substrate fertility iceland and Alaska
adding fertiliser does not immediately establish critical nutrient cycles and too much fertiliser may result in dominance by densely growing grasses or herbs that inhibit tree establishment through competition for nitrogen phosphorus water or light appropriate levels of fertiliser , combined with species that are short-live or grow less densely ,can act as nurse plants for seedling of later successional plants and facilitate succession . Legume introduced to increase soil nitrogen may benefit tree growth if their densities are kept low .Attempts to accelerate reforestation in iceland with commercial fertilisers or by planting tree seedlings into stands of the nonnative nitrogen -fixing lupine (lupinus nootkatensis) have shown some promise for nonnative tree such as sitka spruce (picea sitchensis)However ,overfertilisation or overreliance on lupine may lead to dominance by nonnative herbs or conifers in some part of iceland . Fertilisation of nonnative grasses on the Alaska pipeline corridor delayed recolonisation of native tundra species by several de cades low-fertility site where competition is reduced and where all key species are introduced initially have the greatest chance of restoration success