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Why forest fails to recover after repeated wildfires in Amazonian floodplains? Experimental evidence on tree recruitment limitation
Journal of Ecology ( IF 5.3 ) Pub Date : 2021-08-21 , DOI: 10.1111/1365-2745.13769 Bernardo M. Flores 1, 2, 3 , Milena Holmgren 1
中文翻译：
为什么在亚马逊洪泛区反复发生野火后森林未能恢复？树木补充限制的实验证据
更新日期：2021-10-11
Journal of Ecology ( IF 5.3 ) Pub Date : 2021-08-21 , DOI: 10.1111/1365-2745.13769 Bernardo M. Flores 1, 2, 3 , Milena Holmgren 1
Affiliation
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- Amazonian floodplain forests are particularly vulnerable to wildfires that spread during extreme droughts, causing large-scale forest dieback. After a second wildfire, these forests persist trapped with low tree cover and empty seed banks, yet the mechanisms that could explain this arrested succession remain unknown.
- Here we use a 4-year field experiment to test whether tree recruitment failures in burnt floodplain forests are caused by environmental filtering, limiting early seedling emergence and establishment. We sowed seeds and planted seedlings of six floodplain trees with contrasting life strategies, and tested the roles of environmental filters by comparing tree seedling performances under different habitats (i.e. unburned forest, forest edge with burnt site, forest burnt once and forest burnt twice), and by manipulating soil root mats and herbaceous cover.
- Our results show that seedling emergence was around 15% across all habitats. In general, seedlings performed best in burnt forests. Seedling growth was highest in forests burnt once, possibly because of high nutrient availability after fire. In forests burnt twice, tree seedlings grew relatively less, as nutrients become limiting due to flood erosion; yet, seedlings survived longer, possibly because of lower competition with sparse, naturally recruiting trees. We found similar patterns for seedlings that emerged in the field from sowed seeds.
- Synthesis. Our experimental evidence suggests that environmental filtering related to soil nutrient limitations may slow down forest recovery after repeated wildfires. Yet, our findings showing that floodplain trees are able to germinate from seeds and establish successfully in twice burnt forests suggest that seed limitation may be the reason why forest recovery fails persistently. A corollary to the problem is that repeatedly burnt forests seem to be trapped by a self-reinforcing feedback, in which low tree cover reduces seed dispersal and consequently seed availability, keeping tree cover low. Overall, our findings indicate that active restoration initiatives based on seeding native tree species may help accelerating the recovery of degraded floodplain forests after repeated wildfires.
中文翻译：
为什么在亚马逊洪泛区反复发生野火后森林未能恢复？树木补充限制的实验证据
- 亚马逊河漫滩森林特别容易受到在极端干旱期间蔓延的野火的影响，导致大规模森林枯死。在第二次野火之后，这些森林仍然被困在低树覆盖和空的种子库中，但可以解释这种停滞的连续性的机制仍然未知。
- 在这里，我们使用为期 4 年的田间试验来测试被烧毁的洪泛平原森林中的树木补充失败是否是由于环境过滤、限制了早期幼苗的出现和建立造成的。我们用对比鲜明的生活策略播种了六棵洪泛区树木的种子并种植了幼苗，并通过比较不同栖息地（即未烧毁的森林、有烧毁地点的林缘、一次森林烧毁和两次森林烧毁）下的树木幼苗表现来测试环境过滤器的作用，并通过操纵土壤根垫和草本覆盖物。
- 我们的结果表明，所有栖息地的幼苗出苗率约为 15%。一般来说，幼苗在被烧毁的森林中表现最好。烧过一次的森林中的幼苗生长最高，可能是因为火灾后养分利用率高。在两次烧毁的森林中，由于洪水侵蚀，养分变得有限，因此树木幼苗长得相对较少；然而，幼苗存活的时间更长，这可能是因为与稀疏的、自然招募的树木的竞争较低。我们发现了从播种的种子在田间长出的幼苗的相似模式。
- 合成。我们的实验证据表明，在反复发生野火后，与土壤养分限制相关的环境过滤可能会减缓森林恢复。然而，我们的研究结果表明，洪泛区树木能够从种子发芽并在两次燃烧的森林中成功建立，这表明种子限制可能是森林恢复持续失败的原因。这个问题的一个推论是，反复燃烧的森林似乎被一种自我强化的反馈所困，其中低树木覆盖减少了种子的传播，从而减少了种子的可用性，使树木覆盖率保持在低水平。总体而言，我们的研究结果表明，基于播种本地树种的积极恢复计划可能有助于在反复发生野火后加速退化的洪泛区森林的恢复。
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