Vegetation management effects on the nitrogen nutrition of white spruce seedlings

Abstract

Fertilization, site preparation, and vegetation management are the main methods used to improve soil nutrient availability in the forest environment. The study was conducted to examine the effect of managing naturally occurring vegetative species on plant stress and nitrogen nutrition of white spruce (Picea glauca [Moench] Voss) seedlings. Site preparation was achieved using the TTS Delta Powered Disc Trencher, and native vegetation was controlled by trimming at the ground surface with manual brush saws. Ammonium nitrate fertilizer (34-0-0) double labeled with 15N was applied to a 1 m2 plot at a rate of 100 kg N ha-1 (2.2923% enrichment). The white spruce seedlings and above-ground native vegetation were destructively sampled at the end of the next two growing seasons. Needles were also removed from white spruce seedlings to assess plant stress by measuring tissue 13C concentrations. Site preparation and vegetation management doubled the fertilizer use efficiency (FUE) of the white spruce seedlings; however, total recovery of fertilizer nitrogen was quite low (2-6% of applied nitrogen fertilizer). The FUE of the major competitors (fireweed [Epilobium Angustifolium L.], grasses, and trembling aspen [Populus tremuloides Michx.]) was decreased by site preparation and vegetation management. Vegetation management increased the tissue 13C concentration of the white spruce seedlings, indicating the seedlings were more stressed than the control and Delta disc trenched treatments. Vegetation management and site preparation increased the uptake of applied nitrogen fertilizer by limiting the fertilizer nitrogen uptake of native vegetation. However, vegetation management may cause greater stress to white spruce seedlings by increasing the light intensity through the removal of the native vegetation.