Growth Responses of Co-occurring Dryland Woody Species to Climate Variability in Southeastern Ethiopia

Abstract

The objective was to understand the growth ring formation and climate growth relationships of two species, namely Acacia senegal and Commiphora africana. Wood disc samples of 30 trees belonging to the species of under study site (15 samples each) were used to develop climate sensitive ring-width chronologies us-ing standard dendrochronological techniques. The sampled tree species were an-alyzed both manually and microscopically to check the occurrence of growth rings. The results showed that both studied species form distinct growth boundaries, while differences in distinctiveness were revealed between the species. Thin pa-renchyma bands define growth rings of Acacia senegal. In contrast, growths rings of Commiphora africana were delineated with a transition from fibers with thicker cell wall (latewood) to fibers with thinner cell wall (early wood). Apart from wood section analysis, ring patterns were investigated on standing trees of both species based on the concept of cambial marking by wounding (pinning) the tree and an-alyzing the number of growth rings formed between the time of wounding and cut-ting. The result showed the formation of three growth rings after wounding within 2.6 years across the entire samples and this represented the radial growth for the years that revealed the ring formations were annual. In particular, tree ring width of Acacia senegal and Commiphora africana showed strong and significant rela-tionships with average rainfall of the rainy season (r =0.53, and r = 0.40, p<0.05) respectively. It is believed that the outcome of this study has importance in resto-ration of degraded lands; thereby contributing to the conservation and manage-ment of forest ecology of the study area.