Understanding fire and large herbivore interactions in interior western forests is critical, owing to the extensive and widespread co‐occurrence of these two disturbance types and multiple present and future implications for forest resilience, conservation and restoration. However, manipulative studies focused on interactions and outcomes associated with these two disturbances are rare in forested rangelands. We investigated understory vegetation response to 5‐year spring and fall prescribed fire and domestic cattle grazing exclusion in ponderosa pine stands and reported long‐term responses, almost two decades after the first entry fires. In fall burn areas open to cattle grazing, total understory cover prior to utilization was about 12% lower compared with fall burn areas where cattle were experimentally excluded. This response was not strongly driven by a particular palatable or unpalatable plant functional group. Fire and grazing are likely interacting in a numerically mediated process, as we found little evidence to support a functionally moderated pathway. Post‐fire green‐up may equalize forage to a certain extent and concentrate herbivores in the smaller burned areas within pastures, constraining a positive understory response to burning. Fall fire and grazing also increased annual forbs and resprouting shrubs. The effects of spring burning were relatively minor, and we found no interaction with grazing. The nonnative annual grass Bromus tectorum (cheatgrass) remains a problematic invader linked to fall burning but not grazing in stands that had higher propagule pressure when the experiment was initiated. At these sites, exotic grass was a major component of the vegetation by 2015, and invasion was also increasing in spring burn and unburned areas. Information from our study suggests that frequent fall fires and cattle grazing combined may reduce understory resilience in similar dry ponderosa pine forests. Consideration of longer fire return intervals, resting areas after fire, virtual fencing, or burning entire pastures may help to mitigate the effects noted in this study.

中文翻译：

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长期频繁的火灾和放牧改变了干燥的森林林下植被


了解西部内陆森林火灾和大型食草动物的相互作用至关重要，因为这两种干扰类型广泛且广泛地同时发生，并对森林恢复力、保护和恢复的当前和未来产生多重影响。然而，在森林牧场中，关注与这两种干扰相关的相互作用和结果的操纵性研究很少。我们调查了黄松林下林下植被对五年春季和秋季规定的火灾和家牛放牧排除的反应，并报告了在第一次进入火灾后近二十年的长期反应。在可供牛放牧的秋季烧伤地区，利用之前的林下总覆盖率比实验上排除牛的秋季烧伤地区低约 12%。这种反应并不是由特定的可口或不可口的植物功能组强烈驱动的。火灾和放牧很可能在数字调节过程中相互作用，因为我们几乎没有发现证据支持功能调节途径。火后绿化可以在一定程度上均衡草料，并将食草动物集中在牧场内较小的烧毁区域，限制林下对燃烧的积极反应。秋季火灾和放牧也增加了一年生杂草和重新发芽的灌木。春季燃烧的影响相对较小，我们发现与放牧没有相互作用。外来一年生草本植物雀麦（cheatgrass）仍然是一种有问题的入侵者，与秋季燃烧有关，但在实验开始时繁殖体压力较高的林中不吃草。 到 2015 年，外来草已成为这些地点植被的主要组成部分，春季烧毁和未烧毁地区的入侵也在增加。我们的研究信息表明，频繁的秋季火灾和牛群放牧可能会降低类似干燥黄松林的林下恢复能力。考虑更长的火灾返回间隔、火灾后的休息区、虚拟围栏或燃烧整个牧场可能有助于减轻本研究中指出的影响。