Season of prescribed fire determines grassland restoration outcomes after fire exclusion and overgrazing
Season of prescribed fire determines grassland restoration outcomes after fire exclusion and overgrazing
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规定的火灾季节决定了防火和过度放牧后的草原恢复结果
DOI：
10.1002/ecs2.3730
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发表时间：
2021
期刊：
影响因子：
2.7
通讯作者：
Veldman, Joseph W.
中科院分区：
文献类型：
--
作者：
Novak, Erin N.;Bertelsen, Michelle;Davis, Dick;Grobert, Devin M.;Lyons, Kelly G.;Martina, Jason P.;McCaw, W. Matt;O'Toole, Matthew;Veldman, Joseph W.
防火和管理不善的放牧是全球范围内中等 C4 草原和稀树草原环境变化的重要驱动因素。尽管人们对用规定的火来恢复草原越来越感兴趣，但我们几乎没有长期实验证据来证明燃烧季节对草本植物群落的恢复、树木和灌木的侵占以及外来草类的入侵的影响。我们在德克萨斯州中部历来禁止火灾且过度放牧的草原上进行了规定的火灾实验（2001 年至 2019 年间发生了 7 次烧伤）。地点被分配到四种实验处理之一：夏季烧伤（温暖季节、闪电季节）、秋季烧伤（凉爽季节早期）、冬季烧伤（凉爽季节晚期）或未燃烧（火排除）。为了评估实验的恢复结果，我们在 2019 年确定了古老的草地作为参考点。所有实验地点的草本层植物群落在组成和功能上都与古老的草地不同，多年生C4草和长寿杂草几乎没有恢复。未燃烧地点的特点是有多种乔木、灌木和藤本植物；夏季地点以某些 C3 草和杂草为特征；秋季和冬季场地的组成介于未燃烧和夏季场地的中间。尽管成分存在差异，但所有处理都具有可比的地块水平植物物种丰富度（范围 89-95 种/1000 m2）。在局部范围内，夏季场地（23 种/平方米）和古老草地（20 种/平方米）比未燃烧场地（15 种/平方米）拥有更高的丰富度，但与秋季或冬季场地没有显着差异。在火处理中，夏季和冬季烧伤最一致地产生了古老草原的植被结构（例如，平均木本冠层覆盖率为 9%）。但是，冬季烧伤通过维持树冠覆盖度较低的区域促进了白羊草的入侵，而夏季烧伤同时限制了木质植物的侵占并控制了B. 缺血侵袭。我们的研究结果支持越来越多的文献表明，仅规定火而不引入植物繁殖体不一定能恢复古老的草原群落组成。尽管如此，这项长期实验表明，在夏季实施的规定烧伤可以通过防止木质侵占同时控制入侵草类来有益于恢复。我们建议在草原恢复规划和生态研究中应更多关注火灾季节。
Fire exclusion and mismanaged grazing are globally important drivers of environmental change in mesic C4grasslands and savannas. Although interest is growing in prescribed fire for grassland restoration, we have little long‐term experimental evidence of the influence of burn season on the recovery of herbaceous plant communities, encroachment by trees and shrubs, and invasion by exotic grasses. We conducted a prescribed fire experiment (seven burns between 2001 and 2019) in historically fire‐excluded and overgrazed grasslands of central Texas. Sites were assigned to one of four experimental treatments: summer burns (warm season, lightning season), fall burns (early cool season), winter burns (late cool season), or unburned (fire exclusion). To assess restoration outcomes of the experiment, in 2019, we identified old‐growth grasslands to serve as reference sites. Herbaceous‐layer plant communities in all experimental sites were compositionally and functionally distinct from old‐growth grasslands, with little recovery of perennial C4grasses and long‐lived forbs. Unburned sites were characterized by several species of tree, shrub, and vine; summer sites were characterized by certain C3grasses and forbs; and fall and winter sites were intermediate in composition to the unburned and summer sites. Despite compositional differences, all treatments had comparable plot‐level plant species richness (range 89–95 species/1000 m2). At the local‐scale, summer sites (23 species/m2) and old‐growth grasslands (20 species/m2) supported greater richness than unburned sites (15 species/m2), but did not differ significantly from fall or winter sites. Among fire treatments, summer and winter burns most consistently produced the vegetation structure of old‐growth grasslands (e.g., mean woody canopy cover of 9%). But whereas winter burns promoted the invasive grassBothriochloa ischaemumby maintaining areas with low canopy cover, summer burns simultaneously limited woody encroachment and controlledB. ischaemuminvasion. Our results support a growing body of literature that shows that prescribed fire alone, without the introduction of plant propagules, cannot necessarily restore old‐growth grassland community composition. Nonetheless, this long‐term experiment demonstrates that prescribed burns implemented in the summer can benefit restoration by preventing woody encroachment while also controlling an invasive grass. We suggest that fire season deserves greater attention in grassland restoration planning and ecological research.