Factors affecting annual plants assemblages on banner-tailed kangaroo rat mounds

Abstract

We studied patterns of annual plants assemblages and soil properties of banner-tailed kangaroo rat (Dipodomys spectabilis) mounds. The spring annual flora on mounds was dominated by Descuraina pinnata and Eschscholtzia mexicana; intermound areas were dominated by Eriastrum diffusum. The peak above-ground standing biomass of spring annuals on mounds and intermounds respectively was 133·3 ± 5·9 g m−2 and 25·6 ± 6·3 g m−2. In summer, the mounds had a high density and biomass of Tidestromia lanuginosa. Intermound areas were dominated by Haplopappus gracilis and Eriogonum abertianum. The peak above-ground standing biomass of summer annuals on mounds and intermounds respectively, was 172·7 ± 7·3 g m−2 and 98·4 ± 2·3 g m−2. The above-ground standing biomass of annual plants on irrigated mounds in spring and summer was greater than on non-irrigated mounds. Bulk density was lower on mounds; nitrate and total nitrogen contents of the mound soils were higher than those of intermound soils. Available nitrate measured by absorption on ion exchange resins was consistently higher in mound soils than in intermound soils except for the period from March to April. Mound soils dried faster than intermound soils. Soil water potentials on mounds and intermounds at depths of 20 and 30 cm decreased continuously from January until mid-May, and then fluctuated in response to individual rainstorms. Irrigation of 6 mm of water per week had little effect on the soil water potentials except at the 10-cm soil depth of intermound areas. Differences in species composition and biomass production of annual plants between kangaroo rat mounds and intermound areas are attributed to the differences in both soil physical properties and nitrogen availability.