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主导地位，但落叶树在大多数北方地区很常见，经常在北极和高山地区形成树线。这些植物群之间的共存和竞争是重要的，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。拟议的研究计划调查了落叶和常绿树木的共存，使用物种对纸桦树和黑云杉。我们试图确定可能解释寒带和亚北极地区落叶乔木成功的三个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。这项研究将沿着四个地点的气候梯度进行，从亚北极高山林木线（舍弗维尔或加尼亚皮斯科）到北方和温带森林的过渡地带（劳伦泰兹）。1)为了解决物种间养分限制的差异，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养分矿化率。2)通过测定沿梯度分布的桦树和云杉林分的光合作用和树液流量，探讨不同林分的碳限制差异。我们将通过使用管道模型理论分析生物量分配（即分析支持叶片所需组织的成本）来明确地尝试理解叶面积的间接成本。3)将通过在田间操纵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定量重要性。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.