I. Milukova

Severtsov Institute of Ecology and Evolution, Moskva, Moscow, Russia

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Publications (7)22.36 Total impact

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    ABSTRACT: Total and forest floor carbon dioxide flux densities (FCO2) and environmental variables were measured for 18 consecutive mid-summer days during July 1996 in a 215-year-old stand of Pinus sylvestris L. trees located 40 km southwest of the village of Zotino in central Siberia, Russia (61°N, 89°E, 160 m asl). Forest floor FCO2 was regulated by surface soil water content, related to the limited storage capacity of the sandy soil equivalent to only 4 mm water per 100 mm depth of soil. Following 12 mm rainfall, forest floor FCO2 increased by 52% to a maximum value of 4.1 μmol m−2 s−1. However, the rate had returned to the general lower level by the next day in response to rapid drying of the surface soil. There was little correspondence between forest floor FCO2 and the distributions of root and soil carbon or soil temperature. However, for soil samples returned to the laboratory, sieved to remove roots and re-watered, microbial respiration rate was positively and exponentially related to temperature. Measurements of forest floor FCO2 by eddy covariance were in good agreement with the chamber data during the daytime when the atmosphere was regularly mixed by turbulence. Micrometeorological flux measurements at the forest floor and above the trees showed how, on average, 77% of the carbon sequestered by tree canopy photosynthesis was lost to the atmosphere by root and soil microbial respiration during the observation period. On a daily basis, the boreal forest was generally a modest net sink (−75 mmol m−2 per day), but also a small carbon source on hot and dry days.
    Agricultural and Forest Meteorology 01/1999; · 3.89 Impact Factor
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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: Total forest evaporation, E, understorey evaporation, Eu, and environmental variables were measured for 18 consecutive mid-summer days during July 1996 in a 215-year-old stand of Pinus sylvestris L. trees located 40 km southwest of the village of Zotino in central siberia, Russia (61°N, 89°E, 160 m asl). Tree and lichen (Cladonia and Cladina spp.) understorey one-sided leaf and surface-area indices were 1.5 and 6.0, respectively. Daily E, measured by eddy covariance, was 0.8–2.3 mm day−1 which accounted for 15–67% of the available energy, Ra. Following 12 mm rainfall, daily E reached a maximum on the second day (the first clear day) but declined rapidly thereafter to reach minimum rates within one week. The sandy soil had a range of water content equivalent to only 4 mm water per 100 mm depth of soil. It was estimated that 38% of soil water was utilised before water deficit began to limit E. Eu, also measured by eddy covariance and by lysimeters, was 0.5 to 1.6 mm day−1 or 33–92% of E. Eu was proportional to Ra, but in response to soil drying, the slope of this linear relation declined by a factor of three to a minimum value only three days after the rainfall. Based on the measurements and climatological data, including average annual precipitation of 600 mm year−1 with half as rain during the nominal growing season (1 May to 30 September), water balance calculations suggested E was 265 mm per growing season.
    Journal of Hydrology 01/1998; · 2.96 Impact Factor
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    ABSTRACT: Total forest evaporation (λE), understorey evaporation, and environmental variables were measured on nine summer days under different weather conditions in a 130-year-old stand of Larix gmelinii (Rupr.) Rupr. trees located 160 km south of Yakutsk in eastern Siberia, Russia (61°N, 128°E, 300m above sea-level (a.s.l.)). Tree and broad-leaved understorey vegetation one-sided leaf area indices were 1.5 and 1.0, respectively. Agreement of λE and sensible heat flux (H), both measured by eddy covariance, and the available energy (Ra) was generally good: (H + λE) = 0.83 Ra + 9 W m−2 with r2 = 0.92 for 364 half-hour periods and the mean ± 95% confidence limit was 129 ± 17 for (H + λE) and 144 ± 19 for Ra. Daily E was 1.6–2.2 min, less than half of the potential evaporation rate and accounting for 31–50% of Ra, with the lowest percentage on clear days. A perusal of the sparse literature revealed that average daily E of boreal coniferous forest during the tree growing season (1.9 mm day−1 for this study) is relatively conservative, suggesting that low evaporation rates are a feature of this biome's energy balance. Using the Penman-Monteith equation, the maximum bulk-surface conductance (Gsmax) was 10 mm s−1. E and Gs were regulated by irradiance, air saturation deficit, and surface soil water content during a week-long dry period following 20 mm rainfall. From lysimeter measurements, 50% of E emanated from the understorey at a rate proportional to Ra. Based on the measurements and published climatological data, including average annual precipitation equal to 213 mm, water balance calculations indicated growing season forest E equal to 169 mm, the occurrence of a late summer-autumn soil water deficit, and annual runoff of 44 mm by snowmelt.
    Agricultural and Forest Meteorology 01/1997; · 3.89 Impact Factor
