Non-native plant invasions are often catalyzed by wildfires and may alter the structure, function, and composition of ecosystems. Of particular concern are non-native annual grasses that promote increased fire frequency and compete with native vegetation for early season moisture. While these effects are well studied in non-forested ecosystems, relatively few studies document invasions of non-native annual grasses in forested ecosystems. We document non-native plant invasion following repeated high-severity wildfire in mixed-conifer/hardwood forests dominated by Douglas-fir (Pseudotsuga menziesii) in the Klamath Mountains of northern California. Despite great concern regarding the loss of conifer dominance and transitions to non-forested states related to recent and projected increases in wildfire activity, there is little known about invasions of non-native plant species following fire in this region. Non-native plant species capable of long-distance dispersal had an average total cover of 26% and were ubiquitous across a systematic, gridded sample of twenty 800 m² plots. Non-native forbs included multiple species of common post-disturbance invaders (e.g. Cirsium vulgare, Senecio sylvaticus, Lactuca serriola). Non-native annual grasses comprised more of the vegetative cover than non-native forbs (17% vs. 9%), and were dominated by two species, Aira caryophyllea and Vulpia myuros, which reached as high as 80% cover. Our findings indicate that non-native annual grasses are a novel stressor that may accelerate projected loss of conifer dominance in the Klamath Mountains by facilitating fire spread and increasing competition for early season soil moisture. Additional monitoring will be crucial to understanding the impacts of non-native plants as fire activity in this region continues to increase.

非本地植物的入侵通常是由野火引起的，并可能改变生态系统的结构，功能和组成。尤其值得关注的是非本地一年生禾草，它们会提高火频并与本地植被争夺早期水分。虽然在非森林生态系统中对这些影响进行了很好的研究，但相对较少的研究记录了森林生态系统中非本地一年生草的入侵。我们记录了在由道格拉斯冷杉（Pseudotsuga menziesii）主导的针叶树/硬木混交林中反复发生高强度野火后的非本地植物入侵）位于北加州的克拉马斯山脉。尽管人们对针叶树种优势的丧失以及与最近和预计的野火活动增加有关的向非森林状态的过渡感到担忧，但对该地区火灾后非本土植物物种的入侵知之甚少。能够进行长距离扩散的非本地植物物种的平均总覆盖率为26％，并且在20个800 m ²地块的系统化网格样本中普遍存在。非本地的前堡包括多种常见的扰乱后入侵者（例如，大花Ci（Cirsium v​​ulgare），千里光（Senecio sylvaticus），山毛榉（Lactuca serriola）。非原生一年生草的营养覆盖率高于非原生一年生草（17％比9％），并且以两个物种Aira caryophyllea为主。和Vulpia myuros，覆盖率高达80％。我们的发现表明，非原生一年生草是一种新型胁迫物，可通过促进火势蔓延和增加对早期土壤水分的竞争来加速克拉马斯山区针叶树优势的预计损失。随着该地区火灾活动的继续增加，额外的监控对于了解非本地植物的影响至关重要。