The foundations of ecological science were laid down at those times when the problem of a possible loss of local and global environmental sustainability was not as acute as it has become today. To make sure that the proposed scientific solutions to this problem are responsible, it is useful to revise the existing frameworks of environmental thought. In this paper, we present quantitative evidence suggesting that the persistence of an environment suitable for life for any appreciable period of time is only possible as long as a substantial area on the planet's surface is occupied by natural ecosystems undisturbed by anthropogenic activities. Once the natural biotic mechanism of environmental control is destroyed, both local and global environment rapidly (over a time scale of hundreds of years) degrade to a state unfit for life, even if any direct anthropogenic environmental impact like industrial pollution is absent. It is therefore important to quantitatively assess the stabilizing impact of natural ecosystems and to determine the necessary and sufficient global area that must be exempted from anthropogenic activities and let be occupied by natural ecosystems, so that the latter have power enough to sustain the global environment in a stable life-compatible state. This urgent scientific task emerges as the major challenge for modern ecological science. We discuss how the proposed conceptual approach to the biota-environment interaction relates to the important paradigms of biological theory.

A detailed study of lichen diversity and estimation of epiphytic lichen cover characteristics on spruce as a key ecosystem component was performed in boreal forests of Karelia (NW Russia). The aims of the present paper are: (1) to study lichen diversity on Norway spruce in the middle boreal forests of southern Karelia (NW Russia), and (2) to estimate the main characteristics of epiphytic lichen cover on spruce trunks and branches. In total, 158 species of lichens and allied fungi were found on spruce, including 108 species on trunks, 78 on branches and 55 on snags. Seventeen species are listed in the Red Data Book of Republic of Karelia. Ten species are new for the biogeographical province Karelia transonegensis and two for the province Karelia onegensis. Twenty-two species are considered old-growth forest indicators. The total epiphytic lichen cover on spruce trees averaged 59% at the trunk base, 12% at a height of 1.3 m above ground level and 61% on branches. Predominantly, only 12 species contributed to the lichen cover of trunk and branches. Despite the predominance of crustose lichens colonising spruce trees, the main epiphytic lichen cover both on trunks and branches was provided largely by foliose species (57% of the total cover). Due to a variety of morphological features, spruce provides diverse microhabitats, which leads to high lichen species richness with different ecological requirements. Spruce trees play a significant role in maintaining the diversity and conservation of rare species.

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