Effects of Exotic Plantation and Management Intervention on Woody Plant Species Diversity, Regeneration and Soil Seed Bank in Tarmaber District, Ethiopia

Abstract

Plantations have many economic and environmental benefits, but exotic plantations are widely viewed negatively mainly in relation to biological diversity conservation, and regenerations to prove this dilemma this study is necessary. This study was carried out in Tarmaber district north shewa zone Ethiopia to determine the effect of plantation forest with management intervention on woody plant species diversity, regeneration and soil seed bank species composition in five different forest types. A total of 75 circular sample plots of 314 m² were established along a transect lines. Soil seed bank analysis was done from soil samples collected in each of the plots (225 samples) to examine the similarity between the soil seed bank and aboveground flora. Different diversity index and ANOVA was used in SPSS software for analysis. The result showed that a total of 51 woody plant species was recorded in adjacent natural forest (41), managed <i>C. lusitanica</i> (27), not managed <i>C. lusitanica</i> (9), managed <i>E. globules</i> (22) and not managed <i>E. globules</i> (13) species. Regeneration of seedlings were 3538, 5567, 707, 1462 and 2524 mean stems ha^-1 for natural forest, managed <i>C. lusitanica</i>, not managed <i>C. lusitanica</i>, managed <i>E. globules</i>and not managed <i>E. globules</i>respectively. Unmanaged <i>C. lusitanica</i>plantations had significantly lower densities of mature tree stems ha^-1 as compared to managed <i>C. lusitanica</i>, managed <i>E. globules</i>and adjacent natural forest (F=14.03, p<0.05). Similarly in terms of sapling density ha^-1 unmanaged <i>C. lusitanica</i> was significantly lower from other forest types (F=7.37, p <0.05). However managed <i>C. lusitanica</i>had significantly higher seedling regeneration (stem density ha^-1) than other plantation and adjacent natural forests (F = 16.11, p < 0.05). Generally meanstem densities including tree, sapling and seedling of woody species among different forest types managed <i>C. lusitanica</i> was significantly higher among different forest types (F= 13.01, p<0.05). From the soil seed bank a total of 22 plant species (20 native and 2 exotic) species were recovered. In different forest types the number of species recorded was in adjacent natural forest (19), managed <i>C. lusitanica</i> (11), unmanaged <i>C. lusitanica</i> (4), managed E. globules (7) and unmanaged <i>E. globules</i> (5). The similarity of the soil seed bank was more or less similar to the above ground flora with maximum Sorenson’s similarity values of 0.633. Generally with appropriate management intervention undergrowth vegetation and soil seed bank status in plantation forest had good species composition and diversity.