Climatic variation and simulated patterns in seedling establishment of two dominant grasses at a semi-arid and grassland ecotone. Peters, D. Journal of Vegetation Science, 2000.
Climatic variation and simulated patterns in seedling establishment of two dominant grasses at a semi-arid and grassland ecotone [pdf]Paper  abstract   bibtex   
Seedling establishment by two congeneric C4 perennial grasses (Bouteloua gracilis and B. eriopoda) that dominate semiarid and arid North American grasslands was simulated by modeling multiple temporal frequencies of climate at their ecotonal boundary. The occurrence of a recruitment event in each year was determined by comparing simulated soil water content through time with amount and timing of soil water required for establishment based on data in the literature for each species. The two Bouteloua species had different regeneration strategies. B. gracilis had a broad pattern of establishment that occurred from June through October with a peak in September and October when year-to-year variation in precipitation was high. B. eriopoda had a narrow distribution of establishment events that peaked in the middle of summer (July) when precipitation amounts were most reliable. Interdecadal variation in climate had species-specific effects on establishment. Climatic condition from 1949 through 1968 were more favorable for B. eriopoda establishment compared to the cooler, wetter conditions from 1969 through 1988 that favored B. gracilis. Establishment of B. eriopoda was negatively affected by El Nino events, whereas B. gracilis establishment was positively affected by conditions associated with El Nino events. A long-term directional increase in annual precipitation resulted in a small shift in the geographic location of the ecotonal boundary based upon the location of similar establishment probabilities for the two species. These results indicate that temporal partitioning of soil water required by seedlings may account for species coexistence at an ecotonal boundary.

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