Seasonal dynamics of forest communities

The implementation of a series of phenological observations began in 1963, as an extension of phytosociological-ecological and ecoclimatic studies conducted in the Białowieża Geobotanical Station in the years 1951-1962. Based on the results of the previous studies, a hypothesis on the phenological individuality of plant communities was put forward. In the light of this hypothesis, each plant community demonstrates a specific seasonal dynamics, and plant species in each community differ in their performance in terms of life phases in the annual course, which is determined by the variability of microclimatic conditions.

Due to its zonal character, prevalence and good conservation status in the Białowieża Forest, local variability and floristic-phytosociological and habitat-ecological diversity, it was concluded that the oak-hornbeam forest is the most appropriate research object in which this hypothesis can be verified. Four research areas were established in one, vast biochore of mixed deciduous forest in the Białowieża National Park, located north of the Orłówka stream. They covered four sub-associations of the oak-hornbeam forest: Tilio-Carpinetum corydaletosum, Tilio-Carpinetum stachyetosum, Tilio-Carpinetum typicum and Tilio-Carpinetum calamagrostietosum.

In the initial observation period, a 5-day observation interval was adopted, then it was extended to 10 days, bearing in mind that it should allow for contrasting real changes in the development of plants and the forest community as a whole, both during the period of their clear acceleration and slowdown. In the study, an elongated area was used, in the shape of a 50 m x 2 m rectangle, additionally internally divided into 25 squares 2 m x 2 m. Within each square, the date of passage of each plant species through the successive phenological phases: vegetation, budding, flowering, fruiting, sowing and dormancy is recorded. The temperature is also measured on each of the four experimental plots at three levels above the soil surface: 5, 50 and 200 cm and two levels below the soil level: 20 and 50 cm. Additionally, on all 25 squares within each of the four research plots, the thickness of snow cover is measured.

In order to objectivize and enrich the scope of observation, since 1972, repeated photographic recording has been applied. The repeatability of photographic registration of changes in the forest herb layer and forest canopy was ensured by using a set of projection frames installed on the forest floor permanently and a special 4-legged tripod easily connected to the frame. The connection between the camera and the tripod was achieved by specially designed head allowing for vertical images: herb layer and tree canopy. The size and shape of the projection frame (internal dimensions: 0.5 m2 = 577.4 mm x 866.1 mm) was adapted to the format of a rectangular film frame in a standard camera and a fixed, comfortable shooting height (approx. 170 cm from the ground). 25 frames were installed in each of the 25 squares at the edge of the surface. Each frame has a plate with the surface and square number.