The Influence of Different Forest Landscapes on Physiological and Psychological Recovery
1. Introduction
Since the previous century, there has been a global shift toward economic reform and expansion, paralleled by rapid industrial growth and extensive urbanization. The World Bank estimated in 2023 that 56% of the world’s population lived in urban areas, a figure projected to increase by 1.5 times to 6 billion by 2045 [1]. The swift pace of urban development has been a catalyst for economic and social advancement, yet it has also given rise to a host of environmental challenges and changes in lifestyle, such as local climate alteration [2,3,4,5], increased air and water pollution [6,7,8], a major reduction in natural vegetation production [9,10,11,12], and decreased ecosystem services [13]. These problems are eroding human physical and mental health and increasing exposure to environmental stressors. Urban environments today, characterized by their unceasing and diverse distractions, may hinder individuals’ ability to concentrate on vital matters or to attain states of relaxation [14,15]. This crisis was particularly pronounced among college students, who face multiple health risk factors [16,17,18,19,20,21]. Previous studies have shown that approximately half of the college student population reports significant levels of stress, anxiety, depression, or their combination [22], underscoring the growing need for effective stress management and healthy living approaches [23,24]. The restorative effect of natural environments is increasingly recognized in environmental psychology and public health domains [25,26,27]. A report in 1974 by M. Lalonde [28] introduced the “Health Field Concept”, which broadly considered environmental factors and identified them as one of the determinants of health promotion. The theory of therapeutic landscapes [29] explored why certain environments contribute to a healing sense of place. And building on this work, the contemplative landscape model by Olszewska-Guizzo et al. [30] focuses on how certain landscapes, such as forests, can be designed or identified to promote mental and physical recovery by providing a space for contemplation and relaxation. Moreover, the Attention Restoration Theory suggested that depleted directed attention caused mental fatigue and that exposure to natural environments facilitated the restoration of the capacity for directed attention [31]. Stress Reduction Theory suggests that the non-threatening natural setting as a restorative environment could evoke positive emotions and block negative emotions [32,33]. More and more studies have corroborated the restorative effects of the natural environment as a medium for people’s physical and mental health [25,26,34,35]. Restorative primarily translates into physiological and psychological advantages of exposure to the natural environment. That is, positive physiological and psychological changes resulting from exposure to forest landscapes have a restorative effect on people’s physical and mental health [36].
Forests have been studied a lot of times as typical restorative environments [37,38,39]. These studies directly proved or inferred that the forest environment was effective in relieving stress and depression, and individuals felt more relaxation, dynamism, and rest when exposed to the forest [31,40,41,42]. Studies focusing on the physiological effects of relaxation exposure to the forest space showed that exposure to the forest could decrease pre-frontal cortex cerebral blood flow, lower blood pressure and heart rate [39,40], enhance parasympathetic activity, inhibit sympathetic activity [42,43,44], decrease salivary cortisol stress hormone concentrations [42,43], and enhance anticancer proteins and natural killer cells activities [45,46], thereby enhancing immune performance. This was mainly due to various environmental elements in the forest, such as sufficient oxygen, phytoncides, sunlight, sound, etc. Additionally, studies have demonstrated that forest settings, as opposed to urban ones, enhance positive mood states, alleviate negative emotions like depression and anxiety [47,48,49], and improve specific psychological responses such as attention recovery, self-esteem, and life quality [50,51,52].
However, the capacity of forest environments to improve human health was influenced by landscape type and characteristics [31,53,54], which meant that some types or characteristics were more effective for health recovery. Green plants were more favored by people than other colored plants [55,56,57]. Nordh et al. [58] applied choice-based conjoint analysis to assess the restorative value of small urban parks, identifying landscape features such as grass, trees, and shrubs as key factors in restoration likelihood. A study of landscape types and landscape elements in urban parks showed that different landscape types elicit varied physiological and emotional reactions; landscapes mimicking natural mountain forests showed the highest restorative impacts [59], coniferous forests provided relaxation for the subjects, and broadleaved forests produced the most stable mood [60]. Furthermore, various specific landscape features, including “open view” [61], “stand density” [60,62], “planting with flower cover” [63], etc., have been identified as significant in creating restorative environments within each study’s specific context.
Similar to green landscapes, blue landscapes are also increasingly recognized for their therapeutic and public health benefits [31]. Bell et al. discovered that physical activity, social interaction, and psychological benefits were evident in people visiting blue spaces [64]. The research by Tang et al. [65] used fMRI to compare the rejuvenating effects of different landscapes (urban, mountain, forest, water), noting that water landscapes, unlike urban ones, increased neural activity in brain regions associated with attention, implying a stimulatory effect on the attention system. They found that in contrast to urban landscapes, viewing water landscapes was associated with increased brain neural activity in the attention area, suggesting that viewing water landscapes might stimulate the rest of the attention system. In addition, a study on seven different forest landscape types for stress relief showed that exposure to forest–water spaces, especially dynamic water landscapes, was more effective for psychological stress relief [66]. Moreover, a study of Han [67] on landscape preferences showed that the highest-ranked forest scenes contained water.
