Peculiarities of Stipapennata L. growing and population condition at the northern border of its occurrence

Stipa pennata L. is a rare species that is now exposed to extermination at entire extent of its range by ploughing up and overgrazing. In that case the importance of the species studying under conditions of its exclaves is suggested. In Sverdlovsk region the periphery populations are located at long distance from the main range and considered as relict. We investigated population age structure to reveal the rules of morphometric features changes in periphery S. pennata populations in the Urals. At the northern border of S. pennata occurrence we studied three populations in exclaves located at latitude scale covering two natural zones (forest-steppe and boreal). We showed that feather grass in its northern habitats in the Urals keeps dominating. With that in the northern direction the species abundance decreases in phytocenosis with feather grass participation, and the share of species of steppe and forest-steppe floristic complex increases in total projective cover of the community. This can be explained by aggregation of xerophilous petrophyte-steppe species at most insolated rocky spots which are adverse for zonal vegetation. With northwards advance the decrease of basic features values both in vegetative and generative set in middle-aged individuals of feather grass (the main group providing population reproduction) is noted. All morphometric features in populations are characterized by low or very low variability (C _V < 12%). Ontogenetic spectra of the inspected populations are normal and entire, and essentially differ from those of S. pennata populations in the main range where the maximum falls on group of old generatives. There are two variants of ontogenetic spectrum formation in the Middle Urals: in southern populations with intensive seed reproduction a leftside age spectrum is formed with maximum in virginal group; weak seed reproduction in northern population brings about right-sided age spectrum with predominance of subsenile group. Assessment of populations vitality (IVC) by individual size spectra revealed the gradient of growth condition worsening from south to north as follows: Zlatoustovskaya (IVC=7.75) - Uktusskaya (IVC=2.12) - Lenevskaya (IVC=0.93). Also in the sequence the main demographic parameters change: decrease in density, revival and substitution indexes, and concurrent increase in senescence index.

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