The role of enclosures in the recovery of woody vegetation in degraded dryland hillsides of central and northern Ethiopia

The role of enclosures in the recovery of woody vegetation was investigated by studying species composition, density, diversity and regeneration status of woody species and soil seed banks in enclosures and adjacent open areas at two widely separated sites known as Biyo-Kelala and Tiya in central and northern Ethiopia, respectively. Fifty-eight woody species, representing 30 plant families, were recorded at Biyo-Kelala, of which only 25 were recorded both in the enclosure and open area while two were recorded outside of the sample plots. At Tiya, 31 woody species, representing 19 families, were recorded in the enclosure but only 15 of these species were encountered in the open area. Woody plant densities were 1746 and 2215 individuals/ha in the enclosure and open area at Biyo-Kelala, respectively, and 3705 and 3048 individuals/ha in the enclosure and open area at Tiya, respectively. Dodonaea angustifolia and Acacia etbaica were the most dominant species at Biyo-Kelala and Tiya, respectively. The enclosure at Biyo-Kelala had about twice the diversity value of the open area, while the corresponding values were 2.5 and 2 for the enclosure and open area at Tiya, respectively. The total numbers of species recovered from the soil samples collected in Biyo-Kelala site were 48 for the enclosure and 30 for the open area with mean seed densities of 2765 ( 124) and 1663 (+/-117) seeds m(2), respectively. At Tiya, 30 and 16 species were recovered in the enclosure and open area, respectively, with mean seed densities of 2811 (+/-276) and 996 (+/-243) seeds m(2), respectively. The diversity of all plant species in the soil seed bank was greater in the enclosure than the open area at both sites. Herbs and grasses dominated the soil seed banks at both sites while several of the woody species recorded in the above-ground vegetation were not represented at all. Overall results from this study indicate strongly that establishment of enclosures is very advantageous over other methods since it is a fast, cheap and lenient method for the rehabilitation of degraded lands. (C) 2004 Elsevier Ltd. All rights reserved.