Barton Andrew M, Poulos Helen
Department of Biology University of Maine at Farmington Farmington ME USA.
College of the Environment Wesleyan University Middletown CT USA.
Ecol Evol. 2021 Oct 5;11(21):14715-14732. doi: 10.1002/ece3.8158. eCollection 2021 Nov.
Drastic changes in fire regimes are altering plant communities, inspiring ecologists to better understand the relationship between fire and plant species diversity. We examined the impact of a 90,000-ha wildfire on woody plant species diversity in an arid mountain range in southern Arizona, USA. We tested recent fire-diversity hypotheses by addressing the impacts on diversity of fire severity, fire variability, historical fire regimes, and topography.
Chiricahua National Monument, Chiricahua Mountains, Arizona, USA, part of the Sky Islands of the US-Mexico borderlands.
Woody plant species.
We sampled woody plant diversity in 138 plots before (2002-2003) and after (2017-2018) the 2011 Horseshoe Two Fire in three vegetation types and across fire severity and topographic gradients. We calculated gamma, alpha, and beta diversity and examined changes over time in burned versus unburned plots and the shapes of the relationships of diversity with fire severity and topography.
Alpha species richness declined, and beta and gamma diversity increased in burned but not unburned plots. Fire-induced enhancement of gamma diversity was confined to low fire severity plots. Alpha diversity did not exhibit a clear continuous relationship with fire severity. Beta diversity was enhanced by variation in fire severity among plots and increased with fire severity up to very high severity, where it declined slightly.
The results reject the intermediate disturbance hypothesis for alpha diversity but weakly support it for gamma diversity. Spatial variation in fire severity promoted variation among plant assemblages, supporting the pyrodiversity hypothesis. Long-term drought probably amplified fire-driven diversity changes. Despite the apparent benign impact of the fire on diversity, the replacement of two large conifer species with a suite of drought-tolerant shrubs signals the potential loss of functional diversity, a pattern that may warrant restoration efforts to retain these important compositional elements.
火灾模式的剧烈变化正在改变植物群落，促使生态学家更好地理解火灾与植物物种多样性之间的关系。我们研究了一场9万公顷的野火对美国亚利桑那州南部干旱山区木本植物物种多样性的影响。我们通过探讨火灾严重程度、火灾变异性、历史火灾模式和地形对多样性的影响，来检验近期的火灾-多样性假说。
美国亚利桑那州奇里卡瓦山脉的奇里卡瓦国家纪念区，是美墨边境地区天空岛的一部分。
木本植物物种。
我们在2011年马蹄二号火灾之前（2002 - 2003年）和之后（2017 - 2018年），在三种植被类型中，跨越火灾严重程度和地形梯度，对138个样地的木本植物多样性进行了采样。我们计算了伽马多样性、阿尔法多样性和贝塔多样性，并研究了火烧样地与未火烧样地随时间的变化，以及多样性与火灾严重程度和地形关系的形状。
在火烧样地中，阿尔法物种丰富度下降，贝塔和伽马多样性增加，而在未火烧样地中则没有变化。火灾引起的伽马多样性增加仅限于低火灾严重程度的样地。阿尔法多样性与火灾严重程度没有呈现出明显的连续关系。贝塔多样性因样地间火灾严重程度的差异而增加，并随着火灾严重程度的增加而上升，直至非常高的严重程度时略有下降。
结果否定了阿尔法多样性的中度干扰假说，但对伽马多样性提供了微弱支持。火灾严重程度的空间变化促进了植物群落间的差异，支持了火多样性假说。长期干旱可能加剧了火灾驱动的多样性变化。尽管火灾对多样性的影响看似有益，但两种大型针叶树种被一系列耐旱灌木所取代，这表明功能多样性可能丧失，这种模式可能需要进行恢复努力以保留这些重要的组成元素。
