Soil Mining by Pocket Gophers along Topographic Gradients in a Mima Moundfield
1990
Cox, George W.
To account fully for the pattern of translocation of soil by pocket gopher activity in Mima moundfields, I investigated soil mining in relation to location along the mound—intermound topographic gradient. From September 1986 to November 1987, at Miramar Mounds National Landmark in coastal San Diego County, California, the total soil mined by pocket gophers (Thomomys bottae) was estimated by measuring the mass of soil deposited in surface heaps and counting the number of plugged surface—access tunnels on mound and intermound zones associated with 10 Mima—type mounds. Surface heap deposition was greatest in late fall and early winter, whereas the digging of surface—access tunnels was most frequent in spring and early summer. Both the mass of soil in surface heaps per unit area and the number of surface—access tunnels per unit area tended to decrease with distance from the center of mounds. When the areas of concentric zones at increasing distance from the mound center were taken into account, however, the total mas of soil mined increased with distance from mound centers. At this site, deposition of soil in surface heaps estimated to be 8.23 Mg°ha— ¹°yr— ¹ and subsurface deposition to be 20.31 Mg°ha— ¹°yr— ¹, so that total soil mining equalled 28.54 Mg°ha— ¹°yr— ¹. Total mass of soil mined bore a log—linear relation to distance from the mound center. This relation was combined with that relating distance of movement of mined soil to mound height and distance from the mound center, to give a preliminary model of mound growth dynamics as influenced by pocket gopher activity. This model suggests that maximum mound size is largely determined by the pattern of soil mining and translocation by these mammals.
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