Influence Of Environmental Variables On The Distribution Of Selected Tree Species In Lake Manyara Upper Catchment, Northern-Tanzania

ABSTRACT

This study was conducted to analyse the influence of environmental variables on the distribution of selected tree species in Chemchem River in the Manyara National Park under current conditions. The specific objectives were to assess the current distribution status, identify important environmental variables associated with the distribution and predict potential habitats of selected tree species in relation to environmental variables under current conditions. The area was stratified by elevation. Two transects in each elevation stratum were laid parallel to the river flow. Rectangular plots each of 0.02 ha were established. In each plot, trees were enumerated, identified by their scientific names and GPS points taken. Seven (7) environmental variables were used. Tree data was summarised into respective families, genera and species. Dominant tree species were selected based on index of dominance. All analysis were carried out in excel software. Prediction of the current habitats was done using Maximum Entropy Modelling (Maxent) software. Maxent models performed better than random, with average training and test AUC values of 0.8497 and 0.8577±0.0235 respectively. A total of forty five (45) tree species belonged to 36 genera and 21 families were found. Dominant species were Acacia tortilis (0.0415), Ficus sycomorus (0.0366), Acacia robusta (0.0135) and Trichilia emetica (0.0127). Species were distributed following the river flow with lower elevations inhabiting most species. The increase in elevation and temperature seasonality increased the probability of occurrences of most species. Significant predictive contribution of elevation was observed to particular species of Albizia petersiana (83.05%) and Ficus thoningii (75.72%). Furthermore, suitable habitats increased with increasing annual precipitation and temperature of the driest quarter and were predicted in the central and north eastern of the study area. These habitats were fragmented with some patches. Park management should help the communities conserve the upper areas of the river so as to minimize illegal tree cut and farming in catchment areas. Furthermore, restoration and conservation efforts should be done targeting fragmented habitats, unsuitable habitats and species with small habitats.