SMEAR I - Värriö
The Värriö Subarctic Research Station and Forestry Field Station for Measuring Ecosystem-Atmosphere Relationship (SMEAR I, established in 1991) are located at the Arctic-alpine timberline in Värriö; strict nature reserve, Finnish Lapland (67.75oN, 29.61oE, 400 m a.s.l.). The area has a clear subarctic character (Hari and Mäkelä 2003; Kolari et al. 2007; Dengel et al. 2013) and the SMEAR I station is surrounded by a homogenous, 10 m tall Scots pine (Pinus sylvestris L.) forest. The main emphasis at SMEAR I is on interactions between forest and atmosphere, air quality and aerosols. Another aim of the station is to study the possible effects of air pollution on forest growth.
In 2012, an eddy-covariance (EC) flux measurement system was installed to study the carbon dioxide and water vapour exchange between the atmosphere and forest at ecosystem level (Figure 1). In 2013-2105, another setup was employed to study exchanges within the sub canopy space. The flux measurements show the forest to act as a sink for carbon dioxide with relatively high proportion being absorbed by the understorey vegetation itself (Kulmala et al. 2019). Furthermore, automated chambers are measuring CO2 fluxes of pine shoots. While the EC and shoot chambers are recording throughout the year, additional automated soil chambers are recording ground CO2 fluxes during snow free periods.
SMEAR II - Hyytiälä
Ivan Mammarella, Kukka-Maaria Erkkilä, Üllar Rannik, Pasi Kolari, Tiia Grönholm, Timo Vesala
The measurements of energy and matter exchange between forest ecosystem and the atmosphere are carried out since 1996 at our Forestry Field Station for Measuring Ecosystem-Atmosphere Relationship (SMEAR II) located in Hyytiälä;, southern Finland (Figure 2). The measurements cover, among others, flux monitoring of CO2, H2O, CH4, N2O, O3, CO, VOCs (volatile organic compounds) and , which is tested as a proxy for photosynthetic carbon uptake. The fluxes are determined applying micrometeorological techniques (including gradient and eddy-covariance methods), automatic and manual chambers for soil, woody-tissue and shoot components, and soil gradient method. SMEAR II forms a unique facility for soil-tree-atmosphere continuous measurements that have been used in several international projects and during field courses and summer schools. As an example Figure 2 shows 12 years of CO2 exchange measurements at SMEAR II.
- Vesala et al. (2010) show that increasing autumn temperature enhances carbon efflux from the Hyytiälä Scots Pine forest, because respiration is strongly temperature dependent and it dominates over photosynthesis especially during late autumn when radiation levels are low. The long-term eddy-covariance dataset from SMEAR II was used in the study.
- Launiainen (2010) analysed twelve-years of eddy-covariance measurements to assess the seasonal and inter-annual variability of surface conductance and energy partitioning, whereas Ilvesniemi et al. (2010) studied the water balance of SMEAR II.
- In Rannik et al. (2009) size-integrated aerosol particle fluxes ranging from 10 nm to 1 μm were analysed for the diurnal, seasonal and annual variation using seven years of eddy-covariance measurements. They observed that the normalised deposition rate was higher in winter than in summer and even in spring period when frequent nucleation events occur and particle concentrations are dominated by small particles.
- Analysis of the functional dependence of particle deposition on driving environmental variables, particle size and possible other factors was analyzed by Mammarella et al. (2011), who found that the seasonal differences in deposition velocities are driven primarily by differences in particle size distribution. The higher winter-time deposition velocities were explained mainly by prevailing bi-modal distributions dominated by larger sizes.
- The recent paper by Rannik et al. (2012) focused on ozone deposition characteristics and partitioning into stomatal and non-stomatal fractions, using ten years of canopy-level ozone fluxes measured at SMEAR II.
Prof. John Grace University of Edinburgh
Prof. Jaana Bäck, Department of Forest Sciences, UHEL
Prof. Pertti Hari, Department of Forest Sciences UHEL
Dr. Mari Pihlatie, Department of Forest Sciences UHEL
Finnish Meteorological Institute
Figure 1: SMEAR I station tower. Photo: Sigrid Dengel.
