High severity fire may promote or reduce plant understory diversity in forests. However, few empirical studies have tested long-standing theoretical predictions that productivity may help to explain observed variation in post-fire plant diversity. Support for the influence of productivity on disturbance-diversity relationships is found predominantly in experimental grasslands, while tests over large areas with natural disturbance and productivity gradients are few and have yielded inconsistent results. Here, we measured the response of post-fire understory plant diversity to natural gradients of fire severity and productivity in a large-scale observational study in California’s subalpine forests. We found that plant species richness increased with increasing fire severity and that this trend was stronger at high productivity. We used plant traits to investigate whether release from competition might contribute to increasing diversity and found that short-lived and far-dispersing species benefited more from high severity fire than their long-lived and near-dispersing counterparts. For far-dispersing species only, the benefit from high severity fire was stronger in high productivity plots where unburned species richness was lowest. Our results support theoretical connections between fire severity, productivity and plant communities that are key to predicting the consequences of increasing fire severity and frequency on diversity in the coming decades.

中文翻译：

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生产力改变了火灾严重程度对林下多样性的影响

严重的火灾可能会促进或减少森林中植物林下的多样性。然而，很少有实证研究检验了长期存在的理论预测，即生产力可能有助于解释观察到的火灾后植物多样性的变化。支持生产力对干扰-多样性关系的影响主要是在实验草原中发现的，而在具有自然干扰和生产力梯度的大面积区域的测试很少，并且产生了不一致的结果。在这里，我们在加利福尼亚亚高山森林的一项大规模观察研究中测量了火灾后林下植物多样性对火灾严重程度和生产力的自然梯度的响应。我们发现植物物种丰富度随着火灾严重程度的增加而增加，并且这种趋势在高生产力下更为强烈。我们使用植物性状来研究从竞争中释放是否可能有助于增加多样性，并发现短命和远距离分布的物种比它们长寿命和近分散的物种更能从高强度火灾中受益。仅对于分布较远的物种，在未燃烧物种丰富度最低的高生产力地块中，高强度火灾带来的好处更大。我们的结果支持火灾严重程度、生产力和植物群落之间的理论联系，这些联系对于预测未来几十年火灾严重程度和频率增加对多样性的影响至关重要。