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

森林管理决策考虑了许多因素。这些因素之一是森林将如何对生长方面的决定做出反应。更根本的是，即使树木的生长和发育已经被研究了一个多世纪，关于树木如何相互作用的问题仍然很多。例如，几项研究表明，有几个树种的森林比只有一个树种组成的森林可以生长得更多。如果我们能够理解为什么多树种森林生长得更好，就可以重新定义管理做法，以便利用增长的优势。然而，研究人员只是提出了解释这些观察结果的假设，而没有对它们进行彻底的测试。因此，这项研究方案的长期目标是通过了解树木如何相互作用来改善多树种森林的管理做法。 在树木使用的资源中，光是重要的，因为它决定了二氧化碳气体的量，二氧化碳气体被转化为糖用于生长。一棵树接受的光量受其邻居的大小和树种的影响。例如，糖枫等落叶树种的树冠不会像香脂冷杉等常绿树种那样拦截光线。树木还需要被根部吸收的养分和水分，这两者的有效性都受到土壤过程的影响。这些过程受林木组成的影响，因为森林凋落物由树叶和其他有机物质组成，单树种森林和多树种森林的营养成分不同。 在这项研究计划中，将通过研究地上和地下的动态来研究树木之间的相互作用。使用产生高精度3D信息的地面激光扫描仪，将量化树木之间的相互作用，以评估树木将光转化为生物量生长的效率，以及这种效率如何从只有一个物种的森林转变为多物种森林。还将调查养分可获得性和循环，以评估单一树种森林和多树种森林之间的差异。为了充分了解混交林生长更好的原因，光能利用效率将与土壤特性相关。 最后，由于林业历来对树干感兴趣，而不是对树枝、树叶或树根等部分感兴趣，因此还将在该方案中审查树木各隔间(如树干、树枝、树叶、树根)之间的生长分配。随着使用森林作为供应源的生物燃料和生物化学品等其他行业的发展，人们对每个隔间可获得多少生物质的知识的需求将会增加。 关于空气相互作用、土壤过程和分配的研究结果将被综合到基于生态学和生物力学的代谢理论的建模框架中。该理论将生物体的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。该理论的基本假设将根据方案每个组成部分所取得的成果加以调整。然后，这种适应将被包括在一个树木生长模拟器中，该模拟器将被开发出来，以帮助森林管理者在管理多树种森林时做出合理的决定。因此，这些结果将有助于加拿大森林业保持竞争力。此外，该方案将有助于确定解释为什么多树种林有更好的生长，以及多树种林生物量的增加是否能导致林业木材供应增加的过程。

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.