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<br />s <br />analysis of the relative canopy cover and density were similar, <br />therefore only the canopy cover data are presented. Species <br />richness was analyzed by treatment as an additional variable, for <br />each year separately and overall. <br />At the termination of the experiment (September 1990), each <br />plot was divided into quarters and samples of five major species <br />representative of different seral positions at the site were <br />collected from each quarter. In the event that a given species was <br />not present within a quarter, another sample was collected Prom one <br />of the remaining quarters. Approximately 5 g of aboveground <br />material was collected (clipped to ground level) for each species <br />within each quarter from one individual, or from several <br />individuals if there was insufficient material available from a <br />single plant. All samples within a quarter were collected from <br />locations as near to each other as possible to minimize <br />microtopographical variation. In addition, one soil sample (1-20 <br />cm composite) was taken from the center of each quarter. All <br />samples were dried and analyzed for total nitrogen content by the <br />micro-Kjeldahl process. <br />The species sampled included two annual forbs (Kochia scooaria <br />and Salsola iberica), one perennial forb ( ster canescens), one <br />perennial grass (Aaroovron smithii), and one shrub (Chrvsothamnua <br />nauseosus). The five species formed the seral gradient <br />Salsola > Kochia > Aster > Agropyron > Chrvsothamnus <br />