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Abstract:
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"This study explored some of the basic environmental factors that affect the natural regeneration of four mahogany species existing in the Budongo Forest Reserve, Uganda. The four species studied are: Khaya anthotheca, Entandrophragma cylindricum, E. utile and E. angolense. For each species, the biology, ecophysiology, silviculture and management are reviewed. Diverse published reports were critically reviewed and efforts made to highlight their contributions and identify knowledge gaps. Whereas forest understorey light is emphasized as the major hindrance to tropical natural forest regeneration, this study also investigated the effects of past logging in the Budongo forest reserve on soil factors and microenvironments (illumination, photosynthetically active radiation and forest temperature) and on mahogany regeneration.
Three forest categories ('treatments') including unlogged (one compartment), earlier logged (seven compartments) and later logged (three compartments) were identified from the Budongo forest main block and the two outlying forest patches (Siba and Kaniyo Pabidi). Data were collected from plots established in each compartment. A total of 258 plots were sampled. The plots were 25m x 50m each. Within each plot, mahogany seedlings, saplings and trees were sampled. From the same plots, soil samples were collected and were analyzed for texture, pH and nutrients and compared within and between treatments. Furthermore, illumination, photosynthetically active radiation (PAR) and temperature (below ground, forest floor and forest understorey-air) were evaluated to ascertain whether there were any variations in and between the three treatments.
There was significant difference between the unlogged and the logged treatments (05 < P >= 0. 01) in terms of regeneration, edaphic and micro-environmental factors. K. anthotheca was observed to be quantitatively the most significant mahogany timber species in Budongo Forest Reserve. Next in abundance were E. cylindricum and E. angolense respectively. The least important, in terms of regeneration density was E. utile. Exploitation generally affected individuals in the larger sizes (>= 80cm dbh). Differences in light regimes are between logged and unlogged forest tracts. The earlier and later logged treatments were quite similar, but PAR effects were detectable between the extreme forest categories (unlogged vs. later logged). Values of PAR and illumination were lowest in the unlogged forest than in the logged treatments. Contrasts between forest treatments were most marked in the later logged treatment, particularly with illumination and temperature (below ground and on the forest floor). Lower temperatures in the unlogged forest and higher temperatures in the most recently logged compartments were observed. Direct multivariate analysis of data using DCA and CCA techniques showed a significant correlation between local patterns of mahogany regeneration and some of the soil variables, available phosphorus, potassium and total nitrogen being the most important
Given the significance of the role of light/PAR and temperature variations in the treatments sampled, more silvicultural effort, such as enrichment planting and conservation should be placed on compartments that were logged earlier, preferably in the 1960s."
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