Reversing tree expansion in sagebrush steppe yields population‐level benefit for imperiled grouse

Abstract

Woody plant expansion into shrub and grasslands is a global and vexing ecological problem.In the Great Basin of North America, the expansion of pinyon-juniper (Pinus spp.-Juniperus spp.) woodlands is threatening the sagebrush (Artemisia spp.) biome. The Greater Sage-grouse (Centrocercus urophasianus; sage-grouse), a sagebrush obligate species, is widespread in the Great Basin and considered an indicator for the condition of sagebrush ecosystems. To assess the population response of sage-grouse to landscape-scale juniper removal, we analyzed a long-term telemetry data set and lek counts with a Bayesian integrated population model in a before-after-control-impact design. Population growth rates (λ) in a treatment area (Treatment) with juniper removal and a control area (Control) without juniper removal indicated the two areas generally experienced population increase, decrease, and stability in the same years. However, the difference in λ between study areas indicated a steady increase in the Treatment relative to the Control starting in 2013 (removals initiated in 2012), with differences of 0.13 and 0.11 in 2016 and 2017, respectively. Retrospective sensitivity analysis suggested the dynamics in λ were driven by increases in juvenile, adult, first nest, and yearling survival in the Treatment relative to the Control. These findings demonstrate the effectiveness of targeted conifer removal as a management strategy for conserving sage-grouse populations in sagebrush steppe affected by conifer expansion. Examples of positive, population-level responses to habitat management are exceptionally rare for terrestrial vertebrates, and this study provides promising evidence of active management that can be implemented to aid recovery of an imperiled species and biome.

Acute and lagged fitness consequences for a sagebrush obligate in a post mega‐wildfire landscape

“…The continued decline in λ since 2016 suggested the loss of 186,972 ha of sagebrush habitat and slow regeneration of sagebrush plants post‐fire may prolong recovery of sage‐grouse after a mega‐wildfire (Steenvoorden et al, 2019). Mean estimates of λ during 2016–2018 were much lower in the Trout Creek study area (0.75) compared to a study in Oregon during the same time period that was not affected by fire (0.93; Olsen et al, 2021). Moreover, estimates of λ were low compared to other studies that reported long‐term trends in λ across the distribution of sage‐grouse (Dahlgren et al, 2016; Garton et al, 2011; Johnson & Braun, 1999).…”

“…Vital rates most important for driving sage‐grouse population change ( λ ) can vary among populations (e.g., Walker & Naugle, 2011 vs. Dahlgren et al, 2016). For example, several studies have reported λ to be most sensitive to changes in adult female survival, juvenile (fledging to 1‐year old) survival, and chick survival (Dahlgren et al, 2016; Johnson & Braun, 1999; Olsen et al, 2021; Taylor et al, 2012). However, nest success explained most of the variation in λ across multiple populations representing the current sage‐grouse distribution, in part due to the high temporal variation in this vital rate (Taylor et al, 2012).…”

Reversing Tree Encroachment Increases Usable Space for Sage‐Grouse during the Breeding Season

“…Previous analysis in our study area indicated annual female survival increased 6.6% and nest survival increased 18.8% in the Treatment relative to the Control during the first 3 years after conifer removals were initiated (Severson et al 2017d). A longer-term assessment of demographic consequences of conifer removal indicated an 11-13% increase in population growth rate (λ) in the Treatment relative to the Control 5-6 years after conifer removals began (Olsen et al 2021). Conifer expansion may increase perch sites for avian predators of sagegrouse (Paton 1994, Wolff et al 1999) and contribute to environments with higher risk of mortality, even when trees are sparse and scattered (Coates et al 2017, Prochazka et al 2017).…”

“…Positive effects of conifer removal on habitat availability for sage-grouse may also result in demographic benefits (Sandford et al 2017, Severson et al 2017d, Olsen et al 2021. Sage-grouse broods in Utah were more likely to be successful (≥1 chick surviving ≥50 days) when occupying habitat at lower conifer levels and closer to conifer removal areas (Sandford et al 2017).…”

“…Radio telemetry studies indicate that sage-grouse are more likely to select sagebrush habitats with conifer cover levels ≤4%, and as low as 1.5%, indicating a low tolerance for conifers even in areas with intact sagebrush understories (Coates et al 2017, Severson et al 2017a). Sage-grouse vital rates are generally negatively affected by the presence of conifers in sage-grouse habitat (Coates et al 2017, Sandford et al 2017, Olsen et al 2021, and sage-grouse navigating landscapes affected by conifer expansion move more quickly and have increased predation risk, particularly among juveniles (Prochazka et al 2017).…”