03048nas a2200133   4500008004100000245007900041210006900120300001500189490000700204520255000211653002202761100002402783856010702807       1992                        eng d00aFire frequency and community heterogeneity in tallgrass prairie vegetation0 aFire frequency and community heterogeneity in tallgrass prairie   a2001 -20060 v733 a<p>Few studies have directly addressed the effects of disturbance on spatial and temporal heterogeneity. Spatial hererogeneity is the degree of dissimilarity in species composition from one point to another in a community, wheras 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 heterogenity and disturbance frequency as predicted by the intermediated disturbance hypothesis (IDH), 2)if disturbed and undistubed 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 different burning frequencies at Konza Prairie Research Natual Area, Kansas, USA. The relationship between disturbance frequency and within-site heterogeneity was opposie that predicted by the IDH. Heterogeneity was lowest at intermediate disturbance frequencies. Heterogeneity in anually 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 disturbance frequency and within-site heterogenity was opposite that predicted by the IDH. Heterogenity was lowest at intermediate disturbance frequencies. Heterogeneity in annually burned prairie was lower than in unburned prairie and prairies burned once every year 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 annually 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. Key words: Andropogon gerardii, fire, grassland vegetation, intermediate disturbance hypothesis, Konza Prairie, spatial heterogeneity, species density, species diversity</p>10atallgrass prairie1 aCollins, Scott., L.  uhttp://knz.lternet.edu/content/fire-frequency-and-community-heterogeneity-tallgrass-prairie-vegetation