In this study, we quantify the impacts of climate and land use on soil N O and CH fluxes from tropical forest, agroforest, arable and savanna ecosystems in Africa. To do so, we measured greenhouse gases (GHG) fluxes from 12 different ecosystems along climate and land-use gradients at Mt. Kilimanjaro, combining long-term in situ chamber and laboratory soil core incubation techniques. Both methods showed similar patterns of GHG exchange. Although there were distinct differences from ecosystem to ecosystem, soils generally functioned as net sources and sinks for N O and CH respectively. N O emissions correlated positively with soil moisture and total soil nitrogen content. CH uptake rates correlated negatively with soil moisture and clay content and positively with SOC. Due to moderate soil moisture contents and the dominance of nitrification in soil N turnover, N O emissions of tropical montane forests were generally low (<1.2 kg N ha year ), and it is likely that ecosystem N losses are driven instead by nitrate leaching (~10 kg N ha year ). Forest soils with well-aerated litter layers were a significant sink for atmospheric CH (up to 4 kg C ha year ) regardless of low mean annual temperatures at higher elevations. Land-use intensification significantly increased the soil N O source strength and significantly decreased the soil CH sink. Compared to decreases in aboveground and belowground carbon stocks enhanced soil non-CO GHG emissions following land-use conversion from tropical forests to homegardens and coffee plantations were only a small factor in the total GHG budget. However, due to lower ecosystem carbon stock changes, enhanced N O emissions significantly contributed to total GHG emissions following conversion of savanna into grassland and particularly maize. Overall, we found that the protection and sustainable management of aboveground and belowground carbon and nitrogen stocks of agroforestry and arable systems is most crucial for mitigating GHG emissions from land-use change.
The montane forests on Mount Kilimanjaro are part of the ecologically protected area and provide ecosystem services to the local communities on the lower slopes. Despite their ecological value, the montane forests on the northern slope of Mount Kilimanjaro have been affected by increased livestock grazing pressure due to prolonged drought and expansion of agricultural land. We examined the impacts of livestock grazing on plant species composition in the montane forests on the northern slope of Mount Kilimanjaro. The study area was sub-divided into heavily grazed, moderately grazed, lightly grazed and ungrazed sites. A quadrat method was used for field data collection. A total of 115 plant species distributed within 93 genera and 39 families were identified. Moderately grazed and lightly grazed areas had higher plant species diversities than heavily and ungrazed areas. This observation concurs with the intermediate disturbance hypothesis. However, plant species that contributed to high species richness and diversity in grazed areas were mainly grasses, shrubs and herbs. It was concluded that livestock grazing in montane forests on the northern slope of Mount Kilimanjaro has serious impacts on vegetation community composition. Conservation of montane forest habitat and improvement of rangelands on communal land are necessary.
Livestock grazing is considered to be of great ecological importance in terrestrial ecosystems if sustained at acceptable levels. Overgrazing has ecological ramifications which lead to degradation of the ecosystem. This has become a problem in many parts of Tanzania. A study was conducted in Northen Slopes of Mount Kilimajaro in order to examine the impact of grazing on natural regeneration of the grazed vegetation. This paper is guided by the hypothesis that the species richness, species diversity and density of regenerants vary across grazing intensities. The study area was divided into four zones as per grazing intensity namely heavily grazed areas, moderately grazed, least grazed and ungrazed areas. Ten rectangular quadrats of 20 m × 25 m were established in each zone, making a total of 40 quadrats in the entire study area. A stratified random sampling procedure was used in locating quadrats in each zone of grazing intensity whereby two subquadrats of 2 m × 5 m were nested in bigger quadrats. Natural regeneration was assessed in terms of species diversity and density of seedlings, saplings and poles. Results indicate that species regeneration varied among areas with different grazing intensity. The variations of seedlings and saplings density among areas with different grazing intensity were statistically significant. The species diversity of regenerants differed significantly among areas with different grazing intensity. Keeping the grazing intensity at low and moderate levels will stimulate more plant growth and diversity as opposed to heavy grazing which will lead to vegetation retrogression.
The tree species density and basal area form structural and functional variables of healthy forest ecosystems. Tree density and basal area are among useful parameters for management of natural forest resources. A study was carried out in Image Forest Reserve (IFR) in 2019 to determine tree species density and basal area. A total of 170 plots measuring 20 m x 40 m were set along the land cover types at an interval of 250 m from each other. Trees with a diameter at breast height (DBH - cm) ≥ 5 cm were measured for their DBH at a height of 1.3 m from ground level and used to calculate the basal area (BA) (m2). The tree individuals were used to calculate the density (D). The largest basal area was recorded from forest cover (13 279 m2 ha-1), followed by woodland (4394.09 m2 ha-1), and wooded grassland was the least). The minimum BA was recorded from woodland, while the largest was from forest (6.881 m2 ha-1). In all land cover types the DBH class (cm) >40 cm had the largest BA. Woodland had the highest density of all other land cover types, followed by forest and wooded grassland was the least. The maximum density was recorded from woodland followed by forest and wooded grassland
Plants natural regeneration is a means to forest recovery after disturbances in a particular ecosystem. Forest recovery in any particular ecosystem depends on the growth stages of tree species. This study assessed the tree species regeneration potential in the disturbed Image Forest Reserve. An assessment was carried out in 170 sample plots of 20 m x 40 m each that were established in the three different land cover types, namely forest (67 plots), woodland (65 plots), and wooded grassland (38 plots). A total of 153 tree species distributed among 59 families and 122 genera were identified. Each of the three land cover types recorded a higher number of saplings than poles and seedlings. The low number of individuals for seedlings was caused by human disturbances that killed them. The human disturbances included wildfires, livestock grazing, and felling trees during logging for timber. The number of poles decreased because several saplings failed to survive due to anthropogenic activities. ANOVA statistical test results revealed a significant difference in trees growth stages (p < 0.05), while there was no significant difference in H' (p > 0.05) in the tree growth stages within the land cover types. Image Forest Reserve accommodates relatively high plant species diversity Therefore, the conservation of Image Forest Reserve will sustain the regenerating tree species and enhance the forest health and sustainability.
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