Vesala, T., Hari, P. & Kulmala, M. 2001: Preface: Forest-atmosphere interactions and forest ecology research at SMEAR stations. Boreal Env. Res. 6: 1
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Ilvesniemi, H. & Liu, C. 2001. Biomass distribution in a young Scots pine stand. Boreal Env. Res. 6: 3–8.
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Kurka, A.-M. 2001. The use of cellulose strips to study organic matter decomposition in boreal forested soils. Boreal Env. Res. 6: 9–17.
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Kähkönen, M.A., Wittmann, C., Kurola, J., Ilvesniemi, H. & Salkinoja-Salonen, M. S. 2001. Microbial activity of boreal forest soil in a cold climate. Boreal Env. Res. 6: 19–28.
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Perämäki, M., Vesala, T. & Nikinmaa, E. 2001. Analysing the applicability of the heat balance method for estimating sap flow in boreal forest conditions. Boreal Env. Res. 6: 29–43.
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Sevanto, S., Vesala, T., Perämäki, M., Pumpanen, J., Ilvesniemi, H. & Nikinmaa, E. 2001. Xylem diameter changes as an indicator of stand-level evapo-transpiration. Boreal Env. Res. 6: 45–52.
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Aalto, T. & Juurola E. 2001. Parametrization of a biochemical CO2 exchange model for birch (Betula pendula Roth.). Boreal Env. Res. 6: 53–64.
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Markkanen, T., Rannik, U., Keronen, P., Suni, T. & Vesala, T. 2001. Eddy covariance fluxes over a boreal Scots pine forest. Boreal Env. Res. 6: 65–78.
Abstract
Full text (pdf format)
Ilvesniemi, H. & Liu, C. 2001. Biomass distribution in a young Scots pine stand. Boreal Env. Res. 6: 3–8.
Kurka, A.-M. 2001. The use of cellulose strips to study organic matter decomposition in boreal forested soils. Boreal Env. Res. 6: 9–17.
Kähkönen, M.A., Wittmann, C., Kurola, J., Ilvesniemi, H. & Salkinoja-Salonen, M. S. 2001. Microbial activity of boreal forest soil in a cold climate. Boreal Env. Res. 6: 19–28.
Perämäki, M., Vesala, T. & Nikinmaa, E. 2001. Analysing the applicability of the heat balance method for estimating sap flow in boreal forest conditions. Boreal Env. Res. 6: 29–43.
Sevanto, S., Vesala, T., Perämäki, M., Pumpanen, J., Ilvesniemi, H. & Nikinmaa, E. 2001. Xylem diameter changes as an indicator of stand-level evapo-transpiration. Boreal Env. Res. 6: 45–52.
Aalto, T. & Juurola E. 2001. Parametrization of a biochemical CO2 exchange model for birch (Betula pendula Roth.). Boreal Env. Res. 6: 53–64.
Markkanen, T., Rannik, U., Keronen, P., Suni, T. & Vesala, T. 2001. Eddy covariance fluxes over a boreal Scots pine forest. Boreal Env. Res. 6: 65–78.
The standing biomass of a young Scots pine stand was measured at the SMEAR II experimental station in Hyytiälä, southern Finland. The stem volume was found to be 119 m3 ha–1, corresponding to 41450 kg ha–1 in stem biomass. The needle biomass was 5100 kg ha–1 and was constituted mainly by the two youngest needle age classes. The branch biomass was 9040 kg ha–1 and the root biomass 12 520 kg ha–1. The height of the first living branches was found to vary from 2.2 to 6.9 m, whereas the variation in tree height was between 4.1 and 14 m. The needle surface area was 3.9 m2 m–2 and the root length and surface area were 4180 m m–2 and 8.8 m2 m–2, respectively. More than half of the total fine root surface area was found in the upper 10 cm of the soil.
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This paper addresses the use of cellulose strips (softwood pulp) as a method for studying the decomposition of soil organic matter. The eight study sites were located in four forested catchments in Finland (between 61°–69°N). The sites comprised mineral soil and peat soil plots subjected to minimal anthropogenic influence. The cellulose strips were placed on the soil surface, on the surface and covered with litter, and in the subsurface (0–5 cm) for 49 weeks and the weight loss measured. Significant, positive correlations were found between the weight loss of cellulose strips and the weight loss of local Scots pine needle litter (up to r = 0.98, p < 0.001), and between the weight loss of cellulose strips and basal respiration (up to r = 0.65, p = 0.007). The cellulose strip method can be easily and successfully used to measure cumulative decomposition activity over a period of time.
