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Uncertainty in future climate projections is widely recognised, yet few impact model studies explore the implications of this uncertainty on catchment hydrological and biogeochem-ical responses. Here, we report a novel model chain using HBV, INCA-C and MyLake to simulate runoff, snow dynamics, ice cover, soil moisture, lake thermal stratification and in-lake DOC concentrations in Valkea-Kotinen, a headwater lake in a forest-covered boreal catchment. Impact response surfaces (IRSs) were constructed with 63 combinations of changes in temperature (-2 °C to +14 °C) and precipitation (-10% to +50%). Superimposing probabilistic projections of climate change onto the IRSs, we illustrate the uncertainty in impacts under projected climate change. Projected climate warming is likely to result in drier soils, shorter snow and ice periods, as well as earlier onset and longer duration of lake stratification. In contrast to earlier results, in-lake DOC concentrations are projected to decrease slightly (-6%), primarily due to decreased terrestrial runoff. [ABSTRACT FROM AUTHOR]

The long-term impacts of current forest management methods on surface water quality in Fennoscandia are largely unexplored. We studied the long-term effects of clear-cutting and site preparation on runoff and the export of total nitrogen (total N), total organic nitrogen (TON), ammonium (NH-N), nitrate (NO-N), total phosphorus (total P), phosphate (PO-P), total organic carbon, and suspended solids (SS) in three paired-catchments in Eastern Finland. Clear-cutting and soil preparation were carried out on 34 % (C34), 11 % (C11), and 8 % (C8) of the area of the treated catchments and wide buffer zones were left along the streams. Clear-cutting and soil preparation increased annual runoff and total N, TON, NO-N, PO-P, and SS loads, except for SS, only in C34. Runoff increased by 16 % and the annual exports of total N, TON, NO-N, and PO-P by 18, 12, 270, and 12 %, respectively, during the 14-year period after clear-cutting. SS export increased by 291 % in C34, 134 % in C11, and 16 % in C8 during the 14, 6, and 11-year periods after clear-cutting. In the C11 catchment, NO-N export decreased by 12 %. The results indicate that while current forest management practices can increase the export of N, P and SS from boreal catchments for many years (>10 years), the increases are only significant when the area of clear cutting exceeds 30 % of catchment area. [ABSTRACT FROM AUTHOR]

Temporal trends in inorganic and organic nitrogen (N) export in the stream water between 1979 and 2006 were studied in eight forested headwater catchments in eastern Finland, where an increasing air-temperature trend and a decreasing N-deposition trend has been observed since the 1980s. The Seasonal Kendall test was conducted to study if the stream water N concentrations have changed concurrently and a mixed model regression analysis was used to study which catchment characteristics and hydrometeorological variables were related to the variation in stream water N. The annual concentrations of total organic N (TON) increased at two catchments and the concentrations of nitrate (NO3-N) and ammonium (NH4-N) decreased at three and four catchments, respectively. The main factor explaining variation in concentrations and export of N was percentage of peatlands in a catchment. The NH4-N concentrations were also related to the N deposition, and the exports of NO3, NH4 , and TON to precipitation. Quantitative changes in both the N concentrations and exports were small. The results suggested relatively small changes in the N concentrations and exports between 1979 and 2006, most probably because the effects of increased air and stream water temperatures largely have been concealed behind the concurrent decrease in N deposition. [ABSTRACT FROM AUTHOR]

