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strokes per km
2
annually. Of course, not every stroke leads to a forest
re. Nev-
ertheless, in different regions of land, lightning strokes lead to 2
30 % of forest
-
res.
During the historical period, geography and quantity of
fires had been changing,
but their role in the formation of forest landscapes has remained constant. Many
species of trees, such as pine, larch, birch, and aspen had a pyrogenic period in their
development. Owing to
fires these species have preserved their natural habitats and
had not been ousted by spruce, cedar, and
fir. In the process of evolution, the light-
demanding species have become
fire resistant due to, for instance, the thick bark
and deep root system of the larch and pine, and the birch and aspen
'
s ability to give
rich shoots from the roots after a
fire. Some species of American pines exhibit
protective reaction. For instance, they open their cones only after a
re, when
conditions for seeds
sprouting are favorable.
Some investigators believe in an objective idea according to which practically all
current taiga forests in Russia had been changing due to
'
fires (Furiayev 1996).
Present studies make it possible to con
rm the above-said with respect to taiga
forests in the historical and pre-historical past. This is con
rmed, in particular, by
paleoecological developments carried out in the USA and Finland. Studies of
res
using the method of pollen analysis and of traces of burning
fixed in strati
ed lake
deposits in eastern Finland testify to a large scale of
fires. During the last
2,100 years, fires have been an integral factor of development of the taiga forests in
this region. The repeatability of large-scale
fires in eastern Finland varies from 7
-
110 to 130
fires became more frequent after 600 AD,
when the impact of humans on forests became stronger.
According to calculations of Kurbatsky (1964), in the early Holocene there had
been several thousands of forest
180 years. It was noticed that
-
fires caused by lightning strokes. Of course, a
human had also played a substantial role in the origin of
fires in the forest eco-
systems (
(first due to carelessness with
fire, and then as a result of loosing control of
fire during propagation of the slash-and-burn method used to clear the forests for
agriculture). In the 1950s, on all continents, about 200,000 forest
res happened
every year, with 3 % of this quantity having been caused by lightning strokes. It is
not excluded that all forest ecosystems of the planet in the historical and pre-
historical past had suffered from
fire. There had long been a version of the pyro-
genic origin of the present savannas over a vast territory of the Hindustan Penin-
sula, considered to have propagated in place of the burned tropical forests.
Thus, the problem of forest
negative and positive. The
negative side is connected with apparent damage to forest ecosystems and eco-
nomic losses for humans. The positive aspect consists in the evolutionary role of
forest
fires has two sides
—
re renewal of pine forests over vast territories is
known to take place easily and rapidly compared to clearings during which the
seeds get destroyed. At the
fires. For instance, the post-
fire-sites where the seeds have not been destroyed,
shoots and underwood appear rapidly and all together. Moreover, in different global
regions, an increase of the post-
re productivity of forest ecosystems has been
observed. In particular, it was found out that in the regions of Slovenian Karst and
Istria at the south-west of the Republic Slovenia, the
res that happened there
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