Seasonal and Depth Related Patterns of Fine Root Mass in Four Indigenous Tree Species of A Tropical Dry Afromontane Forest in Ethiopia

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Addis Ababa University


The seasonal pattern and vertical distribution (up to 60 cm) of fine root of four indigenous tree species; Celtis africana and Croton macrostachyus, (deciduous) Prunus africana and Podocarpus falcatus (evergreens) were investigated in the dry afromontane forest of Munesa-Shashamane, South Ethiopia, using the sequential coring method. While seasonal changes were more pronounced in the deciduous species compared with the evergreens, marked seasonal changes in total fine root mass, fine root biomass, and fine root necromass were observed in all the studied species. The highest values of measured fine root parameters were recorded during major rain season followed by small rain and dry seasons. In all species, total fine root mass, fine root biomass, and necromass in the major rain season were significantly higher than other seasons. In the two wet seasons, Croton macrostachyus had highest total fine root mass, fine root biomass and necromass followed by Celtis africana, Prunus africana and Podocarpus falcatus in that order. In contrast, in the dry season, generally, the evergreens had higher total fine root mass, fine root biomass and necromass compared with the deciduous species. In the dry season, the highest total fine root mass record was that of P. africana and then decreased, in order, from Croton macrostachyus to Podocarpus falcatus to Celtis africana. Further, fine root biomass of Prunus africana > Podocarpus falcatus >Croton macrostachyus > Celtis africana in the dry season. Dry season fine root necromass data analysis showed inconsistent results. Fine root accumulation was significantly largest in the uppermost 10 cm soil layer. A general decrease in total fine root mass, fine root biomass and fine root necromass with increasing depth was recorded for all the species studied in all seasons. The decline in fine root biomass concentration with increasing depth might be attributed to the decreased organic carbon and nitrogen, increased acidity and clay content downwards in the examined soil profile. The distribution of fine root necromass was similar to that of fine root biomass with the highest concentration on the upper surface. This can be expected compared to the lower depths given greatest amount of live fine root biomass in the upper soil profiles that eventually die at the end leading to higher necromass on the upper layers as compared to the lower depths. The above results are discussed in light of understanding the forest under investigation and its management.