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Organic matter degrading microbial activities in economically managed, acid boreal Scots pine forest soils were analysed in different seasons. We observed Q10 values ranging from 2.3 to 2.8 for the production of CO2 from endogenous detrital matter at close to in situ temperatures, when the soils were in natural state, immediately after sampling. The Q10 of methane oxidation, beta-glucosidase, C2- and C4-esterases, exhibited values of 1.6 to 2.1 and the corresponding apparent activation energies were from 40 to 70 kJ mol–1. Detrital decomposition extrapolated to zero activity at –7 +/- 1 °C but the actual soil temperature under snow cover never dropped below –3 °C. The degrading activities towards 0.2 to 2 ppm of phenanthrene and of 2,4,5-trichlorophenol showed Q10 values of 2.0 to 4.4 in the fine roots and the rhizosphere fraction of aspen forest soil but there was no activity in the bulk soil. Our results show that the detritus degrading microbial activities in forest soil were only moderately temperature dependent and significant activity continued over the winter.
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A simple quasistationary dynamic model was constructed to analyse the performance of the stem heat balance method for estimating sap flow in tree stems. Model predictions were compared with field measurements of sap flow in a 35-year-old dominant Scots pine tree and in a smaller understorey mountain ash. The sap flow was measured with the Dynamax Flow32&tm; Stem-Flow Gauge system. Results indicate that the heat balance method underestimates the sap flow in steady-state conditions, especially with stems of larger diameters. The reason for the underestimate of the flow in the case of bigger stems is the inaccurate estimation of sap temperature increase DT when measured on the surface of the stem. Additionally, the difference between air and sap temperatures, which is typical of boreal conditions in the early summer mornings, may cause substantial peaks in the sap flow estimates. Increasing the power input will decrease the latter problem but this may result in problems with overheating of the stem.
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Xylem diameters of living trees change diurnally. According to the cohesion-tension theory these changes result from changes in sapwood water content. A model based on the assumptions of that theory was used to predict diameter changes from the water vapour exchange in a boreal Scots pine forest. The total evapo-transpiration was measured with the eddy-covariance technique and the contribution of the understorey with open chambers together with the monitoring of the soil water content by the Time-Domain Reflectometry (TDR) method. Comparisons between measured and calculated xylem diameter changes are presented and discussed. The results reveal that diameter changes follow quite well the water vapour exchange in the cases when there was no rain.
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Gas exchange of one-year-old silver birch (Betula pendula Roth.) seedlings of boreal habitat was studied in laboratory conditions. Seedlings were exposed to stepwise changes in CO2 concentration and irradiance in five constant temperatures ranging from 9 to 33 °C. The Farquhar biochemical model was fitted to the response curves. Values for the photosynthesis parameters Jmax and Vc(max) as well as their temperature dependences were derived from the measurements. Following characteristics of the boreal growth conditions, the response curves were determined also at temperatures below 20 °C. This was, indeed, reflected to photosynthesis parameters, though results showed relatively large variation due to differences among leaves. The gas exchange rates of separate leaves could vary by 40% and also the temperature dependences were slightly different. The slope and curvature of the light response curve were relatively constant above 19 °C and decreased at low temperatures.
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We report the results on eddy covariance measurements of net ecosystem exchange (NEE) and accompanying latent and sensible heat fluxes for 44 months in boreal Scots pine forest (southern Finland). We analysed the temperature dependence of ecosystem respiration and PPFD (photosynthetic photon flux density) dependence of daytime CO2 exchange and calculated the annual carbon budget filling the gaps in data series with the temperature and light dependences. The estimated annual balances of the NEE's were –234 g C m–2, –262 g C m–2 and –191 g C m–2 in 1997, 1998 and 1999, respectively. We calculated also NEE's for every possible 365-day periods included in the data series and the maximum and minimum of such NEE's were –165 g C m–2 and –304 g C m–2. The growing season started around 28 April, 16 April and 25 March in 1997, 1998 and 1999, respectively. The maximum light saturated CO2 uptake rate reached the value of 12 umol m–2 s–1 gradually by the end of June. In autumn, the uptake did not decline gradually but ceased rapidly round the beginning of November. The non-growing season activity is also important, because soil carbon decomposition occurs all year around, even in cold climates under snow cover. The wintertime average CO2 respiration rate was 0.44 umol m–2 s–1.
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