Plant functional groups and species contribute to ecological resilience a decade after woodland expansion treatments

Abstract

Woody plant expansions are altering ecosystem structure and function, as well as fire regimes, around the globe. Tree-reduction treatments are widely implemented in expanding woodlands to reduce fuel loads, increase ecological resilience, and improve habitat, but few studies have measured treatment outcomes over long timescales or large geographic areas. The Sagebrush Treatment Evaluation Project (SageSTEP) evaluated the ecological effects of prescribed fire and cut-and-leave treatments in sagebrush communities experiencing tree expansion in North American cold desert shrublands. We used 10 yr of data from the SageSTEP network to test how treatments interacted with pre-treatment tree dominance, soil climate, and time since treatment to affect plant functional groups and dominant species. Non-sprouting shrub (Artemisia spp.), sprouting shrub, perennial graminoid, and annual grass responses depended on tree dominance and soil climate, and responses were related to the dominant species' life-history traits. Sites with warm and dry soils showed increased perennial graminoid but reduced Artemisia shrub cover across the tree dominance gradient after prescribed burning, while sites with cool and moist soils showed favorable post-burn responses for both functional types, particularly at low to moderate tree dominance. Cut-and-leave treatments sustained or increased native perennial plant functional groups and experienced smaller increases in exotic annual plants in both soil climates across the tree dominance gradient. Both treatments reduced biocrust cover. Selecting appropriate tree-reduction treatments to achieve desired longterm outcomes requires consideration of dominant species, site environmental conditions, and the degree of woodland expansion. Careful selection of management treatments will reduce the likelihood of undesirable consequences to the ecosystem.

Episodic occurrence of favourable weather constrains recovery of a cold desert shrubland after fire

“…establishment, after which recruitment may have been limited by competition from other species that were increasing in abundance (Freund et al, 2021). This observed window of establishment is longer than previously suggested (Wijayratne & Pyke, 2012;Ziegenhagen & Miller, 2009).…”

“…Fires typically produce resource pulses that result in short establishment windows before resources are used by competing residual and newly established plants (Jentsch & White, 2019). We found a 4–5‐year window for post‐fire A. tridentata establishment, after which recruitment may have been limited by competition from other species that were increasing in abundance (Freund et al., 2021). This observed window of establishment is longer than previously suggested (Wijayratne & Pyke, 2012; Ziegenhagen & Miller, 2009).…”

Assessing runoff and erosion on woodland‐encroached sagebrush steppe using the Rangeland Hydrology and Erosion Model

“…The regional multidisciplinary Sagebrush Steppe Treatment Evaluation Project (SageSTEP, http://www.sagestep.org) was developed in 2005 in part to study ecological responses of woodland‐encroached sagebrush steppe to various tree‐removal treatments (McIver et al, 2014; McIver & Brunson, 2014). Over more than a decade and beginning in 2006, SageSTEP scientists evaluated the initial and midterm effects of pinyon and juniper removal across a network of 11 sagebrush sites within the Great Basin and in various phases of woodland encroachment (Chambers, Miller, et al, 2014; Freund et al, 2021; Miller et al, 2014; Roundy, Miller, et al, 2014; Roundy, Young, et al, 2014; Williams et al, 2017). Treatment effects in the study exhibited some variation with woodland type, initial woodland phase and site conditions, and treatment method, but were generally consistent with other short‐ and long‐term studies of tree removal in the region (see Miller et al, 2013, 2019).…”

“…By the sixth year posttreatment, sagebrush cover was similar across control and burned plots, but was generally low in both (1%–14%) (Williams et al, 2017). Ten years after fire, burned plots maintained greater perennial grass cover than control plots, but sagebrush cover remained low, particularly for sites with warm/dry soil temperature/moisture regimes (Chambers et al, 2021; Freund et al, 2021). Cheatgrass cover remained higher for burned than control plots 10 years postfire (Chambers et al, 2021; Freund et al, 2021).…”

“…Ten years after fire, burned plots maintained greater perennial grass cover than control plots, but sagebrush cover remained low, particularly for sites with warm/dry soil temperature/moisture regimes (Chambers et al, 2021; Freund et al, 2021). Cheatgrass cover remained higher for burned than control plots 10 years postfire (Chambers et al, 2021; Freund et al, 2021). For mechanical treatments, sagebrush cover was largely unaffected initially and cover of perennial bunchgrasses in treated areas exceeded that of controls in the first 2–3 years after tree removal (Miller et al, 2014) and in the sixth year posttreatment (Williams et al, 2017).…”