Root growth capacity: relationship with field root growth and performance in outplanted jack pine and black spruce

Summary First- and second-year results from a study of mounding site preparation for regenerating boreal forest cutovers in Ontario using bareroot jack pine and black spruce are reported. At each of 4 sites 5 treatments were investigated: (a) control; (b) shoulder of standard Bräcke patch; (c) bottom of Bräcke patch; (d) a 20-L mound of mineral soil on the mineral soil on the shoulder of Bräcke patch; (e) a similar mound on the double layer of organic matter (original forest floor + inverted organic matter from Bräcke patch) immediately distal to the patch. At each site, 600 pines or spruces were planted as 4 replicates of 30-tree plots for the 5 treatments. Field root growth (FRG) was determined on 5 trees for each plot 30 days post-planting. Survival and growth were assessed after 1 and 2 growing seasons.Root growth capacity (RGC) tests revealed large differences between lots of planting stock. Only with black spruce was a higher RGC associated with better nursery performance. Only one third of a tree's RGC could be explained in multiple regression with initial top height, stem diameter, and root area index. Field performance of outplants was highly site- and treatment-specific, but in both species on all sites, stem diameter increment and FRG were consistently high for the mound treatment. FRG, (r>0.50 in 8 of 16 cases), was best correlated with first- + second-year stem diameter increment. Correlations between FRG and RGC were inconsistent and generally low.