K.I. Kobak

University of Bayreuth, Bayreuth, Bavaria, Germany

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Publications (7)22.26 Total impact

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    ABSTRACT: We investigated the daily exchange of CO2 between undisturbed Larix gmelinii (Rupr.) Rupr. forest and the atmosphere at a remote Siberian site during July and August of 1993. Our goal was to measure and partition total CO2 exchanges into aboveground and belowground components by measuring forest and understory eddy and storage fluxes and then to determine the relationships between the environmental factors and these observations of ecosystem metabolism. Maximum net CO2 uptake of the forest ecosystem was extremely low compared to the forests elsewhere, reaching a peak of only ∼5 μmol m−2 s−1 late in the morning. Net ecosystem CO2 uptake increased with increasing photosynthetically active photon flux density (PPFD) and decreased as the atmospheric water vapor saturation deficit (D) increased. Daytime ecosystem CO2 uptake increased immediately after rain and declined sharply after about six days of drought. Ecosystem respiration at night averaged ∼2.4 μmol m−2 s−1 with about 40% of this coming from the forest floor (roots and heterotrophs). The relationship between the understory eddy flux and soil temperature at 5 cm followed an Arrhenius model, increasing exponentially with temperature (Q10∼2.3) so that on hot summer afternoons the ecosystem became a source of CO2. Tree canopy CO2 exchange was calculated as the difference between above and below canopy eddy flux. Canopy uptake saturated at ∼6 μmol CO2 m−2 s−1 for a PPFD above 500 μmol m−2 s−1 and decreased with increasing D. The optimal stomatal control model of Mäkelä et al. (1996) was used as a `big leaf' canopy model with parameter values determined by the non-linear least squares. The model accurately simulated the response of the forest to light, saturation deficit and drought. The precision of the model was such that the daily pattern of residuals between modeled and measured forest exchange reproduced the component storage flux. The model and independent leaf-level measurements suggest that the marginal water cost of plant C gain in Larix gmelinii is more similar to values from deciduous or desert species than other boreal forests. During the middle of the summer, the L. gmelinii forest ecosystem is generally a net sink for CO2, storing ∼0.75 g C m−2 d−1.
    Agricultural and Forest Meteorology 01/1998; · 3.89 Impact Factor
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    ABSTRACT: Estimates of changes in carbon pools of vegetation and soils during the Holocene are contradictory due in part to incomplete information. The peat carbon pool has increased in northwestern Russia due to paludification but the intensity of paludification and carbon accumulation rate was not constant during the Holocene. We estimate that the average long-term accumulation rate in peatlands of Russia was 44·109 kg C/yr or 28.6·10−3 kg C/m2 yr. According to our model calculations, the maximum rate of peat accumulation in northwestern Russia was reached in the Boreal (early Holocene) (34.5·10−3 kg C/m2 yr) and the late Atlantic time (mid Holocene) (about 30·10−3 kg C/m2 yr). The rate decreased during the Subboreal time to 17·10−3 kg C/m2 yr. Modern rates of carbon accumulation in some types of peatlands of Russia, calculated by peat-growth model, range from 20·10−3 kg C/m2 yr to 100·10−3 kg C/m2 yr. The forest composition of northwestern Russia also changed during the Holocene, but the changes in carbon pool of phytomass did not exceed 5% from the mid-Holocene to the present.
    Global and Planetary Change 01/1998; · 3.71 Impact Factor
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    ABSTRACT: In July 1993, we measured leaf conductance, carbon dioxide (CO(2)) assimilation, and transpiration in a Larix gmelinii (Rupr.) Rupr. ex Kuzen forest in eastern Siberia. At the CO(2) concentration of ambient air, maximum values (mean of 10 highest measured values) for CO(2) assimilation, transpiration and leaf conductance for water vapor were 10.1 micro mol m(-2) s(-1), 3.9 mmol m(-2) s(-1) and 365 mmol m(-2) s(-1), respectively. The corresponding mean values, which were much lower than the maximum values, were 2.7 micro mol m(-2) s(-1), 1.0 mmol m(-2) s(-1) and 56 mmol m(-2) s(-1). The mean values were similar to those of Vaccinium species in the herb layer. The large differences between maximum and actual performance were the result of structural and physiological variations within the tree crowns and between trees that reduced maximum assimilation and leaf conductance by about 40 and 60%, respectively. Thus, maximum assimilation and conductance values averaged over the canopy were 6.1 micro mol m(-2) s(-1) and 146 mmol m(-2) s(-1), respectively. Dry air caused stomatal closure, which reduced assimilation by an additional 26%. Low irradiances in the morning and evening had a minor effect (-6%). Daily canopy transpiration was estimated to be 1.45 mm day(-1), which is higher than the value of 0.94 mm day(-1) measured by eddy covariance, but similar to the value of 1.45 mm day(-1) calculated from the energy balance and soil evaporation, and less than the value of 2.1 mm day(-1) measured by xylem flux. Daytime canopy carbon assimilation, expressed on a ground area basis, was 0.217 mol m(-2) day(-1), which is higher than the value measured by eddy flux (0.162 mol m(-2) day(-1) including soil respiration). We discuss the regulation of leaf gas exchange in Larix under the extreme climatic conditions of eastern Siberia (temperature > 35 degrees C and vapor pressure deficit > 5.0 kPa).
