Woldu, Zerihun (PhD)Abate Asferachew2018-06-212023-11-082018-06-212023-11-081994-06http://etd.aau.edu.et/handle/123456789/2552Three indigenous tree species namely Acacia tortilis (Forssk.) Hayne, Acacia senegal (L.) Willd. and Balanites aegyptiaca (L.) Del. were studied to explore their potential for agroforestry practices. Studies on the ecology and growth characteristics of the three tree species and their influence on environment were conducted at three different sites; Adamitulu, Awash and Abajata Shalla National Parks in the rift valley. A total of 15 releves (50 x 50 m), five releves in each of the sites were established. In each of the releves presence and abscence and frequency of all tree species was recorded. From each site a total of 15 trees, five for each study tree, were randomly selected for detailed investigation. Tree characteristics which included tree height, diameter at breast height (DBH), canopy depth, canopy radius and canopy diameter of each of the study trees were measured. Cover of undercanopy vegetation was estimated for each of the study trees to assess the influence of trees on undercanopy species diversity. To investigate the influence of trees on undercanopy soil, samples were collected from 50, 250, and 450 cm distances at 02.5, 5.0 - 8.0, and 20 - 23 cm depths along the transect radiating from tree boles. Texture, pH, conductivity, organic carbon, total nitrogen, available phosphorus and exchangeable potassium of the soil samples were analyzed. For comparison purposes cover of vegetation outside tree canopies and soil physical and chemical properties beyond the canopies of trees were also investigated. Of the three sites, Abijata Shalla area was characterized by high tree density (61/ 2500 m2 ), followed by Awash National Park (36/ 2500 m2 ) and Adamitulu area (17/ 2500 m2 ). Acacia torti/is had the highest DBH (0.42 ± 0.12 m), canopy diameter (13.64 ± 2.25 m) and canopy radius (6.91 ± 0.79 m) whereas the highest tree height (5.18 ± 0.77 m) and canopy depth (2.14 ± 0.73 m) were recorded for B. aegyptiaca. Undercanopy vegetation diversity of A. tortilis was highest (2.13) foIlowed by A. senegal (1.92) and B. aegyptiaca (1.78). In all sites undercanopy species diversity was significantly higher than vegetation diversity outside of tree canopies. Texture and pH did not vary between under and outside canopy soils implying that tree canopies did not affect these soil properties. Surface soil conductivity, organic carbon, total nitrogen, available phosphorus and exchangeable potassium were significantly higher under tree canopies for all the study trees compared with outside canopy soils. Comparison of the study trees top soil nutrient contents indicated that under canopy soils of A. tonilis had higher values foIlowed by A. senegal and B. aegyptiaca, respectively. Acacia tortilis and A. senegal had comparable seedling growth rates whereas the former had a higher seedling emergence vigor. The results showed that the study trees significantly enriched soil under their canopies and created a suitable environment for the growth of undercanopy vegetation. Over all A.tortilis had better growth characteristics and improVed most undercanopy soil. The significance of the findings for agroforestry are discussed.enBiologyThesis