Nonlinear rainfall effects on savanna fire activity across the African Humid Period
Nonlinear rainfall effects on savanna fire activity across the African Humid Period
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DOI：
10.1016/j.quascirev.2023.107994
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发表时间：
2023-03
影响因子：
4
通讯作者：
A. Karp;K. Uno;M. Berke;J. Russell;C. Scholz;J. Marlon;J. Faith;A. Staver
中科院分区：
文献类型：
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作者：
A. Karp;K. Uno;M. Berke;J. Russell;C. Scholz;J. Marlon;J. Faith;A. Staver
火灾是热带和亚热带热带稀树草原的关键生态系统过程，其作用取决于水文气候，也取决于火灾与植被之间的反馈。在热带稀树草原，火灾对降雨量变化的响应取决于年平均降雨量：在干旱和半干旱系统中，燃烧面积随着降雨量的增加而增加，而在燃料含水量高的mesic系统中，燃烧面积随着降雨量的增加而减少。燃烧面积与降雨量之间的非线性关系可能部分是由于火灾活动的限制因素发生了变化，随着降雨量的增加和季节性的减少，稀树草原上燃烧的限制因素从燃料量转变为燃料湿度。植被-火灾反馈还可以促进从易发火灾的热带草原植被向随着降雨量增加而抑制火灾的森林分类群的转变。然而，根据定义，现代观测仅限于短期动态，降水变化对火灾活动的长期影响尚未得到评估。这些长期影响对于评估生物群系随着水文气候和火灾活动的变化而变化的过渡尤为重要。晚更新世和全新世早期的非洲湿润期（AHP；约14.5-5.5 ka），当降雨量在非洲北部和赤道地区大幅增加时，提供了一个机会来研究具有不同年平均降雨量的地点对降水增加的长期火灾响应。在这里，我们将两个东非湖泊盆地（维多利亚湖和图尔卡纳湖）的新多环烃（PAHs）古火活动记录与先前发表的五个地点（GeoB7920-2、GeoB9508-5、Chala湖、Tanganyika湖和Bosumtwe湖）的火记录（即木炭、左旋葡聚糖）结合起来，研究了沿降雨量梯度（从<200 mm到1500 mm）的火活动响应。我们的综合揭示了与现代生态系统动力学一致的火灾动态，并表明每个站点的火灾活动遵循整个AHP的预测模式，这取决于初始平均降雨量，干旱至半干旱站点的火灾活动增加，而湿润至湿润站点的火灾活动减少。结果表明，火灾对水文气候的响应是非线性的，同一方向的降水变化会引起不同的火灾响应，这取决于一个站点的总降水量。考虑到水文气候的异质性，甚至在生物群落内部，可能会改善对火灾活动如何响应未来降雨制度变化的预测。
Fire is a key ecosystem process in tropical and subtropical savannas, with a varying role that depends on hydroclimate but also on feedbacks between fire and vegetation. In savannas, fire response to changes in rainfall depends on mean annual rainfall: in arid and semi-arid systems, burned area increases as rainfall increases fuel amount, whereas in mesic systems with high fuel moisture, burned area decreases as rainfall increases. The non-linear relationship between burned area and rainfall may be due in part to changes in the constraints on fire activity that shift the limiting factor for burning in savannas from fuel amount to fuel moisture with increasing rainfall and decreasing seasonality. Vegetation-fire feedbacks can also promote a shift from fire-prone savanna vegetation to forest taxa that suppress fire as rainfall increases. However, modern observations are, by definition, constrained to short-term dynamics, and the longer-term effects of precipitation changes on fire activity have not been evaluated. These longer-term impacts are especially relevant for evaluating biome transitions changing in response to variable hydroclimate and fire activity. The Late Pleistocene and early Holocene African Humid Period (AHP; ∼14.5–5.5 ka), when rainfall increased substantially across northern and equatorial Africa, provides an opportunity to examine long-term fire responses to increased precipitation at sites with different mean annual rainfall amounts. Here, we combine new polycyclic aromatic hydrocarbons (PAHs) records of paleofire activity at two East African lake basins (Lakes Victoria and Turkana) with previously published fire records (i.e., charcoal, levoglucosan) at five sites (GeoB7920-2, GeoB9508-5, Lakes Chala, Tanganyika and Bosumtwe) to examine responses of fire activity along a rainfall gradient (from <200 mm to 1500 mm). Our synthesis reveals fire dynamics that are consistent with modern ecosystem dynamics and shows that fire activity at each site followed predicted patterns across the AHP depending on initial mean rainfall, with increased fire activity at arid to semi-arid sites and decreased fire activity at mesic-to-humid sites. Results illustrate that fire responses to hydroclimate are nonlinear, such that the same direction of change in precipitation can elicit different fire responses depending on the total precipitation at a site. Accounting for heterogeneity in hydroclimate, even within biomes, may improve predictions of how fire activity will respond to future changes in rainfall regimes.