This paper focuses on the forest zone located in Northern Mongolia from 46°30′-52°00 N and 98°00-113°00′ E. Mongolian forests are characterized by discontinuous fire seasons with a long spring fire period starting with the onset of long drought accounting for 80% of all fires and a short autumn fire period when 15-18% of fires occur. In summer, fires are very rare because of frequent abundant rainfalls. Steppe fires are considered to be primarily responsible for starting fires in forest-steppe ecotone and in the subtaiga, since they spread into forest stands under favourable conditions. In the belt of the mountain taiga, particularly in its upper zone, most fires are started by lightning (Valendik et al.1997, 1998). Therefore, the forest danger in the northern region of the country is a natural phenomenon with a repeating character that is linked to the droughts of spring and autumn.
Forest fire hazard and fire regimes
Fire occurrence in the forest regions of Northern Mongolia are resulting from inappropriate human activities and have increased from year to year. Currently they contribute to 95 percent of all fires occurring annually in the country. Besides of that, warming of climate, the trend of desertification and droughts are natural conditions that favour the spread of fires and blowups.
During the last few years, the fire regimes of forests in high-altitude zones have changed dramatically. The evaluation of the a pyrological classification is shown in the Table 1. The classification distinguishes forest fire occurrence (n) on 100,000 ha:
n<0.5 = low
0.6<n<2 = moderate
2.1<n<4.0 = high
4.1<n<6 = very high
6.1<n = extreme
The distribution of fires between forest fire districts was generally even and moderate between 1975-1989, and high and very high during 1990-1994, and developed to the extreme rating in 1995-1999 (other than mountain taiga and mountain sub-taiga districts of Khuvsgul and Khentii).
Extremely large fires occurred in some years. In 1996-1997 13.4% of the total forest fund area had been affected by fire and greatly altered the characteristics of fire hazard. However, not every forest fire influences the forest ecosystem negatively. Surface fires that consume raw humus and surface fuels in low-productivity forests of the tundra and taiga zones influence the frost regime of the soils and lead to better growth conditions and formation of high-quality forests.
Table.1.Change of fire occurrence and regimes in forests of Northern Mongolia between1975 and 1999.
* n – fire occurrence; c – degree of area affected by fire
Forest fire danger
Long-term and short-term seasonal frost and permafrost sites are characteristic features of mountain forest sites in Northern Mongolia. This zone is characterized by continental cold and dry climate. Moisture supply for the vegetation is secured by rainfall and additionally by the moisture that is set free by melting seasonal frost that will supply the needed moisture for the root system of plants and woods. Occurrence and impacts fires entering forest sites with seasonal frost depend on the season. During the period June to August the melting frost supplies sufficient moisture to the upper soil, the organic and litter layers and the understory vegetation, thus reducing the spread and intensity of fires. Under the cold spring and autumn conditions, the surface fuels are dry and support the spread of fires and the development of fires with intensities that are higher than the summer fires and thus more damaging.
The degree of fire danger in Northern Mongolia depends on the following natural factors (Chuluunbaatar 1998):
Long-periods of daylight during the spring, causing an increase in solar radiation
A strong, cyclone-caused continental wind
High wind and solar radiation penetration of the forest canopy of the subalpine, pseudotaiga and forest-steppe high altitudinal belt forests
Rapid fire development rich in dead plants.
The forest vegetation is divided into following classes characterized by fire:
Except for the data on the percent of moisture in terrestrial cover it is necessary to know the percent of moisture in conifer needles, strobes, bark and all other litter-fall fractions. Research conducted in Mongolia revealed that during the fire season the moisture content (percentage of moisture compared to dry weight) in terrestrial combustible matter was variable depending on the period following the onset of vegetative growth. Thus the warm season of each year in the mountainous region of northern part of Mongolia was conventionally divided into four pyrologically active phenologyc periods (Chuluunbaatar 2001), namely:
1st period – until leaf initiation. This is the most fire-hazardous period when terrestrial cover fraction consists of dead (cured) grass and litter. The moisture content in forest combustion fuell at this period is as follows: In forb-pine forests: conifer needles 4.0-14.6, bark 3.6-14.8, sprigs 2.5-16.6, strobes 2.8-19.1, mosses 3.9-34.2, litter 17.1-100.9, grass 6.1-167.3. In forb-larch forests the percent of moisture of combustion fuel was as follows: conifer needles 3.4-7.9, sprigs 4.6-15.6, strobes 4.4-10.6, mosses 19.9-155.9, litter 9.6-151.1, grass 6.6-136.5, cowberry (Vaccinium vitis-idea L.) 77.2-143.1. In forb-birch forests: leaf 5.3-14.6, sprigs 6.1-24.8, litter 50.0-97.8, grass 7.8-157.8.