We determined the landscape variation of forest floor (FF) CO2 uptake (photosynthesis, P), FF CO2 emission (respiration, R) in relation to net ecosystem CO2 exchange (NEE) and environmental factors along a forest-mire ecotone in Finland. The 450 m long ecotone extended from xeric, upland pine dominated habitats, through spruce and transitional spruce-pine-birch forest, to sedge peatlands downslope. The CO2 fluxes were measured at nine stations during 2005 using chamber and IR techniques. Instantaneous P and R measurements for each station were interpolated by fitting their response to continuous records of light (mean R2= 0.66) and temperature (mean R2= 0.77) recorded nearby to give annual estimates. Stand biomass increment was used to estimate the annual CO2 exchange contribution of the trees. Annual P values from −307 to −1632 gCO2m−2yr−1 were inversely correlated with FF light (r =−0.96), FF above-ground biomass (r =−0.92) and canopy openness (r =−0.95). Annual R values from 1263 to 2813 gCO2 m−2 yr−1 were correlated with tree stand foliar biomass (r = 0.77). Estimated NEE values varied from 546 to −1679 gCO2m−2/yr−1, with P contributing from −307 to −1632 gCO2m−2yr−1 (4–90%) to gross ecosystem photosynthetic production (GPP), and R from 1263 to 2813 gCO2m−2yr−1 (70–98%) to gross ecosystem respiration (GR). [ABSTRACT FROM AUTHOR]

Questions: How have tree growth and growth trends varied in structurally complex old‐growth forests? What determines this variation and how this differs among species? Location: Natural boreal old‐growth forests, northern Finland. Methods: We sampled trees over 10‐cm diameter on 48 randomly located 0.1‐ha plots in three landscapes and compiled a data set of 1,565 trees including all three main species, and a full range of sizes and competitive states in northern boreal old‐growth forests. We extracted tree ring samples from every tree and used ring widths to reconstruct tree sizes and their neighbourhood for the past 50 years for Pinus sylvestris and Picea abies, and 30 years for Betula pubescens. We used mixed‐effects models to study variation in tree growth. In the models, we used annually varying environmental variables, forest and tree structural variables and site variables as predictors. We also measured soil hydraulic properties for a water balance model to specifically include soil moisture deficits as predictors. Results: Tree growth rates had increased during the analysis period for all three species, with the highest increases for P. sylvestris and B. pubescens. All three species grew well during warm summers, but P. sylvestris and P. abies growth was also negatively influenced by soil moisture deficits. Competition in these sparse forests had a small influence on growth. However, its influence increased over time. Conclusions: The trees showed positive growth trends, but the increasing competition means that such strong positive trends are unlikely to continue over the long term. For year‐to‐year variability, negative influence of droughts implied that increasing temperatures are not only beneficial to tree growth even in these high‐latitude forests. Overall, the findings demonstrate the site‐ and species‐dependent complexity in tree responses to environmental and structural changes we may expect in the future. Tree growth rates in the northern boreal old‐growth forests in Finland showed increasing trends in the recent decades. However, at annual resolution, droughts negatively influenced the growth of Norway spruce and Scots pine, implying that even in these high latitude (67°N) forests the benefits of increasing temperatures to tree growth are limited. [ABSTRACT FROM AUTHOR]

New measures for effective monitoring and controlling of bark beetle infestations are needed as a response to intensified outbreaks caused by the climate change. Various environmental factors affect tree health and susceptibility, as well as stand predisposition to bark beetles. European spruce bark beetle Ips typographus L. abundance and outbreak frequency in Finland has significantly increased during the last decade. The ability to identify sites under a high risk of infestation would facilitate adaptation to this new situation and help target limited forest health management resources. Accordingly, our goal was to investigate the importance of various stand, soil and topographic characteristics in the assessing predisposition of Norway spruce dominated urban forest in southern Finland to I. typographus infestations. Information on the environmental factors was assessed in the field in 2014 and derived from a digital elevation model. Ips typographus infestation intensity was classified into three infestation index classes based on tree-wise symptoms of resin flow, discoloration and defoliation. Cumulative logit link models were utilized for investigating stand-level infestation probability. The best explanatory factors were aspect, slope, site type and soil texture. Models with the highest cumulative probabilities for severe infestation were linked with eastern aspect, moderate steep slope and rich site type fertility (0.72) and eastern aspect, shallow soil and rich site type fertility (0.71). Higher soil C/N ratios with east aspect and rich site type fertility was associated with an increased risk of severe infestation in a third model. The lowest risk was associated with southern and southwestern aspects, fine soil texture, moderate site fertility and gentle slopes. [ABSTRACT FROM AUTHOR]