TREE MAPPING FOR A STRICT NATURE RESERVE IN AKURE FOREST RESERVE, NIGERIA

Abstract

Tree mapping for four Permanent Sample Plots (PSPs) in Akure forest reserve, Ondo State, Nigeria was carried out with the aim of examining the spatial distribution of the tree species in relation to one another. Each plot was a square plot of 50 m x 50 m (i.e. 0.25 ha). A Global Positioning System (GPS) could not be used for geo-referencing each tree due to canopy cover, an alternative method had to be used to get the exact location of each tree in the plots. For each plot, the four corners were labelled as A, B, C and D, while the four sides were AB, BC, CD and DA. This alternative method involved measuring and recording the perpendicular distance from each tree to each of the two nearest sides of the plot. The use of perpendicular distance was to ensure that the distance from the side of the plot to each tree was measured consistently at right angle. The angle subtended by the two lines from the sides of the plot to each tree was also a right angle. Each tree species was identified by a taxonomist. The distance data collected were then plotted on a graph sheet and the position of each tree was indicated as the point of intersection of the two lines from the sides of the plot. The graph was scanned and saved as raster data for further use on a Geographic Information System (GIS) platform. Using GIS software, the graph for each plot was geo-referenced and digitized to obtain the spatial map. The results indicate that the average inter-tree distances for the four plots are 4.4, 4.6, 5.8 and 6.5 metres, respectively. The variation in the distances is because the plots are located within the natural forests and not within plantations. The number of different tree species in Plots 1, 2, 3 and 4 were 23, 24, 18 and 18, respectively. On the whole, the tree frequency for each of the four plots is 62, 87, 62 and 40, respectively. The most prominent family is Sterculiaceae family which dominates Plots 1, 2 and 3. In Plot 4, Annonaceae was the commonest family. The spatial pattern of tree distribution in all the four plots is typical of the lowland tropical rain forest ecosystem. The spatial pattern of tree distribution will assist the management to make reasonable decision during their various researches on examining the spatial distribution of the tree species in relation to one another and determining exact tree location in the study area. By the virtues of the contribution of this study, it is hereby recommended that the dot maps obtained in this study is adequate enough for further usage to generate better information on examining exact tree location in the forest. It is equally recommended that there should be extensive review on the practical applications of Geographic Information System (GIS) in forest data assessment.