森林树种竞争能力和拓殖能力的测量及树种竞争拓殖权衡的检验

The competition-colonization trade off means that the competitive ability of a species needs to trade with its ability to colonize vacant space. Consequently, the species with strong competitive ability cannot arrive at all the sites, leaving sites for the competitively weaker species. In forest, the coexisting species compete with one another for resources and the deaths of trees can provide sites for colonizer. It is highly probable that a competition-colonization trade-off works in forests. Yet, because of the long life history of tree species and the slow forest dynamics, there were very few studies focused on the competition-colonization trade-off among tree species. In this project, we put forward an approach to directly measure the colonization and competition abilities among coexisting species.To measure colonization ability, we are going to measure the germination rates of common species in different habitat types in a forest and to investigate the relationships between diameter at breast heigh(DBH) and time, seed number and DBH, seed arrival probability and dispersal distance using well-designed experiments and field work. According to the germination rate and these relationships of a species, we simulate the growth and reproduction of that species for the time its propogule needs to arrive and germinate at a certain distance from its mother tree. The inverse of this time will be used as a measure of colonization ability. We design pairwise seedling experiment and allow the seedlings of each species compete with the seedlings of other species selected for experiment, each at a time. We will also investigate the relationship between mortality rate and neighborhood crowding using field data. The result from seedling experiment provides the relative competitive ability of each species at seedling stage. The mortality rate at crowding condition provides a measure of the competitive ability of each species at stages with DBH larger than 1cm. Based on the colonization and competition abilities measured, we will test whether there is a negative correlation between them among species. Our study will contribute to the understanding of species coexistence in forests and the competition-colonization trade-off among tree species.

竞争-拓殖的权衡是指物种的竞争能力需要与占领和开拓新空间的能力进行交换。因此竞争力强的物种不能到达所有空间，为竞争力弱的物种留下了生存空间。森林中，共存着的物种围绕资源进行竞争，树木的死亡为拓殖者提供空间。竞争-拓殖权衡很可能在森林中起作用。由于树木生活史较长，森林动态进展缓慢，关于树种竞争-拓殖权衡的研究极少，且这些研究都是通过种子性状间接检验这个权衡。本项目提出有效测量拓殖和竞争能力的方法。本项目对与拓殖能力有关的4个因素（胸径生长与时间的关系、种子数量与胸径的关系、种子到达概率与传播距离的关系和萌发率）通过实验和野外观测进行精确测量，据此模拟常见树种的繁殖体到达一定距离并萌发所需的时间，这个时间的倒数作为拓殖能力；同时根据两两树种配对的幼苗实验结果及死亡率与邻近密度的关系作为树种各阶段竞争力的测量；在此基础上检验两者是否存在权衡。本项目有助于了解树种间拓殖-竞争的权衡及物种共存问题。

项目背景. 物种多样性是生态学研究的核心内容。在多年的研究中，生态学家提出了许多解释物种共存的假说，如中性理论、生态位分化、密度制约效应等等。但是直到目前，这些研究还没有形成一个让人普遍信服的结果。物种多样性如何维持还需要再深入探索。. 竞争-拓殖的权衡被认为是物种多样性共存的机制之一。竞争-拓殖的权衡是指物种的竞争能力需要与占领开拓新空间的能力进行交换，因此竞争力强的物种不能到达所有的空间，从而为竞争力弱的物种留下了生存空间。因此竞争力强的物种不能到达所有空间，为竞争力弱的物种留下了生存空间。森林中，共存着的物种围绕资源进行竞争，树木的死亡为拓殖者提供空间。竞争-拓殖权衡很可能在森林中起作用。由于树木生活史较长，森林动态进展缓慢，关于树种竞争-拓殖权衡的研究极少，且这些研究都是通过种子性状间接检验这个权衡。..主要研究内容. 本项目提出有效测量拓殖和竞争能力的方法。本项目对与拓殖能力有关的4个因素：生长速率，繁殖力，传播距离和萌发率通过实验和野外观测进行进行精确测量，据此模拟常见树种的繁殖体到达一定距离并萌发所需的时间，这个时间的倒数作为拓殖能力；同时根据两两树种配对的幼苗实验结果及死亡率与邻近密度的关系作为树种各阶段竞争力的测量；在此基础上检验两者是否存在权衡。. 建立关于各物种存活率与邻域情况的回归模型及生长速率模型，结合生境信息，基于此分析物种生境关联。. 个别学者认为拓殖力除了包括繁殖和扩散，还应该包括幼苗建成。因此，另外也用新长到1cm胸径的个体补充率作为拓殖力。用观测到的最大胸径作为竞争力，检验拓殖竞争权衡。..重要结果与关键数据.. 所研究的物种中，除林下种外，存在着显著的拓殖竞争权衡。拓殖竞权衡直到胸径20cm还仍然是显著的。拓殖竞争权衡可能与更新生态位同时起作用。因为一些功能性状如，叶面积，木材密度与这个权衡相关。拓殖者可能通过繁殖、扩散与快速生长的优势获取生存空间。. .科学意义. 研究表明亚热带森林中存在着显著的拓殖竞争权衡。一些功能性状可以反映物种在拓殖竞争轴上的位置。