Department of Natural Resources and Environmental Studies, College of Environmental Studies, National Dong Hwa University, Hualien, Taiwan.
Department of Biological Sciences, National Sun Yat-sen University, Kaohsiung, Taiwan.
PeerJ. 2022 May 10;10:e13270. doi: 10.7717/peerj.13270. eCollection 2022.
Disturbances are crucial in determining forest biodiversity, dynamics, and ecosystem functions. Surface fire is a significant disturbance in tropical forests, but research on the effect of surface fire on structuring species and functional composition in a community through time remains scarce. Using a 20-year dataset of tree demography in a seasonal evergreen tropical forest in Thailand, we specifically addressed two essential questions: (1) What is the pattern of temporal turnover in species and functional composition in a community with frequent fire disturbance? (2) How did the temporal turnover vary with tree size?
We analyzed species compositional and functional temporal turnovers in four different tree size classes among five tree censuses. We quantified species turnover by calculating Bray-Curtis dissimilarity, and investigated its underlying mechanisms by comparing pairwise dissimilarity of functional traits with simulations from null models. If fire disturbances contribute more to a stochastic process, the functional composition would display a random pattern. However, if they contribute more towards a deterministic process, the functional composition should reveal a non-random pattern.
Over 20 years (1994-2014), we observed changes in species composition, whereas functional composition remained relatively stable. The temporal turnover patterns of species and functional compositions varied with tree sizes. In particular, temporal functional turnover shifted very little for large trees, suggesting that changes in species composition of larger trees are contributed by species with similar functional traits through time. The temporal functional composition turnovers of smaller trees (DBH ≤ 5 cm) were mostly at random. We detected a higher functional turnover than expected by null models in some quadrats throughout the 50-ha study plot, and their observed turnover varied with diameter classes.
Species compositional changes were caused by changes in the abundance of species with similar functional traits through time. Temporal functional turnover in small trees was random in most quadrats, suggesting that the recruits came from the equal proportions of surviving trees and new individuals of fast-growing species, which increased rapidly after fires. On the other hand, functional composition in big trees was more likely determined by surviving trees which maintained higher functional similarities than small trees through time. Fire disturbance is important for ecosystem functions, as changing forest fire frequency may alter forest turnover, particularly in functional composition in the new recruits of this forest.
干扰在确定森林生物多样性、动态和生态系统功能方面至关重要。地表火是热带森林的一种重要干扰，但关于地表火如何通过时间影响物种结构和功能组成的研究仍然很少。本研究利用泰国季节性常绿热带森林 20 年的树木动态数据集，专门解决了两个基本问题：（1）在频繁火灾干扰的情况下，群落中物种和功能组成的时间周转率模式是什么？（2）时间周转率如何随树木大小而变化？
我们在五次树木普查的四个不同树木大小类群中分析了物种组成和功能的时间周转率。我们通过计算 Bray-Curtis 不相似性来量化物种周转率，并通过比较功能性状的成对不相似性与来自零模型的模拟来研究其潜在机制。如果火灾干扰更多地导致随机过程，则功能组成将呈现随机模式。然而，如果它们更多地导致确定性过程，则功能组成应该显示出非随机模式。
在 20 年（1994-2014 年）的时间里，我们观察到了物种组成的变化，而功能组成相对稳定。物种和功能组成的时间周转率模式随树木大小而变化。特别是，较大树木的时间功能周转率变化很小，这表明随着时间的推移，较大树木的物种组成变化是由具有相似功能特征的物种贡献的。较小树木（DBH≤5cm）的时间功能组成周转率大多是随机的。我们在整个 50 公顷研究地块的一些样方中检测到比零模型预期更高的功能周转率，并且它们的观察到的周转率随直径类群而变化。
物种组成的变化是由具有相似功能特征的物种丰度随时间的变化引起的。大多数样方中小树木的时间功能周转率是随机的，这表明新的树木来自于幸存树木和快速生长物种的新个体的等比例，这些树木在火灾后迅速增加。另一方面，大树的功能组成更有可能由随着时间的推移而保持更高功能相似性的幸存树木决定。火灾干扰对于生态系统功能很重要，因为改变森林火灾频率可能会改变森林的周转率，特别是在新的森林植物的功能组成方面。
