Isoprene and monoterpene emissions from alder, aspen and spruce short rotation forest plantations in the UK

Gemma Purser, Julia Drewer, Mathew R. Heal, Robert A.S. Sircus, Lara K. Dunn, James I. L. Morison

Research output: Contribution to journalArticlepeer-review

Abstract

An expansion of bioenergy has been proposed to help reduce fossil-fuel greenhouse gas emissions, and short-rotation forestry (SRF) can contribute to that expansion. However, SRF plantations could also be sources of biogenic volatile organic compound (BVOC) emissions, which can impact on atmospheric air quality. In this study, emissions of isoprene and 11 monoterpenes from the branches and forest floor of hybrid aspen, Italian alder and Sitka spruce stands in an SRF field trial in central Scotland were measured during two years (2018–2019) and used to derive emission potentials for different seasons. Sitka spruce was included as a comparison as it is the most extensive plantation species in the UK. Winter and spring emissions of isoprene and monoterpenes were small compared to those in summer. Sitka spruce had a standardised average emission rate of 15 μg C g−1 h−1 for isoprene in the dry and warm summer of 2018, more than double the emissions in 2019. However, standardised average isoprene emissions from hybrid aspen were similar across both years, approximately 23 μg C g−1 h−1 and standardised average isoprene emissions from Italian alder were very low. Average standardised total monoterpene emissions for these species followed a similar pattern of higher emissions in the warmer year: Sitka spruce emitting 4.5 μg C g−1 h−1 and 2.3 μg C g−1 h−1 for 2018 and 2019, aspen emitting 0.3 μg C g−1 h−1 and 0.09 μg C g−1 h−1 and Italian alder emitting, 1.5 μg C g−1 h−1 and 0.2 μg C g−1 h−1, respectively. In contrast to these foliage emissions, the forest floor was only a small source of monoterpenes, typically one or two orders of magnitude lower than foliage emissions on a unit ground area basis. Estimates of total annual emissions from each plantation type per hectare were derived using the MEGAN 2.1 model. The modelled total BVOC (isoprene and monoterpenes) emissions of SRF hybrid aspen plantations were approximately half those of Sitka spruce for plantations of the same age. Italian alder SRF emissions were 20 times smaller than from Sitka spruce. The expansion of bioenergy plantations to 0.7 Mha has been suggested for the UK to help achieve net-zero greenhouse gas emissions by 2050. The model estimates show that with such an expansion total UK BVOC emissions would increase between < 1 % and 35 %, depending on the tree species planted. Where increases might be small on a national scale, regional increases might have a larger impact on local air quality.
Original languageEnglish
Article numberbg-18-2487-2021
Pages (from-to)2487-2510
Number of pages24
JournalBiogeosciences
Volume18
Issue number8
Early online date20 Apr 2021
DOIs
Publication statusE-pub ahead of print - 20 Apr 2021

Keywords

  • Bioenergy
  • biosphere-atmosphere exchange
  • a-Pinene
  • Short rotation forestry
  • BVOC emissions

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