Environmental impacts of harvesting biomass from the Nordic forests. Nicholas Clarke Norwegian Forest and Landscape Institute

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1 1 Environmental impacts of harvesting biomass from the Nordic forests Nicholas Clarke Norwegian Forest and Landscape Institute

2 Background 2 Increased use of forest biomass for energy might lead to conflict between different interests: on the one side, the need for a secure and renewable source of energy as well as rural employment, and on the other ecologically sound long-term timber production, biological diversity and other uses of the forest. Sustainability principles and criteria have therefore to be incorporated into policy frameworks and support schemes. To do this, a sound scientific basis is essential.

3 3 Environmental sustainability challenges 1. Effects of biomass removal on soil/soil water Risk for nutrient loss Effects on carbon storage Physical changes e.g. erosion and compaction 2. Effects of biomass removal on surface water 3. Effects of biomass removal on biodiversity

4 4 Environmental sustainability challenges 1. Effects of biomass removal on soil/soil water Risk for nutrient loss Effects on carbon storage Physical changes e.g. erosion and compaction 2. Effects of biomass removal on surface water 3. Effects of biomass removal on biodiversity

5 Risk for nutrient loss A large part of the nutrients (for example N, P and base cations) are concentrated in the needles and branches. With intensive removal (i.e. removal of slash), or if the rotation period is too short, large amounts of nutrients can be removed, causing lower growth in the next rotation. 5 Raulund- Rasmussen et al. 2008

6 Field experiment In 2008 we started a field experiment at Tjerne gård, Gaupen in Hedmark, to compare the effects of stem-only (SOH) and whole-tree (WTH) harvesting on soil and soil water chemistry (carbon and nutrients), ground vegetation and regeneration. Harvesting in March 2009 and slash removal in September The plot at Gaupen before felling (photo: Kjersti Holt Hanssen)

7 Paired plots with SOH and WTH WTH plots: piles of harvesting residues, residues removed Each plot has 2 lysimeters for soil water sampling (30 cm)

8 How much slash is actually removed? 8 Kg dry weight R5 Total slash Slash removed R12 Thanks to Kjersti Holt Hanssen

9 Long-term sustainability depends on the soils ability to replenish the nutrient stores: Classification of soils as robust (R) or sensitive (S) in relation to increased biomass removal (from Raulund-Rasmussen et al. 2008) 9

10 Concentrations of nitrogen and base cations in soil water can increase after harvesting 10 6,0 5,0 4,0 3,0 2,0 SOH WTH pile WTH removal 1,0 0, Results from the Gaupen field experiment: NO 3 -N concentrations in soil water (mg/l)

11 11 1,6 1,4 1,2 1,0 0,8 0,6 SOH WTH pile WTH removal 0,4 0,2 0, Results from the Gaupen field experiment: Mg concentrations in soil water (mg/l)

12 Concentrations of nutrients in soil water highest in the second year after harvesting (except for ammonium) Similarities between SOH and WTH piles, compared to where slash was removed Peaks in concentrations higher where there had been piles, compared to SOH

13 13 Does nutrient leaching lead to increased runoff of nutrients? Water runoff increases after harvesting. Although possibly locally important, nitrate runoff after stem-only harvesting may be relatively unimportant on a larger spatial and temporal scale compared to other nitrate sources (Futter et al. 2010)

14 The carbon cycle: Biomass harvesting affects the ability of forests (including forest soils) to sequester carbon 14 C storage in soil (dashed line) and above-ground tree biomass (whole line) during harvesting and the next rotation (from Nilsen et al. 2008): 1) the soil begins to accumulate C again (net sink), 2) the soil has reached its original C content, 3) net ecosystem productivity becomes positive again after harvesting, and 4) mean annual carbon increment culmination.

15 Harvesting intensity and forest type are important. The C content in the A horizon may increase after sawlog (stemonly) harvesting but be reduced after whole-tree harvesting (Johnson and Curtis 2001). 15

16 Harvesting has several effects relevant to carbon stores and fluxes, including: 1. Biomass removal. 2. Loss of litter input. 3. Root death and decomposition; reduced autotrophic respiration. 4. Increased soil temperature during the growing season, which may increase decomposition, leading to increased carbon release from the soil. 5. Unfavourable moisture conditions might inhibit decomposition. 6. Increased runoff and decreased evapotranspiration. 7. Soil mixing caused by harvesting machines may increase decomposition. Different harvesting technologies could have different effects. 8. Nutrient removal might affect growth in the next rotation. Differences in the relative importance of these factors on a site-by-site basis might explain the differences in observed results 16

17 Predicted carbon binding in productive forest (trees and soil) with three different felling alternatives. All figures in million tonnes. 17 Felling alternative Current level with branches and tops Current level without branches and tops Biomass 2002 in trees and soil Biomass after 50 yr in trees and soil C after 50 yr in trees and soil CO 2 equivalents after 50 years CO 2 equivalents sequestered during 50 years No felling CO 2 equiv./yr Nilsen et al. 2008

18 18 Summary Much slash left on-site, even under WTH The risk for nutrient depletion in the soil varies greatly depending on the characteristics of the soil Raised concentrations of nutrients in soil water suggest increased leaching in the years immediately post-harvest. However, these effects are probably transient and limited in space Effects of WTH vs. SOH on the carbon content of the soil vary, possibly due to the interaction of a large number of different factors. WTH may not lead to a much greater loss of carbon from the soil than SOH.

19 19 Thank you for your attention Gaupen, Hedmark (photo: Kjersti Holt Hanssen)