North American grasslands have experienced increased relative abundance of shrubs and trees over the last 150 years. Alterations in herbivore composition, abundance and grazing pressure along with changes in fire frequency are drivers that can regulate the transition from grassland to shrubland or woodland (a process known as woody encroachment). Historically, North American grasslands had a suite of large herbivores that grazed and/or browsed (i.e. bison, elk, pronghorn, deer), as well as frequent and intense fires. In the tallgrass prairie, many large native ungulates were extirpated by the 1860's corresponding with increased homesteading (which led to decreased fire frequencies and intensities). Changes in the frequency and intensity of these two drivers (browsing and fire) has coincided with woody encroachment in tallgrass prairie. Within tallgrass prairie, woody encroachment can be categorized in to two groups: non-resprouting species that can be killed with fire, and resprouting species that cannot be killed with fire. Resprouting species require additional active management strategies to decrease abundance and eventually be removed from the ecosystem. In this study we investigated plant cover, ramet density and physiological effects of continuous simulated browsing and prescribed fire on Cornus drummondii C.A. Mey, a resprouting clonal native shrub species. Browsing reduced C. drummondii canopy cover and increased grass cover. We also observed decreased ramet density that allowed for more infilling of grasses. Photosynthetic rates between browsed and unbrowsed control shrubs did not increase in 2015 or 2016. In 2017, photosynthetic rates for browsed shrubs were higher in the unburned site than the unbrowsed control shrubs at the end of the growing season. Additionally, after the prescribed fire, browsed shrubs had ~ 90% decreased cover, ~50% reduced ramet density, and grass cover increased by ~ 80%. In the roots of browsed shrubs after the prescribed fire, non-structural carbohydrates (NSC) experienced a 2-fold reduction in glucose and a 3-fold reduction in both sucrose and starch. The combined effects of browsing and fire show strong potential as a successful management tool to decrease the abundance of clonal-resprouting woody plants in mesic grasslands and illustrate the potential significance of browsers as a key driver in this ecosystem.

中文翻译：

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浏览和火灾降低了木质侵占草原中重新发芽灌木的优势

在过去的 150 年中，北美草原的灌木和树木的相对丰度有所增加。草食动物组成、丰度和放牧压力的变化以及火灾频率的变化是可以调节从草地向灌木地或林地过渡的驱动因素（这一过程称为木本侵占）。从历史上看，北美草原有一套大型食草动物，它们放牧和/或浏览（即野牛、麋鹿、叉角羚、鹿），以及频繁和强烈的火灾。在高草草原，许多大型本地有蹄类动物在 1860 年代灭绝，这与增加的宅基地（导致火灾频率和强度降低）相对应。这两个驱动因素（浏览和火灾）的频率和强度的变化与高草草原的木质侵占同时发生。在高草草原内，木本侵占可分为两类：可被火杀死的非重芽物种和不能被火杀死的重芽物种。重新发芽的物种需要额外的积极管理策略来减少丰度并最终从生态系统中移除。在这项研究中，我们调查了植物覆盖、分株密度和连续模拟浏览和指定火对山茱萸（一种重新发芽的克隆本地灌木物种）的生理影响。浏览减少了 C.drummondii 冠层覆盖并增加了草覆盖。我们还观察到分株密度降低，这使得更多的草填充。2015 年或 2016 年，已浏览和未浏览的对照灌木之间的光合速率没有增加。 2017 年，在生长季节结束时，未烧过的灌木的光合速率高于未烧过的对照灌木。此外，在规定的火灾之后，灌木丛的覆盖率降低了约 90%，分株密度降低了约 50%，草覆盖率增加了约 80%。在规定的火后，在经过处理的灌木的根部，非结构性碳水化合物 (NSC) 的葡萄糖减少了 2 倍，蔗糖和淀粉减少了 3 倍。浏览和火灾的综合影响显示出作为一种成功的管理工具的强大潜力，可以减少中性草原中克隆再生木本植物的丰度，并说明浏览器作为该生态系统中关键驱动因素的潜在意义。在规定的火灾后，灌木丛的覆盖率降低了约 90%，分株密度降低了约 50%，草覆盖率增加了约 80%。在规定的火后，在经过处理的灌木的根部，非结构性碳水化合物 (NSC) 的葡萄糖减少了 2 倍，蔗糖和淀粉减少了 3 倍。浏览和火灾的综合影响显示出作为一种成功的管理工具的强大潜力，可以减少中性草原中克隆再生木本植物的丰度，并说明浏览器作为该生态系统中关键驱动因素的潜在意义。在规定的火灾后，灌木丛的覆盖率降低了约 90%，分株密度降低了约 50%，草覆盖率增加了约 80%。在规定的火后，在经过处理的灌木的根部，非结构性碳水化合物 (NSC) 的葡萄糖减少了 2 倍，蔗糖和淀粉减少了 3 倍。浏览和火灾的综合影响显示出作为一种成功的管理工具的强大潜力，可以减少中性草原中克隆再生木本植物的丰度，并说明浏览器作为该生态系统中关键驱动因素的潜在意义。非结构性碳水化合物 (NSC) 的葡萄糖减少了 2 倍，蔗糖和淀粉减少了 3 倍。浏览和火灾的综合影响显示出作为一种成功的管理工具的强大潜力，可以减少中性草原中克隆再生木本植物的丰度，并说明浏览器作为该生态系统中关键驱动因素的潜在意义。非结构性碳水化合物 (NSC) 的葡萄糖减少了 2 倍，蔗糖和淀粉减少了 3 倍。浏览和火灾的综合影响显示出作为一种成功的管理工具的强大潜力，可以减少中性草原中克隆再生木本植物的丰度，并说明浏览器作为该生态系统中关键驱动因素的潜在意义。