However, there are also differences in the effects of green and blue landscapes on physical and mental health. A study by Li et al. investigated the restorative effects of exposure to water, lawn, and topography landscape environments and showed significant differences between the three landscapes on participants’ blood pressure, brain activity, and mood states [59]. In addition, the effect of urban blue space on users’ health enhancement was prominent [68]. On the contrary, Zhao et al. [69] reported in their study that water features reduced the quality of restoration of vegetated pathway landscapes.
As a result of these studies, various types of landscapes have been found to affect the perceived degree of physical and mental health improvement. However, little evidence has been collected regarding specific landscape types in relation to the sympathetic nervous system and emotional states. In this study, we sought to discover the different restorative effects between vegetated landscapes in forests and water landscapes with vegetated elements. Therefore, diverse landscape settings including broadleaved forests, coniferous forests, mixed forests, topography forest landscapes, flower, open nature landscapes, and a variety of water features with vegetated elements were applied as experimental stimuli. This was carried out to improve our understanding of landscape types and elements using scientific and evidence-based research, aiming to identify the effects of these more resource-intensive natural environments in promoting health.
In recent years, virtual reality (VR) has been used a lot in improving health; nevertheless, VR offers a more realistic experience, but it also faces technical and logistical challenges. Numerous studies have explored and validated the differences between direct interviews and indirect exposures, finding that viewing pictures might, to some extent, substitute for on-site surveys [70,71,72]. Therefore, in this study, we used pictures as experimental stimuli, set the urban landscapes as opposed to restorative environments as negative stimuli, and used images to evaluate the physical and mental restorative effects during exposure to different types of landscape.
The aim of this study is to evaluate the differential impacts of purely vegetated forest landscapes and water landscapes with vegetated elements on stress reduction and mood improvement. We specifically address the following research questions: (1) Do purely vegetated landscapes (VL, included broadleaved, coniferous, mixed forests, and topography-influenced forest landscapes) and water landscapes (WL) featuring vegetative elements differ in their restorative effects on individuals? (2) Among these landscapes, do water features integrated with vegetation more effectively promote health than purely vegetated landscapes? This investigation seeks to enhance understanding of the health-promoting capacities of diverse natural environments through scientific and evidence-based research to inform decisions about landscape design and healthcare interventions.
4. Discussion
4.1. Physiological Effects
In this study, salivary α amylase (SAA) and heart rate variability (HRV) were employed as biomarkers to evaluate the influence of viewing forest images on the autonomic nervous system of college students. Under experimental conditions, compared to baseline measurements, both paired-sample t-tests and Wilcoxon signed-rank tests revealed that exposure to landscapes featuring forest vegetation and water scenarios, a notable decrease in salivary α amylase and a significant increase in parasympathetic activity post-exposure to these environmental settings. However, there was no significant difference between the vegetated and water landscapes.
Notably, LF/HF ratios declined significantly only after viewing water landscapes, while changes associated with vegetated landscapes were minor and not statistically significant. These outcomes are consistent with extensive prior research [35,54,67,82,83,84,85], suggesting a beneficial influence of forest landscapes on autonomic nervous system function. Furthermore, our study explored the comparative restorative impacts of vegetated versus water views. Water views demonstrated a marginally greater influence on physiological recovery than vegetated landscapes, though the disparity between the two was not statistically notable. This finding echoes other studies [56,86] indicating minimal variance in restorative effects among different natural environments. Patrik and Ulrika’s research [87] supports the notion that not only visual but also other sensory experiences shape the psychological response to green environments. In accordance with Stress Reduction Theory (SRT), humans are innately drawn to safe, natural settings abundant with trees, water, and varied vegetation, eliciting immediate positive responses [32,88]. Additional studies [89,90] have emphasized the stress-relieving properties of water features, which might be potentially linked to a preference for blue spaces [67].
4.2. Psychological Effects
Our study indicated that viewing both vegetated and water landscapes significantly ameliorated negative emotions, improved activity, and reduced stress. However, comparing the three types of landscape, the impact of water landscapes on emotion improvement and stress relief was marginally greater than that of vegetated landscapes, but the difference was not significant. In addition, self-esteem was significantly boosted only after exposure to the vegetated landscapes.
