4.1. Mood States
Consistent with previous studies [
2,
5,
10,
11,
14,
17,
33,
34], this study confirmed that short periods of forest recreation in a snow-covered forest (in this case: 15 min of relaxation in this environment) have a significant effect on the mood states of participants. The negative indices of mood states, including tension/anxiety, anger/hostility, depression/dejection, confusion, and fatigue, decreased after exposure to the forest environment. This confirms our hypothesis that this type of intervention results in a positive outcome. The positive index of mood states (vigor) did not increase after exposure, but neither did it decrease significantly. This is not consistent with a previous study [
14] or another study conducted only among females [
4]. Lower levels of indicators of negative mood have many positive outcomes, confirming that brief forest recreation during the winter, when snow has occurred, can be successfully conducted for the purpose of stress reduction among females. Females may, however, react differently to the forest environment than men [
17], which indicates the need for further testing of these effects on both sexes.
The effect of lowering negative mood states is useful information for therapists who work with individuals living with high levels of stress, such as a highly stressful work environment. The positive effect of nature therapy on this topic is already known [
6,
7,
8,
9], but a novel element of this study was the addition of snow cover. As snow occurs in the winter in many countries, the way in which this element affects individuals requires examination. A positive effect of forest recreation was still observed with snow cover in this study, and there are several hypotheses as to why this effect was observed. It is possible that snow in the forest environment does not obstruct the view that is generally visible in this environment. Some authors suggest that some fractal dimensions are responsible for the existence of the effect of visual stimulation on mood states. For example, some kinds of natural fractals might, hypothetically, induce this positive effect [
35,
36], and in a snow-covered forest, these fractal dimensions are still perceivable to respondents. This stimulation during forest recreation is crucial, and this reaction of humans is possibly some special effect connected to the biophilia hypothesis [
37], which states that people evolved in a natural environment and hence feel healthy in a natural environment like a forest [
38].
4.2. Positive and Negative Affect
Previous studies have indicated that subjects exhibit a significant decrease in negative affect after forest recreation and a significant increase in positive affect [
17,
27]. In the current study, an effect on positive affect was observed, as this indicator increased in the forest environment. Negative affect did not decrease in the forest environment after the experiment, however, although it did increase after exposure to the urban street environment. These two indicators, positive and negative affect, are important in psychological research, as their usage gives researchers and therapists information concerning the mental state of participants and patients [
24].
The interpretation of results regarding negative affect is similar to that of the negative mood states of POMS—any negative symptoms are not necessary, so any decrease in this effect is welcome. In this case, a lowering effect on this indicator was unfortunately not observed. In the urban street environment, an increase in negative affect was observed, possibly due to the higher level of noise in that environment [
39]. Further research should compare environments with more similar levels of noise. In the case of positive affect, a difference was observed when comparing forest and urban street environments. In the forest environment, this indicator had higher values, suggesting that in the forest environment, successful recreation could be conducted with positive effects. Because positive affect increased in the forest environment, this tendency might be explained by the biophilia hypothesis [
37,
38].
4.5. A Rigorous Comparison with the Previous Study
Previously, the same areas were used to study the impact of winter forest recreation (without snow cover) on the psychological relaxation of the subjects [
17]. It is worth referring to the results of these studies in this manuscript. Particular attention should be paid to comparing the impact of environments on psychological relaxation after conducting an experiment. In the case of the POMS questionnaire results, current research showed a significant difference between: Tension/anxiety (
p < 0.001), depression/dejection (
p = 0.029), anger/hostility (
p = 0.047), fatigue (
p = 0.002) and confusion (differences for these two environments are irrelevant for the ‘vigor’ subscales). In the previous study [
17], the tension/anxiety subscale had lower values after exposure to the forest environment compared to the urban street environment, similarly to the subscale depression/dejection, anger/hostility, fatigue and confusion. The results for the ‘vigor’ subscales reached significantly higher values. All differences were compared at a significance level of
p < 0.05. Comparing these two studies, it can be seen that the only difference was the significance for the vigor; the forest environment, compared to urban street environment, therefore causes psychological relaxation regardless of the presence or absence of snow cover, but this impact is somewhat smaller with snow cover.
In the case of the PANAS scale, the negative aspect in current research did not differ significantly after exposure to two different environments (forest vs. urban street environment), but the positive aspect was significantly higher after exposure to the forest environment (
p = 0.033). In studies without snow cover [
17], the negative aspect was significantly lower in the forest environment and the positive aspect was significantly higher in this environment (with a significance level of
p < 0.05). Therefore, the forest environment without snow cover had a slightly stronger impact on the subjects.
