Rangeland evaluation and perceptions of the pastoralists in the Borana zone of southern Ethiopia

[摘要] The study was conducted in the Borana rangeland of southern Ethiopia. In the last fewdecades the Borana rangelands have been degraded while the pastoralists adhered to thetraditional grazing strategies. The main aims with this study were to investigate the soilcharacteristics as well as aboveground plant communities and to assess the condition ofthe rangeland. In addition, the pastoralists' perceptions and cattle-rangelandmanagement practices were evaluated.The botanical composition of the grass layer, woody vegetation structure, soil and therangeland condition were studied in four communal grazing areas (Did Yabello, DidHarra, Dubuluk and Melbana), three land use systems (communal land, governmentranch and traditional grazing reserve) and along distance gradients from water source.Species composition and basal cover of the grass layer was estimated using frequency ofoccurrence of plant species. Woody plant data were standardized to tree equivalent ha-l(l TE = 1 tree, 1.5 m high). Rangeland condition was assessed based on ecologicalcondition index, weighted palatability composition of the grass layer, the structure ofwoody plants and soil compaction. Soil seed bank was studied under three land usesystems and along a distance gradient from water source. Survey on cattle-rangelandmanagement practice and pastoral perceptions was conducted on 40 individualhouseholds and 118 elders (7 per group).Survey results of the pastoral households and elders indicated that the average householdin the study area was 7 members. The percentages of male and female children whoattended schools were 26 % and 9 % respectively. Livestock holding per household wasestimated to be 14 cattle, 10 goats, 6 sheep and 2 camels. Cultivation is widespread inthe study area. Major constraints in livestock production were in order of importance:drought, feed shortage, water scarcity, animal diseases, predators and communal landtenure. According to the pastoralists, contributing factors to rangeland degradation werein descending order: recurrent drought, human and livestock pressure, expansion ofcultivation, ban on fire and development of water ponds.A total of 49 grass species were identified in this study. The communal land had higherand lower percentages (P<0.05) of annual and perennial grasses, respectively, than thegovernment ranch and the traditional grazing reserve. There were no marked differences(P>0.05) among the four communal grazing sites and the three different distances fromwater concerning both annuals and perennials. The occurrence of Chrysopogon aucheriwas higher (P<0.05) on the government ranch (23 %) and traditional grazing reserve (27%) than on the communal land (14 %). The frequency of C. aucheri did not varybetween the communal grazing sites (average = 14 %) and along distance gradient fromwater (average = 12 %). Leptothrium senegalensis and Chloris myriostachya did notvary (P<0.05) between the land use systems (average = 4 % and 1 %, respectively) andalong the distance gradient from water (average = 2 % for both species). The frequencyof Sporobulus nervosus was highest (P<0.05) in the communal land (13 %), whereas theoccurrence of S. pyramidalis did not differ markedly (average = 32 %) between the landuse systems (P>0.05). Both species did not show prominent variations along the distancegradient from water (average = S. nervosus-14 % and S. pyramidalis-36 %). Grass basalcover was fairly low and similar in the land use systems, communal grazing sites anddistance gradients from water.A total of 54 woody plants were identified. Total density of woody plants was higher(P<0.001) on the communal land (l 083 TE ha-I) or the government ranch (l 188 TE hal)than on the traditional grazing reserve site. Within the communal grazing sites, thedensities at Did Yabello (l 318 TE ha), Did Harra (l 088 TE ha) and Melbana (1 178TE ha) were higher (P<0.05) than on the fourth site, Dubuluk. Results from thedistance gradient from water revealed that differences were not significant (P>0.05)between the near, middle and far sites (average = 1 150 TE ha-I). Overall figure showedthe advancement of woody encroachment in the semi-arid Borana rangelands. The mostimportant invaders were Commiphora africana, Grewia tembensis, Acaciadrepanolobium and A. brevispica.Soil chemical analysis revealed low nutrient contents, which did not vary significantly(P>0.05) in all the study areas. Similarly, differences in pH, soil texture, soil bulkdensity and soil compaction were not significant.Assessment of rangeland condition indicated that both ecological condition index (ECI)and weighted palatability composition (WPC) were highest on the government ranch(711 and 55 %, respectively). Along the distance gradient from water, differences inrangeland condition (P>0.05) were not significant (average: ECI = 533 and WPC = 29%). Within the communal grazing sites, Dubuluk and Melbana had relatively higher ECIand WPC values (average: 602 and 36 %, respectively) than the other two sites (average= 520 and 25 %, respectively).The soil seed bank study revealed that a total of 44 plant species were identified. Ofthese, 25 % were grasses and 75 % were non-grass plant species. As for the land usesystems, seedling and floristic density of the graminoids were higher (P<0.05) on thetraditional grazing reserve (798 seedling m-2 and 361 plants m-2, respectively) than onthe communal land and the government ranch. Along the distance gradient from water,the differences were not significant (P>0.05). Similarity between grass flora of seedbank and above ground plant community was low.It can be concluded in this study that the deteriorating conditions of the Boranarangelands were revealed by changes in the structure and composition of the grass layer,woody vegetation, soil fertility and by the status of the soil seed bank. Bushencroachment is the critical problem. Therefore, workable control programs need to bedevised immediately. It is also vital to develop a clear policy at national level on the useand management of the communal rangeland resource.

[发布机构] University of the Free State