- Additional Plants: native plants
- Animals: bovine
- Animal Production: range improvement
- Education and Training: extension, workshop
- Natural Resources/Environment: habitat enhancement, soil stabilization
- Pest Management: weed ecology
- Soil Management: soil microbiology, soil quality/health
Biocrusts (biological soil crusts) provide key ecosystem services such as erosion resistance and nitrogen fixation to western rangelands. There is also evidence that biocrusts may inhibit cheatgrass ( Bromus tectorum) establishment. This possibility has ramifications for sustainable livestock production given the threats posed by cheatgrass and other invasive plants that decrease the quality and yield of perennial forages, increase production costs for the livestock industry and exacerbate wildfire threats. We therefore propose to investigate the influence of biocrusts on the establishment of native perennial grasses and cheatgrass and the conditions under which biocrusts might make rangelands more resistant to exotic grass invasion, and thereby serve as a potential restoration tool for producers. Our goalis to determine the extent to which nativity and seed attributes (e.g., size, presence/absence of awns) influence grass establishment outcomes on biocrusted and non-crusted soils and whether a restored biocrust community can confer resistance to cheatgrass invasion. Our objectivesare to: 1) quantify the influence of biocrust type and integrity on cheatgrass germination and establishment; 2) determine if grass seed morphology affects grass germination and establishment on biocrusts; and 3) quantify the effect of biocrust restoration on the re-establishment of native grasses and reinvasion of cheatgrass. We propose a comparative approach to test our hypothesis that the type and integrity of biocrusts interacts with plant seed attributes to differentially influence native and exotic grass establishment. We will conduct field experiments on the Kane and Two Mile Ranches on the Colorado Plateau in northern Arizona to determine how the type/integrity of biocrusts affect the establishment of cheatgrass and native grasses with contrasting seed architectures. Seeds will be manipulated by removing appendages or leaving them intact. Manipulated and non-manipulated seeds will be placed on contrasting soil surfaces; including intact, disturbed and restored biocrust communities, and germination and establishment will be quantified. If biocrusts limit cheatgrass establishment, management of rangelands to resist invasion could incorporate strategies for retaining or re-establishing biocrusts. Along these lines, the proposed research would complement ongoing, large-scale biocrust restoration research and existing and future research on livestock management and biocrusts. Knowledge of how biocrust properties and seed morphologies interact to influence grass establishment will provide useful criteria for formulating species mixtures in re-seeding efforts. Information will be shared with producers, scientists and the public through several forums. We will host a field day for producers and managers at the Kane and Two Mile Ranches and collaborate with the University of Arizona’s Cooperative Extension program to disseminate results to producers and the public. In addition, we will work with Grand Canyon Trust, V Bar V Ranch and other educational organizations to incorporate our results into education/outreach programs and materials. We will also disseminate results via refereed publications.
Project objectives from proposal:
Our goal is to determine the extent to which nativity and seed attributes (e.g., size, presence/absence of awns) influence grass establishment on biocrusted and non-crusted soils and whether a restored biocrust community can confer resistance to future invasions. Our objectives are to:
1) quantify biocrust influence on cheatgrass establishment;
2) determine if grass seed morphology affects establishment on biocrusts;
3) determine if biocrust type and integrity affect grass establishment; and
4) quantify the effect of biocrust restoration on establishment of native grasses and reinvasion of cheatgrass.
Hypothesis 1 (Objectives 1 and 2): The influence of biocrusts on grass germination and establishment (positive, neutral or negative) varies according to seed characteristics. Specifically, (a) biocrusts will reduce recruitment of plants whose seeds have large awns or appendages compared to smoother seeds; (b) biocrusts will reduce recruitment of large-seeded species compared to small-seeded species; and (c) biocrusts will reduce recruitment of exotic grasses compared to native grasses. Rationale: We suppose that biocrusts constitute a mechanical barrier that reduces seed contact with the soil surface. The high evaporation rates in deserts make soil contact crucial for seeds to obtain sufficient water for germination. We predict that large seeds or seeds having large appendages (e.g., long awns) would be less likely to achieve soil contact when biocrusts are present compared to small seeds and seeds lacking appendages. Many exotic grasses did not evolve with biocrusts and, therefore, lack the traits that enable native grasses to germinate and establish where biocrusts are present (e.g., Warren and Eldridge 2003).
Hypothesis 2 (Objective 3): Grass germination and establishment varies with biocrust type and integrity. Specifically, (a) lichen/moss biocrusts are a more effective barrier than cyanobacterial biocrusts when of comparable roughness; (b) biocrusts form a physical, not biological barrier to seeds; and (c) intact biocrusts are a more effective barrier against exotic grasses than broken biocrusts. Rationale: Lichen/moss biocrusts are epedaphic and can form mats above the soil surface. Therefore, we expect lichen/moss crusts to form a more impenetrable barrier than cyanobacterial crusts, whose biomass is just below the surface and occurring as individual filaments with spaces between them. As such, it should be more difficult for seeds to achieve soil contact and burial on the lichen biocrusts. Biocrusts should no longer pose a physical barrier once disrupted.
Hypothesis 3 (Objective 4): Restoration of biocrust communities following cheatgrass control (a) decreases the probability of reinvasion and (b) increases or has a neutral effect on re-establishment of native grasses. Rationale: Establishment of biocrusts reforms the barriers that inhibit soil contact by the exotic plant seed (Hypothesis 2), but effects will vary depending on plant seed traits (Hypothesis 1).