Department of Environmental Science, Policy and Management, 137 Mulford Hall, MC#3114, University of California, Berkeley, California 94720, USA.
Ecology. 2011 Jan;92(1):121-32. doi: 10.1890/09-1843.1.
We provide an empirical, global test of the varying constraints hypothesis, which predicts systematic heterogeneity in the relative importance of biomass resources to burn and atmospheric conditions suitable to burning (weather/climate) across a spatial gradient of long-term resource availability. Analyses were based on relationships between monthly global wildfire activity, soil moisture, and mid-tropospheric circulation data from 2001 to 2007, synthesized across a gradient of long-term averages in resources (net primary productivity), annual temperature, and terrestrial biome. We demonstrate support for the varying constraints hypothesis, showing that, while key biophysical factors must coincide for wildfires to occur, the relative influence of resources to burn and moisture/weather conditions on fire activity shows predictable spatial patterns. In areas where resources are always available for burning during the fire season, such as subtropical/tropical biomes with mid-high annual long-term net primary productivity, fuel moisture conditions exert their strongest constraint on fire activity. In areas where resources are more limiting or variable, such as deserts, xeric shrublands, or grasslands/savannas, fuel moisture has a diminished constraint on wildfire, and metrics indicating availability of burnable fuels produced during the antecedent wet growing seasons reflect a more pronounced constraint on wildfire. This macro-scaled evidence for spatially varying constraints provides a synthesis with studies performed at local and regional scales, enhances our understanding of fire as a global process, and indicates how sensitivity to future changes in temperature and precipitation may differ across the world.
我们提供了一个经验性的、全球性的测试，以检验变化约束假说，该假说预测了在长期资源可用性的空间梯度上，生物质资源对燃烧的相对重要性和适合燃烧的大气条件（天气/气候）会出现系统的异质性。分析基于 2001 年至 2007 年期间每月全球野火活动、土壤湿度和中层大气环流数据之间的关系，这些数据是在资源（净初级生产力）、年平均温度和陆地生物群落的长期平均值梯度上综合得出的。我们证明了变化约束假说的支持，表明虽然发生野火必须同时存在关键的生物物理因素，但燃烧资源和湿度/天气条件对火灾活动的相对影响表现出可预测的空间模式。在资源在火灾季节始终可用的地区，例如具有中高年度长期净初级生产力的亚热带/热带生物群落，燃料湿度条件对火灾活动施加了最强的约束。在资源更有限或更易变的地区，例如沙漠、干旱灌丛或草原/热带稀树草原，燃料湿度对野火的约束减弱，指示前一个湿润生长季节产生的可燃燃料可用性的指标对野火的约束更为明显。这种空间变化约束的宏观尺度证据与在局部和区域尺度上进行的研究相结合，增强了我们对火灾作为一个全球过程的理解，并表明对未来温度和降水变化的敏感性可能会在全球范围内有所不同。
