Influence of vegetation management and fertilization on Pinus pinaster growth and on understory biomass and composition

Abstract

To study the influence of understory vegetation management and fertilization, on pine growth and competing vegetation, a field trial was established in a 6-year old pine forest. Treatments included: control (C), vegetation cutting and removal, with and without fertilization (CRF and CR treatments), vegetation chipping, with and without fertilization (CDF and CD treatments). Treatments were replicate three times and arranged in completely randomized blocks. Pine volume was determined between 2002 and 2007 and understory was surveyed, quantified and analysed for macronutrients in 2002 and 2003. Vegetation chipping plus fertilization lead to the largest (p < 0.05) increase in pine volume (9.6 m3 ha–1 year–1) while removal of understory resulted in the lowest (p < 0.05), 5.1 m3 ha–1 year–1. In the other treatments, the average increase in volume was similar (6.4 m3 ha–1 year–1). When understory was removed nutrient output was rather large, especially the N output since Ulex minor was in 2002 the dominant species (65%). CD treatment was the most effective in reducing understory biomass (–76%), followed by CR (–65%), CDF (–57%) and CRF (–46%) treatments. In Control, vegetation biomass increased 48%. These results indicate that removal of understory without fertilizer addition is not a suitable practice. Chipping of vegetation besides avoiding nutrient output, decreased the amount of fuel, hence decreases fire risk, and if used with fertilizers leads to a significant increase in pine growth.