Litterfall production and associated carbon and nitrogen fluxes of seven woody species grown in indigenous agroforestry systems in the south-eastern Rift Valley escarpment of Ethiopia

Abstract

We compared the litterfall production and associated carbon (C) and nitrogen (N) fluxes for seven woody species grown in three agroforestry systems practiced on the slopes of the south eastern Rift Valley escarpment of Ethiopia. Five of the species were native (Coffea arabica L., Cordia africana Lam., Croton macrostachyus Del., Erythrina brucei Schweinf. and Millettia ferruginea (Hochst.) Bak) and two were non-native fruit tree species (Mangifera indica L. and Persea americana Mill.). Together, these species accounted 85 % or more of the crown area of each agroforestry system: the Enset system (occurring at 2,100–2,400 m asl), the Enset-Coffee system (1,900–2,200 m asl), and the Fruit-Coffee system (1,500–1,900 m asl). Enset or false banana [Ensete ventricosum (Welw.) Cheesman] is a staple food crop in this region of Ethiopia and coffee and fruit trees are grown as cash crops. Monthly litterfall was collected from 4 to 6 trees of each species during 2010 and dry mass, carbon and nitrogen contents determined. The annual litterfall production per unit area of crown decreased in the order: C. macrostachyus (1,014 g m−2), E. brucei (929), C. africana (917), P. americana (809), M. indica (807), C. arabica (446) and M. ferruginea (362). The simple linear regression equation using breast height diameter explained 95 % of the variation in the litterfall production of M. ferruginea, but only 55 % for C. africana. The annual litterfall production of the seven species combined per unit area of land was the highest for the Fruit-Coffee system (average 12,938 kg ha−1), followed by the Enset-Coffee system (10,187) and the Enset system (7,430). The associated annual C fluxes (kg ha−1) were 5,145 (Fruit-Coffee system), 3,928 (Enset-Coffee system) and 2,803 (Enset system), and corresponding N fluxes 278 (kg ha−1), 257 and 190. The combined litterfall production of the seven species in our study was higher than has been reported for other agroforestry systems and tropical forests.