Evaluating tree mortality and regeneration processes at multiple scales

最近的情况表明，在世界许多地方，古老的北方森林是普遍现象，而不是例外。这是因为火灾虽然壮观，但并不经常影响大面积的森林，特别是在北美东部。 相反，这些森林受到其他干扰。这些部分干扰（如昆虫爆发，风吹，和老年相关的死亡率）释放资源，将允许不同的物种招募。干扰频率、干扰规模以及被杀树木的数量和种类的差异将影响补充和树木多样性。然而，干扰可能不是影响北方混交林树种多样性的唯一因素。预计干扰和场地生产力之间会有相互作用。换句话说，当土壤生产力低时，很少有物种能够补充，而当生产力高时，干扰将允许不同的物种根据其对土壤资源或地上资源（如光）的需求进行补充。了解这些相互作用是非常重要的，因为北方混交林受到气候变化和人类活动（如木材采伐）的巨大压力。因此，我的研究将集中在树种组成的变化与不同的严重程度和频率的局部干扰沿着现场生产力梯度。我假设，不同的频率不同的严重程度的干扰将创建一个时间的小生境招聘的长寿物种与特定的建立需要，否则将被排除在完整的森林。它也预计，这种干扰介导的多样性将是最大的高生产力网站。虽然这种研究是在温带和热带森林进行的，但在北方地区，尽管这一森林很重要，但基本上被忽视了。我的工作将集中在过渡性的北方混交林，因为这个地区包括最大的树木多样性，作为一个过渡区也是气候因素变化的最大风险（即在干扰制度等）。这项研究将基于航空摄影分析，树木生态学分析和建模相结合。

Old boreal forests have recently been shown to be the rule rather than the exception in many parts of the world. This is because fires, although spectacular do not regularly affect large areas of the forest, especially in eastern North America. Instead these forests are affected by other disturbances. These partial disturbances (such as insect outbreaks, windthrow, and old-age related mortality) release resources that will allow different species to recruit. Differences in disturbance frequency, size and the number and species of trees killed will affect recruitment and tree diversity. However, disturbances alone will probably not be the only factor affecting tree diversity of boreal mixedwoods. It is expected that there will be an interaction between disturbances and site productivity. In other words, when soil productivity is low few species should be able to recruit whereas when productivity is high then disturbances will permit different species to recruit depending on their needs for soil resources or above ground resources such as light. Understanding these interactions is important as boreal mixedwood forests are under great pressure from climate change and human activities such as timber harvesting. My research will thus focus on how tree species composition changes with different severity and frequency of partial disturbances along a site productivity gradient. I hypothesise that a varying frequency of different severity disturbances will create temporal niches for the recruitment of long-lived species with specific establishment needs that would otherwise be excluded from intact forests. It is also expected that such disturbance mediated diversity will be greatest on high productivity sites. Although such research has been conducted in temperate and tropical forests it has basically been ignored in boreal regions despite the importance of this forest. My work will focus on the transitional boreal mixedwoods as this region encompasses the greatest tree diversity and being a transition zone is also under the greatest risk of change (i.e. in disturbance regimes, etc) to climatic factors. This research will be based on a combination of aerial photographic analysis, dendroecological analysis and modeling.