The Role Of Termites In Litter Decomposition And Soil Translocation With Special Reference To Odontoterms In Arid Lands Of Northern Kenya
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This research work on the role of termites in an arid ecosystem covered elev~n months (August 1981 to June 1982). It was conducted at the site of the UNESCO Integrated project in Arid Lands (UNESCO - IPAL). This area is in Western ¥arsabit district,- Kenya. About 80% of this area is semi-arid thorn bush scrubland and receives annual rainfall from about 100 to 600 mID. A survey of the termite fauna as a whole was carried out around most of the IPAL Field camps. Main investigation sites were located at Balesa Kulal and Olturot. The two sites lie about 8 km from each other, Olturot being more to the south eastern slopes of Mt. Kulal than Balesa Kulal. Balesa Kulal lies in riverine woodland vegetation while Olturot is at the boundary of annual grassland and dense woodland vegetation. The woodland vegetation where my experiments were located is not typical of the IPAL area as a whole, which has 3.5% woodlands and even in woodland my sites were perhaps comparatively productive . Rainfall occurs in two seasons (in April and in November) at both sites and maximum daily temperatures are often above 30°C. Ad hoc collecting of termite species was made. Five sub-families were recorded: Kalotermitinae) Nasutitermitinae, Termitinae, Amiter-rmtinaei and Macrotermitinae. A total of 15 species were recorded and their habitats described in relation to elevation, annual rainfall, soils and vegetation. The quadrat method was used to estimate. the standing crop of dead and live plant materials. This information was gathered in order to understand the food resources available to termites. At Olturot where most of the study took place, mean standing crop of grass litter, woody (less than 4 cm diameter) litter, standing grass and standing Shrubs were estimated as 90.4 g, 70.Og and 132.4 g per m respectively. Net primary production was estimated at 488 g perm2 per year. Termites were found to consume about 430g m ~ yr of the estimated primary production, which is about 87% consumption. However the consumption of plant materials varied from month to month. There was a general decline of grass 1itter from l\ ugus t to November 1981 and then from January to April 1982. Also the amount consumed by termites declined simultaneously. This indicated that termites are resource limited. The foraging activity of termites measured full terms of soil brought up for covering food portions had the highest peaks in September to Octooar, then December to January and lastly April to June. These peaks appeared after or before rains. Rainfall and other environmental variables influenced the foraging activity as demonstrated in this study. The consumption of plant materials by termites was assessed by weighing a known quantity of plant litter before placing it ,on the ground and re-weighing after termite.attack. Rate of plant litter consumption by termites mainly Odontotermes was estimated at-2 -1 -2 1.08 g md for grass litter while 0.U9 g m-1d was estimated for woody litter. Food preference studies were carried out using the bait sampling technique. The results indicated that termites do not show statistical preference at plant species level, but preferred grasses to woody materials. This was found to be significant at p = 0.01. Odontotermes were the most common termites occurring in the study sites and therefore responsible for 90% of attacks on plant materials. The assessment of soil translocated by termites mainly Octontotermes was made using (i) randomly located foraging strips, (ii) a paired sample technique (two open-ended tins). The results revealed that an enormous quantity of soil about 13 tons per hectare per year was used for covering food portions on the surface. It was shown that the amount of soil used for covering food resources is related to the amount of food consumed at that particular place. A regression of soil translocated against grass consumption gave the relation y = 14.6x - 653, r = 0.921, N = II, indicating that termites are important as plant consumers and in soil movement. The foraging density of termites was estimated by counting individuals within 2 x 20 m plots during peak foraging hours (morning and evenings). The density was estimated as 145.84 m-2 for Odontotermes workers while the mean surface foraging biomass was 125 g per hectare. This study showed that termites play a key role in the arid ecosystem. Their percentage consumption of Ilet primary production is higher than those reported for camels, sheep and goats combined (7%) Field (1979), and grasshoppers (acridids) 2.Bl% by Okelo (1981), in the riverine woodland ecosystem at Balesa Kulal. Although their main resources are dead plants, they sometimes consume standing and live plant materials when the habitat is denuded of plant litter by overgrazing. At this stage termites may come into direct competition with grazing mammals. Termites play a positive role in nutrient recycling, but where fungus growing termites occur much of the nutrients are locked in the fungus gardens which serve as reserve food. Nutrients are also channelled through predation. Soils used for constructing surface sheetings are often eroded by wind and rain in these arid conditions where soils are loose and poorly structured. Loss of soil fertility leads to poor plant growth which may significantly encourage desertification.