Height growth of jack pine (Pinus banksiana) in relation to site types in boreal forests of Abitibi, Quebec

A combination of surface deposit and moisture regime class was used to investigate the utility of site type as a predictor of jack pine growth in northwestern Quebec. Height-age curves produced from stem analyses of dominant trees from 96 sample plots produced three jack pine (Pinus banksiana Lamb.) productivity classes. The low productivity class includes moderately dry shallow tills, shallow organic deposits over bedrock, and fluvioglacial sands with moisture regime classes moderately dry and fresh. Moderately dry to very moist deep tills and moderately dry to moist clays are classified as having high and very high productivity, respectively. The large difference in height growth between these latter two groups and the low productivity class precluded the definition of a moderate productivity class. The form of the height-growth curves was very similar among site types except for sandy, moderately dry sites, which showed a growth delay at young ages. On dry sites, particularly on well-drained tills, density and basal area were higher than on clay sites. Although volume yield of natural stands on tills and clays would thus be similar, it would likely be spread among a greater number of stems on tills. There was little difference in site index between natural jack pine growing on clays and tills. The low nutrient and moisture requirements and strung taproot of jack pine could explain why soil depth and bulk density are more important than soil richness. Although site type, expressed as a combination of surface deposit and moisture regime class, may be more detailed than needed, it provided an adequate prediction of potential jack pine productivity.