As for the ROS and SVS scales, the ROS scale value in the study was significantly higher in the forest environment (
p < 0.001), similarly to the SVS scale (
p = 0.002). In the compared study [
17], exactly the same tendency was observed (with a significance level of
p < 0.05), so the environments in both studies had similar effects on the results obtained in the ROS and SVS scales.
Focusing on the predominance of any of the analyzed variants (snow vs. no snow) is not easy, because the demographics of the group and its numbers varied. This should be taken into consideration when interpreting these results.
4.6. Limitations
This study has several limitations. First, in this study, the psychological effect of relaxation while simply standing in the forest environment was measured. These effects should be measured during other activities in a forest with snow cover. In fact, some reports indicate that being involved in certain activities may harm the positive effects of nature relaxation [
43]; it is therefore worth examining why some activities induce relaxation and some do not.
Second, only females (20.97 ± 0.65 years) were involved in this study. Future studies should investigate how recreation in a snow-covered forest influences females of different age groups, as well as how this activity influences males of different ages [
4,
5].
Third, only psychological measurements were used in this case; the physiological effects of this activity were not considered [
44].
Fourth, different respondents went to each research site. The respondents at each research point can therefore not be compared directly, meaning that the differences among individuals in the two respondent groups could have caused the significant differences observed between the urban and forest environments. In future studies, this occurrence could be eliminated by exposing respondents from the two groups to both environments in reverse order [
45].
Fifth, as respondents walked to each point on foot, they would have viewed surrounding scenery before getting to either experimental point. It is therefore possible that the time period during which respondents were exposed to the stimulus was not exactly 15 min in length. It is worth mentioning, however, that the walks to the two analyzed environments were conducted through either the urban street environment or the forest (
Figure 1), so only one environment was able to influence each group [
46].
Sixth, in the planned experiments, a carryover effect could possibly have occurred, as the positive effect of forest recreation on health can persist for a longer period of time in subjects, and the tests had to be carried out as soon as possible (due to only periodic snowfall). Conducting a crossover study could therefore be burdened with a carryover effect, and the use of this research system could be abandoned. Thus, a parallel study could be carried out in which the carryover effect was avoided. In addition, such a study can be carried out in a relatively short time. This study would not compare the effects of forest recreation to the effects of conventional recreation (active control), which would not take place under forest conditions. This is a limitation of the current research and should be investigated in future work [
46].
Seventh, in this study, it was assumed that snow was present in the forest landscape if 90% of the ground’s surface was covered by it. It is not known, however, what amount of snow affects the psychological reactions of subjects. This requires future research.
Eighth, in the described research, it was tested whether the forest environment with the existing snow cover affects the psychological relaxation of the subjects. Indeed, it has been shown that in a forest environment with a snow cover causes a psychological relaxation effect. The aim of the study was not to compare the forest with the snow cover with the forest environment without snow cover; however, in future studies, this type of comparison could be done (including the same participants) to find out whether the snow cover in the forest environment affects another way on the subjects than the forest environment without snow cover [
18].
Ninth, it will also be important to examine how different seasons, during which forest stands in the temperate climate zone change, can affect the intensity of the psychological relaxation of subjects [
47]. Research regarding this should be carried out in the future.
Tenth, this paper focuses on examining the impact of a forest environment on the psychological relaxation of young adult students. In the future, it is worth investigating how forest recreation, also conducted in winter, can affect people of different ages and from other demographic groups (e.g., older people, and working).
Eleventh, this study did not include men, so future studies concerning recreation in a forest environment with snow cover present should include this group [
5,
11].
Twelfth, it is also possible that spending too much time in the forest may have a negative effect, depending on the temperature. For this reason, encouraging people to move around to stay warm may be less stressful. The effect of ambient temperature should be examined in future research [
47]. It is worth noting that the physical sensations may have been different in the urban street environment than in the forest environment. This study did not measure these feelings in this experiment. It would be useful in further studies to include a measurement of physical sensations and possibly control the positioning of experimental fields to eliminate differences between environments. It is worth adding, however, that the day of the experiment was chosen so that the wind intensity was as low as possible and the differences between the environments were as small as possible.
Thirteenth, in the experiment, there was less snow in the urban street environment, but it was noticeable in this landscape. In the experiment, it was important to check whether the forest landscape with snow actually affected psychological relaxation—research confirms that this is the case. The intensity of snow occurrence in the urban landscape (in the control environment) is less important [
47].
Fourteenth, the impact of phytoncides from trees growing in the forest may also be significant and are worth investigating in future studies. It is worth emphasizing that in winter, this effect may not occur (lack of photosynthesis) in comparison to forest areas in spring and summer [
48].
All these limitations could likely be overcome in further experiments in the area of forest recreation research. Future studies should also test the effect of forest recreation on males and on different age groups (e.g., on elderly participants).