2nd period – from leaf initiation stage until the standing of grass and litter decay. From this stage spreading of fire becomes almost impossible. At this periods the moisture content in the fire hazardous fuel is the following: In forb-pine forests: conifer needles 20.4-40.1, bark 13.2-32.3, sprigs 20.5-34.0, strobes 30-47.6, mosses 49.0-191.8, litter 64.1-198.4, grass 173.3-500.8, cowberry (Vaccinium vitis-ideaL.) 88.7-139.7; in forb-birch forests: leaf 10.2-283.0, sprigs 16.6-85.4, mosses 68.5-322.2, cowberry (Vaccinium vitis-idea L.) 112.8-157.2, litter 63.4-149.7, grass 288.6-492.6.
3 rd period – lasts until wilting of the grass-herb layer. Under dry weather conditions, the spread of fires is easily possible. The moisture content in combustion fuel during this period is as follwos: In forb-pine forests -conifer needles 9.3-29.3, bark 8.3-32.3, sprigs 19.2-33.5, strobes 33.0-45.6, mosses 33.6-116.5, litter 62.5-213.8, grass 185.2-226.3; in forb-larch forests: conifer needles 19.8-66.7, strobes 20.3-64.4, sprigs 20.0-30.0, mosses 106.4-227.4, cowberry (Vaccinium vitis-idea L.) 120.2-134.9, litter 84.9-264.8, grass 21.4-323.7; in forb- birch forests: leaf 27.3-50.8, sprigs 33.9-57.9, mosses 119.4-205.2, cowberry (Vaccinium vitis-idea L.) 123.0-142.7, litter 83.1-191.8, grass 27.2-304.4.
4th period – starts at leaf-fall and lasts until the onset of snow cover formation. At this period the grass stand continues dying off and wilting. The hazard of natural fires is lowered though under conditions of dry long and warm autumn widespread forest fires can break out. The moisture content in combustion fuel forms in forb-pine forests: conifer needles 11.1-20.5, bark 14.3-21.3, sprigs 13.8-18.8, strobes 12,5-34.3, mosses 37.1-96.1, litter 42.6-152.7, grass 167.3-185.5; in forb-larch forests: conifer needles 11.5-47.7, strobes 13.3-30.1, sprigs 14.1-21.5, mosses 51.1-96.6, cowberry (Vaccinium vitis-ideaL.) 112.9-117.1, litter 39.2-168.9, grass 38.6-156.4; in forb-birch forests: leaf 23.3-26.6, sprigs 19.3-34.1, mosses 74.7-104.7, cowberry (Vaccinium vitis-idea L.) 123.0-125.0, litter 103.0-154.5, grass 109.7-169.2.
Classification scale of forest fire danger (fire weather)
We have evaluated the forest fire danger of each of districts within the pyrological subdivision zones of Northern Mongolia. Up to 15 to 20% of the total number of forest fires which occur annually in Northern Mongolia break out at weather / temperature conditions in the above-mentioned provinces are below zero degree Celsius. As for the above weather condition, the following formula (Telitzyn et al. 1981) can be used to evaluate a forest fire danger (Sofronov 1985, Chuluunbaatar 1998):
å= is sum
t = air temperature at 15:00 h
t = dew point temperature at 15:00 h
It is an expression suitable for our country because it includes the amount of precipitation of 3 mm and above, 1-3 mm, and <1 mm. It also includes below-zero values of air temperature.
There are strong differences between spring-summer and summer-autumn. Concluding from this, the summer estimation scale is not necessarily useful for above regions, but the period of the continuation of the autumn fire danger and the number is a few, the sum (å(t-t),°C) of the deficit of the dew point and the temperature does not exceed the variation of the temperature of fire danger in spring, and these showed that it is possible to evaluate the fire danger in spring and autumn by one estimation scale (Tab.2).
