Ecophysiology of the coexistance between deciduous and coniferous trees in the boreal zone

虽然大多数生态学家预测，针叶寿命长的针叶树将在北方和亚北极气候中占据主导地位，但落叶树在大多数北方地区很常见，在北极和高山地区经常形成树线。这些植物种群之间的共存和竞争很重要，因为气候变化和不断变化的林业制度正在改变加拿大的森林。拟议的研究方案使用白桦树和黑云杉树种对调查落叶树和常绿树的共存情况。我们试图确定三个可能解释北方和亚北极地区落叶树木成功的关键理论的相对重要性：资源限制理论、汇限制理论和霜冻干燥理论。这项研究将沿着从亚北极高山树线(Schefferville或Caniapiscau)到北方和温带森林过渡地带(Laurentides)的四个地点的气候梯度进行。1)为了解决不同树种之间营养限制的差异，我们将沿着气候梯度比较桦树和云杉覆盖下的凋落物分解和营养矿化速率。2)通过测量白桦和云杉林分沿梯度的光合作用、液流来研究碳限制的差异。我们将明确地尝试通过使用管道模型理论分析生物量分配来了解叶面积的间接成本(即分析支持叶片所需的组织的成本)3)将通过操纵田间春季土壤温度来研究霜冻干燥的重要性。这将通过在冬季改变积雪深度来实现。4)一个更大的操作实验，包括落叶、脱芽、施肥和土壤温度操作，将被用来区分不同的理论。5)将使用基于过程的建模来理解结果的数量重要性。该研究将产生四篇硕士论文和一篇博士论文。

While most ecologists predict that coniferous trees with long lived needles will dominate in boreal and subarctic climates, deciduous trees are common in most boreal zones and often form treelines in arctic and alpine areas. The coexistence and competition between these plant groups is important since climate change and changing forestry regimes are changing the Canadian forests. The proposed research programme investigates the coexistence of deciduous and evergreen trees using the species pair paper birch and black spruce. We try to determine the relative importance of three key theories that can potentially explain the success of deciduous trees in boreal and subarctic regions: the resource limitation theory, the sink limitation theory and the frost desiccation theory. The research will be done along a climatic gradient of four sites from a subarctic alpine treeline (Schefferville or Caniapiscau) to the transition zone of boreal and temperate forests (Laurentides). 1) To address differences in nutrient limitations between the species we will compare the litter decomposition and nutrient mineralization rates under birch and spruce cover along the climatic gradient. 2)Differences in the carbon limitations will be investigated by measuring photosynthesis, sapflow of birch and spruce stands along the gradient. We will explicitly try to understand indirect costs of leaf area by analysing biomass partitioning using the pipe model theory (i.e. analyse the costs of tissues required to support foliage)3)The importance of frost desiccation will be investigated by manipulating spring soil temperature in the field. This will be done by changing snow depths during the winter.4)A larger manipulation experiment including defoliation, debudding, fertilisation and soil temperature manipulations will be used to discriminate between the different theories. 5)Process based modelling will be used to understand the quantitative importance of the results The research will result in four master theses and one doctoral thesis.