Rainfall simulation at an average intensity of 124 mm·h was used to compare infiltration and run off on arid areas where subterranean termites had been eliminated four years prior to the initiation of the study (termite free) with adjacent areas populated by subterranean termites (termites present). Infiltration rates on termite free plots with less than 5% perennial plant cover were significantly lower 51.3±6.8 mm·h than rates on comparable termites present plots 88.4±5.6 mm·h. On plots centered on Larrea tridentata shrubs, there were no differences in infiltration rates with or without termites. Plots with shrub cover had the highest infiltration rates 101±6 mm·h. Highest run-off volumes were recorded from termite free <5% grass cover plots and the lowest from plots with shrubs. There were no differences in suspended sediment concentrations from termites present and termite free plots. Average bed load concentration was more than three times greater from termite free, <5% cover plots than from termites present, <5% cover plots.The reduction in infiltration, high run-off volumes and high bedloads from termite free areas without shrub cover is related to increased soil bulk density resulting from the collapse of subterranean galleries of the termites that provide avenues of bulk flow into the soil. Subterranean termites affect the hydrology of Chihuahuan desert systems by enhancing water infiltration and retention of top soil. The presence of a shrub canopy and litter layer cancels any effect of subterranean termites on hydrological parameters. Since approximately 2/3 of the area is not under shrub canopies, subterranean termites are considered to be essential for the maintenance of the soil water characteristics that support the present vegetation.
We conducted studies of mass losses from surface and buried litter bags in four North American hot desert areas to test the following hypotheses: (1) leaf litter disappearance in hot deserts is independent of actual evapotranspiration, (2) buried litter disappearance is a function of actual evapotransporation, (3) the pattern of microarthropod colonization of buried leaf litter is a function of the stage of decomposition, and (4) elimination of microarthropods results in reduced rates of decomposition and increased numbers of free—living nematodes. Mass losses from surface Larrea tridentata leaf litter bags ranked highest to lowest: Chihuahuan desert, Sonoran desert, Mojave desert, Coloradan desert. Mass losses from buried litter bags were essentially equal. °40%, in each of the deserts for bags buried from March to October. There was low correlation between rainfall and mass loss of buried litter and surface litter in the North American hot deserts. Mass losses from insecticide—treated buried bags were lower than from untreated bags. There was a greater abundance of nematodes in insecticide—treated bags than in untreated bags. Tarsonemid mites were found only in litter bags from the Chihuahuan desert. The most abundant microarthropods in buried leaf litter in the other deserts were predatory raphignathids, tydeids, and arctacarids. Decomposition (litter disappearance) in North American hot deserts was highly correlated with long—term rainfall patterns, which we hypothesize have served as the selective agents for the soil biota active in the decomposition process. Thus litter disappearance does not respond to annual fluctuations in rainfall amounts.
We sampled the soil microarthropod community monthly in the oak-mesquite sand hill ecosystem. Small fungiphagous prostigmated mites (pyemotids, lordalychids and tarsonemids) that dominated the soil fauna in winter were replaced by large predaceous mites (rhodacarids and laelapids) in summer and autumn.We compared organic matter loss and microarthropod and nematode populations in shinnery oak (Quercus harvardii) using insecticide and untreated litter in fiberglass litterbags.Microarthropods extracted from litterbags showed a seasonal pattern similar to the soil cores except that collembolans and psocopterans were abundant in the litter and not in the soil cores. Numbers of free living nematodes were consistently greater than from untreated litter. The ratio of non-stylet to stylet bearing nematodes extracted from litter decreased from 4:1 in one month bags to 0.8:1.0 in the one year bags. Laboratory experiments showed that rhodacarid mites fed voraciously on nematodes.Untreated litter exhibited higher rates of organic matter loss than the insecticide treated litter; 20% and 35% respectively.We suggest that the abundant mesostigmatid mites prey on free living nematodes and that eliminating the predators allows the nematodes to overgraze the fungi and bacteria. The soil modifies the microclimate in buried litter allowing for higher biological activity, hence higher rates of decomposition.
We examined the effects of organic amendments and topsoiling on the soil biota and decomposition in order to evaluate the relative efficacy of the amendments in restarting soil processes. We studied decomposition of barley straw (Hordeum vulgare) and populations of soil biota on strip coal‐mine spoils in northwestern New Mexico. The spoils had been amended with straw mulch, bark, topsoil, or no organic additives. Decomposition rates were highest in the unmined area and the bark, amended spoils (K = 0.64 yr−1) (K = first‐order rate constant), and lowest on the topsoil amendment and unamended spoil (K = 0.34 yr−1). Few differences were observed in the populations of soil microflora. Where differences were observed, the bark‐amended spoils had the highest populations and biomass. Soil microflora activity, as indicated by decomposition rates, was enhanced by bark amendment. Soil microfaunal populations were highest on the bark‐amended spoils and unmined soil. Important soil mites (soil Acari), the oribatids, were found only in the bark‐amended spoils and the unmined soils. These studies suggest that addition of selected organic amendments (bark) to mine spoils may be as effective in developing a soil as the more expensive topsoil/mulch procedures currently used in reclamation procedures.
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