Growth and survival of black spruce trees after commercial thinning: influence of root grafting and tree competition

传统上，树木被认为是相互竞争资源的个体。然而，我们知道，它们不是不同的个体，因为它们可能共享物质，或者通过频繁的根移植直接影响彼此的生长。间伐等造林做法旨在通过减少树干数量和将资源（光、水和养分）集中于剩余的作物树木来增加林木的商品产量和盈利能力。然而，在许多情况下，树木生长在间伐后停滞或减少（标记为“间伐冲击”），并且林分通常显示出高死亡率。 我们已经表明，杰克松，根嫁接可以解释生长减少树木间伐后，因为残留的树木继续支持根和树桩的生物量删除树木。本项目的主要目标是确定在纯林和混交林中进行根嫁接的生态意义。具体来说，我们想1）了解根嫁接在黑云杉林分对间伐的反应中的作用，包括生长、处理后的死亡率和风吹易感性。其次，我们想2）检查根嫁接是否提供了一个竞争优势，对另一个或相同物种的树木使用纯和混合的黑云杉-杰克松林和3）开发一个模型，使用地上性状来预测地下根嫁接动态。疏林和未疏林的林分将被水力挖掘以暴露根系，根、茎和根移植物将使用树木年代学技术进行回顾性分析。

Trees are traditionally considered as individual entities competing with each other for resources. We know, however, that they are not distinct individuals because they may share substances or directly affect each other's growth through the frequent presence of root grafts. Silvicultural practices such as thinning are designed to increase merchantable yield and profitability of forest stands by reducing the number of stems and concentrating resources (light, water and nutrients) on remaining crop trees. In many cases, however, tree growth stagnates or decreases after thinning (labeled as «thinning shock») and stands often show high mortality rates. We have shown for jack pine that root grafting could explain growth decreases trees after thinning because residual trees continue to support the root and stump biomass of removed trees. The main goal of this project is to determine the ecological significance of root grafting in pure and mixed black spruce stands. Specifically, we want to 1) understand the role of root grafting in the response of black spruce stands to thinning in terms of growth, mortality post treatment and windthrow susceptibility. Secondly, we want to 2) examine if root grafting offers a competitive advantage to trees against trees of another or the same species using pure and mixed black spruce-jack pine stands and 3) develop a model, that uses above-ground traits to predict belowground root grafting dynamics. Thinned and unthinned stands will be hydraulically excavated to expose roots systems, and root, stems and root grafts will be retrospectively analyzed using dendrochronology techniques.