Relative Impacts of Elephant and Fire on Large Trees in a Savanna Ecosystem
Relative Impacts of Elephant and Fire on Large Trees in a Savanna Ecosystem
复制标题
大象和火灾对稀树草原生态系统中大树的相对影响
作者：
G. Shannon;M. Thaker;A. Vanak;B. Page;Rina C. Grant;R. Slotow
大象和火被认为是改变非洲热带草原生态系统的最重要因素之一。虽然这两个关键的生态驱动因素之间的协同关系是有据可查的，但事实证明，随着时间的推移，要确定它们对稀树草原植被结构的相对影响要困难得多。在这项研究中，我们探讨了火灾和大象对南非克鲁格国家公园2,522棵大树（高度≥5米）的比较影响。从2006年4月第一次调查的21个样带收集数据，并于2008年11月重新调查，以确定这些因子过去造成的损害对随后的影响和死亡率的相对重要性。2006年发生的火灾或大象破坏影响了随后被这两种媒介移除的树木体积的数量;大象从先前烧毁的树木中移除了更多的树木体积，随后的火灾对先前烧毁或大象利用的树木的影响高于未受损的树木。死亡率也受到以前和最近的损害之间的相互作用的影响，因为死亡的可能性是最高的树木遭受火灾或大象利用后被推倒。随后的火灾损害，但不是大象利用，对剥皮的树木也增加了死亡率的概率。死亡率是进入≥5 m高度等级的树木的两倍（每年4.6%），表明在30个月的研究期间，大树密度总体下降。大型树木的反应是物种和树木的敏感性大象和火灾的影响，以及死亡率和发展到≥5米的高度级。这些结果强调需要精细尺度的特定站点的知识，有效的景观水平的了解稀树草原动态。
Elephant and fire are considered to be among the most important agents that can modify the African savanna ecosystem. Although the synergistic relationship between these two key ecological drivers is well documented, it has proved much more difficult to establish the relative effects they have on savanna vegetation structure at a fine-scale over time. In this study, we explore the comparative impacts of fire and elephant on 2,522 individually identified large trees (≥5 m in height) in the Kruger National Park, South Africa. Data were collected from 21 transects first surveyed in April 2006 and resurveyed in November 2008, to determine the relative importance of past damage by these agents on subsequent impacts and mortality. The occurrence of fire or elephant damage in 2006 affected the amount of tree volume subsequently removed by both these agents; elephant removed more tree volume from previously burned trees and the impact of subsequent fire was higher on previously burned or elephant-utilized trees than on undamaged trees. Mortality was also affected by an interaction between previous and recent damage, as the probability of mortality was highest for trees that suffered from fire or elephant utilization after being pushed over. Subsequent fire damage, but not elephant utilization, on debarked trees also increased the probability of mortality. Mortality was twice (4.6% per annum) that of trees progressing into the ≥5 m height class, suggesting an overall decline in large tree density during the 30-month study period. The responses of large trees were species and landscape-specific in terms of sensitivity to elephant and fire impacts, as well as for levels of mortality and progression into the ≥5 m height class. These results emphasize the need for fine-scale site-specific knowledge for effective landscape level understanding of savanna dynamics.