Plant community responses to historical wildfire in a shrubland–grassland ecotone reveal hybrid disturbance response

Abstract

Citation: Porensky, L. M., J. D. Derner, and D. W. Pellatz. 2018. Plant community responses to historical wildfire in a shrubland-grassland ecotone reveal hybrid disturbance response. Ecosphere 9(8):Abstract. Most ecotones include structural and taxonomic elements from both adjacent communities, but it remains unclear how these elements function and interact within ecotones. We investigated long-term plant community responses to wildfire in a 7000-km 2 ecotone between mixed-grass prairie and sagebrush steppe ecosystems, which have dramatically different historical fire regimes. We asked whether plant community responses to wildfire in the ecotone were more similar to mixed-grass prairie, sagebrush steppe, or a hybrid of these two. We sampled plant community composition at 70 pairs of transects located inside and outside of wildfires that burned from 1937 to 2012. We determined whether (1) wildfires predicted plant community composition, (2) plant community response to fire varied based on abiotic factors, and (3) effects of wildfire varied based on time since fire. Plant community responses to wildfire did not vary substantially across the study region, despite continuous plant community variation in response to abiotic factors. Overstory responses were characteristic of sagebrush steppe. Burned transects had <10% as much big sagebrush cover as unburned transects, and cover did not increase with time since fire. In contrast, understory plant community responses to fire were similar to mixed-grass prairie. Burned sites had high forb cover in the short term and perennial grass cover in the long term. Within an ecotone, different components of the plant community can maintain functional fidelity to their home ecosystems, despite being spatially juxtaposed. The idea of hybrid disturbance response may provide new opportunities for targeted management within ecotones.

Direct and indirect effects of a keystone engineer on a shrubland‐prairie food web

“…Prairie dog disturbance was associated with a shift from C 3 and C 4 perennial graminoids to annual forbs (Fig. 3A; Coppock et al 1983, Johnson‐Nistler et al 2004) as well as decreased shrub cover (Johnson‐Nistler et al 2004) and visual obstruction (Winter et al 2002). Because annual forbs provide lower quality livestock forage than perennial grasses, our findings help explain how prairie dogs can reduce available forage for livestock while also having minimal effects on total herbaceous biomass (Derner et al 2006, Augustine and Springer 2013, Connell et al 2018).…”

“…2). Mean annual precipitation ranged from 25 to 35 cm, and generally fell during spring and summer (Porensky et al 2018). The study area included a mosaic of sagebrush ( Artemisia spp.)…”

“…Based on the literature we anticipated that most effects on arthropods would be associated with burrowing and vegetation structure (Davidson and Lightfoot 2007) while birds (specifically non‐raptors) would respond mainly to vegetation structure (Augustine and Baker 2013). Conversely, we expected direct effects of prairie dogs on both vegetation structure and community composition (Winter et al 2002, Johnson‐Nistler et al 2004). In addition to elucidating these ecological mechanisms, this study was also intended to determine those aspects of prairie dog disturbance most critical for associated taxa, an important step in balancing ecological and economic services on public rangelands.…”

Thresholds are in the eye of the beholder: plants and wildlife respond differently to short‐term cattle corrals

“…, Porensky et al. ), though resilience to these disturbances also is common in rangeland ecosystems (Fuhlendorf et al. , Valone et al.…”

Anthropogenic and Natural Disturbance Differentially Affect Sagebrush Bird Habitat Use

“…This species is important for grassland birds including the mountain plover (Charadrius montanus) and burrowing owl (Athene cunicularia) because it alters vegetation and soil structure to provide breeding habitat for these species, but long-term prairie dog disturbance can reduce sagebrush cover, potentially reducing habitat availability for sagebrush birds in some areas (Duchardt et al 2019). In addition, vegetation structure within sagebrush ecosystems along the eastern Author Manuscript edge of sagebrush range differs from elsewhere in the sagebrush steppe (Chambers et al 2016), exhibiting a denser grass understory, often a mixture of perennial and annual grasses (Porensky et al 2018). More broadly, populations are generally lower and more variable in both space and time at the edge of a species' range (Andrewartha andBirch 1954, Kirkpatrick andBarton 1997).…”