Fire frequency effects on vegetation of an upland old growth forest in eastern Oklahoma

Scope and method of study. The purpose of this study was to determine the effects of prescribed fire frequency on the forest understory plant community and forest composition in an old-growth forest of eastern Oklahoma. The study was conducted at the Okmulgee Game Management Area in the summer of 2008. Prescribed fires over the past 20 years had a frequency of zero to five per decade. Tree density and basal area was measured on 20 plots of 0.01 ha in each of eight treatment units. Overstory canopy cover, ground cover, and understory plant cover were sampled from four -- 1 m2 sub-plots nested in each of the sample plots.;Findings and conclusions. Frequent low-intensity fire is necessary to maintain the dominance of fire tolerant oak species and the high biodiversity of herbaceous plants in the forest understory. Fire-intolerant shrub and sapling density and richness increase as fire frequency is reduced from five to zero fires per decade. Twenty years of low intensity fire at a frequency of five per decade is not sufficient for the reduction in tree density and canopy cover. Frequent low intensity fires in the range of two to five per decade are sufficient to maintain oak overstory dominance, as this frequency will control fire-sensitive woody shrubs and saplings while not reducing the density of oak saplings that eventually grow into the canopy. Fire frequencies from two to five per decade can significantly improve the habitat for wildlife that benefit from increased diversity and production of palatable herbaceous plants. Fire frequencies as low as two per decade can reduce the habitat quality for wildlife species that benefit from a high density and diversity of shrubs and saplings in forest understories. While no herbaceous species were reduced in presence or cover by higher fire frequencies, many herbaceous species responded positively to increased fire frequencies. Landscapes with a diverse mosaic of forest understories can be produced by prescribe burning at varying frequencies and times since last fire.