Abstract：
Understanding the resilience of ecosystems globally is hampered by the complex and interacting drivers of change characteristic of the Anthropocene. This is true for drylands of the western US, where widespread alteration of disturbance regimes and spread of invasive non-native species occurred with westward expansion during the 1800s, including the introduction of domestic livestock and spread of Bromus tectorum, an invasive non-native annual grass. In addition, this region has experienced a multi-decadal drought not seen for at least 1200 years with potentially large and interacting impacts on native plant communities. Here, we present 24 years of twice-annual plant cover monitoring (1997-2021) from a semiarid grassland never grazed by domestic livestock but subject to a patchy invasion of B. tectorum beginning in ~1994, compare our findings to surveys done in 1967, and examine potential climate drivers of plant community changes. We found a significant warming trend in the study area, with more than 75% of study year temperatures being warmer than average (1966-2021). We observed a native perennial grass community with high resilience to climate forcings with cover values like those in 1967. In invaded patches, B. tectorum cover was greatest in the early years of this study (1997-2001; ~20%-40%) but was subsequently constrained by climate and subtle variation in soils, with limited evidence of long-term impacts to native vegetation, contradicting earlier studies. Our ability to predict year-to-year variation in functional group and species cover with climate metrics varied, with a 12-month integrated index and fall and winter patterns appearing most important. However, declines to near zero live cover in recent years in response to regional drought intensification leave questions regarding the resiliency of intact grasslands to ongoing aridification and whether the vegetation observations reported here may be a leading indicator of impending change in this protected ecosystem.
摘要：
人类世变化特征的复杂和相互作用的驱动因素阻碍了对全球生态系统复原力的理解。美国西部的旱地也是如此,在1800年代，随着向西扩张，扰动制度和外来入侵物种的广泛改变发生了，包括引入家畜和传播Bromustectorum，一种侵入性非本地的一年生草。此外,该地区经历了至少1200年未见的年代际干旱，对本地植物群落产生了潜在的巨大和相互作用的影响。这里,我们提供了24年的两次植物覆盖监测（1997-2021年），该监测来自从未被家畜放牧但从1994年开始遭受B.tectorum零星入侵的半干旱草地，将我们的发现与1967年的调查进行比较，并研究了植物群落变化的潜在气候驱动因素。我们在研究区域发现了明显的变暖趋势，超过75%的研究年温度高于平均水平(1966-2021年)。我们观察到一个本地的多年生草群落，对气候强迫具有很高的适应能力，其覆盖值与1967年相似。在入侵的补丁中，在这项研究的早期（1997-2001年；〜20％-40％），但随后受到气候和土壤细微变化的限制。对原生植被的长期影响的证据有限，与早期的研究相矛盾。我们预测功能群和物种覆盖率的逐年变化的能力，气候指标各不相同，12个月的综合指数和秋冬模式显得最为重要。然而,近年来，由于区域干旱加剧，活盖下降到接近零，这让人们质疑完整草原对持续干旱化的弹性，以及此处报告的植被观测是否可能是这种受保护生态系统即将发生变化的主要指标。
