Fetene Masresha (Professor)Beck Erwin (Professor)Seyoum Yigremachew2018-07-172023-11-082018-07-172023-11-082013-01http://etd.aau.edu.et/handle/123456789/9031A good understanding of species coexistence and the extent of variations in interspecies resource utilization by investigating suits of functional traits is useful for predicting the vegetation dynamics and productivity of an ecosystem. Such documented information can be incorporated into silvicultural treatments designed to manage a natural forest towards preset social, ecological and economical targets as well as to initiate reforestation programs of a mixed forest. The present study investigated coexistence strategies of different functional types of trees in the Munessa Natural Forest by evaluating phenology, carbon and water relations of representative indigenous trees (Podocarpus falcatus (Thunb.) Mirb., Prunus africana (Hook.f.) Kalkm., and Croton macrostachyus (Hochst).ex Del) between 2009 and 2011. In the first component, foliage dynamics, growth and some ecophysiological traits were investigated. The degree of inter- and intra-individual synchronization of foliage phenophases was examined to evaluate the contributions of endogenous and external factors to the dynamics of the foliages. In the second component of the tudy, plant water status and its diurnal variation was assessed by measuring predawn and midday leaf water potentials. Moreover, sap flux at the bases of the tree trunk and of selected branches was determined using Granier type thermal dissipation sensors. Branch and basal sap flux patterns were compared to assess water movement through the stem and quantify potential water reservoirs. To that end, the daily water use by the whole trees was determined from the sap flux data and sapwood area of trees with comparable DBH. Analysis of the δ 18O signatures of water samples from different soil horizons and from twigs were performed to determine the depth of the soil from which the studied functional types of trees extracted water for transpiration. Additionally, δ 13C of leaf samples were used to assess gas exchange characteristics over the entire life time of the leaves. In the third component, the daily and seasonal gas exchange patterns of the leaves of the studied species were measured during the dry and wet seasons of 2009 and 2010. Water use efficiencies of carbon capture by the studied functional types of trees were also determined from the gas exchange data. The phenological findings showed that the onset of the rain in triggering bud break depends on the functional type of the tree. Furthermore, the study proved the significance of endogenous control on the life spans of the leaves, and on the overall foliage dynamics of P. falcatus and C. macrostachyus. Moreover, leaf life-span is identified as an important trait of functional types of trees closely correlating with other functional traits. On the other hand, the water relation study showed that spatiotemporal differences in soil water use are among the ecophysiological strategies that enabled resource partitioning and coexistence among different functional types of trees. Additionally, stem tissue water storage, day-time use of that reservoir and night/day time recharging, were noted as species specific strategies stabilizing coexistence of the different functional types of trees. With respect to photosynthetic carbon capture, the study showed similar biomass production by all three functional types of trees which results from exploiting fluctuating niches of irradiance and soil moisture. The later finding emphasizes the importance of temporally changing patterns of irradiance and moisture for stabilizing the coexistence of adult individuals of different life-forms, and in turn, plant diversity. v According to this finding, the long term courses of irradiance and soil moisture could be used as a tool for predicting the impact of environmental changes on plant biodiversity and ecosystem services. Furthermore, the study implies that enrichment planting to rehabilitate degraded forests should be carried out with species representing different functional types of trees. This would guarantee an optimized carbon and hydraulic budget of the entire ecosystem. Another essential outcome is the fact that forest management plans should recognize the significance of different soil water sources for the diversity of species with respect to the hydrology of seasonally dry forests. The study also provides species-specific environmental requirements that may assist forest managers in matching planting purpose and species with site conditions.enBiologyThesis