Dan Binkley Northern Arizona University and SLU (thanks to KSLA and Wallenberg professorship)

Transcription

1 Comprehensive carbon accounting for forests: issues of time and space Dan Binkley Northern Arizona University and SLU (thanks to KSLA and Wallenberg professorship)

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3 Three conclusions for today: The flows of C in forests are complex: big flows (fluxes) are rapid; changes in pool sizes are slow. Big changes in C accumulation occur in the trees, not so much in the soils The net C accumulation in forests is very important in Sweden s C budget, but not so large for Planet Earth

4 Temporal scales Photosynthesis: RuBisCO enzyme is the most abundant protein on Earth Catalyzes the addition of one molecule of CO 2 onto a sugar at a rate of 3-10 times/second

5 Temporal scales Photosynthesis adds about 10 g C/m 2 in a day in a productive forest The trees allocate about 4 g C/m 2 to the soil daily

6 Temporal scales The trees allocate about 4 g C/m 2 to the soil daily How much of that will still be in the soil 1 year later? Perhaps only 0.8 g C/m 2 (20%) Meanwhile, the soil loses 0.8 g C/m 2 from older soil C so there s no net change. Giardina et al. 2004

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8 How does the uptake and release of C change when we clearcut and regrow this Eucalyptus forest?

9 Eddy Covariance (or flux): Measure wind direction and speed, CO 2 concentrations in air above forest CO 2 sensor Net C release 3-D wind speed sensor Net C uptake Net C release From Yann Nouvellon and colleagues

10 From Yann Nouvellon and colleagues

11 Flux of C (μmol m -2 sec -1 ) Average daily pattern for each month: Harvest Replanting Less C uptake in the dry season than in the wet season Months after Feb From Yann Nouvellon and colleagues

12 Flux of C (μmol m -2 sec -1 ) Average daily pattern for each month: Harvest Replanting The site loses C after harvest (a net source of C to the atmosphere) Months after Feb From Yann Nouvellon and colleagues

13 Flux of C (μmol m -2 sec -1 ) Average daily pattern for each month: Harvest Replanting Months after Feb The replanted forest became a net sink for C about 6 months after planting From Yann Nouvellon and colleagues

14 Flux of C (μmol m -2 sec -1 ) Average daily pattern for each month: Harvest Replanting 2 year-old forest better C sink than 7 yr old forest Months after Feb From Yann Nouvellon and colleagues

15 A Nordic example: Scots pine in S. Finland Recent clearcut 40-yr-old stand Kolari et al. 2004

16 The right method for the time scale of the question: Measure C output How much energy did this elephant expend today? Measure C intake

17 What was the elephant s net change in mass for a year? Daily input/output could be summed, but any errors accumulate and give poor long-term estimate January 1 December 31

18 At the geographic scale of the entire country and a single year (2013), the C stock of Swedish forest biomass grows faster than harvests:

19 At the geographic scale of the entire country and a century: The C stock of Swedish forest biomass doubles

20 Does the increased C stock of Swedish forests result from low harvests or from accelerating growth? One of the most important facts about Swedish forests: growth is increasing dramatically Annual growth as % of Increase = 1.2% annually r 2 = 0.91, P < Year

21 Percent of O horizons How fast does the C content of forest soils change? s Avg = 8.9 cm P = 0.13, so we cannot be very confident of any real change in 20 yr 2000s Avg = 9.2 cm We can be very sure that any real change was very small (~0.05 m 3 ha -1 yr -1 of wood equivalent) O horizon thickness (cm) raw, preliminary data provided by J. Stendahl, National Forest Soils Inventory

22 Percent of B horizons Is soil C content of mineral soils changing? A little? s s B horizon %C raw, preliminary data provided by J. Stendahl, National Forest Soils Inventory

23 The timescale of a forest rotation includes harvesting: how does soil C change with clearfelling? A meta-analysis: 1 0 Overall change O horizons Upper mineral Lower mineral Change in soil C content (%) Nave et al. 2010

24 But what if the climate changes? C flux (g m -2 yr -1 ) Globally, Gross Primary Productivity (GPP) increases: o 500 g m -2 yr Litton and Giardina Mean annual temperature ( o C)

25 C flux (g m -2 yr -1 ) and total belowground C flux (TBCF) also increases o 500 g m -2 yr o 250 g m -2 yr -1 Litton and Giardina Mean annual temperature ( o C)

26 Soil heating increases the flow of CO 2 out of soils BUT, much of the increase is extra root production and respiration NOT loss of soil organic matter. Relative soil CO 2 efflux (4 o C = 1.0) Norway spruce in Austria Decomposition + root respiration Decomposition Soil temperature ( o C) Schindlbacher et al., 2009

27 The bottom line: Sweden s forests are the country s major sink for C

28 But: We can t ask Sweden s forests to save the world s climate

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31 Carbon kept out of the atmosphere over 3 rotations: Min. soil O horizon 2010