Vegetation Ecology and Dynamics of Land Cover Change of Abune Yosef Mountain Range, Lasta District, Amhara Regional State, Northern Ethiopia
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Date
2020-02-02
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Addis Ababa University
Abstract
The understudied flora, Abune Yosef mountain range, is under pressure from land use changes.
This research was conducted to study the vascular plant composition, plant communities,
diversity, conservation status, species richness pattern along elevation gradient, and
spatiotemporal land use and land cover change. A total of 85 nested sample plots measuring
20 X 20 m, 5 X 5 m and 1 X 1 m were established for trees, shrubs, and herbs respectively.
Topographic, edaphic and disturbance variables were also collected from each plot. IUCN Red
List and a combination of density of mature individuals, habitat specificity, and species local
range was considered to assess global and local rarity respectively. Two Landsat satellite
imageries from 1986 (Thematic Mapper, TM) and 2017 (Operational Land Imager, OLI) were
used. Aerial photographs were used for ground referencing of the 1986 satellite image.
Agglomerative hierarchical clustering and Shannon diversity index were employed to classify
plant communities and quantify community diversity and evenness. Canonical correspondence
analysis (CCA) was used to describe vegetation-environment-disturbance relationships.
Descriptive statistics and rarity forms ratio were used for vascular plants conservation status
analysis. To investigate land use land cover change (LULCC), supervised classification using
Maximum Likelihood Classifier of two Landsat images from 1986 and 2017 was performed.
Ground reference points and aerial photographs were used for accuracy assessment. One
hundred ninety nine vascular plant species belonging to 64 families and 155 genera were
recorded in five plant communities. The most species rich families were Asteraceae 42(21.1%),
Poaceae 15(7.5%), Lamiaceae 12(6.03%) and Fabaceae 11(5.5%) respectively. Thirty two
families were represented by a single species. The species richness followed a monotonically
decreasing pattern towards higher elevation. Of the vascular plants assessed following IUCN
Red List criteria, about 5% are threatened and the remaining are of least concern. Locally,
only 17 species (8.54%) of the plants revealed common, and the remaining entertained six
forms of rarity. The first axis explained 43.63% of the overall inertia and is correlated with
Elevation, pH, slope aspect, total Nitrogen, soil organic Carbon & Clay. On the other hand,
the second axis explained 32.06% of the total inertia and is correlated with bulk density, slope,
logging, & available Phosphorus. The LULCC results demonstrated that the area of Afroalpine
grassland has declined by -64.76% over the last 31 years, from 10, 500 ha to 3700 ha. Other
declines were seen in grazing land (-72.15%, 5,900 ha), open woodland from (-100%, 3,900
ha) and shrubland (-7.04%, 2,500 ha). On the other hand, agricultural land area has increased
from 38, 300 to 48, 700 ha (+27.15%), barren land from 5,400 to 8,900 ha (+64.81%), rivers,
riverbeds and gullies from 1,100 to 3,700 (+236.56%), plantation forests from 2,500 to 4,700
ha (+88%) and urban settlements from 300 to 500 ha (+66.66%). The present study revealed
that topographic variables have a profound influence on species distribution. Exclusive to
church forests, the vegetation cover showed a declining trend over the study period. The main
drivers of LULCC were identified as increased human population pressure, and temperature
and precipitation variability. Since the majority of the plants are rare in the mountain range,
landscape level conservation approach by establishing corridors between the vegetation types
to maintain ecological and evolutionary processes is recommended.
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Keywords
Elevation Gradient, Floristic Composition, Lulc, Multivariate Analysis, Plant Community, Plant Rarity, Remote Sensing