Fire frequency affects structure and composition of xeric forests of Eastern Oklahoma

Abstract

Since European settlement, changes in the fire regime of eastern deciduous forests of North America have led to changes in biological diversity and stand structure. These changes may be attenuated in xeric forests at the western limit of the eastern deciduous forest where woody plant species richness is low, and dominance high, due to the rigorous biotic and physical environment. Effects of fire frequency on woody plant species richness and stand structure were studied in a xeric, oak-dominated (Quereus spp.) old-growth forest in eastern Oklahoma where prescribed burning had been conducted over 20 years at frequencies ranging from zero to five fires per decade. Regeneration (stem height < 1.4 m) cover was not affected by fire frequency. Increasing fire frequency had a strong negative effect on species richness of saplings and shrubs (stem dbh < 5 cm) but no significant effect on small tree (stems 5 cm < dbh < 10 cm) and large tree (stems dbh > 10 cm) species richness. While oak sapling density was not affected by fire frequency, the density of non-oak saplings and shrubs was very high at zero and one fire per decade and strongly reduced by fire frequencies of two or more per decade. Although 20 years of treatment may not have been sufficient to show fire frequency effects on canopy trees, the effect on species composition of saplings was strong and may have long-term consequences for forest canopy composition. These results suggest that, without at least two fires per decade, tree species richness of these forests will increase and oak dominance will diminish.