Biomass production of Norway spruce (Picea abies (L.) Karst.) growing on abandoned farmland

Abstract

Biomass production of forests has been studied for at least a century. Tree biomass is used in Sweden both as industrial raw material and an energy source. Few studies dealing with biomass yield from Norway spruce (Picea abies (L.) Karst.) growing on farmland are published. Practical recommendations are sparsely. The aim of this study was to construct dry weight equations for Norway spruce growing on farmland. Dry weight equations for fractions of Norway spruce trees were made. Biomass production was estimated in 32 stands of Norway spruce growing on abandoned farmland. The stands were located in Sweden at latitudes ranging from 58°to 64°N, and their total age varied from 17 to 54 years. A modified 'mean tree technique' was used to estimate biomass production; i.e. the tallest tree was chosen for sampling. The actual mean total dry weight above stump level for the 32 stands was 116 ton ha-1, with a range of 6.0 to 237.4 ton d.w. ha-1. When previous thinning removals were included, the mean biomass value was 127 ton ha-1 (6.0-262.8). In addition to estimating conventional dry weights of trees and tree components, basic density, specific leaf area, total surface area and leaf area index, among other measures, were estimated. Norway spruce biomass yields on plots subjected to different thinning were compared. The total harvested biomass was 75-120 ton d.w. ha-1 in heavy thinnings from below. Stands were thinned four to five times, with the first thinning at 23-27 years and the last at 51-64 years. The harvested biomass obtained in the first thinning was 18-38 ton d.w. ha-1. Total biomass production was 178-305 ton d.w. ha-1. Stands thinned from above supplied 71-130 ton d.w. ha-1 in total and 17-42 ton d.w. ha-1 in the first thinning. The total biomass supply was 221-304 ton d.w. ha-1. Unthinned stands produced a total of 155-245 ton d.w. ha-1.