Cheatgrass (Bromus tectorum), red brome (B. rubens), buffelgrass (Pennisetum ciliare), and other non-native, invasive plants pose a serious threat to Southwestern rangelands. Our project aims to understand the situations in which biological soil crusts (biocrusts) might increase an ecosystem’s resistance to invasion. Biological soil crusts (biocrusts) are communities of lichens, mosses, cyanobacteria and other microbes that live in and on the open spaces on soils in arid and semi-arid regions. Biocrusts provide ecosystem services such as erosion resistance and nutrient contributions. However, our understanding of how biocrusts influence the composition of plant communities is somewhat limited.

In some situations, biocrusts can inhibit non-native annual plants such as cheatgrass. Across multiple plant species and biocrust communities, previous research has found that biocrusts have a neutral, positive, or negative effect on the germination of plant seeds but we know little about how biocrusts influence establishment of plants. In addition, we do not have a solid understanding of the mechanisms underlying these variable outcomes. A better understanding of the mechanisms could help develop restoration strategies and benefit land managers.

We are conducting a series of experiments in field and semi-controlled environments to determine how biocrusts interact with plant seed morphology to influence the germination and early establishment of native and non-native grasses. We are conducting these experiments on the Colorado Plateau, where biocrusts are pinnacled, and the Sonoran Desert, where biocrusts are comparatively smoother, to investigate the roll of the microtopography of the biocrusts.

We speculate that biocrust characteristics (dominant species, microtopography, integrity) interact with seed characteristics (nativity, size, shape, appendages) to determine the amount of seed-soil contact as well as the ability of seeds to enter the soil. We think that this interaction is critical to determining the rates of seed germination and early establishment of seedlings. We speculate that native grasses, grasses with small seeds and/or seeds lacking or having small appendages (e.g., awns, bristles) are most likely to establish on biocrusts in both the Sonoran Desert and on the Colorado Plateau.