Influence of spring and autumn frosts on Impatiens glandulifera populations in the Sofia region (Bulgaria)

The present study aims to analyze and determine to what extent spring and autumn frosts affect the population size and life cycle of this invasive alien species (IAS). The study area is located in the immediate vicinity of the capital Sofia and covers the  Iskar River stream and its tributaries in the gorge between Plana and Lozenska Mountains (Southwestern Bulgaria). The study was carried out in the period 2020-2022. Six permanent sample plots (PSP), each measuring 10 m 2 , were established in characteristic localities of I. glandulifera populations along the Iskar River and its tributaries (Table 1). Each year, during the spring and autumn frosts, the percentage of dead individuals of I. glandulifera relative to the total number of individuals of this species in the PSP was recorded. During the autumn frosts, the number of alive individuals in the following phenological stages was also recorded: flowering; fruiting; dispersal of fruits and seeds; end of growing season. The results show that frosts in the study area did not significantly affect the population size and life cycle of I. glandulifera . The death of the whole population оccurs only in permanent periods of negative daytime temperatures, however a significant part of the individuals at that time are in a generative stage of development. The temperature conditions in the area favor the invasiveness of I. glandulifera , extending the vegetation period of this species and the possibilities for its reproduction and spread.