Hovick Torre J, Elmore R Dwayne, Fuhlendorf Samuel D, Engle David M, Hamilton Robert G
Ecol Appl. 2015 Apr;25(3):662-72. doi: 10.1890/14-1067.1.
Grasslands are inherently dynamic in space and time, evolving with frequent disturbance from fire and herbivores. As a consequence of human actions, many remaining grasslands have become homogenous, which has led to reduced ecosystem function, biodiversity loss, and decreased ecological services. Previous research has shown that restoring inherent heterogeneity to grasslands can increase avian diversity, but the amount of heterogeneity (i.e., number of patches or fire return interval) and the impact on avian community stability have yet to be investigated. We used a unique landscape-level design to examine avian response to interacting fire and grazing across multiple experimental landscapes that represented a gradient of fire- and grazing-dependent heterogeneity. We used seven landscapes (430-980 ha; x = 627 ha) with varying levels of patchiness ranging from annually burned (one single patch) with spring-only fires to a four-year fire return interval with spring and summer fires (eight patches). This design created a range of heterogeneity as a result of pyric herbivory, an ecological process in which fire and grazing are allowed to interact in space and time. We found that greater heterogeneity across experimental landscapes resulted in increased avian diversity and stability over time. An index of bird community change, quantified as the sum of the range of detrended correspondence analysis axis site scores, was nearly four times greater in the most homogenous experimental landscape when compared to the most heterogeneous experimental landscape. Species responses were consistently positively associated with increased heterogeneity at the landscape scale, and within-experimental-landscape responses were most often related to litter cover, litter accumulation, and vegetation height. We conclude that increased fire- and grazig-dependent heterogeneity can result in high variability in the bird community at finer, transect scales, but increased diversity and stability at broad landscape scales. We recommend that future management efforts in rangelands focus on restored disturbance processes to increase heterogeneity and improve grassland bird conservation.
草原在空间和时间上具有内在的动态性，随着火灾和食草动物频繁的干扰而演变。由于人类活动，许多留存下来的草原变得同质化，这导致生态系统功能下降、生物多样性丧失以及生态服务减少。先前的研究表明，恢复草原固有的异质性可以增加鸟类多样性，但异质性的程度（即斑块数量或火灾重现期）及其对鸟类群落稳定性的影响尚未得到研究。我们采用了一种独特的景观尺度设计，以研究鸟类对多个实验景观中火灾与放牧相互作用的反应，这些景观代表了依赖火灾和放牧的异质性梯度。我们使用了七个景观（430 - 980公顷；x = 627公顷），斑块程度各不相同，从每年仅春季发生一次火灾的单一斑块到春季和夏季火灾的四年火灾重现期（八个斑块）。这种设计由于火食草作用创造了一系列的异质性，火食草作用是一种生态过程，其中火灾和放牧在空间和时间上相互作用。我们发现，随着时间的推移，实验景观中更大的异质性导致鸟类多样性和稳定性增加。鸟类群落变化指数，量化为去趋势对应分析轴位点得分范围的总和，与最异质的实验景观相比，在最同质化的实验景观中几乎大四倍。物种反应在景观尺度上始终与异质性增加呈正相关，实验景观内的反应最常与凋落物覆盖、凋落物积累和植被高度有关。我们得出结论，依赖火灾和放牧的异质性增加会在更精细的样带尺度上导致鸟类群落的高变异性，但在广阔的景观尺度上会增加多样性和稳定性。我们建议，未来牧场管理工作应侧重于恢复干扰过程，以增加异质性并改善草原鸟类保护。
