The role of root grafting in competitive/cooperative relationships between trees

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***Natural root grafting (anastomosis) challenges the notion of plant individuality and the consideration of forests as groups of individual trees competing with each other for resources. The sharing of substances (e.g. water, sugars) between trees, allows for cooperative relationships to occur. The long term objective of this research program is to demonstrate the ecological significance of root grafting. In the short term, I want to answer the following question: are root-grafted trees better competitors? First, occurrence, timing and effect of spacing on root grafting will be assessed in monospecific plantations of hybrid poplar, white and Norway spruce. Root grafts will be collected and brought to the lab for dendrochronological analysis. Size and age of roots at grafting, and distance between grafted trees will be determined and linked to root grafting frequency and timing. Then, using densely planted plots, inter- vs intraspecific competition/facilitation relationships will be evaluated in mixed-species plots in relation to root grafting. Relationships between trees will be characterized using distance-dependent and independent competition indices. Using dendrochronology techniques, timing of root grafting will be determined and linked with chronological competition index values throughout the lifespan of the stands. This will enable us to determine if stand development exhibited a predictable time-sequence spatial pattern resulting from competition for resources or if root grafting stalled stand development by allowing trees to respond (and compete) as a group rather than as individual stems. The different spacings and mixed species plantations will also allow us to examine stand development sequence to see if competition forces act as a trigger for root grafts to form between neighboring trees.***Ecological significance of root grafting forces us to reconsider traditional forest stand dynamics concepts such as competition, dominance and succession, concepts on which modern forestry is based on. The proposed research will throw light on the role that root grafting plays in tree-to-tree interactions during stand evolution by looking at stand-level grafting in plantations and in balsam fir natural forests. So far, my research has shown a general positive impact of root grafting on growth of connected trees, and suggests that grafted groups of trees benefit from each other to confront stress. From an applied perspective, few practitioners have associated successful or unsuccessful silvicultural operations to root connections. For example, it is often said that some suppressed trees are unable to respond to thinning (reduced competition), while the answer lies in skewed root-shoot ratios created by reducing leaf area of stands sharing communal root systems. Our work in plantations thus has the potential to impact how intensively managed plantations are established. *****