Figure 2: Scenery from the SMEAR II site. Photo: Juho Aalto.
Figure 3: The weekly running means of net ecosystem exchange (NEE), photosynthesis (GPP) and ecosystem respiration (Reco) derived from our EC measurements from 2001 to 2012. For details of the carbon balance and its variability at the site see Kolari et al. (2009).
Dengel S, Siivola E, Vesala T (in prep.) On the complexity of measuring CO2 exchange of a northern subarctic Pinus Sylvestris L. forest in a complex terrain environment.
Dengel S, Grace J, Aakala T, Hari P, Newberry SL, Mizunuma T (2013) Spectral characteristics of pine needles at the limit of tree growth in subarctic Finland. Plant Ecology and Diversity 6:31-44. 10.1080/17550874.2012.754512
Hari P and Mäkelä A (2003) Annual pattern of photosynthesis in Scots pine in the boreal zone. Tree Physiol. 23:145-155.
Ilvesniemi H, Pumpanen J, Duursma R, Hari P, Keronen P, Kolari P, Kulmala M, Mammarella I, Nikinmaa E, Rannik Ü, Pohja T, Siivola E, Vesala T (2010) Water balance of a boreal Scots pine forest. Boreal Environ.Res. 15:375-396.
Kolari P, Lappalainen HK, Hanninen H, Hari P (2007) Relationship between temperature and the seasonal course of photosynthesis in Scots pine at northern timberline and in southern boreal zone. Tellus Series B-Chemical and Physical Meteorology 59:542-552. 10.1111/j.1600-0889.2007.00262.x
Kolari P, Kulmala L, Pumpanen J, Launiainen S, Ilvesniemi H, Hari P, Nikinmaa E (2009) CO2 exchange and component CO2 fluxes of a boreal Scots pine forest. Boreal Environ.Res. 14:761-783.
Kulmala L, Pumpanen J, Kolari P, Dengel S, Berninger F, Köster K, Matkala L, Vanhatalo A, Vesala T, Bäck J (2019) Inter- and intra-annual dynamics of photosynthesis differ between forest floor vegetation and tree canopy in a subarctic Scots pine stand. Agricultural and Forest Meteorology 271: 1-11. https://doi.org/10.1016/j.agrformet.2019.02.029
Launiainen S (2010) Seasonal and inter-annual variability of energy exchange above a boreal Scots pine forest. Biosci. 7:1-20.
Mammarella I, Rannik U, Aalto P, Keronen P, Vesala T, Kulmala M (2011) Long-term aerosol particle flux observations. part II: Particle size statistics and deposition velocities. Atmos.Environ. 45:3794-3805. 10.1016/j.atmosenv.2011.04.022
Rannik Ü, Mammarella I, Aalto P, Keronen P, Vesala T, Kulmala M (2009) Long-term aerosol particle flux observations part I: Uncertainties and time-average statistics. Atmos.Environ. 43:3431-3439. 10.1016/j.atmosenv.2009.02.049
Rannik Ü, Altimir N, Mammarella I, Back J, Rinne J, Ruuskanen TM, Hari P, Vesala T, Kulmala M (2012) Ozone deposition into a boreal forest over a decade of observations: Evaluating deposition partitioning and driving variables. Atmospheric Chemistry and Physics 12:12165-12182. 10.5194/acp-12-12165-2012
Suni T, Rinne J, Reissell A, Altimir N, Keronen P, Rannik Ü, Dal Maso M, Kulmala M, Vesala T (2003) Long-term measurements of surface fluxes above a Scots pine forest in Hyytiälä, southern Finland, 1996-2001. Boreal Environ.Res. 8:287-301.
Vesala T, Launiainen S, Kolari P, Pumpanen J, Sevanto S, Hari P, Nikinmaa E, Kaski P, Mannila H, Ukkonen E, Piao SL, Ciais P (2010) Autumn temperature and carbon balance of a boreal Scots pine forest in southern Finland. Biogeosciences 7:163-176.