Competition, Fire, and Nutients in a Mixed‐Grass Prairie

Abstract

Variation in the intensity of competition has been proposed as a mechanism that may control the species diversity and composition of many kinds of communities, including North American prairie. Competition intensity is predicted to increase with soil fertility and decrease with disturbance, causing variation in the abundances of competitively subordinate species. Variation in competition intensity was examined in an experiment in which fire and fertilizer were applied to native mixed—grass prairie. Treatments consisted of annual burns, a single burn, and untreated control, and fertilization (N ≥ 15 replicates) applied to 7 x 5 m plots for two growing seasons. The experiment was repeated at a second site 15 km away. Fire reduced standing crop and litter, and increased the frequency of bare ground. Nutrient addition increased standing crop and decreased bare ground. Species composition and diversity were largely unaffected by fire. Two common species, Bouteloua gracilis and Carex obusata, were significantly more abundant in fertilized vegetation than in controls at both sites; species diversity decreased in fertilized plots. Vegetation responses to the treatments were similar at the two sites. To tests for variation in competition intensity with fire and nutrient availability, removal experiments were performed in each treatment at one site. Two tussocks each of Festuca ovina and Stipa spartea were chosen in each plot. One plant of each pair had all neighbors within 30 cm clipped and removed during two growing seasons. Each species grew larger and faster in the absence of neighbors, but the magnitude of this effect did not vary with fire, fertilizer, or standing crop. Fire and nutrient addition produced significant changes in the community structure of mixed—grass prairie but did not alter competition intensity in the manner predicted.

Competition intensity and its importance: results of field experiments with Anthoxanthum odoratum

“…Wilson and Keddy 1986;Campbell and Grime 1992;Turkington et al 1993;Bonser and Reader 1995;Gaudet and Keddy 1995;Kadmon 1995) or to have no relation to productivity (e.g. Welden et al 1988;Di Tomasso and Aarssen 1991;Wilson and Shay 1990;Wilson and Tilman 1993;Cahill 1999). Our results show a clear relationship between community above-ground phytomass and competition intensity when the latter is calculated using population-level measures, such as number of shoots.…”

Growth and elemental content of several sagebrush-steppe species in unburned and post-wildfire soil and plant effects on soil attributes

“…The direction, magnitude, and depth of influence of these changes in the soil depends on myriad factors including maximum burn temperature, length of burn, fuel composition, soil texture, and water content (Wright and Bailey, 1982). The changed nutrient status of the soil, as well as, heat-induced production of germination cues, release of competition, production of phytotoxic substances, and destruction of germination inhibitors, all influence post-fire natural plant recruitment dynamics and post-wildfire community structure (Christensen and Muller, 1975;Keeley et al, 1985;Sonneveld and Voogt, 1973;Went et al, 1952;Wilson and Shay, 1990).…”

Abiotic constraints on the competitive ability of exotic and native grasses in a Pacific Northwest prairie

“…These changes in morphology will likely translate into increased biomass and seed count during successive seasons due to increased light capture ability (Schmitt and Dudley 1996). Similarly, Wilson and Shay (1990) found that basal circumference increased in perennial grasses when neighbors were removed in a Canadian mixed-grass prairie. L. multiflorum, the only non-perennial, was able to capitalize on the reduction in competition to produce more aboveground biomass, which was highly correlated (r = 0.92) with seed production.…”