Abstract：
Dryland ecosystems in the western United States are affected by invasive species, wildfires, livestock grazing, and climate change in ways that are difficult to distinguish. Biocrusts perform important ecological roles in these systems and are sensitive to all of these pressures.
We revisited a Washington, USA, site sampled for biocrusts in 1999 to focus on effects of exotic annual grass invasion and wildfires in the absence of livestock grazing. We examined changes between 1999 and 2020 using a Bayesian directed acyclic graph (DAG) to interpret direct and indirect causal impacts of wildfire on perennial bunchgrasses, exotic annual grasses, and biocrusts.
Between 1999 and 2020, exotic annual grass cover increased in all plots and in unburned plots by 16% and 18%, respectively, bunchgrass cover decreased by 21% and 25%, and biocrust cover decreased by 8.9% and 9.8%. Our DAG suggested that decreases in bunchgrass increased exotic annual grass, which reduced biocrust cover. Wildfires did not directly influence changes in bunchgrass, exotic annual grass, or biocrust cover. Areas dominated by exotic annual grass had less abundant and diverse biocrusts than areas with less exotic annual grass.
Biocrust community changes were more strongly related to increasing exotic annual grasses than to wildfires. Changes may relate to other soil disturbances or broad-scale changes in climate or air quality. The minimal influence of wildfire on exotic annual grass and biocrusts suggests that apparent negative impacts of wildfire at other sites may be due to exacerbation by livestock grazing or other surface disturbance.
We revisited a Washington, USA, site sampled for biocrusts in 1999 to focus on effects of exotic annual grass invasion and wildfires in the absence of livestock grazing. We examined changes between 1999 and 2020 using a Bayesian directed acyclic graph (DAG) to interpret direct and indirect causal impacts of wildfire on perennial bunchgrasses, exotic annual grasses, and biocrusts.
Between 1999 and 2020, exotic annual grass cover increased in all plots and in unburned plots by 16% and 18%, respectively, bunchgrass cover decreased by 21% and 25%, and biocrust cover decreased by 8.9% and 9.8%. Our DAG suggested that decreases in bunchgrass increased exotic annual grass, which reduced biocrust cover. Wildfires did not directly influence changes in bunchgrass, exotic annual grass, or biocrust cover. Areas dominated by exotic annual grass had less abundant and diverse biocrusts than areas with less exotic annual grass.
Biocrust community changes were more strongly related to increasing exotic annual grasses than to wildfires. Changes may relate to other soil disturbances or broad-scale changes in climate or air quality. The minimal influence of wildfire on exotic annual grass and biocrusts suggests that apparent negative impacts of wildfire at other sites may be due to exacerbation by livestock grazing or other surface disturbance.
摘要：
目标：美国西部的旱地生态系统受到入侵物种的影响，野火,放牧的牲畜,和气候变化难以区分。生物锈菌在这些系统中发挥着重要的生态作用，并且对所有这些压力都很敏感。
方法：我们重访了华盛顿，1999年，美国对生物锈病进行了采样，重点是在没有放牧的情况下，外来的年度草入侵和野火的影响。我们使用贝叶斯有向无环图（DAG）检查了1999年至2020年之间的变化，以解释野火对多年生野草的直接和间接因果影响。异国情调的一年生草，和生物锈病。
结果：在1999年至2020年之间，所有和未燃烧地块的外来年度草覆盖率分别增加了16％和18％，束草覆盖率下降了21%和25%，生物覆盖率下降8.9%和9.8%。我们的DAG建议，束草的减少增加了异国情调的一年生草，这减少了生物信任的掩护。野火并没有直接影响束草的变化，异国情调的一年生草，或者双性恋封面。与外来一年生草含量较低的地区相比，以外来一年生草为主的地区的生物锈病较少。
结论：Biocrust群落的变化与外来一年生草的增加有关，而与野火有关。变化可能与其他土壤干扰或气候或空气质量的广泛变化有关。野火对外来一年生草和生物锈病的影响最小，这表明野火在其他地点的明显负面影响可能是由于牲畜放牧或其他地表干扰加剧所致。本文受版权保护。保留所有权利。
方法：我们重访了华盛顿，1999年，美国对生物锈病进行了采样，重点是在没有放牧的情况下，外来的年度草入侵和野火的影响。我们使用贝叶斯有向无环图（DAG）检查了1999年至2020年之间的变化，以解释野火对多年生野草的直接和间接因果影响。异国情调的一年生草，和生物锈病。
结果：在1999年至2020年之间，所有和未燃烧地块的外来年度草覆盖率分别增加了16％和18％，束草覆盖率下降了21%和25%，生物覆盖率下降8.9%和9.8%。我们的DAG建议，束草的减少增加了异国情调的一年生草，这减少了生物信任的掩护。野火并没有直接影响束草的变化，异国情调的一年生草，或者双性恋封面。与外来一年生草含量较低的地区相比，以外来一年生草为主的地区的生物锈病较少。
结论：Biocrust群落的变化与外来一年生草的增加有关，而与野火有关。变化可能与其他土壤干扰或气候或空气质量的广泛变化有关。野火对外来一年生草和生物锈病的影响最小，这表明野火在其他地点的明显负面影响可能是由于牲畜放牧或其他地表干扰加剧所致。本文受版权保护。保留所有权利。
