Spatial variation of arthropod communities in virgin and managed sites in the Kibale Forest, western Uganda.

http://www.elsevier.com/locate/issn/03781127The structure of arthropod communities in the forest floor vegetation in four differently managed forest sites (virgin forest, lightly selectively logged, heavily selectively logged, and exotic Pinus caribaea plantation) in Kibale Forest National Park, western Uganda, was studied by sweep net between March and May 1985 and July 1995. For the analysis three (or four) 800 sweeps samples were collected from each habitat. In the samples eight arthropod groups (Araneae, Hymenoptera, Heteroptera, Homoptera, Coleoptera, Orthoptera, Lepidoptera, caterpillars (Lepidoptera larvae)) formed over 95% of all the individuals of the arthropod caught in all habitats. The variation within one habitat was smaller than variation between habitats in samples of the same year. Thus, the arthropod communities in differently managed forests differ from each other after over 20 years of management practices (selective logging and clear-cut plus pine plantation) as well as from adjacent virgin forest, and the differences seem to become greater during the succession in managed sites. Samples taken in the same habitat type, 10 years apart, differed greatly from each other. This is the result of both long-term succession and seasonal variation

Effects of a hydropower plant on Coleopteran diversity and abundance in the Udzungwa Mountains, Tanzania

The effects of river flow diversion on biodiversity were assessed using Coleoptera as an indicator group in three habitats of the Kihansi Gorge (Udzungwa Mountains, Tanzania), before and after commissioning of a hydropower plant. Data collected using sweep netting and pitfall traps showed that the effect of diversion of the river flow was site-specific, affecting particularly the spray habitat. Rarefaction analysis of both sweep netting and pitfall samples indicated that the expected richness of Coleoptera declined significantly in all habitats after commissioning of the power plant. Sweep netting and pitfall samples showed that the highest Shannon-Wiener diversity index value before the diversion of the river flow was in the spray zone, but the index value decreased after diversion. Changes in the other two habitats were less prominent. Analysis of variance using diversity index values from five pitfall samples in each habitat type before and after commissioning indicated that there were no statistically significant differences in the diversity index between the two sampling periods or among the three habitat types. Renkonen's similarity index between habitats showed that pitfall samples had higher similarity (87%) than did samples from sweep netting (69%). It is suggested that for mitigation purposes, artificial spray systems, which have been installed in other wetlands of the Kihansi Gorge, also be installed to cover the whole Lower Wetland in which this study was undertaken. In order to maintain overall biodiversity in the Kihansi Gorge, it is suggested that the ecosystem conservation approach be prioritised

Urban afforestation in Tanzania: Lessons from Sokoine University of Agriculture landscape inventory

A study to ascertain the extent to which tree-planting in urban areas of Tanzania have been adhering to the prescribed standards essential for provision of the anticipated services was carried out by taking Sokoine University of Agriculture main campus landscape as a case study. Data pertaining to species and genera composition, age distribution, and overall heath status were collected through a survey which involved 100% sampling intensity. All trees and shrubs encountered were identified by their botanical names, along with taking measurements on their appropriate location, tree-size, and overall health status. The study revealed a tendency of concentrating on few plant species, while much other potential were available. While the acceptable standard requires species not to exceed 10 %, some species were represented by more than 24 %. Diversification at genera level ideal as none of the genera exceeded the prescribed standard of 30%. The distribution of plants in terms of age class was not ideal as the observed proportion in the young (283%), mature (62.7%), and over mature (9.0) diverged significantly from the respective prescribed standards of 20%, 60%, and 20%. The overall health status of trees was good, with this class representing more than 95% of the total trees observed. Excessive concentration of few species and genera has a disadvantage, particularly in the incidences of pest and disease outbreak. Large areas could be left bare if a species happened to be severely attacked, which in turn reduces the overall beauty of a landscape. Inappropriate age class distribution complicate future landscape maintenance since many trees may have to be removed and replanted at once. This tends to increase the cost of maintenance, and may make replacement exercise impossible. It is concluded that urban afforestation in most towns of Tanzania are likely to have not adhered to the prescribed standards, as policies related to tree planting have been similar in most cities. It is recommended that cities and urban authorities should consider the use of landscape experts in deciding the appropriate ways of handling urban forest, so as to maximize the benefits that could accrue

Tree diversity in western Kenya: using profiles to characterise richness and evenness

Species diversity is a function of the number of species and the evenness in the abundance of the component species. We calculated diversity and evenness profiles, which allowed comparing the diversity and evenness of communities. We applied the methodology to investigate differences in diversity among the main functions of trees on western Kenyan farms. Many use-groups (all trees and species that provide a specific use) could not be ranked in diversity or evenness. No use-group had perfectly even distributions. Evenness could especially be enhanced for construction materials, fruit, ornamental, firewood, timber and medicine, which included some of the most species-rich groups of the investigated landscape. When considering only the evenness in the distribution of the dominant species, timber, medicine, fruit and beverage ranked lowest (> 60% of trees belonged to the dominant species of these groups). These are also use-groups that are mainly grown by farmers to provide cash through sales. Since not all communities can be ranked in diversity, studies that attempt to order communities in diversity should not base the ordering on a single index, or even a combination of several indices, but use techniques developed for diversity ordering such as the Renyi diversity profile. The rarefaction of diversity profiles described in this article could be used in studies that compare results from surveys with different sample sizes