Exotic Annual Bromus Invasions: Comparisons Among Species and Ecoregions in the Western United States

Brooks, Matthew L.; Brown, Cynthia S.; Chambers, Jeanne C.; D’Antonio, Carla M.; Keeley, Jon E.; Belnap, Jayne

doi:10.1007/978-3-319-24930-8_2

Cited by 52 publications

(56 citation statements)

References 176 publications

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“…This is because: (i) there is no evidence to suggest woody cover in the mid‐and high‐elevation zones would not be lost to the same degree as in the low elevation zone after frequent fire; (ii) B. rubens and B. tectorum are known to dominate cover in areas that burn at high frequency (Brooks ; Brooks et al . ); and (iii) feedbacks between invasive grass and frequent fire have been well‐described for many years (Brooks et al . ; Brooks ).…”

Section: Discussionmentioning

confidence: 99%

“…The zone is usually considered to have relatively low to moderate resistance to invasive grasses and low resilience to fire (Brooks et al . ). The middle‐elevation zone (≈>1200 and <≈1800 m) is dominated by shrubs, but their density is greater and they are taller than in the low‐elevation zone.…”

Section: Methodsmentioning

confidence: 97%

“…Vegetation communities in the high‐elevation zone are generally thought to be relatively resistant to invasive grasses and resilient to fire (Brooks et al . ).…”

Section: Methodsmentioning

confidence: 97%

“…Based on previous studies as well as a general conceptual model of the grass/fire cycle (Brooks ), we expected high fire frequency to lead to low resilience of native desert vegetation and low resistance to invasion by invasive annual grasses (Brooks et al . ). There is very little understanding of the effect burn severity has on invasive plants, but two studies indicated the potential for cover of invasive annual grasses being greater in sites that burned at high severity (Hunter et al .…”

Section: Introductionmentioning

confidence: 97%

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Alternative pathways to landscape transformation: invasive grasses, burn severity and fire frequency in arid ecosystems

Klinger

Brooks

2017

Journal of Ecology

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Summary Arid ecosystems are often vulnerable to transformation to invasive‐dominated states following fire, but data on persistence of these states are sparse. The grass/fire cycle is a feedback process between invasive annual grasses and fire frequency that often leads to the formation of alternative vegetation states dominated by the invasive grasses. However, other components of fire regimes, such as burn severity, also have the potential to produce long‐term vegetation transformations. Our goal was to evaluate the influence of both fire frequency and burn severity on the transformation of woody‐dominated communities to communities dominated by invasive grasses in major elevation zones of the Mojave Desert of western North America. We used a chronosequence design to collect data on herbaceous and woody cover at 229 unburned reference plots and 578 plots that burned between 1972 and 2010. We stratified the plots by elevation zone (low, mid, high), fire frequency (1–3 times) and years post‐fire (YPF; 1–5, 6–10, 11–20 and 21–40 YPF). Burn severity for each plot was estimated by the difference normalized burn ratio. We identified two broad post‐fire successional pathways. One was an outcome of fire frequency, resulting in a strong potential transformation via the grass/fire cycle. The second pathway was driven by burn severity, the critical aspect being that long‐term transformation of a community could occur from just one fire in areas that burned at high or sometimes moderate severity. Dominance by invasive grasses was most likely to occur in low‐and high‐elevation communities; cover of native herbaceous species was often greater than that of invasive grasses in the mid‐elevation zone. Synthesis. Invasive grasses can dominate a site that burned only one time in many decades at high severity, or a site that burned at low severity but multiple times in the same time period. However, high burn severity may predispose areas to more frequent fire because they have relatively high cover of invasive annual grass, suggesting burn severity and fire frequency have both independent and synergistic effects. Resilience in vegetation structure following fire in many arid communities may be limited to a narrow window of low burn severity in areas that have not burned in many decades.

