Using postfire spatial variability to improve restoration success with seeded bitterbrush

Authors: Davies, Kirk; Bates, Jonathan - Jon; Boyd, Chad; Svejcar, Lauren

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2022
Publication Date: 5/13/2022
Citation: Davies, K.W., Bates, J.D., Boyd, C.S., Svejcar, L.N. 2022. Using postfire spatial variability to improve restoration success with seeded bitterbrush. Rangeland Ecology and Management. 83:117-123. https://doi.org/10.1016/j.rama.2022.04.002.
DOI: https://doi.org/10.1016/j.rama.2022.04.002

Interpretive Summary: Restoration of bitterbrush is often a management priority after fire in western rangelands. We compared seeding bitterbrush in former juniper canopy to interspace (between juniper canopy) microsites. Bitterbrush abundance was 3.6-fold greater in former canopy compared to interspaces microsites 3 years after seeding. Bitterbrush growth was also greater in former canopy compared to interspace microsites. These results suggest that bitterbrush should be planted in former canopy microsites. This information is of interest to wildlife and land managers.

Technical Abstract: Seed-based restoration of wildlife-important shrubs following wildfire is a management priority in many ecosystems. However, postfire restoration success is spatiotemporally variable and establishment from seed frequently fails in arid and semiarid rangelands. There may be opportunities to improve restoration success by taking advantage of small-scale spatial variability in environmental characteristics. Woody plants create distinct postfire microsites, which may influence establishment and growth of seeded species, under their canopies (canopies) compared with between their canopies (interspaces). Immediately after fire, former canopies generally have less vegetation and greater soil nutrient concentrations compared with interspaces. Thus, former canopy compared with interspace microsites may be more favorable for establishment and growth of seeded species, but rapid exotic plant invasion of former canopy microsites may hinder success. We evaluated seeding bitterbrush (Purshia tridentata Pursh DC) after wildfire in former western juniper (Juniperus occidentalis ssp. occidentalis Hook) canopy compared with interspace microsites at six locations for 3 yr post seeding. Bitterbrush abundance was 3.6-fold greater in former canopy compared with interspace microsites after 3 yr. Bitterbrush height was 1.5 to 2.5-fold greater in former canopy compared with interspace microsites. The first year after fire, exotic annual grass cover was 15.6-fold greater in interspace compared with canopy microsites. Abundance and cover of other herbaceous vegetation were generally also greater in the interspace. Exotic annual grass and native bunchgrass abundance increased substantially over time in former canopy microsites, suggesting abundant resource availability. Less herbaceous competition and presumably greater resource availability in former canopies probably resulted in greater success of seeded bitterbrush. These results suggest that capitalizing on spatial variability in environments can be used to increase restoration efficiency. After fire in western juniper-encroached rangelands, former juniper canopy microsites are a favorable environment for establishment and growth of seeded bitterbrush and could be targeted for restoration efforts to improve efficiency.