Evaluating tree mortality and regeneration processes at multiple scales

点击翻译按钮获取中文摘要

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.