Effects of spacing, species and coppicing on leaf area, light interception and photosynthesis in short rotation forestry

Abstract

Red alder and Balsam Spire poplar were planted in May 1989 as single stems at 1.0 m spacing on a converted agricultural site in central Scotland. Biomass production, canopy structure and light interception were quantified and the effects of coppicing and of planting at wider (1.5 m) spacing were determined. Bowles hybrid willow was grown as coppice planted at 1.0 m spacing and its canopy characteristics compared with those of coppiced alder and poplar. Total above-ground biomass at 5 years old, ranged from 51 to 81 Mg ha −1 dry matter with an average annual production of 10 Mg ha −1 dry matter. Coppicing reduced poplar and alder biomass by 26% and 47%, respectively. Planting at the wider spacing reduced stocking density by 56% and led to a 35% reduction in biomass. Both coppicing and planting at wider spacing increased root:shoot ratios and leaf weight ratios in alder and poplar and reduced the seasonal interception of photosynthetically active radiation (PAR) for 2 years. Light interception was most influenced by early canopy development due to the annual distribution of PAR. Treatment effects on net photosynthesis were due, primarily, to changes in canopy structure affecting light levels. After 3 years light interception was similar across all treatments suggesting that planting at wider spacing or early coppicing would require additional weed control for one more growing season.