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Kasanen R.,Finnish Forest Research Institute | Terhonen E.,University of Helsinki | Huuskonen S.,Finnish Forest Research Institute | Sun H.,University of Helsinki | Uotila A.,Hyytiala Forestry Field Station
Scandinavian Journal of Forest Research | Year: 2011

The study was made in order to assess the infection rate of conifer stumps by Heterobasidion species in transition zone between southern boreal and middle boreal areas. Majority of surveys of stump infection rate have been made in areas where the fungus is already a considerable problem; typically the effective temperature sum in these areas exceeds 1200 degree days (d.d.). In the study, the incidence of stump infection was surveyed by intensive sampling of cut stump surfaces in the Central Finland in area where the temperature sum is 1100 d.d. and sporadic observations of damages caused by H. annosum s.l. have been made. Residual stumps were surveyed in total of 31 sites where majority of stumps had been harvested. Of those, 24 (75%) were infected. The stump infection rate was less than 20% on most sites. On average, 13% of spruce stumps were infected. The frequency of infected stumps varied considerably between the studied stands. The infection percentage of residual stumps in stump harvesting areas was corresponding to that obtained from earlier studies. Our results demonstrate that although the stump harvesting effectively decreases the number of infected stumps, the stumps left after summer cutting on the clear-cut area may be an additional infection pathway. No clear linear trend between mean temperature and proportion of infected stumps could be found. © 2011 Taylor & Francis. Source


Ilvesniemi H.,Finnish Forest Research Institute | Pumpanen J.,University of Helsinki | Duursma R.,University of Western Sydney | Hari P.,University of Helsinki | And 9 more authors.
Boreal Environment Research | Year: 2010

In terrestrial ecosystems, the amount and availability of water is one of the key factors affecting the net primary productivity and other biological processes of the system. At the SMEAR-II station, we have monitored the water balance of two adjacent micro-catchments since 1997. In this study, we report the long-term measurements of precipitation, throughfall, snow depth, soil water content, runoff and evapotranspiration and the annual water balances based on these measurements and discuss the uncertainties related to different measurements. The proportion of throughfall, evapotranspiration and runoff was 67%, 43% and 32% of the annual precipitation, respectively. The measured amounts of evapotranspiration and runoff were so small that the aim of closing the water balance of the studied system was not fully reached. The largest uncertainties are related to the evapotranspiration measurements and the determination of the actual surface area of the catchments used in the calculation of the runoff. © 2010. Source


Korhonen J.F.J.,University of Helsinki | Pihlatie M.,University of Helsinki | Pumpanen J.,University of Helsinki | Aaltonen H.,University of Helsinki | And 6 more authors.
Biogeosciences | Year: 2013

The productivity of boreal forests is considered to be limited by low nitrogen (N) availability. Increased atmospheric N deposition has altered the functioning and N cycling of these N-sensitive ecosystems by increasing the availability of reactive nitrogen. The most important components of N pools and fluxes were measured in a boreal Scots pine stand in Hyytiälä, Southern Finland. The measurements at the site allowed direct estimations of nutrient pools in the soil and biomass, inputs from the atmosphere and outputs as drainage flow and gaseous losses from two micro-catchments. N was accumulating in the system, mainly in woody biomass, at a rate of 7 kg N ha -1 yr-1. Nitrogen input as atmospheric deposition was 7.4 kg N ha-1 yr-1. Dry deposition and organic N in wet deposition contributed over half of the inputs in deposition. Total outputs were 0.4 kg N ha-1 yr-1, the most important outputs being N2O emission to the atmosphere and organic N flux in drainage flow. Nitrogen uptake and retranslocation were equally important sources of N for plant growth. Most of the assimilated N originated from decomposition of organic matter, and the fraction of N that could originate directly from deposition was about 30%. In conclusion, atmospheric N deposition fertilizes the site considerably, but there are no signs of N saturation. Further research is needed to estimate soil N2 fluxes (emission and fixation), which may amount up to several kg N ha-1 yr-1. © 2013 Author(s). Source


Kajos M.K.,University of Helsinki | Rantala P.,University of Helsinki | Hill M.,Empa - Swiss Federal Laboratories for Materials Science and Technology | Hellen H.,Finnish Meteorological Institute | And 9 more authors.
Atmospheric Measurement Techniques | Year: 2015

Proton transfer reaction mass spectrometry (PTR-MS) and gas chromatography mass spectrometry GC-MS) are commonly used methods for automated in situ measurements of various volatile organic compounds (VOCs) in the atmosphere. In order to investigate the reliability of such measurements, we operated four automated analyzers using their normal field measurement protocol side by side at a boreal forest site. We measured methanol, acetaldehyde, acetone, benzene and toluene by two PTR-MS and two GC-MS instruments. The measurements were conducted in southern Finland between 13 April and 14 May 2012. This paper presents correlations and biases between the concentrations measured using the four instruments. A very good correlation was found for benzene and acetone measurements between all instruments (the mean R value was 0.88 for both compounds), while for acetaldehyde and toluene the correlation was weaker (with a mean R value of 0.50 and 0.62, respectively). For some compounds, notably for methanol, there were considerable systematic differences in the mixing ratios measured by the different instruments, despite the very good correlation between the instruments (mean R Combining double low line 0.90). The systematic difference manifests as a difference in the linear regression slope between measurements conducted between instruments, rather than as an offset. This mismatch indicates that the systematic uncertainty in the sensitivity of a given instrument can lead to an uncertainty of 50-100 % in the methanol emissions measured by commonly used methods. © Author(s) 2015. Source


Petaja T.,University of Helsinki | Vakkari V.,University of Helsinki | Pohja T.,Hyytiala Forestry Field Station | Nieminen T.,University of Helsinki | And 9 more authors.
Aerosol and Air Quality Research | Year: 2013

The characterization of atmospheric aerosol properties and trace gas concentrations in various environments provides a basis for scientific research on the assessment of their roles in the climate system, as well as regional air quality issues. However, measurements of these face many problems in the developing world. In this study we present the design of a transportable aerosol dynamic and atmospheric research trailer, which relies minimally on the existing infrastructure by making use of wireless data transfer. The instrumentation used in this trailer was originally used in various aerosol formation studies, and has been expanded so that it can also monitor air quality. The instruments include a Differential Mobility Particle Sizer (DMPS) for aerosol number size distribution in the range 10-840 nm, a Tapered Element Oscillating Microbalance (TEOM) for aerosol mass concentration, and Air Ion Spectrometer (AIS) for atmospheric ion measurements in the size range 0.5-40 nm. Sulfur dioxide, nitrogen oxides, carbon monoxide and ozone mixing ratios are also monitored, as well as photosynthetically active radiation (PAR) and meteorological parameters. As we have already operated the trailer in South Africa for several years, we discuss the lessons learned during the first years of use in the field. © Taiwan Association for Aerosol Research. Source

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