Each organism is characterized by a specific potential capacity to react to the influence of environmental factors, according to its genetic constitution and hereditary reaction norm. Some species can withstand large variations, others, on the contrary, very small, i.e. ecological valence is the amplitude of the variations of the conditions of existence between which a species is able to live. The totality of ecological valences constitutes the ecological spectrum of the species. In the context of the increasingly obvious manifestations, both of the climate change scenarios and the maintenance of the high level of pollution, especially with SO2, whole associations of some species of stenoic lichens may be threatened with extinction. Important is the conservation of ecobioindicator species that ensure non-instrumental ecological monitoring, promoted by the international Conventions. As a result of field expeditions from 2011-2018, 9 forest-petrophyte ecosystems were evaluated in the bordering area of the Dniester River, on the middle course segment, right bank. The altitude of the territory varies from 280-140 m, in the north, to 80-40 m, in the south. The exposure of the studied ecosystems is dominated by the northern orientation, favorable for the development of lichens. In the forest-petrophitic ecosystems the lichens from 9 protected areas belonging to 34 species were recorded. Of these 12 are rare species). It was established that for 10 species the ecological valences to the substrate, illumination and humidity are very narrow, so the ecological spectrum is very narrow. Among the 10 stenoic species 2 are included in the Red Book and 8 are Rare, so these will be the first affected in the case of changes in the environmental components.