Species diversity after prescribed burns At different intensities and seasons In a high altitude Pinus hartwegii forest

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"In the Ajusco volcano, in Central Mexico, prescribed burningsof low and high intensity were applied in March and May 2002,along with one unburned control for March and another for May,considering conditions of open stands and closed stands, with theobjective of evaluating the vegetation response of the Pinus hartwegiiunderstory. Samplings were conducted every three monthsduring one year. Number of herb and shrub species, density,covering, and frequency were recorded, and the Simpson diversityindex was calculated. According to a principal componentanalysis, the March prescribed burnings of low and high intensityin open stands separate from the other treatments. The t testshowed that the March low intensity burns in open stands yieldeda higher Spring-diversity than the unburned control. For theshrub species diversity, the March and May high intensity burnsin open stands formed a separated group. A χ2 test revealed thespecies that appear preferably in burned areas. The results indicatethat the use of prescribed burnings no later than Marchfavor the richness and diversity of species of the understory."