Browsing by Author "Denu, Dereje"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Floristic Composition and Ecological Study of Bibita Forest (Gura Ferda), Southwest Ethiopia
    (Addis Ababa University, 2006-06) Denu, Dereje; Demissew, Sebsebe (professor); Woldu, Zerihun (Professor)
    This study was carried out at Bibita Forest (Gura Ferda), southwest Ethiopia to determine floristic composition, vegetation structure and to identify community types and to investigate the role of environmental factors in the distribution of the vegetation. 60 relevés, 20 m x 20 m at 25 m altitudinal drop along an altitudinal gradient were laid to collect the data on cover–abundance (for trees and shrubs), DBH, height, density, seedling and sapling count (for trees only). The data on herbaceous species were collected from five, 5 m x 5 m subplots laid at four corners each and one at the centre of the large relevé. Two soil samples were taken from each relevé at a depth of 0–10 cm (topsoil) and 30–50 cm (subsoil). The analysis for soil pH, % sand, % clay, % silt, and Electrical Conductivity (EC) were done. A total of 196 plant specimens belonging to 74 families and 170 genera were identified. The five most dominant families were Rubiaceae and Asteraceae (13 species each), Euphorbiaceae and Acanthaceae (9 species each) and Fabaceae (8 species). Out of 196 species 13 were endemic to Ethiopia. Ipomoea involucrata Beauv. and ? Harungana madagascariensis Lam. ex Poir. belonging to the families Convolvulaceae and Clusiaceae respectively were found to be new records for Ethiopia. Six community types were identified at 0.65 to 0.75 dissimilarity levels and each community was named after dominant tree and/or shrub species. The study on vertical stratification showed that Bibita Forest(Gura Ferda) has the upper storey (above 29 m), middle storey (15–29 m) and lower storey (below 15 m). The study on vegetation and population structure showed that the density of tree species was high at the lower class levels. Density of trees greater than 2 cm DBH (ca. 777/ha), for height greater than 6 m the tree density (ca. 673/ha), basal area (ca. 70/ha), frequency of all the tree species (716/ha) and the respective IVI values for each tree species were also calculated. The comparison of Bibita Forest (Gura Ferda) with other forests in Ethiopia with respect to tree densities, percentage distribution of tree species, basal area and phytogeographical comparison was done. Soil environmental factors such as pH of the top and subsoils, clay and sand particles of both the top and subsoils showed significant relations with altitude, species richness and diversity.
  • No Thumbnail Available
    Item
    Impact of Climate and Land use on Plant Diversity, Carbon Storage and Leaf Area Index in the Jimma Highlands, Southwest Ethiopia
    (Addis Ababa Universty, 2016-06) Denu, Dereje; Kelbessa, Ensermu (Professor)
    The study aimed at the impact of climate and land use on plant diversity, live carbon storage (AGC) and leaf area index (LAI) in the Jimma Highlands of Ethiopia. Data on woody species were collected from 155; 20 m × 20 m sample plots which were subdivided into 2 m×2 m subplots for herbaceous species inventory. Thirty-one plots of one ha each were randomly distributed along a study transect for -measuring diameter at breast height for all woody species with DBH 10 cm. Upward hemispherical images of the forest/tree canopy were taken at 12 points in the 20 m × 20 m plots established within each one hectare plot. Two SPOT5 satellite images (path 134 / row 133) captured simultaneously on 17th December and aerial photographs taken in October 2012 were used for LULC mapping. The transect was classified into five major land use types from SPOT5 images and aerial photography. Natural forest was further separated into the natural forest with coffee shrub/tree beneath and those with no coffee under the canopy based on field observation. Two hundred and eight-seven plant species belonging to 220 genera and 82 families were collected and identified. The highest plant species richness per hectare was recorded from woodland and the least was from the cropland. The highest mean abundance of tree species was recorded from the planation forest and the least was from the pasture. Mean annual temperature and soil pH have significantly explained the variation in herbaceous species richness; sand and clay particles significantly explained the variation in tree species richness. Species richness, abundance and diversity also vary along vertical stratification in semi-forest coffee (SFC) and degraded natural forest (DNF). The highest AGC storage was recorded from the plantation forests (152.25±24.98) followed by DNFs (82.03±32.08) and SFCs (61.52±24.98). Land use types showed significant mean difference in AGC and LAI. Tree species abundance and richness combined, have explained about 82% of the variation in AGC across the land use types. There was significant linear relationship between AGC storage and some climate variables such as mean annual temperature, mean annual rainfall and potential evapotranspiration; between AGC and some edaphic factors such as soil cation exchange, sand and pH. Basal area, richness of shrub, tree and entire plant species combined have significantly explained about 82% and 81% of the variations in LAI_true_v6 and LAI_true_v5 respectively. LAI_true_v6 explained about 75% of the variation in AGC. Mean annual temperature and annual temperature range significantly explained about 21% of the variation in LAI_V5. Climate change under the current and projected scenarios affected the distribution of five plant species across Ethiopia. In conclusion, plant richness, abundance, distribution, carbon storage and leaf area index are affected by land use and climate variables. Key words: Carbon storage, climate change, Jimma highlands, LAI, land use change, plant richness