Allometric equations for estimating aboveground biomass of khat (Catha edulis)-stimulate grown in agroforestry of Raya Valley, Northern Ethiopia

Khat plant (Catha edulis Forsk) is an evergreen perennial cash crop cultivated in east Africa, southwest Arabia, and Madagascar. The plant is known for its production of stimulant fresh leaves, and expanding as expense of other land uses for its short-term financial returns. We, therefore, developed allometric equations for estimating aboveground biomass and carbon (C) removal of khat grown in farmlands of Raya Valley, Northern Ethiopia. A total of 31 plant individuals were harvested destructively on the basis of their diameters and age ranges. The equations were parametrized using biometric variables such as basal diameter (d10), diameter at breast height (d), dominate height (doh) and mean height (h). Results of the analysis showed that, stem accounted for 58%, branch 32% and foliage 10% of the aboveground biomass (AGB). Commercial foliage biomass C removal ranged from 2.3 to 2.7 Mg ha(-1). The power equation, AGB = b1, d(10)(b2)xdoh(b3), was the best (highest ranked using goodness-of-fit statistics), explaining 96% of the variation in aboveground biomass (p < 0.01). Models comparisons showed that our best ranked equation (M6) improved the aboveground biomass estimate by 44% and 48 % that of generic and other species-site specific equations developed in the tropics, respectively. Thus, our best species-site specific equation developed in this study can accurately estimate aboveground of khat plant biomass in the study region.