干旱区生态环境知识资源中心

Termites are important in litter decomposition and nutrient cycling in desert grasslands but little is known about the spatial distribution of termites and how spatial patterns are affected by topography and grazing by livestock. We measured the distribution of surface activity by the subterranean termite Gnathamitermes tubiformans in grazed and ungrazed Chihuahuan Desert grassland along 900 m transects that spanned a topographic gradient. Numbers of termite casts on litter and plants were recorded in 900 contiguous 1 m(2) quadrats along a transect located in a grazed area and in an ungrazed control. Cover of plants and litter were also recorded in 1 m(2) quadrats every 10 m along each transect.

Over 6800 casts were recorded along the control transect and fewer than 3500 casts in the grazed transect. A greater percentage of casts was found on litter (64% control, 57% grazed) than on plants (36% control, 43% grazed). Termite casts were most numerous on threeawn (Aristida spp.) in the ungrazed control and on fluff grass (Erioneuron pulchellum) in the grazed area. Spatial autocorrelation in numbers of termite casts on litter showed a greater fine-scale patterning along the control transect than in the grazed transect. Spectral analysis of termite casts on litter in the control transect also indicated strong spatial patterning at fine scales (2-4 m and 10-20 m) as well as significant variation at broader scales (>100 m). On the grazed transect, however, the fine-scale peak (2-4 m) in spectral density was absent. Termite activity in desert grasslands is therefore strongly influenced by the fine-scale patchiness in litter around plants as well as broad-scale variation in litter availability due to grazing and topography. A loss of fine-scale spatial coupling of termite activity to litter and a decrease in overall termite activity occurs in response to grazing, which may suggest a diminished role of termites with continued livestock grazing and shrub encroachment in desert grasslands. (C) 1998 Academic Press.