ISSN 1239-6095
© Boreal Environment Research 2005

Contents of Volume 10 Number 4

Nyman, M. T. & Korhola, A. A. 2005: Chironomid-based classification of lakes in western Finnish Lapland. Boreal Env. Res. 10: 239–254.
Abstract
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Marjomäki, T. J. 2005: Evaluation of different harvest strategies for a vendace population with highly variable recruitment: a simulation approach. Boreal Env. Res. 10: 255–273.
Abstract
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Solantie, R. 2005: Productivity of boreal forests in relation to climate and vegetation zones. Boreal Env. Res. 10: 275–297.
Abstract
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Vajda, A. & Venäläinen, A. 2005: Feedback processes between climate, surface and vegetation at the northern climatological tree-line (Finnish Lapland). Boreal Env. Res. 10: 299–314.
Abstract
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Nyman, M. T. & Korhola, A. A. 2005: Chironomid-based classification of lakes in western Finnish Lapland. Boreal Env. Res. 10: 239–254.

For the implementation of the Water Framework Directive we need to develop an informative and cost-effective set of biological monitoring and assessment methods, especially for remote areas. Chironomids are known to be an abundant and species-rich group that dominate the aquatic macroinvertebrate assemblages in the north and therefore should be an integral part of monitoring and assessment plans. In this paper, we aim to characterise lake types in subarctic Finnish Lapland using particular chironomid indicator taxa. Contemporary chironomid assemblages and 24 corresponding physical and chemical limnological variables were determined for 63 lakes. Among them, fifty shallow lakes (&Mac178; 10 m) were classified into biological lake groups using Two-Way Indicator Species Analysis (TWINSPAN). The environmental variables best discriminating between the groups were determined using canonical variates analysis (CVA). Classical lake typology was additionally applied to 13 deeper lakes. Among the shallow lakes, three lake groups were separated on the basis of their chironomid assemblages: (i) small and shallow organic-rich lakes, (ii) large and base-rich lakes, and (iii) cold and clear oligotrophic tundra lakes. The deep lakes were all, except one, oligotrophic. The degree of oligotrophy was related to temperature. The results indicate that the classification of shallow lakes using chironomid communities is a useful tool for developing a lake typology and in assessing and monitoring the remote subarctic lakes.
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Marjomäki, T. J. 2005: Evaluation of different harvest strategies for a vendace population with highly variable recruitment: a simulation approach. Boreal Env. Res. 10: 255–273.

In the auto-regulative commercial vendace fishery, the fishing effort is increased if stock decreases in order to reduce interannual variation in supply and revenue. When the revenue per unit effort reaches a profitability threshold, fishing ceases. The performance of this strategy was compared with constant effort and constant revenue strategies combined with different threshold levels of fishing shut-down. A simulation model of an age-structured vendace population was applied. Qualitatively the results were very similar for the Ricker and Cushing stock-recruitment curves with or without negative dependence between consecutive recruitments. The interannual variability of revenue increased with an increase in mean revenue when approaching maximum mean annual revenue. Given a low threshold, the constant effort strategy performed best and constant yield worst with respect to the objectives of maximum mean revenue, low mean effort, and low risk for spawning biomass. For the constant effort strategy, the revenue variation was already high at low revenue levels. For the strategy aiming at constant revenue, the variation was low at a low revenue level but increased rapidly with increasing revenue. At a moderate revenue level, the intermediate strategy produced good trade-offs of rather high mean revenue with reasonable variation and risk to reproduction. A tendency for two-year-cyclicity appeared at a low mean spawning stock level. When the threshold of fishery shut-down was increased, the variability in revenue increased for every strategy and differences in their performance decreased. Simultaneously, the risk of low spawning stock decreased. The threshold regulation increased the instability of stock in cases of high fishing effort. Means for regulating the access to fishing should be established in order to ensure the possibility of flexibility of fishing effort and tolerable revenue variation. Some threshold regulation to protect the spawning stock is also necessary.
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Solantie, R. 2005: Productivity of boreal forests in relation to climate and vegetation zones. Boreal Env. Res. 10: 275–297.

Many properties of forest stands in the boreal main zone have means that are specific to each boreal zone (i.e. subzones of the main climatic zone). These properties are arranged in zonal systems, called forest vegetational zones. The paper examines the vegetative productivity using three climatic variables: the effective temperature sum, the duration of the vegetation period, and the maximum soil frost penetration; each of them means for the period 1961–2000. Soil frost penetration was calculated mainly as a function of snow depth and frost sum. The productivity for each boundary between the boreal forest vegetational zones in Finland was obtained mainly from Ilvessalo, beginning with the boundary between the hemiboreal and southern boreal zones in the south and ending at the boundary between the middle and northern boreal zones in the north. The regional distribution of residuals reflects the regional variation of the soil fertility. A hypothesis that each boundary corresponds to a certain productivity from the western coast of Norway to western Siberia, was tested. The productivity for the boundary between the hemiboreal and temperate zones was found to be in accordance for the limit determined by vegetation. Some applications of the results are presented.
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Vajda, A. & Venäläinen, A. 2005: Feedback processes between climate, surface and vegetation at the northern climatological tree-line (Finnish Lapland). Boreal Env. Res. 10: 299–314.

In northern ecosystems near the climatological timberline, the interactions between vegetation and disturbances, such as forest fire, are particularly important, as the changes in vegetation may produce large feedbacks into the climate. The changed climate and the altered surface conditions may in turn prevent the vegetation from returning to its original state. The effect of fire on local climate and its implications for forest regeneration were studied in the Tuntsa area of Finnish Lapland that was affected by a widespread forest fire in 1960. Direct measurements were applied for determining the variation of climate parameters in a spruce-covered fire refuge and on the treeless tundra environment resulting from the fire. The annual and seasonal dynamics of heat and water fluxes, snow conditions and radiation processes were simulated using an SVAT model known as COUP. Fire-induced deforestation increased the wind velocity by 60%, changed the soil thermal regime through a 20–30 cm reduced snow cover, lowered the evapotranspiration and diminished the Bowen ratio to 0.4. The resulting severe local climate is probably one of the precluding factors in the recovery of the forest in this sensitive region.
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