阔叶红松林功能多样性及生产力对不同强度采伐的响应

Selection cutting is frequently used to optimize forest stand structure, however, it is also an important anthrophonic disturbance common to forests, potentially affecting the structure and function of forest ecosystems. Recent studies have shown that plant functional diversity, which is based on plant functional traits, plays a more important role in ecosystem functioning than the traditionally investigated species diversity. Moreover, functional diversity has been proved to well reflect the responses of plant community to disturbance. Proper forest management practices are crucial to the broad-leaved Korean pine forests. Over the past decade, there is an increasing interest in quantifying the relationship between functional diversity and ecosystem functioning. This project uses the long-term monitoring plots of natural secondary broad-leaved Korean pine forest in Jiaohe, Jilin province. Community structure and dynamics as well as environmental factors were documented 4 and 8 years after selection cutting of different intensities. Functional diversity, biomass productivity and their relationship were compared between pre- and post-cutting. We aim to clarify: (1) how does functional diversity respond to different cutting intensities during different recovery periods, in order to find out what strategies plant communities use to cope with cutting disturbance and whether the community-weighted mean traits and multiple functional diversity indices could be linked to such strategies; (2) how does selection cutting affect the relationship between functional diversity and biomass productivity, whether functional diversity better predicts biomass productivity than species diversity, which of the hypotheses related to “functional diversity-productivity relationship” applies to our study, and finally, what determines biomass productivity in this forest. Our results would help to provide scientific basis for future sustainable forest management.

采伐是调整林分结构的重要手段，也是常见的人为干扰，对森林生态系统结构和功能产生重要影响。近年来研究表明，基于植物功能性状的功能多样性比传统的物种多样性与生态系统功能有更为直接的联系，也是反映植物群落对干扰响应的关键。针对阔叶红松林经营的复杂性和当前“功能多样性与生态系统功能关系”的热点问题，本项目利用吉林蛟河天然次生阔叶红松林长期监测样地，跟踪调查择伐前及不同强度择伐后自然恢复4年、8年的群落特征和林地环境因子，试图阐明：（1）群落功能多样性如何响应不同强度的采伐，这种响应随恢复时间如何变化，通过功能性状群落加权平均值和多个功能多样性指数分析植物群落对采伐的响应策略；（2）采伐干扰如何影响功能多样性与群落生产力的关系，功能多样性是否比物种多样性对生产力的预测力更强，验证功能多样性-生产力关系的相关假说，结合环境因子探讨阔叶红松林生产力的维持机制。通过这些研究为森林的可持续经营提供科学依据。

采伐是森林经营的一项重要措施，如何控制强度，合理的利用采伐优化林分结构和提高生产力一直是研究者关注的焦点和森林经营的重要目标。本项目依托位于吉林蛟河的阔叶红松林采伐试验样地，在植物生长状况监测和群落调查的基础上，探讨不同采伐强度和恢复时间下群落的物种和功能多样性、树木个体及林分生产力的动态变化，明确阔叶红松林对采伐干扰的响应方式。结果表明，尽管物种丰富度对采伐强度的响应不敏感，群落组成却发生了变化。香农指数和物种均匀度的下降表明群落向着优势度更加不均匀的方向发展。生长优势系数（GDC）的下降程度与采伐强度成正比，表明采伐后林分内资源得到再分配，减弱了不对称竞争，采伐提高了小树对于整个林分生产力的贡献。采伐显著提高了邻体功能性状的差异性。中、重度采伐显著促进了林冠层树种的未成熟个体的生长，而只有重度采伐促进了林冠层树种的成熟个体的生长，采伐活动对林下层树种的生长并未呈现出显著的促进作用。树木生长随着最大树高的群落加权平均值（CWM）显著提高，而随木材密度、比叶重（LMA）的CWM增加而降低，叶片氮含量对树木生长速率没有显著影响。进一步将群落生产力的变化分解为三个组分：保留木生长量、进界量、死亡量分析表明，采伐既显著提高了保留木的生长及幼树的生长（进界量），同时也增加了死亡率，尤其是在重度采伐样地内最小径阶（1-10cm）树木死亡率是对照样地的两倍以上。总体来说，物种和功能多样性对林分净生产力的影响较弱，可能与阔叶红松林为顶级群落，生物多样性的作用已接近“饱和”，而多样性的进一步提高可能会造成物种和功能冗余，从而并不能真正的提高互补作用以及对资源的利用有关。另一方面，我们的结果也显示了资源在林内的分布和树木之间的相互作用比生物多样性的差异对林分生产力的影响更大。总体来看，本项目中的轻度采伐对于生物多样性的维持、林分结构的优化和生产力的提高最为有利。上述研究结果为合理控制和利用采伐提高东北阔叶红松林生产力提供科学依据，有助于森林的可持续经营。