Elephant damage, not fire or rainfall, explains mortality of overstorey trees in Serengeti

Generalizations about the drivers of tree demography in tropical savannahs continue to prove difficult because of the complex and dynamic interactions involved, and because multi-year datasets spanning meaningful gradients in potential drivers are lacking. Overstorey trees play disproportionate roles in the long-term dynamics and functioning of savannah ecosystems. Understanding demographic patterns in these trees is complicated by their resprouting ability after being top-killed and few studies have attempted to separate top-kill from true mortality events. We examined the interactive effects of fire frequency, mean annual precipitation and elephant herbivory on overstorey (>2m) tree mortality between 2009 and 2014 across 32 permanent vegetation plots in the Serengeti Ecosystem, Tanzania. Mean tree mortality over the study period was 0.28 ± 0.02 (0.07 yr−1). Among trees that were top-killed (19.1% of all individuals), 31.2% resprouted. Mortality was driven largely by elephant herbiv...

由于所涉及的相互作用复杂且具有动态性，同时缺乏覆盖潜在驱动因子有效梯度的多年期数据集，学界对热带稀树草原树木种群统计驱动因子的一般性规律研究始终难以推进。冠层乔木（overstorey trees）在稀树草原生态系统的长期动态与功能维持中发挥着不成比例的重要作用。由于这类树木在遭遇顶枯（top-killed）后仍具备萌蘖能力，且鲜有研究尝试将顶枯事件与真正的死亡事件加以区分，因此解析其种群统计模式颇具挑战。本研究针对坦桑尼亚塞伦盖蒂生态系统内的32个永久植被样地，分析了2009至2014年间火频度、年平均降水量与大象啃食作用对冠层（高度>2m）树木死亡率的交互影响。研究周期内树木的平均死亡率为0.28 ± 0.02（年均0.07 yr⁻¹）。在遭遇顶枯的个体中（占总个体数的19.1%），有31.2%成功萌蘖。树木死亡率主要由大象啃食驱动……