T Suni

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Published on January 8, 2008

Author: Manuele

Source: authorstream.com

Trace gas fluxes in a boreal forest remain unaltered after thinning :  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 Motivation and objectives:  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 Before:  Before After:  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) Slide6:  Eddy covariance (EC) Turbulence  vertical transport TOWER Vertical wind speed (~10 Hz) + gas/particle concentration (~10 Hz)  net flux (30 min average) Thinning Jan – Mar 2002:  Thinning Jan – Mar 2002 Neutral stratification: 80% of flux originates within 200 m (dashed lines) Sectors for summer 2002 Sector for before/after What happened to CO2 flux?:  What happened to CO2 flux? June-July 16–19°C Measured half-hour flux values (squares) Fitted light-response curves (lines). Summer 2002 Before / after 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). Why has CO2 flux not changed?:  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. Sources of increase and decrease in photosynthesis P::  Sources of increase and decrease in photosynthesis P: Total ecosystem photosynthesis: Canopy 85 – 90% Understorey 10 – 15% Sources of increase and decrease in photosynthesis P::  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) Sources of increase and decrease in soil respiration Rs:  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 Sources of increase and decrease in soil respiration Rs:  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) Conclusions:  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. References:  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 Slide16:  Source area (footprint) varies according to atmospheric stability Slide17:  -200 0 200 -200 0 200 -200 0 200 Very unstable Neutral Very stable Slide18:  Very unstable Neutral Thinned fraction variable Slide19:  Very unstable Neutral Thinned fraction variable Slide20:  Very unstable Neutral Thinned fraction variable Slide21:  Very unstable Neutral Thinned fraction variable Slide22:  Very unstable Neutral Thinned fraction variable Slide23:  Very unstable Neutral Thinned fraction variable Results have not changed (so far):  Results have not changed (so far) Thank you!

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