Analysis of ecological thresholds in a temperate forest undergoing dieback.
Analysis of ecological thresholds in a temperate forest undergoing dieback.
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DOI：
10.1371/journal.pone.0189578
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发表时间：
2017
期刊：
影响因子：
3.7
通讯作者：
Evans PM
中科院分区：
文献类型：
--
作者：
Martin P;Newton AC;Cantarello E;Evans PM
退化驱动因素的正反馈可在自然生态系统中引起阈值反应。虽然阈值反应在水生生态系统的研究中受到了很大的注意，但在陆地系统中，如森林，阈值反应却被忽视了，因为在森林中，监测所需的时间尺度很长，妨碍了研究。在这项研究中，我们探讨了正反馈的作用，在温带森林，已被监测50年，正在经历枯死，主要是由于死亡的冠层优势物种（山毛榉）。统计分析表明，强非线性损失断面积的一些地块，而其他人则表现出相对渐进的变化。山毛榉幼苗密度呈正相关，冠层开放度，但没有观察到类似的关系，树苗，表明反馈，即死亡率在高冠层开放度的地区升高。我们结合这一观察与经验数据的大小和生长介导的死亡率的树木产生一个基于个人的森林动态模型。我们用这个模型来模拟不同的少年和成熟的死亡率概率，以及幼苗和成熟的树木死亡率之间的正反馈的情况下，在100年的森林结构的变化。该模型产生的森林断面积下降时，关键的少年和成熟的死亡率概率超过。青少年死亡率的反馈造成了更大的减少断面积相对于没有反馈的情况。非线性，凹下降的断面积发生时，只有成熟的树死亡率是3-5倍，比在现场观察到的。我们的研究结果表明，树木的寿命可能有助于缓冲森林对环境变化的影响，维护古老的大树可能有助于森林的恢复力。此外，我们的工作表明，森林枯死可能是可以避免的，只要对成熟和幼龄树木的压力没有超过临界阈值。
Positive feedbacks in drivers of degradation can cause threshold responses in natural ecosystems. Though threshold responses have received much attention in studies of aquatic ecosystems, they have been neglected in terrestrial systems, such as forests, where the long time-scales required for monitoring have impeded research. In this study we explored the role of positive feedbacks in a temperate forest that has been monitored for 50 years and is undergoing dieback, largely as a result of death of the canopy dominant species (Fagus sylvatica, beech). Statistical analyses showed strong non-linear losses in basal area for some plots, while others showed relatively gradual change. Beech seedling density was positively related to canopy openness, but a similar relationship was not observed for saplings, suggesting a feedback whereby mortality in areas with high canopy openness was elevated. We combined this observation with empirical data on size- and growth-mediated mortality of trees to produce an individual-based model of forest dynamics. We used this model to simulate changes in the structure of the forest over 100 years under scenarios with different juvenile and mature mortality probabilities, as well as a positive feedback between seedling and mature tree mortality. This model produced declines in forest basal area when critical juvenile and mature mortality probabilities were exceeded. Feedbacks in juvenile mortality caused a greater reduction in basal area relative to scenarios with no feedback. Non-linear, concave declines of basal area occurred only when mature tree mortality was 3–5 times higher than rates observed in the field. Our results indicate that the longevity of trees may help to buffer forests against environmental change and that the maintenance of old, large trees may aid the resilience of forest stands. In addition, our work suggests that dieback of forests may be avoidable providing pressures on mature and juvenile trees do not pass critical thresholds.
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