EFFECTS OF DIRECTED BURNING INTENSITY ON DIVERSITY OF PLANT-SPECIES IN A JACK PINE STAND (PINUS-BANKSIANA LAMB)

Vegetation development was studied in a jack pine (Pinus banksiana) cl ear-cut one and two years after prescribed burning or scarification. E ven if differences were found in species composition, most species pre sent before treatment were also present afterward. However, variations in the abundance of those species were observed: a strong initial dec rease in shrub and grass biomass was noted on the burned-over plots, w hereas scarification affected only the grass biomass. On the second ye ar, the influence of burning and scarification on plant biomass signif icantly decreased. Fire intensity correlated negatively with shrub bio mass and positively with tall forbs biomass. Shannon's diversity index was calculated for each of the vegetation characteristics (percent co ver, number of individuals, frequency and biomass). One year after tre atment, prescribed burning and scarification affected all diversity in dices except those based on the number of individuals. Richness and di versity indices based on percent cover and biomass were lower on the b urned and scarified plots than on the clear-cut plots, while there wer e no differences between the indices based on frequency between burned and clear-cut plots. These effects were, however, neglible two years after treatment. No correlation was found between fire intensity and a ny of the diversity indices one year after treatment, but indices base d on percent cover and number of individuals correlated with fire inte nsity the second year after treatment.