Abstract
Wood energy is derived from a variety of wood-based sources, the most prominent of which is the fuelwood obtained directly from trees and forests. The genus Acacia includes over 1,000 species spread all over the world. Six indigenous acacia species that grow naturally in the southwest region of Saudi Arabia were selected in November 2010 from the Abha and Al-Baha forests to determine the heating values and chemical constituents of their wood on a comparative basis. The results showed that they differed significantly in their chemical components and heating value. The highest heating value (20.45 MJ kg(-1)) was found in the wood of A. tortilis, while A. ehrenbergiana had the lowest (18.00 MJ kg(-1))-although the latter species is the most popular in the Kingdom for firewood. Trees grown in the Al-Baha region had greater heating values than those in the Abha region. The heating values were highly positively correlated with the contents of lignin (R-2=0.70) and total extractives (R-2=0.56).