Browsing by Author "Taylor, Kimberley T."
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Item Bromus tectorum Response to Fire Varies with Climate Conditions(2014-09) Taylor, Kimberley T.; Brummer, Tyler J.; Rew, Lisa J.; Maxwell, Bruce D.The invasive annual grass Bromus tectorum (cheatgrass) forms a positive feedback with fire in some areas of western North America’s sagebrush biome by increasing fire frequency and size, which then increases B. tectorum abundance post-fire and dramatically alters ecosystem structure and processes. However, this positive response to fire is not consistent across the sagebrush steppe. Here, we ask whether different climate conditions across the sagebrush biome can explain B. tectorum’s variable response to fire. We found that climate variables differed significantly between 18 sites where B. tectorum does and does not respond positively to fire. A positive response was most likely in areas with higher annual temperatures and lower summer precipitation. We then chose a climatically intermediate site, with intact sage-brush vegetation, to evaluate whether a positive feedback had formed between B. tectorum and fire. A chronosequence of recent fires (1–15 years) at the site created a natural replicated experiment to assess abundance of B. tectorum and native plants. B. tectorum cover did not differ between burned and unburned plots but native grass cover was higher in recently burned plots. Therefore, we found no evidence for a positive feedback between B. tectorum and fire at the study site. Our results suggest that formation of a positive B. tectorum-fire feedback depends on climate; however, other drivers such as disturbance and native plant cover are likely to further influence local responses of B. tectorum. The dependence of B. tectorum’s response to fire on climate suggests that climate change may expand B. tectorum’s role as a transformative invasive species within the sage-brush biome.Item Disturbance type influences resilience and resistance to Bromus tectorum invasion in the sagebrush steppe(2018-03) Seipel, Tim F.; Rew, Lisa J.; Taylor, Kimberley T.Question: How does type of disturbance alter plant community composition when an invasive species with high intrinsic population growth rate is present? The sage-brush steppe is a cold semi-arid steppe dominated by the native shrub Artemisia tri-dentata Nutt., native bunchgrasses, and has been invaded by the non- native winter annual Bromus tectorum L.Location: Sagebrush steppe, Montana, USA.Methods: We assessed the effect of fire and soil disturbance, due to bulldozing to create a firebreak, on the resilience of plant communities and their resistance to inva-sion by B. tectorum. Plant species richness and species composition were monitored for 3 years at two sites post-fire and firebreak construction.Results: Burned plant communities were resilient and had similar native grass cover and native species richness compared with the unburned sites after 3 years. Soil dis-turbance from firebreak construction resulted in species composition that was dis-tinct and had lower native grass cover. Type of disturbance also affected the community’s resistance to B. tectorum. Bromus tectorum cover was similar in burned and unburned areas, but increased up to three times and remained high where soil disturbance occurred, suggesting a shift to an alternative state.Conclusion: In this northern portion of the sagebrush steppe, communities with na-tive plant cover were resilient to fire but not soil disturbance, which facilitated B. tec-torum increase and a transition to an alternative state. In areas of high native plant cover, management tactics should avoid soil disturbance.Item Drivers of Bromus tectorum Abundance in the Western North American Sagebrush Steppe(2016-09) Brummer, Tyler J.; Taylor, Kimberley T.; Rotella, Jay J.; Maxwell, Bruce D.; Rew, Lisa J.; Lavin, MatthewBromus tectorum can transform ecosystems causing negative impacts on the ecological and economic values of sagebrush steppe of the western USA. Although our knowledge of the drivers of the regional distribution of B. tectorum has improved, we have yet to determine the relative importance of climate and local factors causing B. tectorum abundance and impact. To address this, we sampled 555 sites distributed geographically and ecologically throughout the sagebrush steppe. We recorded the canopy cover of B. tectorum, as well as local substrate and vegetation characteristics. Boosted regression tree modeling revealed that climate strongly limits the transformative ability of B. tectorum to a portion of the sagebrush steppe with dry summers (that is, July precipitation <10 mm and the driest annual quarter associated with a mean temperature >15 degrees C) and low native grass canopy cover. This portion includes the Bonneville, Columbia, Lahontan, and lower Snake River basins. These areas are likely to require extreme efforts to reverse B. tectorum transformation. Our predictions, using future climate conditions, suggest that the transformative ability of B. tectorum may not expand geographically and could remain within the same climatically suitable basins. We found B. tectorum in locally disturbed areas within or adjacent to all of our sample sites, but not necessarily within sagebrush steppe vegetation. Conversion of the sagebrush steppe by B. tectorum, therefore, is more likely to occur outside the confines of its current climatically optimal region because of site-specific disturbances, including invasive species control efforts and sagebrush steppe mismanagement, rather than climate change.Item Hitching a ride: Seed accrual rates on different types of vehicles(2017-12) Rew, Lisa J.; Brummer, Tyler J.; Pollnac, Fredric W.; Larson, Christian D.; Taylor, Kimberley T.; Taper, Mark L.; Fleming, Joseph D.; Balbach, Harold E.Human activities, from resource extraction to recreation, are increasing global connectivity, especially to less-disturbed and previously inaccessible places. Such activities necessitate road networks and vehicles. Vehicles can transport reproductive plant propagules long distances, thereby increasing the risk of invasive plant species transport and dispersal. Subsequent invasions by less desirable