Ecological Study of the Vegetation and Land Use/ Land Cover Change Analysis in Dega Damot District, West Gojjam Zone, Amhara Region, Northwestern Ethiopia
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Date
2020-06-02
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Addis Ababa University
Abstract
The rising of deforestation and habitat fragmentation due to the conversion of forests to
other land use/ land cover types and the increasing human population are major environmental
concerns in the northwestern dry Afromontane forest of Ethiopia. Understanding floristic
diversity along environmental factors is essential in the management of the forest patches. The
objective of the study is to investigate the Ecology of the vegetation and to study Land use/ Land
cover change in Dega Damot district forest patches of Northwestern Ethiopia. Vegetation and
environmental data were collected from 86 plots (30 m × 30 m). A total of 46 plots were used for
the collection of the soil seed bank and aboveground vegetation. Soil samples were collected for
the soil bank study from within the small plots measuring 10 cm × 10 cm from four soil layers.
Shannon Weiner index and evenness were used to assess the species diversity and richness of the
forest. The similarities between forest patches and between plant communities of the study area
were computed using Sorenson’s similarity index. Density, Diameter at Breast Height ( DBH),
basal area, frequency, and importance value indices (IVI) of woody species were computed to
characterize the vegetation structure of the forest. Hierarchical cluster analysis and redundancy
analysis (RDA) were used to identify plant communities and analyze the relationship between
plant community types and environmental variables. This study used Landsat TM, Landsat ETM
+ and OLI data from 1986, 2003 and 2017 to map land use/land cover (LU/LC) in a study area.
LU/LC maps were created using supervised classification, and LU/LC change the mapping for
the 1986-2003 and the 2003-2017 period determined using post-classification comparisons.
Results indicate the presence of 176 plant species belonging to 80 families. Asteraceae and
Fabaceae were the dominant families, and herbs and shrubs were predominant growth forms.
The Shannon diversity index and evenness values of the study area were 2.79 and 0.95
respectively. The total basal area and density of woody species were 51 m2 ha-1 and 2679
individual-1, respectively. The most dominant species as indicated by their important value index
(lVI) were prunes africana(17), Schefflera abyssinica (15) and Ficus sur (14). Five plant
community types were identified: Erica arborea - Osyris quadripartita, Discopodium
penninervium - Echinops pappii, Olea europaeasubsp.cuspidata-Scolopia theifolia, Euphorbia
abyssinica-Prunus africana, Dodonaea anguistifolia-Acokanthera schimperi. The RDA
result showed that the variation of species distribution and plant community formation were
significantly related to altitude, organic matter, moisture content, slope, pH, EC, clay and
phosphorus. A total of 2133 seedlings belonging to 44 species and 27 families were identified
from the soil seed bank, with a viable seed density of 4636 seeds/m2. The species composition of
the seed bank was dominated by 29 herb species (66%) compared to 2 tree species which
accounted for only 5 percent of the total number of species. The similarity between soil seed
bank species composition and aboveground vegetation was low and conclude that the
regeneration potential of the forest from seed bank was limited. The results of the study showed
that agricultural land increased from 85% of the total area in 1986 to 93% in 2017. This
increase coincided with a 4% decrease in a forested area, a 2% decrease in grazing land and a
2% decrease in shrubland. LU/LC was changed significantly due to rapid human populations
and expanding agricultural activities in the study area. Therefore, this study provides baseline
information for the conservation of forest in the study area.
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Keywords
Floristic Composition, Habitat Fragmentation, Vegetation Structure, Plant Communities, Soil Seed Bank, Land Use/ Land Cover Change