|Whitford, Walter - NEW MEXICO STATE UNIV|
Submitted to: Journal of Arid Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 23, 1998
Publication Date: December 1, 1998
Citation: Whitford, W.G. Contribution of pits dug by goannas (Varanus gouldii) to the dynamics of banded mulga landscapes in eastern Australia. Journal of Arid Environments. 1998. v. 40(4). p. 453-457. Interpretive Summary: Many semiarid landscapes are characterized by a patchy distribution of nutrients and water. It is believed that soil pits dug by small animals can trap litter and seeds and become favorable germination sites, contributing to landscape patchiness. In northwestern New South Wales, Australia, the densities of pits dug by goannas lizards preying on burrowing spiders and beetle larvae were measured in three landscape zones: erosion slope, interception zone (run-on areas), and mulga (large shrub) grove. Each of these areas had been subjected to different levels of grazing pressure by livestock. The density of pits was found to be highest at the interception zones in moderate and heavily grazed pastures. Overgrazed areas had the lowest density of soil pits overall and lowest grass cover. The results of this study suggest that soil pits dug by goannas lizards produce a positive feedback mechanism, increasing the germination and establishment of grasses and forbs at the interception zones of mulga landscapes. This study also supports the hypothesis that overgrazing destroys the landscape pattern of soil pits dug by goannas lizards.
Technical Abstract: The densities of pits made by goannas Varanus gouldii were estimated in the three distinct zones of banded mulga landscapes (erosion slope, interception zone, and mulga grove) in paddocks of a grazing study in northwestern New South Wales, Australia. In lightly and moderately grazed paddocks, soil pits were significantly more abundant in the interception zones (M = 119¿7 m to the -2 degree) than in the groves and erosion slopes (M = 16¿7 m to the -2 degree). In the overgrazed paddock, there were no differences in densities of pits in any of the zones. In the groves and erosion slopes, approximately 70-80% of the pits contained litter, seeds, and fruits. However, on the erosion slopes, less than 20% of the pits contained litter and seeds. The data support the hypothesis that soil disturbance by Varanus lizards produces a positive feedback mechanism for the viability of the interception zone and the functioning of banded vegetation landscapes.