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 grow th in northwestern Quebec. Height-age curves produced from stem analys es of dominant trees from 96 sample plots produced three jack pine (Pi nus banksiana Lamb.) productivity classes. The low productivity class includes moderately dry shallow tills, shallow organic deposits over b edrock, and fluvioglacial sands with moisture regime classes moderatel y dry and fresh. Moderately dry to very moist deep tills and moderatel y dry to moist clays are classified as having high and very high produ ctivity, respectively. The large difference in height growth between t hese latter two groups and the low productivity class precluded the de finition of a moderate productivity class. The form of the height-grow th curves was very similar among site types except for sandy, moderate ly dry sites, which showed a growth delay at young ages. On dry sites, particularly on well-drained tills, density and basal area were highe r 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 gr eater number of stems on tills. There was little difference in site in dex between natural jack pine growing on clays and tills. The low nutr ient and moisture requirements and strung taproot of jack pine could e xplain why soil depth and bulk density are more important than soil ri chness. Although site type, expressed as a combination of surface depo sit and moisture regime class, may be more detailed than needed, it pr ovided an adequate prediction of potential jack pine productivity.