Soil erosion is a persistent problem in many monsoon-driven dryland systems of the American Southwest. Continuous soil erosion can lead to loss of topsoils, decreased plant-available water, extreme soil surface temperatures, and freeze-thaw activity, all of which can hinder vegetation establishment and reduce site productivity. An exemplar of this problem are the Pinyon-Juniper woodlands of Bandelier National Monument, NM, which have seen erosion rates as high as one centimeter of soil loss per decade. This threatens not only natural capital, but also archaeological sites the Monument is tasked to protect. Without intervention, this pattern of soil loss is expected to be persistent and irreversible. We hypothesized that dryland biological soil crusts (biocrusts) – a community of mosses, lichens, cyanobacteria, and heterotrophs aggregating the soil surface – may be an effective tool for stabilizing soil surfaces. Here, in a full factorial design, we inoculated plots on the eroding Pinyon-Juniper mesa tops of Bandelier National Monument with native greenhouse cultured biocrusts, and administered the erosion intervention treatments of flashing, slash placement, and seeding. We measured soil stability, biocrusts cover, and phosphorus cycling before and after our pre-monsoon inoculation application to understand how both our treatments and seasonal changes influence soil stability and nutrient cycling.
Results/Conclusions
While we did not see an effect of the inoculum additions or erosion intervention treatments, we did see significant changes to the soil processes and composition between seasons. From May to October 2015 the system experienced a significant reduction in soil stability. Simultaneously, we saw an increase in the formation of physical crust – an abiotic soil crust formed by compaction, rain-splash, or chemical forces. Because physical crusts lack large pore spaces they tend to limit water infiltration, thus increasing water runoff and soil loss. Accordingly, we saw a decrease in P over time, suggesting this already nutrient poor system is losing P to soil erosion. This data points to dynamic seasonal changes, presumably induced by the monsoons, which by forming physical crust maintain the cycle of erosion. The data also suggest that in monsoon driven systems the seasonality of biocrust inoculum addition may be especially important, as Fall application of biocrust inoculum was successful in the winter precipitation dominated Great Basin and Colorado Plateau. Taken together, this data provides an understanding of the intra-annual variation within these dryland mesa top soils and brings us closer to developing effective techniques to halt soil loss from these systems.