    Tree Physiology 10/1997; 17(10):607-15. · 2.85 Impact Factor
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    ABSTRACT: The Russian Federation contains approximately 20% of the world's timber resources and more than half of all boreal forests. These forests play a prominent role in environmental protection and economic development at global, national, and local levels, as well as, provide commodities for indigenous people and habitat for a variety of plant and animal species. The response and feedbacks of Russian boreal forests to projected global climate change are expected to be profound. Large shifts in the distribution (up to 19% area reduction) and productivity of boreal forests are implied by scenarios of General Circulation Models (GCMs). Uncertainty regarding the potential distribution and productivity of future boreal forests complicates the development of adaptation strategies for forest establishment, management, harvesting and wood processing. Although a low potential exists for rapid natural adaptation of long-lived, complex boreal forests, recent analyses suggest Russian forest management and utilization strategies should be field tested to assess their potential to assist boreal forests in adaptation to a changing global environment. Current understanding of the vulnerability of Russian forest resources to projected climate change is discussed and examples of possible adaptation measures for Russian forests are presented, including: (1) artificial forestation techniques that can be applied with the advent of failed natural regeneration and to facilitate forest migration northward; (2) silvicultural measures that can influence the species mix to maintain productivity under future climates; (3) identifying forests at risk and developing special management adaptation measures for them; (4) alternative processing and uses of wood and non-wood products from future forests; and (5) potential future infrastructure and transport systems that can be employed as boreal forests shift northward into melting permafrost zones. Current infrastructure and technology can be employed to help Russian boreal forests adapt to projected global environmental change, however many current forest management practices may have to be modified. Application of this technical knowledge can help policymakers identify priorities for climate change adaptation.
    Climatic Change 04/1997; 36(1):197-215. · 3.63 Impact Factor
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    ABSTRACT: The most widely distributed coniferous forests in the world are the larch forests. In the Russian Federation they occupy 27.6 106 ha. In Siberia, the larch species Larix russica generally grows west of the Yenissei River, and Larix gmelinii grows to the east. The morphological and physiological features of L. gmelinii make it possible for this species to grow in the far north of eastern Siberia, where climate conditions are more severe: The range of air temperature fluctuations in this region is more than 100C, from 38C down to 64C below zero. One of the major adaptions to unfavorable soil conditions is provided by a specific feature of root formation in L. gmelinii, in which the apex central root dies off at the permafrost border and a root system develops in upper soil layers. The major larch vulnerability factors are natural and anthropogenic fires and damage caused by insects, which become more frequent with hot and dry weather. The consequences of projected global warming could be both positive and negative for larch forests. Permafrost melting may result in improved soil nutrition in the areas the larch forests occupy, yet the frequency of forest fires and damage by pathogens are likely to increase. Global warming is expected to cause forest die back and increased areas of steppe in the southern regions of eastern Siberia.
    Water Air and Soil Pollution 10/1996; 92(1):119-127. · 1.75 Impact Factor
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    ABSTRACT: useable, but little data for early stages
    Canadian Journal of Forest Research 06/1995; 25:943-960. · 1.56 Impact Factor
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    ABSTRACT: We measured C02 and HzO fluxes between undis- turbed Larix gmelinii forest and the atmosphere at a remote Eastern Siberian site in July 1993. Scaled-up leaf-level porom- eter measurements agreed with those derived from the eddy correlation technique for the canopy fluxes of COz and HzO. Patch-scale measurements of ecosystem C02 exchange agreed in turn with regional CO2 exchange rates derived from aircraft
    Journal of Biogeography 03/1995; 22(2/3):425-431. · 4.86 Impact Factor