Long-Term Evidence for Fire as an Ecohydrologic Threshold-Reversal Mechanism on Woodland-Encroached Sagebrush Shrublands

Encroachment of sagebrush (Artemisia spp.) shrublands by pinyon (Pinus spp.) and juniper (Juniperus spp.) conifers (woodland encroachment) induces a shift from biotic‐controlled resource retention to abiotic‐driven loss of soil resources. This shift is driven by a coarsening of the vegetation structure with increasing dominance of site resources by trees. Competition between the encroaching trees and understory vegetation for limited soil and water resources facilitates extensive bare intercanopy area between trees and concomitant increases in run‐off and erosion that, over time, propagate persistence of the shrubland‐to‐woodland conversion. We evaluated whether tree removal by burning can decrease late‐succession woodland ecohydrologic resilience by increasing vegetation and ground cover over a 9‐year period after fire and whether the soil erosion feedback on late‐succession woodlands is reversible by burning. To address these questions, we employed a suite of vegetation and soil measurements and rainfall simulation and concentrated overland flow experiments across multiple plot scales on unburned and burned areas at two sagebrush sites in the later stages of woodland succession. Prior to burning, tree cover was approximately 28% at the sites, and more than 70% of the area at the sites was intercanopy with depauperate understory vegetation and extensive bare ground (52–60% bare soil and rock). Burning initially increased bare ground across fine (\u3c1 m2) to patch (tens of metres) scales, resulting in enhanced sediment availability at the fine scale, sustained high run‐off and erosion within degraded intercanopies, amplified run‐off and erosion from tree canopy areas, and amplified sediment delivery across fine to patch scales. However, fire‐induced increases in grass cover over nine growing seasons improved infiltration, limited run‐off and sediment delivery from the fine scale, and reduced intercanopy run‐off and erosion at the patch scale. These changes reflect a switch in vegetation structure, triggered by burning and subsequent vegetation re‐establishment, and a shift to biotic control on run‐off and erosion across spatial scales. The responses and persistence over the 9‐year period postfire at the two sites demonstrate that fire can decrease woodland ecohydrologic resilience by altering plant community physiognomy and thereby can reverse the soil erosion feedback on sagebrush shrublands in the later stages of woodland encroachment

Kentucky bluegrass invaded rangeland: ecosystem implications and adaptive management approaches

USDA-NRCS National Resources Inventory data indicates that between 2011 and 2015 Kentucky bluegrass (Poa pratensis) was present in 14.5% on non-Federal rangelands nationally and 86% in North Dakota, 63% in South Dakota, 40% in Kansas, 38% in Nebraska, and 32% in Montana. Native grasslands provide important services such as nutrient cycling, forage and habitat for wildlife and livestock, pollinator habitat, carbon capture, and regulation of hydrologic cycles, among others. Therefore, grassland degradation due to invasive plant species has far-ranging consequences for both human and ecological systems. We present information from a symposium at the 2019 Society for Range Management Annual Meeting. The symposium covered three topic areas that have been the foci of NGP Kentucky bluegrass research in the last five years: (1) impacts of Kentucky bluegrass on ecosystem services (especially soil water regulation, pollinator services, and forage production); (2) opportunities for using adaptive management approaches that include natural disturbances (such as fire and livestock grazing) for restoring and maintaining diverse grasslands; and (3) how to effectively overcome social barriers to treatment options aimed at restoring these grasslands. We present brief summaries of research progress on these topics. We conclude that despite great advances in knowledge related to Kentucky bluegrass invaded ecosystems there are still knowledge gaps regarding management of this novel ecosystem under changing climatic conditions as well as challenges regarding large scale adoption of management practices needed to manage these systems appropriately

Kentucky bluegrass invaded rangeland: Ecosystem implications and adaptive management approaches

Summary of multidisciplinary research on Kentucky bluegrass expansion throughout the Great Plains based on symposium held at 2019 SRM Annual Meeting. Fire, grazing, and their combination are promising tools for managing Kentucky bluegrass to maintain diverse and productive grasslands. Kentucky bluegrass growth and dominance results in accumulation of surface residues, which alter soil hydrology. Gradients of Kentucky bluegrass abundance in grasslands are associated with shifts in butterfly pollinator communities. Community organization, education, and establishment of burn associations support prescribed fire on the ground, but challenges in adopting fire as a management tool remain. © 2020 The Society for Range ManagementThe Rangelands archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information