Ecosystem-wide responses to fire and large mammal herbivores in an African savanna

Fire and large mammal herbivores (LMH) are the principal top-down forces maintaining savanna structure. Nonetheless, experiments designed to investigate interactions between fire and LMH are rare in savannas, and relationships between environmental variation and biodiversity in the context of fire and LMH are poorly understood. This study addresses these gaps by manipulating the presence of LMH and early and late dry season fires in a tropical African savanna. In addition, this work simultaneously explores environmental variables including soil and foliar quality, vegetation cover, and nearby water sources to more holistically describe factors affecting savanna functioning and biodiversity. After one year of experimental treatments, changes in vegetation were already apparent. Shrub abundance and richness and grass richness were higher in the absence of LMH, while grass biomass increased three-fold in burned plots as compared to unburned plots. Foliar nutrients tended to increase in open plots, while phenolics decreased. Amphibian abundance decreased with early burns and was higher with LMH. In contrast, small mammal abundance and richness increased without LMH and with time since fire. Richness and foraging of LMH were highest after late burns. These results demonstrate ecosystem-wide effects of LMH, illustrating the importance of considering multiple taxa when designing fire management programs. For example, burning negatively affected amphibians and small mammals and changed vegetation at the same time it increased LMH foraging. In the long-term, this experiment will shed light on interacting effects of fire and LMH on savanna biodiversity and function.火与大型草食哺乳动物（Large Mammal Herbivores, LMH）是维持稀树草原结构的核心自上而下调控力量。然而，旨在探究火与LMH之间相互作用的稀树草原相关实验仍较为匮乏，且在火与LMH的背景下，环境变异与生物多样性之间的关联机制仍未得到充分阐释。本研究通过在非洲热带稀树草原中设置LMH存在与否、旱季早期与晚期火烧的处理实验，填补了上述研究空白。此外，本研究同时纳入土壤与叶片品质、植被覆盖度及邻近水源等环境变量，以更全面地解析影响稀树草原功能与生物多样性的各类因素。在开展为期一年的实验处理后，植被群落已出现显著变化。未存在LMH的样地中，灌木多度、灌木物种丰富度与草本物种丰富度均更高；而火烧样地的草本生物量较未火烧样地提升了三倍。开放样地的叶片养分含量整体呈上升趋势，而酚类物质含量则有所下降。两栖动物多度随早期火烧事件出现下降，且在有LMH存在的样地中更高。与之相反，未受LMH影响的样地以及火烧后间隔时间更长的样地中，小型哺乳动物的多度与物种丰富度均有所提升。LMH的物种丰富度与觅食活动在晚期火烧后达到最高水平。上述研究结果证实了LMH对生态系统的全域性影响，阐明了在制定火烧管理方案时需兼顾多个类群的重要性。例如，火烧一方面提升了LMH的觅食活动，另一方面却对两栖动物与小型哺乳动物产生了负面影响，同时改变了植被群落结构。从长期来看，本实验将进一步揭示火与LMH的交互作用对稀树草原生物多样性与生态系统功能的调控机制。