Effect of Thinning on the above Ground Biomass of (Conocarpus erectus L.) Trees in the Western Region of Saudi Arabia

Abstract

Benefiting from introduced exotic trees in Saudi Arabia is mostly limited to municipal uses. In order to establish forest plantations of those species, studies should be conducted concerning the effect of silvicultural practices on the plantations productivity. In the present study, we studied the effect of three thinning treatments, on 7 years old short rotation intensively cultured Buttonwood (Conocarpus erectus L.) plantation after 2 years of application. The thinning treatments were 0, 50 and 67% of stock. In exception of the increase in the dry matter (DM) of foliage, no significant influence of thinning was observed on the above ground dry matter (AGDM) of individual tree components. The average total above ground dry matter (TAGDM) ranged between 15.79 kg for unthinned to 22.44 kg for 67% treatment. In all treatments, stem wood accounted for the largest proportion of AGDM with the highest value for the unthinned (71.72 %), differing significantly from the other two treatments (62.88 and 63.05%). Of all tree dimension parameters, only crown diameter (CrD) and stand basal area (BA) were significantly influenced by the treatments. The 67% thinning treatment had the highest mean CrD (2.16 m), while the unthinned was the highest in BA (17.93 m 2 ha-1). Several allometric equations were constructed relating DM of tree components and stem volume of individual trees with their diameter or diameter and total height. Except foliage DM all the relations were highly significant. The coefficients of determination (R 2) were 0.882, 0.899, 0.945, 0.996, 0.987 and 0.990 for twigs, branches, bark, stem wood, total DM and stem volume respectively.