Fire Frequency and Community Heterogeneity in Tallgrass Prairie Vegetation

Abstract

Few studies have directly addressed the effects of disturbance on spatial and temporal heterogeneity. Spatial heterogeneity. Spatial heterogeneity is the degree of dissimilarity in species composition from one point to another into a community, whereas temporal heterogeneity is compositional change within a site over time. The purposes of this study were to determine (1) if a quadratic relationship exists between within—site heterogeneity and disturbance frequency as predicted by the intermediate disturbance hypothesis (IDH), (2) if disturbed and undisturbed sites have similar heterogeneity as implied by the disturbance heterogeneity hypothesis (DHM), and whether or not these results differed with scale, and (3) if there is a relationship between spatial and temporal heterogeneity as implied by the DHM. Analyses were based on plant species composition data collected over 9 yr in quadrats permanently located in experimental management units subjected to differ burning frequencies at Konza Prairie Research Natural Area, Kansas, USA. The relationship between disturbance frequency and within—site heterogeneity was opposite that predicted by the IDH. Heterogeneity was lowest at intermediate disturbance frequencies. Heterogeneity in annually burned prairie was lower than in unburned prairie and prairies burned once every 4 yr in contrast to predictions of the DHM. However, this relationship did not hold at larger spatial scales. There was a positive relationship between within—site spatial and temporal heterogeneity on annual burned sites, sites burned once every 4 yr, and nearly so on sites burned every other year. Within—site heterogeneity was negatively correlated with cover of Andropogon gerardii, and positively correlated with total richness and species diversity. Studies of variation, in addition to averages, will increase our ability to predict patterns of species distribution and abundance within and between communities in response to disturbance.