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post-
re sites was determined mainly by the decreasing level of respiration due to
the trees
roots.
In the course of all chronological succession of
'
uxes
from soil changed almost twofold at reaching maximum values before joining of the
trees
fires considered, the CO
2
fl
crowns, when the soil was the warmest and an accumulation took place of
both ground and sub-ground biomass. The observed decrease of CO
2
fl
'
flux in the
case of older forest stands can be explained by a lower soil temperature, which is
determined by an accumulated heat-isolating organic substance and other factors.
Boreal forests cover the territory of about 14 million km
2
in the circumpolar
latitudinal band 50
10 % of the global land surface.
These forests contain disproportionately large amounts of soil carbon because of
climatic conditions which are unfavorable for the processes of organics decom-
position. The annual mean temperature in boreal forests is close to 0
70
°
N, which constitutes
-
*
C with a
weakly drained soil explained by prevailing lowlands. The characteristic features of
the considered latitudinal band are widespread permafrost and isolation of deep
ground horizons from summertime heating because of moss and thin roots which
burn in forest
°
fires but restore during decades. This heat-insulation favors the
preservations of permafrost, which complicates the soil drainage and slows down
the processes of decomposition of organic matter stored in deep soil layers beneath
the moss layer. Intensi
cation of respiration due to deep layers measured in July
and August 1996 reached
*
10 kgC ha
−
1
day
−
1
. This enhancement of respiration
correlates with an increase of the deep layers temperature. Thus, organic matter of
deep layers of the soil is characterized by lability with a low rate of decomposition
connected with low temperature.
The data above show that it is necessary to extend the parametric descriptions of
the R
s
fl
flux components, apparently not only for forested territories but also for other
soil-plant biomes in order to raise the accuracy of estimates of sinks and sources of
CO
2
on land. Smith et al. (2003) carried out measurements of CO
2
fl
uxes under
conditions of mountain ecosystem of the steppe wormwood in the south-eastern
part of Wyoming and found out that the difference between CO
2
fl
uxes measured at
different time of day reached 9 %, and that even under conditions of homogeneous
vegetation cover the temporal variability of CO
2
fl
uxes between the ecosystem and
the atmosphere is substantial.
An important consequence of forest
fires is the
fire-induced changes of
atmospheric chemistry due to GHGs
emissions. For instance, large-scale forest
November 1997 in Indonesia, Malaysia and Papua-New Guinea
resulted in about 130 TgCO emitted to the atmosphere, which changed the ozone
concentration by 10 %. The GHGs emitted to the atmosphere propagated over vast
territories, and the total content of CO in December grew by 10
fires in September
-
-
20 % in the
°
°
—
°
—
°
latitudinal band 30
N.
On the whole, global emission of GHGs in biomass burning reached 38
N
-
45
S, by 5
-
10 %
south of 45
S, and <5 %
north of 45
-
4,300 TgC year
−
1
with a very small contribution due to
fires in boreal forests
(23 TgC year
−
1
, or 0.6 %). Emissions of GHGs to the atmosphere due to
fires in
boreal forests in 1998 constituted 290
383 Tg (total carbon), 828
1,105 Tg(CO
2
),
-
-
88
128 Tg(CO), and 2.9
4.7 Tg(CH
4
). The upper
level of
these estimates
-
-
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