Impact of Exclosure on Species Diversity, Population Structure and Regeneration Status of Woody Plants in Lowland Northern Tigray, Ethiopia

Abstract

Aim: This study was conducted to assessing woody plant composition, population structure and regeneration status in lowland exclosure (EX) of Northern Ethiopia.
 Study Design: Investigation of parameters was undertaken from 71 plots with size of 20 m x 10 m laid systematically along transect lines for vegetation data. These 200 m2 plots were used for assessment of trees with DBH >5 cm. Small quadrats of 4 m*4 m (16 m2) nested within the bigger plots was laid at the four corners and center of each plots. These were used for measuring seedling and sapling individuals. To analyze species diversity, population structure and regeneration status of woody plants were by computing abundance, density, basal area, Importance value index (IVI) and using Shannon-Weiner diversity and evenness indices.
 Results: According to vegetation survey result, a total of 23, 17 and 26 woody species were recorded, at Kara, Erba and Shektekli exclosures (EXs), respectively. While 8, 7 and 5 species of woody plant were in open grazing land (OGL). The total mean densities of all woody plants were found to be 1530, 1480 and 2999 individual’s ha-1 at Kara, Erba and Shektekli in EXs.
 Conclusion: The study suggested that the regional government have to considering EXs as useful for restoration or rehabitation strategy in the region, the vegetation in all the EXs in the study sites have a higher species composition, diversity, density, increment of basal area and regeneration woody plants than OGL, as a result of management differences in EXs. However, there are also variation on species composition, diversity, density increment of basal area and regeneration woody plants among exclosures having similar age and altitude for instance the species recorded in Erba site is lower than with other of EXs, This could be due to among local site characteristic variation and high grazing happen before Ex establishment exists. Therefore, we need to apply soil and water conservation, enrichment planting with indigenous tree species and strengthen local management institution in effectively protect the exclosure.