08.08.2015   BIOMASS - DETECTION, PRODUCTION AND USAGE

Poplar

Worldwide, and for a long time, poplars have been used for, inter alia, pulpwood and timber production. Currently, short rotation plantations intended for biomass production are being established. In Sweden poplars have been planted in experiments or plots for practical survey for the last 20 years. Poplar plantations covering small areas of 0.5-2 ha on former farmland can produce 80-100 tonnes ha-1 of wood in ten years (Mean annual increment (MAI): 8-10 tonnes ha-1 years-1). If rotations are longer than 10 years, some of the material harvested will be suitable for use as pulpwood. Nowadays short rotation plantations aiming biomass production has been established. In Sweden poplars have been planted in experiments or plots for practical survey the last 20 years. After harvesting, regeneration of older trees by suckers or sprouts is limited. Certain clones and species produce no or only a few sprouts or suckers. This may be because poplars must be young when they are cut for

sprouts to be initiated. The bark on the poplar stems is thick already when the alders are 15 years old, preventing any buds from growing into sprouts.

 

image152

Fig. 10. Hybrid poplar stand 7.3 Hybrid aspen

Hybrid aspen is a hybrid between European aspen and trembling aspen (Wettstein, 1933). The hybrid was introduced into Sweden in 1939. Today plantations of hybrid aspen are a potential source of bioenergy, pulpwood and timber. The MAI for hybrid aspen is the same as for poplar, 10 tonnes ha-1 year-1. A German study compared the biomass production in repeated five-year rotations of European, trembling and hybrid aspen (Liesebach, et al., 1999). After harvest of the 5-year-old plantation the biomass was: 7 tonnes ha-1 year-1 from European aspen, 18 from trembling aspen and 16-34 from the four clones of hybrid aspen that were examined. The plants were then allowed to produce suckers, resulting in 165,000 suckers ha-1 during the first year and 45,000 suckers ha-1 five years later. During the second rotation, the production was 18 and 20 tonnes ha-1 for European and trembling aspen and 27-41 for the hybrid aspen clones. The amount of biomass after 5 and 10 years could amount to 50 and 100 tonnes ha-1 respectively. If longer rotations are preferred, the focus should be

 

Fig. 11. Hybrid aspen stand

 

image153

on pulpwood and timber production, with bioenergy derived from tops and branches. After harvesting the trees, the stumps produce 50,000-100,000 suckers ha-1. During the subsequent 5-10 year period the sucker biomass will amount to 50-100 tonnes ha-1. However biomass production during a 10-year-old rotation was found to amount to 47, 51 and 87-124 tonnes ha-1 respectively for the aspen stands.