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  • Canopy conductance  (2)
  • Siberia  (2)
  • 1995-1999  (2)
  • 1990-1994  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Above-ground biomass and structure of pristine Siberian Scots pine forests as controlled by competition and fire (1999)
    Springer
    Oecologia 121 (1999), S. 66-80 
    Details
    ISSN: 1432-1939
    Keywords: Key wordsPinus sylvestris ; Siberia ; Biomass ; Self-thinning ; Forest fire
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The study presents a data set of above-ground biomass (AGB), structure, spacing and fire regime, for 24 stands of pristine Siberian Scots pine (Pinus sylvestris) forests with lichens (n = 20) or Vaccinium/mosses (n = 4) as ground cover, along four chronosequences. The stands of the “lichen” site type (LT) were stratified into three chronosequences according to stand density and fire history. Allometric equations were established from 90 sample trees for stem, coarse branch, fine branch, twig and needle biomass. The LT stands exhibited a low but sustained biomass accumulation until a stand age of 383 years. AGB reached only 6–10 kgdw m−2 after 200 years depending on stand density and fire history compared to 20 kgdw m−2 in the “Vaccinium” type (VT) stands. Leaf area index (LAI) in the LT stands remained at 0.5–1.5 and crown cover was 30–60%, whereas LAI reached 2.5 and crown cover was 〉100% in the VT stands. Although nearest-neighbour analyses suggested the existence of density-dependent mortality, fire impact turned out to have a much stronger effect on density dynamics. Fire scar dating and calculation of mean and initial fire return intervals revealed that within the LT stands differences in structure and biomass were related to the severity of fire regimes, which in turn was related to the degree of landscape fragmentation by wetlands. Self-thinning analysis was used to define the local carrying capacity for biomass. A series of undisturbed LT stands was used to characterise the upper self-thinning boundary. Stands that had experienced a moderate fire regime were positioned well below the self-thinning boundary in a distinct fire-thinning band of reduced major axis regression slope −0.26. We discuss how this downward shift resulted from alternating phases of density reduction by fire and subsequent regrowth. We conclude that biomass in Siberian Scots pine forests is strongly influenced by fire and that climate change will affect ecosystem functions predominantly via changes in fire regimes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050908
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  • 2
    Electronic Resource
    Electronic Resource
    Evaporation and canopy characteristics of coniferous forests and grasslands (1993)
    Springer
    Oecologia 95 (1993), S. 153-163 
    Details
    ISSN: 1432-1939
    Keywords: Evaporation ; Aerodynamic conductance ; Canopy conductance ; Humidity response ; Soil water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Canopy-scale evaporation rate (E) and derived surface and aerodynamic conductances for the transfer of water vapour (gs and ga, respectively) are reviewed for coniferous forests and grasslands. Despite the extremes of canopy structure, the two vegetation types have similar maximum hourly evaporation rates (E max) and maximum surface conductances (gsmax) (medians = 0.46 mm h-1 and 22 mm s-1). However, on a daily basis, median E max of coniferous forest (4.0 mm d-1) is significantly lower than that of grassland (4.6 mm d-1). Additionally, a representative value of ga for coniferous forest (200 mm s-1) is an order of magnitude more than the corresponding value for grassland (25 mm s-1). The proportional sensitivity of E, calculated by the Penman-Monteith equation, to changes in gs is 〉0.7 for coniferous forest, but as low as 0.3 for grassland. The proportional sensitivity of E to changes in ga is generally ±0.15 or less. Boundary-line relationships between gs and light and air saturation deficit (D) vary considerably. Attainment of gsmax occurs at a much lower irradiance for coniferous forest than for grassland (15 versus about 45% of full sunlight). Relationships between gs and D measured above the canopy appear to be fairly uniform for coniferous forest, but are variable for grassland. More uniform relationships may be found for surfaces with relatively small ga, like grassland, by using D at the evaporating surface (D0) as the independent variable rather than D at a reference point above the surface. An analytical expression is given for determining D0 from measurable quantities. Evaporation rate also depends on the availability of water in the root zone. Below a critical value of soil water storage, the ratio of evaporation rate to the available energy tends to decrease sharply and linearly with decreasing soil water content. At the lowest value of soil water content, this ratio declines by up to a factor of 4 from the non-soil-water-limiting plateau. Knowledge about functional rooting depth of different plant species remains rather limited. Ignorance of this important variable makes it generally difficult to obtain accurate estimates of seasonal evaporation from terrestrial ecosystems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00323485
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  • 3
    Electronic Resource
    Electronic Resource
    Transpiration and canopy conductance in a pristine broad-leaved forest of Nothofagus: an analysis of xylem sap flow and eddy correlation measurements (1992)
    Springer
    Oecologia 91 (1992), S. 350-359 
    Details
    ISSN: 1432-1939
    Keywords: Canopy conductance ; Canopy transpiration ; Xylem sap flow ; Humidity response of stomatal ; Nothofagus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Tree transpiration was determined by xylem sap flow and eddy correlation measurements in a temperate broad-leaved forest of Nothofagus in New Zealand (tree height: up to 36 m, one-sided leaf area index: 7). Measurements were carried out on a plot which had similar stem circumference and basal area per ground area as the stand. Plot sap flux density agreed with tree canopy transpiration rate determined by the difference between above-canopy eddy correlation and forest floor lysimeter evaporation measurements. Daily sap flux varied by an order of magnitude among trees (2 to 87 kg day−1 tree−1). Over 50% of plot sap flux density originated from 3 of 14 trees which emerged 2 to 5 m above the canopy. Maximum tree transpiration rate was significantly correlated with tree height, stem sapwood area, and stem circumference. Use of water stored in the trees was minimal. It is estimated that during growth and crown development, Nothofagus allocates about 0.06 m of circumference of main tree trunk or 0.01 m2 of sapwood per kg of water transpired over one hour. Maximum total conductance for water vapour transfer (including canopy and aerodynamic conductance) of emergent trees, calculated from sap flux density and humidity measurements, was 9.5 mm s−1 that is equivalent to 112 mmol m−2 s−1 at the scale of the leaf. Artificially illuminated shoots measured in the stand with gas exchange chambers had maximum stomatal conductances of 280 mmol m−2 s−1 at the top and 150 mmol m−2 s−1 at the bottom of the canopy. The difference between canopy and leaf-level measurements is discussed with respect to effects of transpiration on humidity within the canopy. Maximum total conductance was significantly correlated with leaf nitrogen content. Mean carbon isotope ratio was −27.76±0.27‰ (average ±s.e.) indicating a moist environment. The effects of interactions between the canopy and the atmosphere on forest water use dynamics are shown by a fourfold variation in coupling of the tree canopy air saturation deficit to that of the overhead atmosphere on a typical fine day due to changes in stomatal conductance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00317623
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  • 4
    Electronic Resource
    Electronic Resource
    Vulnerability and adaptation of the larch forest in eastern Siberia to climate change (1996)
    Springer
    Water, air & soil pollution 92 (1996), S. 119-127 
    Details
    ISSN: 1573-2932
    Keywords: Siberia ; forest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Notes: 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 100°C, from 38°C down to 64°C 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00175558
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