Habitat Features and Population Status of Dactylorhiza maculata (L.) Soó (Orchidaceae) on the Southern Border of the Range in the Volga-Kama Reserve (Republic of Tatarstan)

Fluctuation dynamics (studied for 9–27 years) of the abundance, density, age, and spatial structure of the Dactylorhiza maculata (L.) Soó population on Lake Dolgoe of the Volga-Kama Reserve reflects the mechanisms of maintaining the population at the southern border of the range. The data were stored into the database. Abiotic and biotic factors of transitional shrub–sedge sphagnum bogs are the most suitable for the conservation of a rare species, where boreal and arctoboreal species are preserved, and favorable microsites are open and moist areas of the mire, with pH 4.1–4.5. The biodiversity of sphagnum mosses in the habitats of Dactylorhiza maculata is represented by nine species, where the carpet species is Sphagnum angustifolium, and Sphagnum divinum appears in open and wet microareas and Sphagnum centrale appears in areas overgrown with open forest. A significant relationship of the species abundance with climatic factors is revealed: a positive relationship with precipitation and a negative relationship with average temperatures of the growing season. The number of reproductive D. maculata does not depend on precipitation in moist microsites. Age stages are reliably identified using the morphometric parameters of vegetative and reproductive plants: juvenile (j), immature (im), virginal (v), young reproductive (g1), and mature reproductive (g2). The ontogenetic spectrum is 11.5: 17: 29: 42.5 (j: im: v: g), and the proportion of prereproductive individuals fluctuated between 57–66% in the period of 9–27 years of study due to a high percentage of fruit formation (up to 60%). The spatial distribution of individuals is predominantly clustered, consisting of aggregations with a radius of 0.5–1.2 m, distributed randomly. The dynamics of spatial mosaics, accompanied by the migration of seeds and individuals of D. maculata to favorable microsites, is a natural compensatory resistance mechanism that ensures the dynamic balance of the population.