| dc.description.abstract | This study aimed at investigating changes in vegetation resources with emphasis on the
woody component in relation to land use changes (i.e. settlements, cultivation and grazing).
It also made an attempt to understand the perception of local communities as regards these
changes in their land-based resources. The study area was characterised by a semi-arid type
of climate, where agropastoral production system was the predominant land use practice.
The methods employed were interpretation of aerial photographs taken at two points in time
i.e. 1964 and 1994, field vegetation survey and analysis, interviews using a structured
questionnaire, and informal and formal discussions.
The results of aerial photograph analyses indicate that conspicuous changes occurred in land
use and vegetation types (physiognomically) over the 30-year period between 1964 and
1994. Changes in land use have apparently caused changes in vegetation structure. These
changes have resulted from introduction of settlements and subsequent practices of flood
recession cultivation. Clearance of vegetation for cultivation in the flood plains was found to
be the major cause of depletion of vegetation resources and overgrazing of the uncultivated
areas thereby leading to environmental deterioration. The size of land under cultivation
increased from 0.27% (97.5 ha) to 7.34% (2,605 ha) of the total area. Settlement increased
from 0.01% (5 ha) to 0.51% (180 ha) and vegetation cover decreased from 87.88%
(31,252.5 ha) to 75.52% (26,787.5 ha).
Field vegetation survey results showed that there was still a moderate woody vegetation
cover dominated by Acacia etbaica wooded bushland in the uncultivated plain areas, the
hills and ridges. However, herbaceous cover was very poor and the understorey vegetation
was mainly dominated by Euphorbia and Aloe species. Woody vegetation identified and
recorded included Acacia, Grewia, Balanites, Salvadora, Cordia, Commiphora and other
related genera. A locational comparison of six selected woody species i.e. Acacia etbaica,
Acacia mellifera, Acacia nubica, Acacia tortilis, Grewia erythrea and Salvadora persica
showed no significant difference (P>0.05) among three study sites (Abala, Shugala and
Murga) for species composition, percent crown cover, density and diversity. Comparison
vi
among distances (in a 10 kilometre transect ran from each of the three selected land uses)
within each site for percent cover and density also showed no significant difference
(P>O.05). Comparison among species for each site and among distances for each species,
however, showed a significant difference (P<O.05). Acacia etbaica had higher species
composition, percent cover and density than other species in all the three study sites.
From the socio-economic survey, it was possible to retrieve information on characteristics of
the indigenous Mars and settled Tigrians, woody vegetation use and perceptions of
environmental degradation. These communities are already aware that settlement and
cultivation in the area hampered the pastoral form of life style and thus forced them to shift
to agricultural practices. They acknowledged the vital role of trees and shrubs since they
provide a range of products and services in their daily life. In sum, declining vegetation
cover, formation of big gullies, declining water availability, reduction of wildlife numbers
and species diversity are the outcomes of recent settlement, cultivation and recurrent
drought in the area.
Based on the findings of this study, recommended actions to mitigate and prevent negative
environmental impacts include encouraging participation of local communities in the
management of natural resources so as to utilise their indigenous technical knowledge,
introducing soil and water conservation measures, protecting the existing grazinglands from
encroaching cultivation, protecting and regenerating important woody species, and selective
clearing and establishment of grazing reserves. The study also recommends further research
on long-term vegetation monitoring, soil and vegetation relationships,
ethnobotany/ethnoveterinary practices, assessment of herbaceous and woody vegetation
biomass, and evaluation of the nutritive value of browse species and crop residues as dry
season feed for livestock. | en |
