Nutrient loaded seedlings reduce the need for field fertilization and vegetation management on boreal forest reclamation sites

Abstract

Tree seedlings loaded with nutrients during nursery production have shown increased growth and survival relative to standard seedlings upon outplanting. We examined outplanting performance of nutrient loaded and standard trembling aspen (Populus tremuloides) seedlings, along with composition and cover of competing vegetation, on a boreal oil sands reclamation site with two different soil types (forest floor mineral mix and peat mineral mix) and four different broadcast fertilizer applications [250 kg/ha immediately available fertilizer (IAF), 500 kg/ha IAF, 670 kg/ha controlled release fertilizer, and an unfertilized control]. Average height growth across all treatments was 19 % greater for nutrient loaded aspen seedlings than standard seedlings after two growing seasons. With respect to soil types, aspen growth was greater on peat mineral mix and seedlings growing in this soil type showed a greater response to both nutrient loading and fertilization; however, this could partially be attributed to greater cover by competing vegetation on the forest floor mineral mix. In the first growing season, trees treated with immediately available fertilizer showed the greatest growth response but in the second growing season only the controlled release fertilizer application resulted in growth rates greater than the controls. Fertilizer regime had similar effects on total cover of competing vegetation, although fertilization additionally promoted increased cover of grasses in the forest floor mineral mix. Overall, we clearly show that nutrient loaded trembling aspen seedlings can be used to offset early field fertilization needs at forest reclamation sites.