Submitted to: Journal of Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/1998
Publication Date: N/A
Interpretive Summary: Demographic studies of the recruitment, growth, and death of plants are rare, yet it is these processes that determine, for the most part, individual plant and population dynamics of rangelands. We analyzed a long- term (41 y) data set collected from permanent plots in western Kansas in order to evaluate these processes and relate them to population dynamics. We digitized each plant of the dominant species, blue grama, on all plots and analyzed the results through time using geographic information system software. We found that 91% of the years from 1938 through 1972 had at least seedling added to the plots. An average of 25.8 plants died each year, and most were younger than 10 years old. The average number of plants in each 5 m2 plot was 29 to 278. Our results are important to our understanding of blue grama population dynamics since these species are important throughout the Central Grasslands of the U.S. and dominate the shortgrass steppe in eastern Colorado. Blue grama has been reported to recover very slowly after disturbances, but few studies exist that document its recruitment, growth, and death through time.
Technical Abstract: We analyzed a data set of locations and sizes of individual plants from five 1 m2 permanent quadrats which had been mapped annually from 1932 to 1972. We digitized each map and used geographic information software to evaluate annual recruitment and mortality, age structure, survivorship and longevity of genets and individuals of Bouteloua gracilis. Ninety-one percent of the years between 1938 and 1972 had at least one seedling recruited. An average of 10.3 genets died annually although the variability among years was high (CV=70%). The number of seedlings recruited each year was significantly correlated to the number of genets dying. Most genets died before age 10 and the average lifespan was 3.7 years. The average number of individuals per genet was 1.3. Excluding seedlings, 56% of the genets were represented by a single individual. The annual number of individuals in the 5 m2 plots ranged from 29 to 278. Average mortality of individuals was 25.8 per year and the variability among years was high (CV=91%).