Policy of Reforesting With Local Tree Seed Questioned

Seed from lodgepole pine trees in southern British Columbia produces faster-growing trees in many other areas of the province than does local seed. When forecasts of climate change are added to the equation, then bringing in the most vigorous tree seed can boost productivity over most of pine's range by up to 36 percent.

These findings call into question the assumptions behind provincial policy to reforest harvested sites only with trees from local seed.

Provenance trials, to assess at a particular location how well lodgepole pine trees from different regions grow, show that seed originating in Montana, Washington, Oregon, Yukon or northern BC develops relatively slow-growing trees, regardless of climate. Trees originating from seed planning units of NElow, at low elevations of the west Kootenays and PGlow, at low elevations in east-central BC, put on more volume than other sources under a wide range of mean annual temperatures. The NElow seed especially holds promise for much of the province.

Mean annual temperature accounts for nearly two-thirds of variation in height growth for lodgepole pine, and annual heat moisture index explains another 6 percent. Overall for BC, researchers forecast pine productivity peaking at 7 percent higher than present in 2030 when mean annual temperatures have risen by 1.5 °C. and mean annual precipitation by 2.7 percent. Migrating tree seed to use the fastest-growing seed source will boost wood volume gains much further under those climate conditions.

As warming continues, pine yields would drop below current levels by 2069, but not if forests were planted with trees from the fastest-growing stock. Using optimal seed for all lodgepole pine in the province could make an average difference of 32 percent in tree volume per hectare when mean annual temperatures are 4 °C higher than today.