64,65].…”

“…), with numerous species of other perennial grasses and forbs also present [31]. The sites used in this study have previously been described by the authors of [21,23,30,32].…”