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Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 97%

“…Vegetation communities in the high‐elevation zone are generally thought to be relatively resistant to invasive grasses and resilient to fire (Brooks et al . ).…”

Section: Methodsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 97%

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Alternative pathways to landscape transformation: invasive grasses, burn severity and fire frequency in arid ecosystems

Klinger

Brooks

2017

Journal of Ecology

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“…One possibility is differences in drought tolerance. In southern California, Bromus diandrus is more common in mesic and coastal regions while Bromus rubens and Bromus madritensis predominate in drier habitats (Brooks et al, ). All of our research plots burned, leaving no comparison time series from comparable unburned habitat.…”

Section: Discussionmentioning

confidence: 99%

Long‐term monitoring of a highly invaded annual grassland community through drought, before and after an unintentional fire

Thomson

Bonapart

King

et al. 2020

J Vegetation Science

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Questions (a) How did seedling numbers and species composition change in the first year after a wildfire during drought, relative to pre‐fire variation? (b) Has the community returned to pre‐fire composition after five years? (c) Has the degree of dominance by exotic annual grasses changed? (d) Is there any evidence that drought conditions affected community cover, before or after fire? Location Exotic‐dominated annual grassland in southern California, USA. Methods We monitored community cover and native annual forb densities for four years before and four (cover) to five (densities) years after an unintentional fire (fall 2013) coinciding with the spring 2012–2019 California drought. We also measured seedling emergence both before and during the first year post‐fire. We assessed post‐fire changes in cover and density relative to pre‐fire variation, and tested correlations between community cover and annual rainfall measures. Results Seedling emergence declined strongly after fire for exotic grasses, but remained stable for exotic forbs. Seedling densities of the most common native forbs declined, but several previously‐rare natives increased. Community cover initially shifted towards the exotic forbs Erodium spp., then returned to higher exotic grass densities. Yet the previously dominant Bromus diandrus declined steeply, even as other exotic grasses and some native forbs increased. Up to five years after fire, relative cover and abundance of the most common exotic and native species still differed from pre‐fire composition. Common species were uncorrelated with annual precipitation, but several may have responded to shorter growing seasons. Conclusions Immediate post‐fire conditions favoured exotic and native forbs over grasses, as predicted. Yet in contrast to many previous studies, the community did not return quickly to pre‐fire composition but showed persistent changes that favoured neither natives nor exotics. Our results suggest post‐fire recovery in this habitat may be contingent on abiotic conditions, with drought one potential explanation for changes.

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Climate‐based seed transfer of a widespread shrub: population shifts, restoration strategies, and the trailing edge

Richardson

Chaney

2018

Ecological Applications

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Genetic resources have to be managed appropriately to mitigate the impact of climate change. For many wildland plants, conservation will require knowledge of the climatic factors affecting intraspecific genetic variation to minimize maladaptation. Knowledge of the interaction between traits and climate can focus management resources on vulnerable populations, provide guidance for seed transfer, and enhance fitness and resilience under changing climates. In this study, traits of big sagebrush (Artemisia tridentata) were examined among common gardens located in different climates. We focus on two subspecies, wyomingensis and tridentata, that occupy the most imperiled warm-dry spectrum of the sagebrush biome. Populations collected across the sagebrush biome were recorded for flower phenology and survival. Mixed-effects models examined each trait to evaluate genetic variation, environmental effects, and adaptive breadth of populations. Climate variables derived from population-source locations were significantly associated with these traits (P < 0.0001), explaining 31% and 11% of the flower phenology and survival variation, respectively. To illustrate our model and assess variability in prediction, we examine fixed and focal point seed transfer approaches to map contemporary and climate model ensemble projections in two different regions of the sagebrush biome. A comparison of seed transfer areas predicts that populations from warmer climates become more prevalent, replacing colder-adapted populations by mid-century. However, these warm-adapted populations are often located along the trailing edge, margins of the species range predicted to be lost due to a contraction of the climatic niche. Management efforts should focus on the collection and conservation of vulnerable populations and prudent seed transfer to colder regions where these populations are projected to occur by mid-century. Our models provide the foundation to develop an empirical, climate-based seed transfer system for current and future restoration of big sagebrush.

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Exotic Annual Bromus Invasions: Comparisons Among Species and Ecoregions in the Western United States

Cited by 52 publications

References 176 publications

Alternative pathways to landscape transformation: invasive grasses, burn severity and fire frequency in arid ecosystems

Alternative pathways to landscape transformation: invasive grasses, burn severity and fire frequency in arid ecosystems

Long‐term monitoring of a highly invaded annual grassland community through drought, before and after an unintentional fire

Climate‐based seed transfer of a widespread shrub: population shifts, restoration strategies, and the trailing edge

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