Effects of diversity on forest production and wood properties and implications for forest management practices

森林管理决策要考虑许多因素。其中一个因素是森林将如何对在增长方面作出的决定作出反应。更根本的是，即使树木的生长和发育已经研究了世纪，但关于树木如何相互作用的问题仍然很多。例如，一些研究表明，有几个树种的森林比只有一个树种的森林生长得更快。如果我们能够理解为什么多物种森林生长得更好，管理方法就可以重新定义，以便利用增加的增长。然而，研究人员只是提出了一些假设来解释这些观察结果，而没有进行彻底的测试。因此，这项研究计划的长期目标是通过了解树木如何相互作用来改善多物种森林的管理方法。在树木使用的资源中，光线很重要，因为它决定了二氧化碳气体转化为用于生长的糖的数量。一棵树接收到的光的量受其邻居的大小和物种的影响。例如，糖枫等落叶树种的树冠不会像香脂冷杉等万年青树种那样拦截光线。树木还需要由根部吸收的养分和水分，这两者的可用性受到土壤过程的影响。这些过程受到森林树木组成的影响，因为由树叶和其他有机物质组成的森林凋落物在单一物种森林和多物种森林之间的营养成分不同。在这项研究计划中，树木之间的相互作用将通过观察地上和地下动态来研究。使用地面激光扫描仪，产生高精度的三维信息，树木之间的相互作用将被量化，以评估树木如何有效地将光转化为生物量增长，以及这种效率如何从只有一个物种的森林变化到多物种森林。还将调查养分供应和循环情况，以评价单一树种森林和多树种森林之间的差异。最后，本方案还将研究树木各部分（如茎、枝、叶、根）之间的生长分配，因为林业历来对树木的茎感兴趣，而不是对枝、叶或根等部分感兴趣。随着利用森林作为供应源的生物燃料和生物化学品等其他产业的发展，将越来越需要了解每个隔间有多少生物量。将根据生态学和生物力学的代谢理论，将空中相互作用、土壤过程和分配的研究结果综合成一个建模框架。该理论将有机体的新陈代谢率与其大小联系起来。当应用于森林生态系统时，新陈代谢理论似乎并不成立。理论的基本假设将根据从方案的每个组成部分获得的结果进行调整。这种适应将被纳入树木生长模拟器，该模拟器将被开发，以帮助森林管理人员在管理多物种森林时做出正确的决定。这些结果将有助于加拿大林业保持竞争力。此外，该方案还将帮助查明多树种林分生长较好的原因，以及多树种林分生物量增长的增加是否会导致林业木材供应的增加。

Forest management decisions take many factors into account. One of these factors is how the forest will react to the decision taken in terms of growth. More fundamentally, even if tree growth and development have been studied for over a century, a lot of questions remain on how trees interact. For example, several studies have shown that forests with several tree species can grow more than forests composed by only one of the species. If we can understand why multi-species forests grow better, management practices could be redefined in order to take advantage of the increased growth. Researchers have however only proposed hypotheses to explain these observations, without thoroughly testing them. The long term objective of this research programme is thus to improve management practices in multi-species forests by understanding how trees interact.Among the ressources used by trees, light is important as it determines the amount of carbon dioxide gas that is transformed into sugars which are used for growth. The amount of light a tree receives is influenced by its neighbours’ size and species. For example, the crown of deciduous species such as sugar maple will not intercept light in the same way that evergreen species like balsam fir do. Trees also need nutrients and water that are picked up by the roots, the availability of both which are influenced by the soil processes. These processes are affected by the forest tree composition since the forest litter, made up by tree leafs and other organic material, will differ in nutrient composition between single species forests and multi-species forests. Within this research programme, the interaction between trees will be studied by looking at both aboveground and belowground dynamics. Using terrestrial laser scanners, which yield high precision 3D information, the interaction between trees will be quantified in order to assess how efficiently trees transform light to biomass growth, and how this efficiency changes from forests with only one species to multi-species forests. Nutrient availability and cycling will also be investigated as to evaluate the differences between single and multi-species forests. The light use efficiency will then be related to soil characteristics in order to fully understand why mixed forests have better growth.Finally, the growth allocation between each compartment of a tree (e.g. stem, branches, foliage, roots) will also be examined within this programme since the forest industry has historically been interested in the stem of the tree, and not the parts such as the branches, foliage or roots. With the development of other industries such as biofuels and biochemicals using the forest as a supply sources, there will be an increase in the need for knowledge on how much biomass is available from each compartment.The findings on aerial interactions, soil processes and allocation will be synthesized into a modeling framework based on the metabolic theory of ecology and biomechanics. The theory relates the metabolic rate of an organism to its size. When applied to forest ecosystems, the metabolic theory does not seem to hold. The underlying hypotheses of the theory will be adapted in light of the results obtained from each component of the programme. This adaptation will then be included in a tree growth simulator which will be developed in order to help forest managers take sound decisions when managing multi-species forests. These results will thus help the Canadian forest industry stay competitive. Furthermore, the programme will help to identify the processes which explain why multi-species stands have better growth, and if the increased biomass growth of multi-species stands can lead to increases in forest industry timber supply.