Tyrväinen et al. [85] noted that environments with distinct characteristics, such as densely vegetated forests and natural reserves, can alleviate stress and fatigue. This could be attributed to negative emotions being more responsive to environmental changes, which may swiftly and instinctively mitigate unpleasant emotions [90]. Blue spaces, in particular, are considered superior for mental restoration [91,92], possibly reflecting a general preference for such environments. Notably, only the ‘fatigue’ dimension showed a significant reduction post-exposure to water features. We hypothesize that the influence of water on self-perception may surpass that of green environments [93,94] and that aquatic environments like beaches and rivers are effective in diminishing negative emotions [95]. This observation was corroborated by PSS measurements.
Moreover, improvements in positive mood were significant in both vegetated and water landscapes. An increase in ‘Vigor’ was noted after exposure to water landscapes compared to vegetated ones, although this change was not significant. This could be attributed to the fact that the monotonous green of vegetation might appear unengaging and visually unappealing [96], whereas the diversity in water landscapes may evoke more pleasant feelings [27,31]. Conversely, vegetated landscapes were more effective than water landscapes in enhancing ‘self-esteem’, a finding exclusively noted in SES measurements. Zhang’s research [97] suggested that visual stimuli from forest landscapes, particularly the green color and tree shapes, are influential in boosting self-esteem. This finding underscores the unique contribution of greenery in forest landscapes to self-esteem restoration.
4.3. Limitations
This study has several limitations. Firstly, while it explored the restorative effects of in-forest vegetated and water landscapes, it did not examine the nine landscape elements within each type individually. In real-world settings, different types of environments may vary in their effectiveness for physical and mental health restoration. Not just visual elements but auditory elements and even olfactory elements may also affect recovery. Future research should expand on this aspect to provide a more comprehensive understanding of the restorative effects of forest environments and explore these nuances in more detail.
Secondly, the absence of a control group in this study may affect its internal validity and increase the potential for bias. Future studies would benefit from employing a randomized controlled trial design to mitigate these concerns and enhance the reliability of findings.
Thirdly, despite college students typically being a stressed population, in reality, other populations also experience a variety of stressors. In the future, the long-term effects of such indirect nature exposure on various populations such as seniors, manual laborers, stay-at-home moms, etc., could provide valuable insights into its efficacy as a sustainable intervention.
Lastly, images were selected as visual stimuli for this study, and although many previous studies have demonstrated the effectiveness of forest landscape images for stress relief, results may vary depending on the image accuracy, subject preference, and exposure order.
Future research could build on our findings, exploring the optimal types and qualities of images that most effectively convey the restorative properties of natural environments. This could include investigating aspects such as image resolution, realism, the inclusion of auditory elements, or even the use of emerging technologies like virtual reality (VR) to provide a more immersive and realistic comparison between vegetated landscapes and water-containing forest landscapes. Such investigations are crucial for identifying the visual and sensory characteristics that most significantly contribute to the restorative experience. Moreover, examining the long-term effects of such indirect nature exposure on various populations could provide valuable insights into its efficacy as a sustainable mental health intervention. Simulating realistic nature experiences could revolutionize approaches to mental health care, providing accessible, effective solutions for stress and mood management.
5. Conclusions
In this research, aiming to provide foundational insights into the benefits of visual exposure to different types of landscapes, we explored the physical and psychological effects resulting from visual exposure to different landscape environments. We specifically investigated whether predominantly vegetated landscapes and water features with vegetation elements exhibit distinct restorative effects on individuals and whether there are differences between the two in their capacity to foster physical and psychological recovery. Our findings illuminate the nuanced benefits of visual exposure to diverse landscape environments, particularly emphasizing the restorative potential of forest landscapes that integrate both vegetation and water elements. We observed that both types of landscapes (vegetated and water features with vegetation elements) contribute positively to human health, enhancing both physiological and psychological well-being. Notably, while water features presented a marginally higher restorative advantage, the difference in recovery effects between purely vegetated landscapes and those including water was not statistically significant. This outcome suggests that forest landscapes, regardless of the inclusion of water, are inherently beneficial, though the presence of water elements tends to augment emotional improvement and stress alleviation slightly more.
In the context of forest therapy, our research underscores the potential of forest landscapes, both with and without water features, as therapeutic environments for enhancing human well-being. This insight can guide the management and utilization of forest landscape resources, suggesting that the inclusion of diverse landscape features, including both vegetation and water, can be beneficial in landscape design and healthcare interventions. Urban planners, landscape architects, and public health policymakers can leverage these findings to design green spaces that optimize the health benefits for the community, particularly for stress-prone populations such as college students. Furthermore, this research could inspire the development of more targeted forest therapy programs that capitalize on the specific elements of forest landscapes that are most effective in promoting physical and mental recovery.
