Crown bole diameter linear equation for Daniellia oliverii (Rolfe) Hutch and Daviz and its application to stand density control in natural stands

Abstract

At present, no adequate information on the application of crown-bole diameter model to stand density and stock control for Daniellia oliverii (Rolfe) Hutch and Daviz open grown trees for sustainable forest management in the study area. The species numbers are threatened, because farmers and foresters do not actively plant this tree species. Livestock, fire, and anthropogenic activities are few factors that limit the success of natural regeneration of the species; and is facing regeneration problem. These have led to the species declining in the natural forest areas and the loss of biological values (genetic hereditary). A total of nine blocks as sample plots sizes 100x100 meters were randomly laid. Simple random sampling was used to collect data on tree diameter at breast height (dbh). Dbh was used to estimate crown diameter using a developed simple linear crown-bole diameter model. Based on this finding, dbh distribution was more (42 tree stands) concentrated at the lower diameter class (10 to 30cm) than at the upper diameter class distribution (31 and above). This could be that such tree stands might have been exploited as timber in the ecosystem. Nowadays, trees of smaller dimension are generally logged immediately they are discovered, especially the most economic and desirable species. The status of the tree species was a reversed “J” shaped distribution curve. The reverse ‘J-shape’ diameter distribution indicated healthy recruitment potentials; the lower class diameter tree stands could develop into mature trees and replace the old ones in the future if proper conservation efforts are sustained. Thus, this structure is typical of a natural forest. This finding estimated limiting stocking and stand density required for producing a complete canopy without effect of competition. D. oliverii with diameter 48.7cm would require a stocking of 168 trees per hectare in terms of total occupancy by tree crowns; stand density of 0.00001863m2ha-1 would be needed. Also, tree stands of 80cm dbh would have 73 tree stands limiting stocking, covering a stand density of 0.00005027m2/ha. Linear crown-bole diameter model could simply be used in forest inventory operations for determining the forest stock with less cost and time consuming. More research is needed with a greater variety of site and stand conditions in addition to a greater variety of tree sizes and ages.