Young Plantations Continue Losing Carbon

Long after harvesting, new forests keep leaking substantial amounts of carbon research in northern British Columbia has revealed. By the time plantations are ten years old, though, carbon accumulating in growing trees begins to outpace ongoing losses. Still, after 20 years, west-central BC sites that were clearcut then burned have not regained their post-harvest carbon stores.

At moderately-moist mid and high-elevation sites of three biogeoclimatic zones: Sub-boreal Spruce, Engelmann Spruce - Subalpine Fir and Interior Cedar - Hemlock, the patterns are similar. Broadcast burning right after clearcutting reduces carbon in slash and soils by 28%. Then the decline continues, amounting to another 23% of the carbon over the next 20 years, for a total loss of 71 Mg/ha.

While seeing losses of carbon from burning is not surprising, the continued dwindling indicates that organic debris decomposes faster than what plants can replenish with shedding leaves. As well, the forest floor never regains any of the 5.5 cm depth it lost during the first five years after harvesting. Altogether, carbon mass drops by 70% in logging slash, 63% in the forest floor and 25% in mineral soil.

During the same period, well-stocked lodgepole pines have reached eight meters in height and accumulated 26 Mg/ha of carbon. By the end of two decades, the sites average 94 Mg of carbon per ha, totalling 70% of what they stored immediately after harvesting. Yet these young plantations have a long ways to go before reaching the 400 Mg/ha of carbon typically contained in central BC's mature forests.