The distribution and estimation of Myrianthus holstii, Engl., a low density dioecious tree species in Binp, Uganda using the belt-transect and the distance line-transect methods

Abstract

Good density estimates for low abundance tree species are costly to achieve especially in rugged or disturbed forest landscapes. More efficient methods would be of considerable value to managers and conservationists. Here I assess a method that has been neglected in this context. I examine and compare distance- line-transects and conventional fixed-width transects for assessing a distinctive low abundance species of conservation significance, Myrianthus holstii Engl., in three separate areas, within a steep, disturbed mountain rain forest. Precision and implied accuracy appeared substantially better with the visual detection line-transect than with the fixed-width transect for equivalent costs and effort at all three landscapes but as the two methods provide different estimates there are questions of possible bias in both approaches. I also determined the density and distribution pattern of M. holstii trees and found out that the density of seedlings in each site was relatively lower compared to density of large trees as estimated by the distance method, the distribution pattern is clumped and most trees occurred within lower slopes and the population size – class structure showed an “Inverse J” suggesting recruitment. In conclusion, the distance method is suited to low density species that are easily identified, even when understorey vegetation and terrain severely impair visibility. However, due to the differences in detection probabilities, populations need to be stratified both by tree size and context. Secondly, the fact that majority of the species are found within the forest edges and are clumped, there is likely chance of competition especially at high altitude areas.