FIRE AFFECTS ECOPHYSIOLOGY AND COMMUNITY DYNAMICS OF CENTRAL WISCONSIN OAK FOREST REGENERATION

Blocks in the forest were burned in April 1987 by a low-intensity controlled surface fire. During the following growing season Acer rubrum seedling density declined by 70% while percent cover increased several-fold in Rubus allegheniensis. In general, leaf concentrations of N, P and K were increased by the fire in all species, although the relative enhancement decreased as the growing season progressed. Daily maximum photosynthetic rates were 30-50% higher in burned than unburned sites for Prunus serotina, Quercus ellipsoidalis, and R. allegheniensis, but did not differ between treatments for A. rubrum. Mean sunlit photosynthetic rates and leaf conductances were stimulated by the burn for all species, with greatest enhancement in photosynthesis measured in Q. ellipsoidalis. Leaf gas exchange in R. allegheniensis was most sensitive to declining leaf water potential and elevated vapor pressure gradient, with Q. ellipsoidalis the least sensitive. Fire had no discernable effect on water status of these plants during a year of relatively high rainfall. In comparison with other species, A. rubrum seedlings responded negatively after fire, both in terms of survival/reproduction (decline in the number of individuals) and relative leaf physiological performance. Fire enhanced abundance of R. allegheniensis and the potential photosynthetic performance of R. allegheniensis, P. serotina and particularly Q. ellipsoidalis. Post-fire stimulation of net photosynthesis and conductance was largely the result of enhanced leaf N concentrations. -from Authors