Trace gas fluxes in a boreal forest remain unaltered after thinning

1
Trace gas fluxes in a boreal forest remain
unaltered after thinning

• T. Suni1, T. Vesala1, Ü. Rannik1, P. Keronen1, T.
  Markkanen1, S. Sevanto1, T. Grönholm1, S.
  Smolander1, M. Kulmala1, R. Ojansuu2, H.
  Ilvesniemi2, A. Uotila3, A. Mäkelä4, J.
  Pumpanen4, P. Kolari4, F. Berninger4, E.
  Nikinmaa4, N. Altimir4, and P. Hari4
• 1Department of Physical Sciences, University of
  Helsinki 2Finnish Forest Research Institute
  3Hyytiälä Forestry Field Station, University of
  Helsinki 4Department of Forest Ecology,
  University of Helsinki, Finland

2
Motivation and objectives

• Effects of management on forest-atmosphere
  interactions
• First commercial thinning of Scots pine forest
  (40 yrs) at SMEAR II, Hyytiälä, southern Finland
• Multiannual record of eddy-covariance fluxes
  (CO2, H2O, O3, particles)

Results for CO2
3
(No Transcript)
4
Before
5
After
Before After Average basal area of stems at
1.3 m 21.9 m2ha-1 16.4 m2ha-1 (25 removed)
All-sided LAI 8 6 Total logging waste
(tree tops, branches, stumps and coarse
roots) 611 g C m-2 (remained) Stems (about
2/3 of biomass) 1000 g C m-2 (removed) Dead
needles and fine roots 165 g C m-2 (estimated)
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Eddy covariance (EC)
TOWER Vertical wind speed (10 Hz) gas/particle
concentration (10 Hz) ? net flux (30 min average)
Turbulence ? vertical transport
7
Thinning Jan Mar 2002
Sectors for summer 2002
Sector for before/after

• Neutral stratification 80 of flux originates
  within 200 m (dashed lines)

8
What happened to CO2 flux?
June-July 1619C Measured half-hour flux
values (squares) Fitted light-response curves
(lines).
Grey intact White thinned
Left Greatest difference between the sectors
1996 (dotted lines). Right Weakest and
strongest light response 2001 (upper dotted
line) 1996 (lower dotted line).
Before / after
Summer 2002
9
Why has CO2 flux not changed?
CO2 flux is the sum of photosynthesis and
ecosystem respiration. It follows that either 1)
Respiration components have increased/decreased
by about the same amount as photosynthesis has
or 2) Respiration and
photosynthesis rates have remained unaltered.
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Sources of increase and decrease in
photosynthesis P

• Total ecosystem photosynthesis
• Canopy 85 90
• Understorey 10 15

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Sources of increase and decrease in
photosynthesis P

• 1) Canopy P decreases
• Measured reduction of intercepted PAR and a
  model for
• radiation interception and canopy P ? canopy P
  -18-20
• ? total P -15-18.
• 2) Understorey P increases
• Transmitted PAR reaching forest floor doubled ?
• understorey P also increased, maybe even
  doubled.
• Originally, estimated understorey P 10-15 of
  total P ?
• 10-15.

(Oker-Blom et al. 1989)
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Sources of increase and decrease in soil
respiration Rs

• Total soil respiration (880 gm-2yr-1)
• Heterotrophic 50 (440 gm-2yr-1)
• Autotrophic 50 (440 gm-2yr-1)

Pumpanen et al. 2003, Högberg et al. 2001
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Sources of increase and decrease in soil
respiration Rs

• 1) Heterotrophic Rs increases
• Decomposition of total logging waste, extra
  needles and fine roots ? original 440 gm-2yr-1
  10 44 gm-2yr-1.
• 2) Autotrophic Rs decreases
• If canopy P decreases by 20, so does
  autotrophic Rs ? original 440 gm-2yr-1 -20 -88
  gm-2yr-1.

(Liski et al. 2003)
14
Conclusions

• A common routine operation (first commercial
  thinning) changes physical processes (light
  penetration, wintertime albedo, particle
  deposition)
• Does not change biologically controlled trace gas
  fluxes redistribution of sources and sinks is
  comprehensively able to compensate for the lower
  foliage area.

15
References

• Högberg, P. et al. Large-scale forest girdling
  shows that current photosynthesis drives soil
  respiration. Nature 411, 789-792 (2001).
• Liski, J., Palosuo, T. and Sievänen, R. 2003. The
  simple Dynamic Soil Carbon Model Yasso. Submitted
  for publication in Biogeochemistry.
• Pumpanen, J., Ilvesniemi H., Perämäki M., and
  Hari, P. 2003. Seasonal patterns of soil CO2
  efflux and soil air CO2 concentration in a Scots
  pine forest comparison of two chamber
  techniques. Global Change Biology 9, 371-382.
• Oker-Blom, P., Pukkala, T. Kuuluvainen, T.
  Relationships between radiation interception and
  photosynthesis in forest canopies effects of
  stand structure and latitude. Ecol. Modell. 49,
  73-87 (1989)
• Sevanto, S. et al. Xylem diameter changes as an
  indicator of stand-level evapo-transpiration.
  Boreal Environment Research, 45-52, 2001

16
Source area (footprint) varies according to
atmospheric stability
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Very stable
Very unstable
Neutral
-200 0 200
-200 0 200
-200 0 200
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Thinned fraction variable
Neutral
Very unstable
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Thinned fraction variable
Neutral
Very unstable
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Thinned fraction variable
Neutral
Very unstable
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Thinned fraction variable
Neutral
Very unstable
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Thinned fraction variable
Neutral
Very unstable
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Thinned fraction variable
Neutral
Very unstable
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Results have not changed (so far)

• Thank you!