Trajectories of change in sagebrush steppe vegetation communities in relation to multiple wildfires

Abstract

Repeated perturbations, both biotic and abiotic, can lead to fundamental changes in the nature of ecosystems, including changes in state. Sagebrush steppe communities provide important habitat for wildlife and grazing for livestock. Fire is an integral part of these systems, but there is concern that increased ignition frequencies and invasive species are fundamentally altering them. Despite these issues, the majority of studies of fire effects in systems dominated by Artemisia tridentata wyomingensis have focused on the effects of single burns. The Arid Lands Ecology Reserve (ALE), in south-central Washington (USA), was one of the largest contiguous areas of sagebrush steppe habitat in the state until large wildfires burned the majority of it in 2000 and 2007. We analyzed data from permanent vegetation transects established in 1996 and resampled in 2002 and 2009. Our objective was to describe how the fires, and subsequent postfire restoration efforts, affected communities' successional pathways. Plant communities differed in response to repeated fire and restoration; these differences could largely be ascribed to the functional traits of the dominant species. Lowelevation communities, previously dominated by obligate seeders, moved furthest from their initial composition and were dominated by weedy, early-successional species in 2009. Higherelevation sites with resprouting shrubs, native bunchgrasses, and few invasive species were generally more resilient to the effects of repeated disturbances. Shrub cover has been almost entirely removed from ALE, although there was some recovery where communities were dominated by resprouters. Bromus tectorum dominance was reduced by herbicide application in areas where it was previously abundant, but it increased significantly in untreated areas. Several resprouting species, notably Phlox longifolia and Poa secunda, expanded remarkably following competitive release from shrub canopies and/or abundant B. tectorum. Our results suggest that community dynamics can be understood through a state and transition model with two axes (shrub/grass and native/invasive abundance), although such models also need to account for differences in plant functional traits and disturbance regimes. We use our results to develop a conceptual model that will be validated with further research.

Pre‐fire vegetation drives post‐fire outcomes in sagebrush ecosystems: evidence from field and remote sensing data

“…A PERMA-NOVA model that included this factor was significant for both focal areas (Table 2), a result consistent with reports of a strong influence of historical community composition on contemporary composition in sagebrush ecosystems (Davies et al 2012, Chambers et al 2014b, Mitchell et al 2017. A PERMA-NOVA model that included this factor was significant for both focal areas (Table 2), a result consistent with reports of a strong influence of historical community composition on contemporary composition in sagebrush ecosystems (Davies et al 2012, Chambers et al 2014b, Mitchell et al 2017.…”

“…According to analyses of field data, cover of most exotic functional groups in burned areas increased whereas native shrub and sagebrush cover decreased between 1982 and 2016 (Table 1), a finding consistent with numerous reports of sagebrush ecosystems in the northern Great Basin being converted to degraded grasslands dominated by exotic plants (Whisenant 1990, Davies et al 2012, Shinneman and McIlroy 2016. Component data had a similar pattern whereby shrub and sagebrush cover declined in burned plots; however, cover of herbaceous components did not change (Table 1).…”

“…3, 4), a pattern which may be a product of competitive interactions. Certain native perennial grass species, including western wheatgrass (Pascopyrum smithii) and Sandberg bluegrass (Poa secunda), may expand after a fire due to competitive release from sagebrush, which recovers more slowly (Vale 1974, Cooper et al 2011, Davies et al 2012, Taylor et al 2014, Ellsworth et al 2016, Shinneman and McIlroy 2016, Ellsworth and Kauffman 2017, Mitchell et al 2017, Condon and Pyke 2018. Certain native perennial grass species, including western wheatgrass (Pascopyrum smithii) and Sandberg bluegrass (Poa secunda), may expand after a fire due to competitive release from sagebrush, which recovers more slowly (Vale 1974, Cooper et al 2011, Davies et al 2012, Taylor et al 2014, Ellsworth et al 2016, Shinneman and McIlroy 2016, Ellsworth and Kauffman 2017, Mitchell et al 2017, Condon and Pyke 2018.…”

“…Plant communities exposed to multiple fires, particularly those at lower elevations that have ideal environmental conditions for annuals like cheatgrass, are prone to remaining in an annual-dominated state (Chambers et al 2007, 2014a, Davies et al 2012. Plant communities exposed to multiple fires, particularly those at lower elevations that have ideal environmental conditions for annuals like cheatgrass, are prone to remaining in an annual-dominated state (Chambers et al 2007, 2014a, Davies et al 2012.…”

Nowhere to Invade: Rumex crispus and Typha latifolia Projected to Disappear under Future Climate Scenarios

“…Species invasion has contributed to the extinction of native species [1], alteration of fire regimes [2], nutrient cycling [3], functioning of ecosystems [4], economic losses [5], reduction of agricultural yield [6], spreading of diseases [7], and gene pollution [8]. Controlling the growth and spread of invasive species is expensive.…”