Max Planck Institute for Biogeochemistry, Hans-Knöll-Str 10, 07745 Jena, Germany.
Oecologia. 2013 May;172(1):219-29. doi: 10.1007/s00442-012-2482-x. Epub 2012 Oct 2.
Surface fires burn extensive areas of tropical forests each year, altering resource availability, biotic interactions, and, ultimately, plant diversity. In transitional forest between the Brazilian cerrado (savanna) and high stature Amazon forest, we took advantage of a long-term fire experiment to establish a factorial study of the interactions between fire, nutrient availability, and herbivory on early plant regeneration. Overall, five annual burns reduced the number and diversity of regenerating stems. Community composition changed substantially after repeated fires, and species common in the cerrado became more abundant. The number of recruits and their diversity were reduced in the burned area, but burned plots closed to herbivores with nitrogen additions had a 14 % increase in recruitment. Diversity of recruits also increased up to 50 % in burned plots when nitrogen was added. Phosphorus additions were related to an increase in species evenness in burned plots open to herbivores. Herbivory reduced seedling survival overall and increased diversity in burned plots when nutrients were added. This last result supports our hypothesis that positive relationships between herbivore presence and diversity would be strongest in treatments that favor herbivory--in this case herbivory was higher in burned plots which were initially lower in diversity. Regenerating seedlings in less diverse plots were likely more apparent to herbivores, enabling increased herbivory and a stronger signal of negative density dependence. In contrast, herbivores generally decreased diversity in more species rich unburned plots. Although this study documents complex interactions between repeated burns, nutrients, and herbivory, it is clear that fire initiates a shift in the factors that are most important in determining the diversity and number of recruits. This change may have long-lasting effects as the forest progresses through succession.
地表火每年都会烧毁大片热带森林，改变资源可利用性、生物相互作用，并最终影响植物多样性。在巴西塞拉多（稀树草原）和高海拔亚马逊森林之间的过渡森林中，我们利用一项长期的火灾实验，对火、养分可利用性和食草作用之间的相互作用进行了因子研究，以了解其对早期植物再生的影响。总的来说，五次年度火烧减少了再生茎的数量和多样性。重复火灾后群落组成发生了实质性变化，塞拉多常见的物种变得更加丰富。火烧区的幼苗数量和多样性减少，但添加氮素后，与食草动物隔离的火烧区的幼苗增加了 14%。添加氮素后，火烧区幼苗的多样性也增加了高达 50%。添加磷素与增加火烧区食草动物开放区的物种均匀度有关。食草作用总体上降低了幼苗的存活率，并增加了养分添加后的火烧区的多样性。这一结果支持了我们的假设，即在有利于食草作用的处理中，食草动物的存在与多样性之间的正相关关系最强——在这种情况下，火烧区的食草动物较多，而多样性较低。在多样性较低的再生幼苗中，食草动物更容易发现，从而增加了食草作用，并发出更强的负密度依赖性信号。相比之下，食草动物通常会降低多样性更丰富的未燃烧区的物种多样性。尽管这项研究记录了重复火烧、养分和食草作用之间的复杂相互作用，但很明显，火引发了决定再生幼苗数量和多样性的最重要因素的转变。随着森林演替的进行，这种变化可能会产生持久的影响。
