The analysis of the occurrence frequency of droughts, floods, hurricanes, avalanches and other natural disasters on the Earth demonstrates that they are not casual and episodic in character, but represent quite a regular phenomenon recurring in accordance with heliocycles and being a permanent evolutionary and ecological factor. This report deals with analysis and generalization of probable changes of the ecogenetic structure, stability and microevolution of dendropopulations under the action of "ecological catastrophes" by the example of fires in light-coniferous forests.
The notion, principles and factors of stability of superorganismic biosystems have not been adequately defined and are debatable. Two types of the dynamics and the stability of populations and biocenosis - "fluctuation" and "pulsed" types - can be recognized. A typical example of the latter is the "pulsed pyrogenic stability" of Pinus sylvestris L. populations and other light conifers in the northern hemisphere. Stimulating the seed bearing and improving the environmental factors (the substrate, the ecoclimate, phyto-, zoo- and microbocenoses) for the pine selfsown, fires are responsible for "waves" of the pine regeneration through the interruption of its replacement by dark conifers and deciduous species and the formation of a mosaic-stepped age-height structure of natural pyrogenic tree stands. This structure is the main factor of their pulsed stability as it prevents the change of a surface to a crown fire providing the mosaic conservation of seed sources, a continuous reproduction and the dominance of pines.
One can think that while eliminating the undergrowth and underdeveloped less stable homozygous part of the tree stands, fires increase their homozygosity, but, at the same time, reduce it by inducing a huge number of new recombination genes in regeneration waves. Small genetically specific families of the selfsown are formed in vast burns because of a casual abrupt "drift of genes" in remaining single parent trees-founders or their groups and the decrease in the exchange of seeds and pollen between them. They can join together and form a new integral population only through the progressive motion and the "relay-race" dispersal of several generations. While reducing the surface area and increasing disjunctivity of insular populations in the south of the natural habitat, fires in xerothermic phases of interglacial periods and the anthropogene can considerably add to processes of homozygotation and inbreeding of pines. However, these processes have been studied little at the quantitative molecular-genetic level.
Considering Timofeyev-Resovsky's hypothesis and our postulate of a regular cyclicity of ecological catastrophes on the Earth, it is possible to formulate a general biological hypothesis of the "pulsed microevolution": because of a cyclic alteration of gradual and catastrophic changes in the environment and the structure of populations, the microevolutionary process represents an aperiodic rotation with time of two phases: relatively slow dynamically equilibrium fluctuations and pulsed (irreversible in the case of severe catastrophes) transformations of their genofund.
The microevolutionary effectiveness of cyclic fires can be confirmed by some ecomorphological "fire" adaptations of adult trees, tree stands and the selfsown of light conifers. They include intimate relations of the bark thickness on tree trunks with the temperature during a fire and the phytomass of the bark in tree stands with the density of lightning-caused fires; a mosaic-stepped structure of natural tree stands; post-fire outbursts of the seed bearing and regeneration; correspondence of the rate and the rhythm of the ontogenesis of selfsown seedlings to the combination and dynamics of the environment in open burns, as well as some other biological features. Pyrogenic adaptations of light conifers can be interpreted (and partly predicted) using our theory of their "petropsammophyteness - pyrophyteness".Note. Abstracts are published in author's edition