Soil organisms control water distribution in rangelands by creating macropores which rapidly conduct water into the soil, by generating stable soil aggregates which prevent crusting and increase water holding capacity, and by controlling litter decomposition. Ants, termites and earthworms have all been shown to increase infiltration capacity; anecdotal evidence suggests that macropore formation by a variety of other macroinvertebrate may have equally dramatic effects. Macroinvertebrates generate aggregates in the form of fecal pellets. Lichens, mycorrhizal fungi, cyanobacteria and other microorganisms also contribute to aggregate formation and soil surface stabilization. The direct effects of rapid litter decomposition on infiltration and soil water storage in arid and semi-arid rangelands is generally negative: litter removal exposes the surface to raindrop impact, which leads to the formation of physical crusts, and increases evaporation from the soil surface. These negative impacts are balanced by the creation of surface-connected macropores and the incorporation of soil organic matter, resulting in the formation of stable aggregates.

Corvallis, OR