Frequency of root grafting in naturally and artificially regenerated stands of Pinus banksiana: influence of site characteristics

Abstract

We investigated the frequency of root grafting in naturally and artificially regenerated stands of jack pine ( Pinus banksiana Lamb.) in the western boreal forest of Quebec, Canada. Twelve 30–60 m2 plots were hydraulically excavated to determine effects of site characteristics on frequency and timing of root grafting. Naturally regenerated stands had grafted tree percentages similar to artificially regenerated stands (21%–71% across plots) but greater numbers of root grafts per tree (naturally regenerated, 0.73 graft·tree–1; artificially regenerated, 0.52 graft·tree–1). Mean percentages of grafted trees, number of grafts per tree, and the speed of graft formation were greater in sandy soils (61%, 0.71 graft·tree–1 and 2.43 years, respectively) compared with clay soils (44%, 0.54 graft·tree–1 and 2.97 years, respectively). Proximity of trees was a better predictor of root grafting than stand density, despite many root grafts being found with distant trees (>2 m) in artificially regenerated stands. Our results suggested that root grafts form early in stand development. Even if trees are initially separate entities, this relatively high level of root grafting produces stands where trees are extensively interconnected.

The clonal root system of balsam poplar in upland sites of Quebec and Alberta

“…Trees were also connected by root grafts in all excavated sites (Table ), indicating that root grafting is a common occurrence in balsam poplar, similar to what was found in aspen (DesRochers & Lieffers, ; Jelínková et al., ), in Pseudotsuga menziesii (Eis, ), and in Pinus banksiana (Tarroux & DesRochers, ). It is generally accepted that root graft formation requires firm physical contact and pressure developed as roots increased in size, where intervening bark is broken down and vascular continuity is established (Bormann, ; Eis, ; Kozlowski & Cooley, ).…”

Effect of natural root grafting on growth response of jack pine (Pinus banksiana) after commercial thinning

“…), where we found a high frequency of natural root grafting (up to 70% or more of the trees; Tarroux and Desrochers, 2010). It has been found that the roots and stumps of dead or cut trees could be kept alive through root grafts with living residual trees (DesRochers and Lieffers, 2001;Fraser et al, 2007;Tarroux and Desrochers, 2010). This indicates that carbohydrates are transferred from living trees to the roots and stumps of removed or dead trees (Fraser et al, 2006).…”

“…Natural root grafts have been found in many tree species (Graham, 1959), including natural stands and plantations of jack pine (Pinus banksiana Lamb. ), where we found a high frequency of natural root grafting (up to 70% or more of the trees; Tarroux and Desrochers, 2010). It has been found that the roots and stumps of dead or cut trees could be kept alive through root grafts with living residual trees (DesRochers and Lieffers, 2001;Fraser et al, 2007;Tarroux and Desrochers, 2010).…”

“…Thinning shock has often been linked to site quality; poor sites were found to have greater growth reductions following thinning compared to higher quality sites (DeBell et al, 2002;Isomäki, 2004a, 2004b). We previously showed that root grafting frequency was higher in sandy soils compared to clayey soils, which are generally more nutrient-rich (Tarroux and Desrochers, 2010). Hence site quality and root grafting could be linked, thereby in turn affecting responses to thinning.…”

“…Three of the sites had been commercially thinned (i.e., stems removed had diameter at breast height (DBH) > 10 cm) in 1998 (stands T) while the two other sites were control unthinned stands (stands C; Sites N1 and N2 in Tarroux and Desrochers, 2010). The stands were located between 48 • 20 N and 48 • 41 N, and between 77 • 16 O and 78 • 8 O in the western balsam fir-paper birch (Abies balsamea-Betula papyrifera) bioclimatic domain of the boreal forest of eastern Canada (Grondin, 1996).…”