Hip holes:: kangaroo (Macropus spp.) resting sites modify the physical and chemical environment of woodland soils

Hip holes are shallow, reniform-shaped depressions found next to the trunks of many trees and shrubs in arid and semi-arid Australia. They are constructed by kangaroos (Macropus spp.), who use them as diurnal resting sites, particularly during hot weather. Physical and chemical properties of soils in hip holes were compared with non-hole microsites adjacent to the trunk ('trunk'), microsites below the canopy ('canopy') and microsites out in the open ('open') under two trees (Eucalyptus intertexta , Alectryon oleifolius ) and one shrub (Dodonaea viscosa ) in a semi-arid woodland in eastern Australia. Overall, there were few effects under D. viscosa apart from a greater (10-fold) mass of litter in the hip holes compared with the trunk microsite. Hip holes under E. intertexta and A. oleifolius , however, contained six times more dung compared with the trunk microsite. For the two tree species, soils in the hip holes were significantly more erodible, as measured by aggregation levels, compared with the other microsites, but there were no significant differences in bulk density nor pH. Steady-state infiltration rates at the hip hole and trunk microsites were significantly greater than those in the open, but there was no significant hip hole effect. Soils in the hip holes contained greater levels of exchangeable calcium and magnesium (E. intertexta ) and greater exchangeable sodium (A. oleifolius ) compared with trunk microsites. Hip holes under E. intertexta contained approximately 68% more organic carbon, total carbon and nitrogen, and 86% more sulfur compared with trunk microsites. Similarly, hip holes under A. oleifolius contained on average 38% more organic and total carbon, and 47% more nitrogen than trunk microsites. Given the density of hip holes and their impact on soil chemistry, kangaroos are considered to be important elements in the maintenance of heterogeneity in these woodlands.