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    ABSTRACT: Xylem sap flow and environmental variables were measured on seven consecutive midsummer days in a 130-year-old Larix gmelinii (Rupr.) Rupr. forest located 160 km south of Yakutsk in eastern Siberia, Russia (61 degrees N, 128 degrees E, 300 m asl). The site received 20 mm of rainfall during the 4 days before measurements, and soil samples indicated that the trees were well watered. The tree canopy was sparse with a one-sided leaf area index of 1.5 and a tree density of 1760 ha(-1). On a clear day when air temperature ranged from 9 to 29 degrees C, and maximum air saturation deficit was 3.4 kPa, daily xylem sap flux (F) among 13 trees varied by an order of magnitude from 7 l day(-1) for subcanopy trees (representing 55% of trees in the forest) to 67 l day(-1) for emergent trees (representing 18% of trees in the forest). However, when based on xylem sap flux density (F'), calculated by dividing F by projected tree crown area (a surrogate for the occupied ground area), there was only a fourfold range in variability among the 13 trees, from 1.0 to 4.4 mm day(-1). The calculation of F' also eliminated systematic and large differences in F among emergent, canopy and subcanopy trees. Stand-level F', estimated by combining half-hourly linear relationships between F and stem cross-sectional area with tree size distribution data, ranged between 1.8 +/- 0.4 (standard deviation) and 2.3 +/- 0.6 mm day(-1). These stand-level F' values are about 0.6-0.7 mm day(-1) (30%) larger than daily tree canopy transpiration rates calculated from forest energy balance and understory evaporation measurements. Maximum total tree conductance for water vapor transfer (G(tmax), including canopy and aerodynamic conductances), calculated from the ratio of F' and the above-canopy air saturation deficit (D) for the eight trees with continuous data sets, was 9.9 +/- 2.8 mm s(-1). This is equivalent to a leaf-scale maximum stomatal conductance (g(smax)) of 6.1 mm s(-1), when expressed on a one-sided leaf area basis, which is comparable to the published porometer data for Larix. Diurnal variation in total tree conductance (G(t)) was related to changes in the above-canopy visible irradiance (Q) and D. A saturating upper-boundary function for the relationship between G(t) and Q was defined as G(t) = G(tmax)(Q/[Q + Q(50)]), where Q(50) = 164 +/- 85 micro mol m(-2) s(-1) when G(t) = G(tmax)/2. Accounting for Q by excluding data for Q < Q(85) when G(t) was at least 85% of G(tmax), the upper limit for the relationship between G(t) and D was determined based on the function G(t) = (a + blnD)(2), where a and b are regression coefficients. The relationship between G(t) and D was curvilinear, indicating that there was a proportional decrease in G(t) with increasing D such that F was relatively constant throughout much of the day, even when D ranged between about 2 and 4 kPa, which may be interpreted as an adaption of the species to its continental climate. However, at given values of Q and D, G(t) was generally higher in the morning than in the afternoon. The additional environmental constraints on G(t) imposed by leaf nitrogen nutrition and afternoon water stress are discussed.
    Tree Physiology 02/1996; 16(1_2):247-255. · 2.85 Impact Factor
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    ABSTRACT: The effects of climatic change on the Picea abies communities of the South European taiga have been analysed at three different scales (i) the scale of long-term fluctuations in climatic patterns over thousands of years; (ii) the scale of climate variability over 100 years; and (iii) the scale of ecophysiological processes over a single growing season. On the basis of pollen-spore analysis, the role of Picea abies as a dominant species in the forests of the South European taiga region (Tver region, Russia) has been shown for the past 17,000 years. In the Holocene, the temperature of the region changed with 1000-1200 and 3000 year periods on the background of a nonstationary trend with a 14,000-year period; wetter periods occurred with 1000, 1500-1600 and 3000-year periods; and the vegetation itself changed with 1000-1100, 1500, 2500 and 14,000-year periods. The warmest period was observed 6000 years ago, but 1500 years later the temperature had decreased to the modern level. Climate warming results usually in intensive and deep reorganization of vegetation (successional replacement). The most intensive reorganizations occur about 500 years after the beginning of simultaneous and opposite oscillations in temperature (warming) and moisture (drying). The low stability of spruce forests to warming and drying can also result in 'catastrophic' reorganization of communities. On the basis of instrumental records over the past 100 years, a slight warming from the end of the 19th century and a slight cooling after the 1940s as well as a general increase in precipitation has been found for this region. In comparison with the beginning of the 20th century and the 1940s, the current climate tends to be less continental. The relative stability of the climate over this 100-year period contrasts with the relative instability of the vegetation communities. Fluctuations of radial increment and observations of stand destruction are consistent with water stress as the major factor. Intensive measurements of photosynthesis and evapotranspiration during individual seasons indicate that aggregate CO2 assimilation is reduced by 15-25% during dry periods.
    Journal of Biogeography 03/1995; 22(2/3):433-443. · 4.86 Impact Factor