Institute of Plant Sciences and Oeschger Centre for Climate Change Research, University of Bern, Altenbergrain 21, Bern, CH-3013, Switzerland.
Glob Chang Biol. 2014 Sep;20(9):2903-14. doi: 10.1111/gcb.12583. Epub 2014 Apr 26.
Rainfall controls fire in tropical savanna ecosystems through impacting both the amount and flammability of plant biomass, and consequently, predicted changes in tropical precipitation over the next century are likely to have contrasting effects on the fire regimes of wet and dry savannas. We reconstructed the long-term dynamics of biomass burning in equatorial East Africa, using fossil charcoal particles from two well-dated lake-sediment records in western Uganda and central Kenya. We compared these high-resolution (5 years/sample) time series of biomass burning, spanning the last 3800 and 1200 years, with independent data on past hydroclimatic variability and vegetation dynamics. In western Uganda, a rapid (<100 years) and permanent increase in burning occurred around 2170 years ago, when climatic drying replaced semideciduous forest by wooded grassland. At the century time scale, biomass burning was inversely related to moisture balance for much of the next two millennia until ca. 1750 ad, when burning increased strongly despite regional climate becoming wetter. A sustained decrease in burning since the mid20th century reflects the intensified modern-day landscape conversion into cropland and plantations. In contrast, in semiarid central Kenya, biomass burning peaked at intermediate moisture-balance levels, whereas it was lower both during the wettest and driest multidecadal periods of the last 1200 years. Here, burning steadily increased since the mid20th century, presumably due to more frequent deliberate ignitions for bush clearing and cattle ranching. Both the observed historical trends and regional contrasts in biomass burning are consistent with spatial variability in fire regimes across the African savanna biome today. They demonstrate the strong dependence of East African fire regimes on both climatic moisture balance and vegetation, and the extent to which this dependence is now being overridden by anthropogenic activity.
降雨通过影响植物生物量的数量和可燃性来控制热带稀树草原生态系统中的火灾，因此，预计在下一个世纪，热带降水的变化很可能对湿润和干燥稀树草原的火灾发生情况产生相反的影响。我们使用来自乌干达西部和肯尼亚中部两个经过良好定年的湖泊沉积物记录中的化石木炭颗粒，重建了东非赤道地区长期的生物量燃烧动态。我们将这些跨越过去 3800 年和 1200 年的高分辨率（5 年/样本）生物质燃烧时间序列与过去水气候变异性和植被动态的独立数据进行了比较。在乌干达西部，大约 2170 年前，气候干燥取代了半落叶林，形成了林地草原，导致燃烧迅速（<100 年）和永久性增加。在接下来的两千年中，在大约公元 1750 年之前，在很大程度上，生物量燃烧与水分平衡呈负相关，尽管区域气候变得更加湿润，但燃烧仍在增加。自 20 世纪中叶以来，燃烧的持续减少反映了现代景观向农田和种植园的强化转化。相比之下，在半干旱的肯尼亚中部，生物量燃烧在中等水分平衡水平达到峰值，而在过去 1200 年中最湿润和最干燥的几十年期间，燃烧水平较低。自 20 世纪中叶以来，这里的燃烧稳步增加，可能是由于为清除灌木丛和养牛而更频繁地故意点火所致。生物质燃烧的观察到的历史趋势和区域对比与当今非洲稀树草原生物群落的火灾发生情况的空间变异性一致。它们表明，东非火灾发生情况强烈依赖于气候水分平衡和植被，以及这种依赖现在在多大程度上被人为活动所超越。
