Using cover crops to establish white and black spruce on abandoned agricultural lands

Abstract

Vegetation control is a critical factor in reforestation. On abandoned agricultural lands, an alternative to herbicide application is the use of cover crops to compete with the weeds and to improve survival and growth rates of transplanted species. A factorial experiment was carried out on four sites to test this hypothesis. The experiment included three factors. The first factor consisted of lime versus no lime application. The second factor included four cover crop combinations and a control. Cover crop combinations were winter barley (Hordeum vulgare) underseeded with either birdsfoot trefoil (Lotus corniculatus), Kentucky bluegrass (Poa pratensis), ladino clover (Trifolium repens), or a mixture of Kentucky bluegrass and ladino clover. The third factor consisted in planting either white (Piceaglauca) or black (Picea mariana) spruce seedlings. Winter barley did not establish as rapidly and vigorously as expected. Nevertheless, the cereal reduced weed populations in the establishment year. For broadleaf weeds, this reduction was not large enough to allow a carryover during subsequent years. In contrast, subsequent increase of the grassy weed populations was slowed down in the presence of cover crops. The establishment of the other cover crops was poor and highly variable from site to site. It is not clear whether this relative failure was due to growing conditions, poor establishment of the cereal cover crop, or to other factors. Liming and cover crops had little effect on spruce growth but black spruce seedlings grew taller than white spruce seedlings at two out of four sites, and basal diameter of white spruce reached larger values than did black spruce. For white spruce, this might constitute an advantage in old fields where seedlings are prone to lodging under weed pressure. Finally, it was noted that seedling survival was exceptionally high in all treatments.