Nutrient return in litter and rainfall under some exotic conifer stands in New Zealand

Abstract

Because changes in the nutrient content of the soil after afforestation may result in slower growth of succeeding tree crops, a study is being made of the changes taking place in pumice soils under exotic conifers in New Zealand. As litter plays a large part in determining the future nutrient status of the soil, monthly litter-fall collections have been made for several years under radiata pine, Corsican pine, Douglas fir, and European larch. The nutrient compositions of the litters are similar to those reported from other countries but the total annual weights of litter fall are greater in New Zealand. The air-dry weight of litter falling under both radiata and Corsican pines exceeded 8000 lb/ac in one year and averaged more than 5000 Ib/ac/yr. The rate of needle fall under Douglas fir does not vary greatly with season but most Corsican-pine needles fall in the autumn. Under radiata pine there is also a peak needle fall in the autumn but considerable quantities of needles fall throughout the year, especially in young stands. Storms influence the fall of twigs from all species. Rain as it penetrates the tree crowns of radiata pine and Douglas fir removes considerable quantities of potassium and phosphorus. The annual rainfall reaching the ground under Douglas fir contains twice as much potassium and approximately the same amount of phosphorus as the litter fall. This removal of nutrients from the tree crowns reaches a maximum in the late summer and autumn. The greater uptake of sodium on a high-sodium soil is discussed. © Taylor & Francis Group, LLC.