## 2 Materials and Methods
### Climate  
According to climatic regionalizations, the study area is located in the Carpathian region, montane and submontane, within the intramontane valley subdivision [29; 30; 31], and in a temperate climatic zone with a mean annual air temperature from 4 to 6 \({}^{\circ}\)C [32]. As in the vicinity of the reserve there are no weather stations with long time series of meteorological measurements available, for the present study, we used data from Zakopane (49\({}^{\circ}\)17\({}^{\prime}\) N, 19\({}^{\circ}\)57\({}^{\prime}\) E, 855 m a.s.l.) and Jablonka (49\({}^{\circ}\)28\({}^{\prime}\) N, 19\({}^{\circ}\)42\({}^{\prime}\) E, 617 m a.s.l.). The data span is 1971-2020. Both weather stations belong to the Institute of Meteorology and Water Management--National Research Institute [33]. They are located about 20 km S and 25 km W, respectively, from the study area. In Zakopane, the mean air temperature (Tmean) throughout the period of 1971-2020 equaled 5.8 \({}^{\circ}\)C and ranged from \(-\)2.7 \({}^{\circ}\)C in January to 15.1 \({}^{\circ}\)C in July (Figure 4). The Tmean in Jablonka was just 0.1 \({}^{\circ}\)C lower (5.7 \({}^{\circ}\)C), but it varied over a broader range compared to Zakopane (from \(-\)4.8 \({}^{\circ}\)C to 15.8 \({}^{\circ}\)C; Figure 4). The annual variability in the Tmax indicates that in Zakopane, even in winter (December-February), the Tmax was above 0 \({}^{\circ}\)C. Jablonka and the Bor na Czerwonem Reserve are located in a basin, in which thermal inversions occur frequently, with temperature drops below 0 \({}^{\circ}\)C. This is why the lowest Tmax values in January of each year were below that value, on average \(-\)0.5 \({}^{\circ}\)C (Figure 4). The monthly mean Tmin values for Zakopane ranged from \(-\)7.4 \({}^{\circ}\)C in January to 10.3 \({}^{\circ}\)C in July, and for Jablonka for the same months, they ranged from \(-\)9.0 \({}^{\circ}\)C to 9.3 \({}^{\circ}\)C. Whereas for Zakopane, the period with mean Tmin values below 0 \({}^{\circ}\)C lasted from November (\(-\)2.0 \({}^{\circ}\)C) to March (\(-\)3.6 \({}^{\circ}\)C), it was longer for Jablonka: from November (\(-\)2.4 \({}^{\circ}\)C) to April (\(-\)0.3 \({}^{\circ}\)C) (Figure 4). In individual years of the study period, ground frost, i.e., days with both Tmax \(>\) 0 \({}^{\circ}\)C and Tmin \(<\) 0 \({}^{\circ}\)C, also occurred at both stations in the summer months (June-August). For this reason, the period of potential ground frost occurrence is all year long. Nonetheless, considering the frequency of ground frostoccurrence, the reserve is more exposed to ground frost than Zakopane, which is located higher above sea level. Multi-year air temperature variability (Tmax, Tmin, Tmean) in the studied 50-year period displays a statistically significant increasing trend at both weather stations, equal to 0.3-0.5 \({}^{\circ}\)C/10 years. Notably, this trend was the strongest for the summer months (June-August). Zakopane belongs to a region with rather high atmospheric total precipitation. Through the period of 1971-2020, the mean annual total of precipitation equaled 1133 mm (Figure 4). Most of the rainfall occurred in summer (June-August), with a maximum in July (180 mm). Precipitation was the lowest during winter (December-February; about 45-50 mm) (Figure 4). The total precipitation for Jablonka was lower, equal to 740 mm, ranging from 34 mm in February to 101 mm in July. The multi-year total of precipitation shows no statistically significant trend. The annual variability in the number of days with snow cover--on average, 120 days a year in Zakopane and 91 days in Jablonka--also testifies to the specific climate of the study region. Snow cover may potentially occur from October to May/June. The latest last day with snow cover recorded in Zakopane was 1 June 1977 (1 cm). In Jablonka, the latest date on which snow cover was observed was 14 May 2019. Notably, however, on 1 May 1985, the thickness of snow cover in Jablonka was up to 20 cm.