Peculiarities of Phenology and Thermal Requirements for the Development of Two Clematis L. (Ranunculaceae) Species under the Conditions of Galich’ya Gora Nature Reserve (Lipetsk Oblast)

The phenodata, thermal requirements, and their regional parameters are compared for six seasonal developmental stages of two ecologically distinct clematis species, Clematis integrifolia and C. recta. The thermal requirements to be compared are determined by an original technique based on the data of phenological observations carried out in 1990–2014 in Galich’ya Gora Nature Reserve (Lipetsk oblast). In C. recta, all of the registered stages except the stage of mass seed ripening occurred later than in C. integrifolia. It is found that C. recta, being a woodland species, requires more heat for its development than C. integrifolia, which grows in grassy habitats. At the stages of the beginning of vegetation, blossoming, and the beginning of seed ripening, this is manifested by higher values of both thermal constants and regional parameters of development. It is assumed also that the development of C. recta did not pause in winter and that it is exactly in this time that flower buds formed. The results of the study indicate that the adaptation of the two species to different environmental conditions, which took place in the course of evolution, has led to physiological changes that are reflected, in particular, in a shift in the thermal requirements for development.