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

树木通常被认为是相互竞争资源的个体。然而，我们知道它们并不是不同的个体，因为它们可能共享物质或通过频繁的根嫁接直接影响彼此的生长。疏林等造林做法旨在通过减少树干数量和将资源（光、水和养分）集中在剩余的作物树上来提高林分的商品产量和盈利能力。然而，在许多情况下，树木在间伐后生长停滞或减少（标记为“间伐冲击”），林分往往显示出高死亡率。我们已经证明，嫁接根茎可以解释间伐后生长下降的树木，因为剩余的树木继续支持被砍伐树木的根和树桩生物量。该项目的主要目标是确定纯黑云杉和混合黑云杉林分嫁接的生态意义。具体来说，我们想要了解1)从生长、处理后死亡率和风投敏感性方面了解嫁接在黑云杉林分对间伐的响应中的作用。其次，我们想用纯黑云杉松和混合黑云杉松来研究根系嫁接是否对其他或同一物种的树木具有竞争优势；3)开发一个模型，利用地上性状来预测地下根系嫁接动态。将对疏林和未疏林的林分进行水力挖掘，以暴露根系，并使用树木年代学技术对根、茎和根嫁接进行回顾性分析。

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.