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Jack pine productivity, regeneration and silviculture

Due largely to its serotinous cones, jack pine is, with white birch and trembling aspen, a major component of the fire-dominated forest mosaic in Abitibi. Stem analyses have shown that best jack pine growth occurs on rich, lacustrine clay soils (fig. 1a; Béland and Bergeron, 1996) However, these soils are also prone to rapid invasion of competitive vegetation following disturbance. If no special action is undertaken following harvesting on these sites, natural regeneration of jack pine is almost nonexistent. Therefore, cutovers on mesic clays must generally be scarified and planted or they will regenerate naturally into mixedwood stands dominated by birch and aspen. One current study is testing the possibility of stimulating jack pine regeneration, in order to develop silvicultural techniques inspired by natural stand dynamics. The study is aimed at determining the factors controlling natural regeneration of jack pine on tills, clays and sandy soils of Abitibi.

The more open stand structure found on sandy sites allows a more abundant production of seed and cones than on clay or till sites (fig 1b). On all the soil types studied, jack pine cones distributed on the ground after harvesting opened and dispersed their seed. Lower temperatures and higher moisture levels of clay sites however are responsible for better seed germination rates than on sandy sites. A silvicultural test of on-site delimbing and scarification has revealed that on clays, scarification is not necessary for jack pine seed germination. Contrary to results of similar studies on sandy sites, density of jack pine seedlings observed two years after harvest on undisturbed seedbeds was greater than that observed on disturbed seedbeds (fig 1c and 1d). Scarification can, however, be useful in reducing slash thickness on the site. We recommend limbing up to the fine end of the stem in order to assure better distribution of seed-bearing cones and reduction of slash thickness (Béland & Bergeron, 1993)

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Fig. 1. a) Jack pine site index by site types. b) Jack pine stand seed production on three soil types. c) Treatments effects on seedbed proportion. d) Density of jakc pine seedlings after two years on each seedbed types.

 

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