Coppiced downy birch on cutaway peatlands: heterotrophic soil respiration and C sequestration in tree biomass Jyrki Hytönen Lasse Aro Coppice forests in Europe, Antwerpen 16th of June 1 17.6.2016
Content Peat and wood in energy production Properties of peat cut-away areas Material and methods Experiment Measurement of heterotrophic soil C Results Biomass and C bound in biomass Conclusions Photos: Jorma Issakainen, Jyrki Hytönen, Olli Reinikainen, Seppo Vihanta & Erkki Oksanen 17.6.2016 2
Wood and peat energy in Finland Energy sources Total consumption 361 TWh (2015) Source: Statistics Finland, Energy supply and consumption 3 17.6.2016 Target: 13.5 million m 3 by 2020 Source: Natural Resources Institute Finland
Peatland and peat production areas in Finland 10 million ha of peatlands Forestry: 4.5 million ha drained for forestry Carbon storage 4,500 5,500 Tg C (mineral forest soils 1,000-1,500 Tg C) Peat production on 60,000 ha (0.7% of peatland area) Annually 2,500 ha peat production areas abandoned 4
Properties of cutaway peatlands for biomass production N Ash: P, K, Ca, Mg, micronutrients Thicknes of remaining peat layer Quality of mineral soil: P, K, Ca, Mg, 5 17.6.2016 5 17.6.2016
Different biomass production options on cutaway peatlands After-use considerations land-use change production of renewable biofuels GHG balance 6
Growing of downy birch thicket Cutaway peatlands released 2500 ha annually Seeding or natural regeneration Growing (no tending, no thinnings) Ash fertilization Sprouting Cleacutting at age of 15-25 vears 7 Profitability
Experiment at Aitoneva cutaway peatland Dense downy birch stand established naturally was clearcut Fertilization treatments applied on stumps Control PK 575 kg/ha (P 50, K 95 kg/ha) Wood ash 5 t/ha (P 108, K 339 kg/ha) Trees were grown for 21 years Aitoneva, Kihniö Aitoneva is one of the oldest peat harvesting areas in Finland 8 17.6.2016
Peat decomposition (heterotrophic soil respiration) Measurement points trenched (30 cm) to cut root connections Green vegetation cut > measurement of heterotrophic soil respiration Soil CO 2 exchange measured with EGM-4 Measurements 2-years weekly during the growing season and once a month during the winter Soil temperature, WT and soil moisture measured simultaneously Continuous soil temperature measurements (data loggers) 9 17.6.2016 Natural Resources Institute 9 Finland
Modelling soil respiration 0,5 Non-linear regression between measured soil temperature (5 cm depth) and soil respiration for each sample plot separately flux = a* EXP(b*T5) Temperature at 5 cm depth explained 57-95% of the variation in soil respiration flux (g CO 2 m -2 yr -1 ) 0,4 0,3 0,2 0,1 0,0-5 0 5 10 15 20 25 Temperature at 5 cm depth in soil, oc Annual soil respiration was calculated using hourly soil temperature data flux (g CO 2 m -2 yr -1 ) 0,6 0,5 0,4 0,3 0,2 site1 / peat/ collar1 modelled flux measured flux 0,1 10 17.6.2016 0,0 200 300 400 500 600 Natural Resources Institute 10 Finland Measurement date
Annual GHG emissions due to mineralisation of soil organic matter ------------------------------------------------------------------------------------------ GHG Cut-away Cultivated Pristine peatland agr. land (mean) ----------------------------------------------------------------------------------------- g m -2 a -1 CO 2 1 397 2 072 100 150(2 CH 4-0.05 0.42 2 25(1 N 2 O 0.15 1.74 0 0.004 ------------------------------------------------------------------------------------------ 1) Turunen et al. 2002 2) Minkkinen & Ojanen 2013 Cultivated organic agricultural 1397 g CO 2 = 381 g C land 320 000 ha > emissions 8.5 Tg CO 2 equivalent/year =14.4% of total GHG emissions reported from Finland 11
Stand measurements Tree stand measured several times (d 1.3, h) during 21 years Biomass of birches (roots > 1 cm, stump, stem, branches) calculated with biomass equations (Repola, J. 2008. Biomass equations for birch in Finland. Silva Fennica) Biomass of willows with own allometric equations C content in stems 49.2% (LECO CHN-analyzer) 17.6.2016 12
Hytönen & Aro 2012 Silva Fennica 46(3): 377-394 Fertilization increased biomass production of coppiced downy birch Leafless above-ground biomass in 21 years 3.0 t/ha/a 4.1 t/ha/a 4.7 t/ha/a MAI, leafless above ground-biomass 4.1 t/ha/a 5.6 t/ha/a 6.3 t/ha/a MAI, leafless above ground-biomass + stumps + roots 13 17.6.2016
Annual heterotrophic C efflux from peat and C bound in the birch stands (stems, branches, stumps, roots, no leaves) 400 Sprout originated birch stand helped to compensate C loss from peat. g C m -2 a -1 300 200 72 g C m 2 /a Adding litter layer formation would still decrease the gap 100 0 O PK Ash C emission 14
Conclusions BIOMASS PRODUCTION Fertilized coppiced birches produced 4.1-4.7 t/ha/a (21- year rotation, leafless above-ground biomass) Fertilization after clear-cutting increased production CO 2 SEQUESTRATION Wood energy production could offset soil CO 2 emissions from peat ECONOMY Cut-away peatlands show potential for profitable production of energy biomass without subvention (Jylhä et al. 2015) Low investments on wood production Increased removal due to clear-cut Minimum rotation more than 20 years Profitability is sensitive to harvesting cost 15 17.6.2016