species have significant implications for the future of threatened species and habitats. The goal of this study was to understand vehicle seed accrual by different vehicle types and under different driving conditions, and to evaluate different mitigation strategies. Using studies and experiments at four sites in the western USA we addressed three questions: How many seeds and species accumulate and are transported on vehicles? Does this differ with vehicle type, driving surface, surface conditions, and season? What is our ability to mitigate seed dispersal risk by cleaning vehicles? Our results demonstrated that vehicles accrue plant propagules, and driving surface, surface conditions, and season affect the rate of accrual: on- and off-trail summer seed accrual on all-terrain vehicles was 13 and 3508 seeds km-1, respectively, and was higher in the fall than in the summer. Early season seed accrual on 4-wheel drive vehicles averaged 7 and 36 seeds km-1 on paved and unpaved roads respectively, under dry conditions. Furthermore, seed accrual on unpaved roads differed by vehicle type, with tracked vehicles accruing more than small and large 4-wheel drives; and small 4-wheel drives more than large. Rates were dramatically increased under wet surface conditions. Vehicles indiscriminately accrue a wide diversity of seeds (different life histories, forms and seed lengths); total richness, richness of annuals, biennials, forbs and shrubs, and seed length didn't differ among vehicle types, or additional seed bank samples. Our evaluation of portable vehicle wash units showed that approximately 80% of soil and seed was removed from dirty vehicles. This suggests that interception programs to reduce vehicular seed transportation risk are feasible and should be developed for areas of high conservation value, or where the spread of invasive species is of special concern.Item Native versus non-native invasions: similarities and differences in the biodiversity impacts of Pinus contorta in introduced and native ranges(2016-01) Taylor, Kimberley T.; Maxwell, Bruce D.; Pauchard, Anibal; Nunez, Martin A.; Rew, Lisa J.Aim To determine whether one of the most invasive pine species introduced to the Southern Hemisphere, Pinus contorta, has changed plant species richness, composition, diversity, and litter depth where it has invaded into native open forest, shrub steppe and grassland communities and to assess whether changes were similar in its native and introduced ranges. Location Río Negro Province, Argentina; Aysén and Araucanía Regions, Chile; Greater Yellowstone Ecosystem, USA. Methods We measured changes in plant species richness, species composition and cover, diversity, and litter depth associated with increasing P. contorta tree cover along the invasion front at three sites in the introduced range (Argentina and Chile) and one in the native range (Montana, USA). Results Plant species richness and cover generally declined with increasing P. contorta canopy cover, at similar rates in both the introduced and native ranges. However, plant cover was not affected by P. contorta in a forested setting in the introduced range. P. contorta invasion explained more of the decline in species richness in the introduced than native range. Native species composition changed more strongly across the invasion gradient in the introduced than native range. Litter depth increased more rapidly with P. contorta cover in the native than introduced range. Main conclusions Our results highlight the potential of pines to alter plant communities whether encroaching from forests in the native range or from plantations in the introduced range. Species richness and plant cover declined in both settings; however, individual species abundance and species composition were more impacted in the introduced range than in the native range. We suggest that invading trees have a greater capacity to cause ecological impacts in their introduced than in their native range, particularly where they represent a novel life-form.Item Pinus contorta invasions increase wildfire fuel loads and may create a positive feedback with fire(2017-03) Taylor, Kimberley T.; Maxwell, Bruce D.; McWethy, David B.; Pauchard, Anibal; Nunez, Martin A.; Whitlock, CathyInvasive plant species that have the potential to alter fire regimes have significant impacts on native ecosystems. Concern that pine invasions in the Southern Hemisphere will increase fire activity and severity and subsequently promote further pine invasion prompted us to examine the potential for feedbacks between Pinus contorta invasions and fire in Patagonia and New Zealand. We determined how fuel loads and fire effects were altered by P. contorta invasion. We also examined post-fire plant communities across invasion gradients at a subset of sites to assess how invasion alters the post-fire vegetation trajectory. We found that fuel loads and soil heating during simulated fire increase with increasing P. contorta invasion age or density at all sites. However, P. contorta density did not always increase post-fire. In the largest fire, P. contorta density only increased significantly post-fire where the pre-fire P. contorta density was above an invasion threshold. Below this threshold, P. contorta did not dominate after fire and plant communities responded to fire in a similar manner as uninvaded communities. The positive feedback observed at high densities is caused by the accumulation of fuel that in turn results in greater soil heating during fires and high P. contorta density post-fire. Therefore, a positive feedback may form between P. contorta invasions and fire, but only above an invasion density threshold. These results suggest that management of pine invasions before they reach the invasion density threshold is important for reducing fire risk and preventing a transition to an alternate ecosystem state dominated by pines and novel understory plant communities.Item Response to fire on the Upper Snake River plain [dataset](2011-06) Taylor, Kimberley T.; Brummer, Tyler J.; Rew, Lisa J.; Lavin, Matthew; Maxwell, Bruce D.This file contains environmental and vegetation data for 10 x 10 m plots along transects through a chronosequence of fires on the Upper Snake River Plain.