Effect of environmental factors on plant species distribution in Pugu forest reserve, Coast region, Tanzania

The present study was carried out with the aim of assessing the extent of environmental influence on plant species distribution in the remaining natural forest in Pugu Forest Reserve. Multivariate techniques were employed to classify and ordinate the data set. A total of 60 plots each 100m2 in area were studied. Plot data were classified and ordinated on the presence/absence basis and for the tree species on density basis as well. The classification derived eight species groups and four sample groups. The species groups overlapped the sample groups which were divided with respect to physiognomic character into moist element, dry forest and two groups which have been called intermediates I and II. The intermediates are possibly transitions between the two major types or represent heavily disturbed forest which is difficult to classify. The ordinations both direct (CCA) and indirect (DCA, PCA) indicate that probable environmental factors influencing species distribution were not measured in the present study, with the exception of topography which contributed to the variation in all ordination runs. Alternative ordinations masking the effect of topography elevation and slope indicate that disturbance to some extent may also have an influence on the plant species distribution in the forest. Monte Carlo permutation tests for CCA ordination runs indicate that the tests are not significant for all the ordination runs with the exception of the CCA ordination on tree density data, using no covariables. Shannon-Weiner diversity indices calculated indicate highest diversity in the moist element vegetation type, conciding with the ordinations which show highest disturbance hence lower diversity in the dry forest where species which are favoured for timber and charcoal extraction more commonly occur.