Table.2.Classification scale of forest fire danger of weather
Influence of forest fires on the forest phytocoenoses
The forest-vegetation are divided into following sections resulting from the characters of fires occurred there:
1. Plants that grow immediately on freshly burned sites (Chamaenerion angustifolium L., Corydalis sibirica L., Polygonatum sibiricum Dealer., Cerastium pauciflorum Steve., Chenopodium album L., Artemisia marcocephala J., Carex amgunensis ER., and others)
2. Plants that grow on burned sites that are part of the phytcenose affected by fire and are promoted by fire effects (Bromus pumpellianus Sc., Poa sibirica Roc., Trisetum sibiricum Rub., Artemisia integrifolia L., Geranium vlassovianum F., Fragaria orientalis Los., and others).
3. Plants that are adapted to forest fire. The fire does not change the vegetation cover and composition but rhizome grasses and sedges are promoted (Chuluunbaatar et al. 1999).
Resulting from the increasing occurrence of extremely large fires, the consequences of fire become increasingly negative, e.g., destruction of forest trees and other plants, affecting rivers, soil erosion in mountain forests, and an overall deterioration forests that results in increasing susceptibility to subsequent fires and a decrease of the natural recovery potential.
Betula platyphylla Sukach. grows by coppices (shoots) and Populus tremula L grows by suckers from roots that have been affected by surface and ground fires. The forest fire character and its influence of this region differs by altitude belt: Forest in the subtaiga belt of mountainous zone that grows in elevations between 600 and 1200 m above sea level (a.s.l.) is effectively affected by medium- and high-intensity ground and surface fires. Here all combustible materials on the forest floor and the lichen layer is totally consumed by fire. As a result severe soil erosion occurs in some places.
In the forest of the mountain subtaiga which grow on altitudes between 1300 and 1700 m a.s.l. intense surface, ground, and spotting fires dominate and often become crown fires.
Medium- to high-intensity fires woodland fires, crown fires and sometimes ground fires occur in the forest of the mountain taiga that grows in altitudes between 1800 and 2100 m a.s.l..
Figure 1. Large-scale clearcuts in the montane-boreal forests of Northern Mongolia, associated with the effects of wildfires, have resulted in extended areas of birch forests that were established by post-fire coppicing with a small share of coniferous species. Source: GFMC.
Birch (Betula platyphylla Sukach.) and pine (Pinus sylvestris L.) grove with grass cover are common for subtaiga mountain zone of Northern Mongolia. As long as the absolute height above sea level reaches its maximum, taiga dark-conifer and larch (Larix sibirica Ldb.) grove become prevailing. The pyrologic characters of these taiga forests don’t noticeably vary during the fire-hazardous season.
In Northern Mongolia, forests fires are one of the major factors determining the trends of altitudinal belt-specific forest formation processes.
IFFN/GFMC contribution submitted by:
Institute of Botany, Mongolian Academy of Sciences
Chuluunbaatar, Ts. 1998. Forest fire danger of Northern Mongolia. Ulaanbaatar, 25 pp.
Chuluunbaatar, Ts. and Zoyoo, D. 1999. The forest fire influence on the forest phytocenoses of the Eastern Khuysugul. In: Diversity of the plant cover within the Baikal Region. Ulan-Ude, 85 pp.
Chuluunbaatar, Ts. 2001.Forest fire danger and its reduction methods. Ulaanbaatar, 125 pp.
Sofronov, M.A. 1985. Drought indicators of forest fire. In: Forest fires and their consequences. Krasnoyarsk, 55-56.
Telitzyn G.P., Kostyrina T.B., Dunda E.E. 1981. Recommendations improve the methods forest fire control in MPR. Khabarovsk, 36 p.
Valendik, E.H., G.A. Ivanova, and Ts. Chuluunbaatar. 1997. The problem of forests in Mongolia. In: Asian ecosystems and their protection. Ulaanbaatar,137 p.
Valendik, E.N., G.A. Ivanova, Z.O. Chuluunbaatar, and J.G. Goldammer. 1998. Fire in forest ecosystems of Mongolia. International Forest Fire News No. 19, 58-63.