Biocrusts of Northern Arizona NAtional Monuments Post 4: Wupatki

This is the latest in a series, see here for a lichen key, here for a moss key, and here for a description of Walnut Canyon biocrusts.

Wupatki-Wupatki was the largest national monument examined. We found that in the case of potential biocrust abundance low to medium values were observed within the monument. All of our outputs suggest that the areas where biocrusts attain the greatest importance are the limestone flats above the Doney cliffs, including Antelope Prairie. This conclusion is deceptive because it does not take into account eolian reworked cinders. Surfaces covered by cinders are not available habitat for BSCs. We had no available spatial data on the extent of cinder deposits, therefore we generated a map of cinder cover based upon interpolation of our surface data (Figure 1). Amos et al. (1981) provide data on thicker cinder deposits, but do not address the thin eolian deposition of cinders that strongly influences western Wupatki. Because mapping cinder cover was outside the scope of our project, this data should be considered a rough approximation only. The cinder map reveals that a large proportion of Wupatki that otherwise could support BSCs likely does not because a large proportion of the available surface is covered with cinders (Figure 2a). There may however be less cinder deposition on the northern portions of the Doney Cliffs where our models predict high potential for BSC abundance, function and biodiversity.

Figure 1. Surface cinder cover in Wupatki National Monument, estimated by interpolation from non-systematic ground-based samples.

 

Overall, BSC cover is sparse in Wupatki, apparently due to several factors. The cinder deposits of the western portions virtually prohibit biocrust development because there is simply no soil at the surface, i.e. no available habitat. To the east, the Wupatki basin has less cinder deposition but is quite arid and hot, and is lacking in sandy soils which tend to support higher biocrust cover on the Colorado Plateau. This area consists mainly of highly eroded exposures of moenkopi shale, and alluvial terraces of various ages. Minor biocrust development was detected on some alluvial terraces, but was not clearly related to terrace age. Occasionally northern exposures (especially shrub mounds within such sites) supported some crust cover (Figure 2). It is possible, especially in the Wupatki Basin, that the landscape is not at its potential due to the legacy of disturbance both from livestock and the widespread prehistoric agriculture that occurred there. Calcareous sandy soils and non-bentonitic shale-derived soils in low disturbance conditions generally support greater biocrust cover than that observed in the Wupatki Basin.

Figure 2. Soil surfaces in Wupatki National Monument. a. A thin veneer of cinder deposition prohibits biocrust development due to little available habitat at the soil surface. b. A biocrust growing on the north side of a shrub mound on an alluvial terrace.