This study investigated the influence of moundbuilding termites on soil particle dynamics on the land surface and in soil-forming processes by examining the amount of soil particles in mound structures of Macrotermes bellicosus in a highly weathered Ultisol of tropical savanna. Soil particle turnover via the mounds was estimated using particle stock data and soil turnover data from previous studies. A 4-ha study plot with six mounds of relatively uniform shape and size was investigated. Soil mass constituting the mounds was 6,166 ± 1,581 kg mound À1 within which the mound wall and nest body accounted for 5,002 ± 1,289 and 1,164 ± 293 kg, respectively. The mound wall contained a significantly larger amount of clay (252 ± 9.97 g kg À1 ) balanced with a lower sand content (676 ± 26.5 g kg À1 ) than in the adjacent surface (Ap1) horizon, (46.4 ± 12.8 g clay kg À1 ; 866 ± 83.2 g sand kg À1 ); the nest body had much higher clay content (559 ± 51.0 g kg À1 ) but less sand (285 ± 79.2 g kg À1 ) than the mound wall. As a result, the mounds of M. bellicosus accumulated clay of 2,874 ± 781 kg ha À1 (corresponding to 2.52% of clay stock in the Ap1 horizon) along with an estimated clay turnover rate of 169 kg ha À1 year À1 . These findings suggest a positive feedback effect from termite mound-building activity on soil particle dynamics in tropical savanna ecosystems: M. bellicosus preferentially use subsoil material for mound construction, resulting in relocation of illuvial clay in the subsoil to the land surface where clay eluviation from the surface soil and its illuviation in the subsoil are major soil-forming processes.

S o i l p r o p e r t i e s o f s e c o n d a r y f o r e s t s u n d e r s h i f t i n g cultivation by the Iban of Sarawak, Malaysia in relation to vegetation condition ABSTRACT

The role of mounds of the fungus-growing termite Macrotermes bellicosus (Smeathman) in nutrient recycling in a highly weathered and nutrient-depleted tropical red earth (Ultisol) of the Nigerian savanna was examined by measuring stored amounts of selected nutrients and estimating their rates of turnover via the mounds. A study plot (4 ha) with a representative termite population density (1.5 mounds ha À1) and size (3.7 AE 0.4 m in height, 2.4 AE 0.2 m in basal diameter) of M. bellicosus mounds was selected. The mounds were found to contain soil mass of 9249 AE 2371 kg ha À1, composed of 7502 AE 1934 kg ha À1 of mound wall and 1747 AE 440 kg ha À1 of nest body. Significant nutrient enrichment, compared to the neighboring topmost soil (Ap1 horizon: 0-16 cm), was observed in the nest body for total nitrogen (N) and exchangeable calcium (Ca), magnesium (Mg) and potassium (K), and in the mound wall for exchangeable K only. In contrast, available (Bray-1) phosphorus (P) content was found to be lower in both the mound wall and the nest body than in the adjacent topmost soil horizon. Consequently, the mounds formed by M. bellicosus contained 1.71 AE 0.62 kg ha À1 of total N, 0.004 AE 0.003 kg ha À1 of available P, 3.23 AE 0.81 kg ha À1 of exchangeable Ca, 1.11 AE 0.22 kg ha À1 of exchangeable Mg and 0.79 AE 0.21 kg ha À1 of exchangeable K. However, with the exception of exchangeable K (1.2%), these nutrients amounted to less than 0.5% of those found in the topmost soil horizon. The soil nutrient turnover rate via M. bellicosus mounds was indeed limited, being estimated at 1.72 kg ha À1 for organic carbon (C), 0.15 kg ha À1 for total N, 0.0004 kg ha À1 for available P, 0.15 kg ha À1 for exchangeable Ca, 0.05 kg ha À1 for exchangeable Mg, and 0.06 kg ha À1 for exchangeable K per annum. These findings suggest that the mounds of M. bellicosus, while being enriched with some nutrients to create hot spots of soil nutrients in the vicinity of the mounds, are not a significant reservoir of soil nutrients and are therefore of minor importance for nutrient cycling at the ecosystem scale in the tropical savanna.

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