Nutrient contents and rate of litter decomposition were investigated in Leucaena leucocephala plantation in the University of Agriculture, Abeokuta, Ogun State, Nigeria. Litter bag technique was used to study the pattern and rate of litter decomposition and nutrient release of Leucaena leucocephala. Fifty grams of oven-dried leaf litter of the species was weighed into 0.2 mm mesh litter bag, 35 cm × 25 cm in size, these bags were closed at all ends. Eighteen litter bags were used for the studies. The litter bags were numbered and placed on the field (above ground) on 26th April 2005. Three bags were retrieved randomly from the field at 20-day intervals for 120 days. The nutrient concentration in L. leucocephala followed the trend N > P > Mg > Ca > K > Na for leaf litter and seed components. Nutrient concentration in twigs and pods ranked N > Mg > P > Ca > K > Na. Among all the litter components, leaf litter contributed more nutrients, especially nitrogen, than other litter components. High potassium concentration during the dry season was due to lack of rainfall to leach out the element. Lower magnesium content in leaf litter was due to chlorophyll decay. High N-flux reflected the quantity and quality of nitrogen in the soil. Mass loss was significantly correlated with calcium (P < 0.05). At 120 days, 80% of the litter had decomposed; this implies that decomposition rate was at 0.6% per day. A net immobilization of all the nutrient elements at 20 days was due to lack of rainfall to leach out the nutrients. High rate of decomposition at the early stage was due to less moisture content in the soil and high temperature. Litter decomposed more during the wet season than the dry season.
Inadequacy of reliable data on the rate and extent of forest conversion remains a major problem threatening sustainable forest management in Nigeria. In this study, we examined land use change pattern in Omo Biosphere Reserve, Nigeria, between 1987 and 2011. Landsat TM imagery for 1987 and Landsat ETM + imagery for 2011 were analyzed for land use change detection using Erdas Imagine 9.2 and ArcGIS 9.2. The results showed that farmlands, disturbed forests, settlements and rivers increased in area while the areas covered by the natural forests, plantations, and roads decreased from the 1987 figures. The farmlands had the highest increase in area (19025 hectares) from 1987 figures, followed by disturbed forests (10917 hectares), settlements (4262 hectares), and rivers (235 hectares). The highest reduction in area was observed for plantations (22699 hectares), followed by natural forest (10803 hectares) and roads (937 hectares). As at 1987, the natural forest was the most extensive land cover type, occupying 39.32% of the reserve. However, the disturbed forest is now the most extensive of all the land use types covering 36.34% of the reserve, followed by the natural forest (32.05%), farmland (14.78%), plantation (10.62%), settlement (4.11%), roads (1.22%), and rivers (0.87%). There was a drift in the abundance of the natural forest ISSN 2157-6092 2014 www.macrothink.org/jee 160 cover from the northeastern part of the reserve in 1987 to the northwestern part in 2011 due to unsustainable exploitation in the former and various conservation projects in the later. It is expected that the information provided in this study will aid decisions that will enhance sustainable management of the reserve. Journal of Environment and Ecology
Deforestation through shifting cultivation to feed the burgeoning population in Nigeria is intensifying without adequate knowledge of its impact on the self-repairing mechanisms of the forest ecosystem. This study examined soil seed bank in three age-sequences of arable land-AF 1 , AF 2 and AF 3 , reflecting short, medium, and long period of cultivation respectively, at three depths-0-5, 5-10 and 10-15 cm. Herbaceous plants accounted for 85% percent of plant species in the seed bank at all age-sequences and soil depths. Species richness dropped sharply with increasing soil depth in all the age-sequences, and was highest in AF 1 , AF 2 , and AF 3 at the 0-5 cm, 5-10 cm, and 10-15 cm respectively. Seedling abundance decreased sharply with increasing soil depth in all age-sequences with AF 3 having the highest number of seedlings at the 0-5 cm depth. Although AF 3 had the highest seedling abundance at the 0-5 cm depth, seedling diversity in the age-sequences decreased with increasing length of cultivation with AF 1 and AF 3 having the highest and lowest diversity, respectively. Longer period of cultivation in AF 3 seems to have favoured the populations of some seemingly more tolerant herbaceous species like Digitaria ternata and Spigelia anthelmia, both of which accounted for 75% of the total seedlings recorded at the 0-5 cm depth in AF 3. Similarity in species composition between age-sequences was over 70% at the 0-5 cm depth but dropped to below 50% at lower depths, and between soil depths in the same age-sequence except between AF 1 10-15 & AF 3 10-15 cm and AF 1 5-10 & AF 2 5-10 cm. The dominance of herbaceous plants in seed banks at AF 1 , AF 2 & AF 3, and the cutting of trees associated with shifting cultivation, imply that the native woody species have slim chance of regenerating in the farmlands. Therefore, a more eco-friendly farming system like agroforestry using indigenous species is recommended for the restoration of the native woody flora in the degraded farmlands.
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