FIRE IMPACT ON POPULATION STRUCTURE AND DIVERSITY OF TREE SPECIES IN WEST USAMBARA CAMPHOR ZONE FORESTS

Abstract

A study was carried out in Lushoto, Tanzania, with the aim of comparing the burnt and unburnt parts of the same forest and determining the economic impact of fire on camphor tree production following an unplanned fire. Two plots of one hectare each were established, one in the burnt and the other in the unburnt part of Magamba forest near Grewal, Lushoto. One hundred percent sampling was done for trees ≥ to 5 cm dbh; trees <5 cm dbh and regenerants were recorded in randomly located quadrants of 5 x 5 m and 2 x 2 m respectively. All trees with dbh greater or equal to 5 cm were identified and measured for dbh and height. Volume, total and relative density, dominance, frequency and hence importance value index (IVI) and Shannon-Wiener index of diversity (H') for each species were calculated. A total of 1045 stems ha^-1 consisting of 30 species were obtained in the burnt plot and 1606 stems ha^-1 with 38 species in the unburnt one. Basal areas were 36 m² ha^-1 and 42 m² ha^-1 in the burnt and unburnt plots respectively. Ocotea usambarensis (camphor) was the dominant species in both plots with 57% and 33.7% of the total basal area. The frequency of this species was also the highest with values of 13 and 10 in the two plots respectively. Ocotea usambarensis, Macaranga capensis, Trichocladus ellipticus, Rapanea melanophloeos, Syzygium guineense and Ficalhoa laurifolia were the most important species with IVI values of between 106 and 15.3 of 300 possible, O. usambarensis being the highest in all areas. The Shannon-Wiener indices of diversity were 2.16 and 2.16 in the burnt and unburnt plots respectively indicating a high species diversity in this forest
community. About 33 275 trees ha^-1 <10 cm dbh were burnt completely and 525 stems ha^-1 with >10 cm dbh died due to fire. Of the 525 dead trees ha^-1, 331 were camphor with a volume of 188 m³ ha^-1 of which about 180 m³ ha^-1 was contributed by trees > 20cm dbh.