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Asia Center of The Academy of Natural Sciences

Forest Ecology and Dendrochronology

Byambasuren Oyunsanaa

Byambasuren Oyunsanaa conducting Dendrochronology at Hovsgol, Mongolia

Research objectives and activities

The original concept for this study was to determine:

  • how tree cohorts form in the Lake Hövsgöl watershed, how forest fires are distributed amongst the six valleys, and
  • whether the valley forests differ in age structure and tree growth as a result of anthropogenic fires whose frequency is related to nomadic pasture use.

The principal methodology comprises:

  • measurement of the basal area and radial growth of trees in similar slope transects in the six valleys
  • the analysis of dendrochronology using both core samples and discs
  • the determination of fire seasonality

Initial Results

  • Growth rates and long-term fire dynamics were determined over the last 410 years. The basal area increment in the past increased from 1830-1850s. During 1950-1970s the growth declined. During the last 20 years the basal area growth has increased. Basal area increments in growth are higher on south-facing versus north-facing slopes in the period 1700 to 2001 AD.
  • In Borsog Valley “major fires” occurred in 1987, 1937, 1924, 1903, and 1867. In Dalbay, Sevsuul, Noyon, Shagnuul and Turag, “major fires” occurred in 1997, 1893, 1867, 1811, and 1806. Fires have occurred most frequently in Turag and Borsog valleys and least commonly in Sevsuul valley. Trees in Turag and Shagnuul Valleys are still dying from the effects of the 1997 fire. Damage to forest trees in general appears to be due primarily to fire rather than tree cutting or insect damage.
  • Determining seasons of past fires is important to understanding the fire ecology of forests and woodlands because the timing of fires is critical to the survival (or mortality) of trees. Some trees are much more (or less) susceptible to fires during different parts of growing period. Thus, the role of fire-scar analysis can be expanded beyond determining the frequency and extent of past fires to establishing the ecologically important season of past fire regimes. Another use of seasonal analysis of fire scars is to test hypotheses about the respective roles of climate vs. humans in controlling fire regimes. Historically, in our study area (eastern shore of Lake Hovsgol) no longer period land use, but from beginning of past century Russian Mongolian border gate is opened. From that time the settlements developed and Russia and Mongolia started to exchange goods. Thus, by determining seasonality of fires in past centuries, fire historians might determine the relative roles and importance of lightning and of people in controlling fire regimes. In our study most fires occurred during the early wood season (May to early June). This time in Mongolia is the most critical dry season. In Khangai Mountain and Trans-Baikal forest zones, fire activity is highest in May and April, 48% and 33.3% respectively of the total number in a fire season. Fires start in late March and early April, immediately after snowmelt when forest fuels are drying rapidly on southern and western-facing slopes.

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