Abstract
This study was conducted with the objectives of study investigates, compare, and try to describe the floristic composition and structure of the vegetation of exclosures and open grazing lands. A stratified preferential sampling design technique with flexible systematic model was used for data collection. Data on vegetation and environmental parameters were gathered from 120 quadrants (90 from restorations or exclosures of different ages and 30 from adjacent open grazing lands), of 20 m x 20 m (400 m2) size. Species richness and the presence or absence of herbaceous plants were recorded like soil samples in a 2 m x 2 m (4 m2) subplot inside each main quadrant from five points, one at each corner and one at the center. A total of 142 plant species belonging to 118 genera and 52 families were identified. All exclosures displayed higher plant species richness, diversity, and aboveground standing biomass compared to the adjacent open grazing lands. Consideration of edaphic (e.g. soil total nitrogen, available phosphorus, CEC, exchangeable bases, soil pH and soil texture) and site (e.g. Stoniness, Grazing) variables will help to optimize the selection of areas for the establishment of future exclosures. Moreover, our study suggests that with time exclosures may increasingly obtain an important role as refugees and species pool similar to church forests and should be protected and managed in a sustainable manner. However, economic and social impacts of exclosures should be included in feasibility studies before establishing exclosures in the future. Altitude, Grazing and some soil parameters like Mg were the major environmental factors in the division of the vegetation into plant community types. The result of the frequency distribution of woody species showed a high proportion of small-sized individuals in the lower diameter classes indicating good recruitment potential of the forest patches and the rare occurrence of large individuals. Such trend was probably caused by past disturbance of the original vegetation resulting in a succession of secondary vegetation. In addition, the analysis of species population structure indicated that some tree species had abnormal population structure with no or few individuals at lower size classes. Moreover, assessment of regeneration status on the basis of age classes indicated that significant proportion of woody species were represented by few or no seedlings, entailing that they were under threat. Substantial numbers of forest species were found to have irregular population structure and are in reduced regeneration status. To prevent local extinction of these species, present efforts of nursery establishment and plantation of indigenous species in the exclosures should be strengthened and extended.
Highlights
IntroductionThe Ethiopian highlands encompass the majority of the African land area covered by Afromontane vegetation which is over 50% Tamrat (1993), of which the largest part is the dry Afromontane forests Demel (2005).This vegetation represents a complex system of successions involving extensive grasslands rich in legumes, This vegetation represents a complex system of successions involving extensive grasslands rich in legumes, shrubs and small to large trees to closed forests at an altitudinal range of 1350 - 3550 m.a.s.l. with an average annual temperature and rainfall of 14 – 25oC and 700 - 1100 mm, respectively Friis (1992), Zerihun (1999).Even though it is difficult to establish the precise cover of the past as well as the present forest vegetation of Ethiopia, it is believed that a substantial portion of the land area in the highlands of Ethiopia was covered with forests having wider coverage than at present Friis (1986)
Consideration of edaphic and site (e.g., Stoniness, Grazing) variables will help to optimize the selection of areas for the establishment of future exclosures
Our study suggests that with time exclosures may increasingly obtain an important role as refugees and species pool similar to church forests and should be protected and managed in a sustainable manner
Summary
The Ethiopian highlands encompass the majority of the African land area covered by Afromontane vegetation which is over 50% Tamrat (1993), of which the largest part is the dry Afromontane forests Demel (2005).This vegetation represents a complex system of successions involving extensive grasslands rich in legumes, This vegetation represents a complex system of successions involving extensive grasslands rich in legumes, shrubs and small to large trees to closed forests at an altitudinal range of 1350 - 3550 m.a.s.l. with an average annual temperature and rainfall of 14 – 25oC and 700 - 1100 mm, respectively Friis (1992), Zerihun (1999).Even though it is difficult to establish the precise cover of the past as well as the present forest vegetation of Ethiopia, it is believed that a substantial portion of the land area in the highlands of Ethiopia was covered with forests having wider coverage than at present Friis (1986). The Ethiopian highlands encompass the majority of the African land area covered by Afromontane vegetation which is over 50% Tamrat (1993), of which the largest part is the dry Afromontane forests Demel (2005) This vegetation represents a complex system of successions involving extensive grasslands rich in legumes, This vegetation represents a complex system of successions involving extensive grasslands rich in legumes, shrubs and small to large trees to closed forests at an altitudinal range of 1350 - 3550 m.a.s.l. with an average annual temperature and rainfall of 14 – 25oC and 700 - 1100 mm, respectively Friis (1992), Zerihun (1999). These include cultivation of cereal crops which require the preparation of a finely tilled seedbed and downslope plowing to facilitate drainage
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