Liu Bo, Chen Han Y H, Yang Jian
CAS Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, China.
Faculty of Natural Resources Management, Lakehead University, Thunder Bay, ON, Canada.
Front Plant Sci. 2018 Dec 12;9:1854. doi: 10.3389/fpls.2018.01854. eCollection 2018.
Understory vegetation accounts for the majority of plant species diversity and serves as a driver of overstory succession and nutrient cycling in boreal forest ecosystems. However, investigations of the underlying assembly processes of understory vegetation associated with stand development following a wildfire disturbance are rare, particularly in Eurasian boreal forests. In this study, we measured the phylogenetic and functional diversity and trait dispersions of understory communities and tested how these patterns changed with stand age in the Great Xing'an Mountains of Northeastern China. Contrary to our expectation, we found that understory functional traits were phylogenetically convergent. We found that random patterns of phylogenetic, functional, and trait dispersions were dominant for most of our surveyed plots, indicating that stochastic processes may play a crucial role in the determination of understory community assembly. Yet, there was an evidence that understory community assembly was also determined by competitive exclusion and environmental filtering to a certain degree, which was demonstrated by the observed clustered phylogenetic and functional patterns in some plots. Our results showed that phylogenetic diversity significantly decreased, while functional diversity increased with stand age. The observed shift trends in phylogenetic and functional patterns between random to clustering along with stand age, which suggested that understory community assembly shifted from stochasticity to competitive exclusion and environmental filtering. Our study presented a difference to community assembly and species coexistence theories insisted solely on deterministic processes. These findings indicated that Eurasian boreal understory communities may be primarily regulated by stochastic processes, providing complementary evidence that stochastic processes are crucial in the determination of community assembly both in tropical and boreal forests.
林下植被占植物物种多样性的大部分，并作为北方森林生态系统中上层演替和养分循环的驱动因素。然而，关于野火干扰后与林分发育相关的林下植被潜在组装过程的研究很少，特别是在欧亚北方森林中。在本研究中，我们测量了中国东北大兴安岭林下群落的系统发育和功能多样性以及性状离散度，并测试了这些模式如何随林分年龄变化。与我们的预期相反，我们发现林下功能性状在系统发育上是趋同的。我们发现，在我们调查的大多数样地中，系统发育、功能和性状离散度的随机模式占主导地位，这表明随机过程可能在林下群落组装的决定中起关键作用。然而，有证据表明，林下群落组装在一定程度上也由竞争排斥和环境过滤决定，这在一些样地中观察到的聚类系统发育和功能模式中得到了证明。我们的结果表明，系统发育多样性显著下降，而功能多样性随林分年龄增加。观察到的系统发育和功能模式从随机到聚类随林分年龄的变化趋势，表明林下群落组装从随机性转向竞争排斥和环境过滤。我们的研究与仅坚持确定性过程的群落组装和物种共存理论有所不同。这些发现表明，欧亚北方林下群落可能主要受随机过程调节，提供了补充证据，证明随机过程在热带和北方森林群落组装的决定中都至关重要。
