Disturbances can mediate species coexistence by disrupting patterns of dominance and competition, providing opportunities for colonization, and inhibiting or allowing persistence of long-live species. We conducted a field experiment to test the question: do small-scale disturbances mediate natural succession in an old-field over the first ten years after abandonment? More specifically, does disturbance inhibit succession to long-lived perennial vegetation? Eight rows of nine 2m x 3m plots were established in a randomized complete block design in a field that had been plowed, then disked, cross-disked, harrowed, and cross-harrowed to homogenize remnants. Each plot was assigned randomly to one of two clipping intensities (all species removed or dominant species removed) and one of four clipping frequencies (2/yr, 1/yr, 1/2yrs, 1/4yrs) for 10 years. Plant species composition and functional groups based on growth form (life history strategies) and life form (taxonomic groups) were analyzed with MRPP to assess differences in treatments along with three measures of diversity: richness, Pielou’s evenness and Shannon-Weiner Diversity.
Results/Conclusions
By the midpoint of the study, all annual species had been replaced by longer-lived perennial species, and by the tenth year, the field was distinctly stratified, with an overstory and understory layer. Disturbance frequency and intensity had a significant effect on species richness and evenness at five years. Richness was greatest in the most frequently disturbed plots (twice/yr) and declined as disturbance frequency declined. In contrast, evenness was lowest in plots clipped twice/yr and highest in plots clipped annually. Disturbance intensity in dominant removal plots had the highest evenness and total removal had the lowest. Growth form significantly changed from year five to year 10 of the experiment with relative abundances of herbaceous perennials increasing in all treatment frequencies and intensities. These results suggest that growth form, more than life form, may predict community responses to disturbance early during succession until some threshold is reached where species responses are altered.