Nature Exposure Achieves Comparable Health and Well-Being Improvements as Best Practice,Positive Psychology Interventions

Abstract

Folk wisdom and scientific research alike suggest that spending time in nature is good for mental and physical health. Despite a growing body of evidence supporting this idea, questions surrounding whether and what kind of “nature prescription” promotes health and well-being, and how these effects compare with non-nature-based active treatments remain. In this study, we assessed the effects of spending time in nature for 2 weeks compared with participating in exercises adapted from positive psychology. Participants who received the nature exposure treatment improved in physical health, well-being, diligence, and fatigue to the same extent as the established interventions from positive psychology, and increased in nature identity above and beyond these comparison groups. In other words, nature may be just as good as established interventions for improving health and well-being while also promoting a connectedness with nature. This study provides further evidence that nature-based interventions can be beneficial and advances the field by providing an ecologically valid test of the effectiveness of nature-based interventions.

Introduction

The idea that nature promotes health is rooted deeply in human history. From ancient Chinese healers who maintained that a spiritual connection to nature was integral to physical and mental health to Voltaire's prescription to tend our gardens to Sacks (2019, p. 245), the late neurologist who wrote that “gardens and nature are more powerful than any medication,” it is common folk wisdom that nature can be deeply restorative.

Research corroborates the idea that nature* may indeed be the salve we are seeking to remedy public health concerns. Cross-sectional and correlational studies show that individuals who spend more time in nature or who live in more nature-dense areas report improved psychological well-being such as improved mood, self-esteem, life satisfaction, and decreased stress (Cox et al., 2017; Kaplan, 2001; Mackerron & Mourato, 2013; Richardson, Cormack, McRobert, & Underhill, 2016). A growing body of experimental research supports similar conclusions: spending time in nature improves psychological well-being (Bratman, Daily, Levy, & Gross, 2015; Nisbet & Zelenski, 2011), decreases stress (Hartig, Evans, Jamner, Davis, & Gärling, 2003; van den Berg & Custers, 2011), increases cognitive abilities (Berman, Jonides, & Kaplan, 2015; Berto, 2005; Hartig et al., 2003), and improves physiological markers (e.g., cortisol, blood pressure, heart rate variability; Lee, Park, Tsunetsugu, Kagawa, & Miyazaki, 2011; Ulrich et al., 1991). Literature reviews (Capaldi, Passmore, Nisbet, Zelenski, & Dopko, 2015; Hartig, Mitchell, de Vries, & Frumkin, 2014; Oh et al., 2017) and meta-analyses (Capaldi, Dopko, & Zelenski, 2014; Pritchard, Richardson, Sheffield, & Mcewan, 2019) synthesize this area of research, and also point to net positive effects of feeling connected to nature or spending time in nature.

Although much of the research to date builds a strong case for the salubrious effects of nature, it is important to note the limitations of past research and thus the limitations on what we know. First, little attention has been paid to assessing the lasting effects of nature on health and well-being. Experimental studies, in particular, have focused largely upon determining the immediate effects of a brief single exposure to nature, for example, by assessing cognition and affect immediately after a 50-min walk in a nature setting compared with an urban setting (Bratman et al., 2015). While establishing these immediate effects is important and can be done rigorously, it is also crucial to know whether the effects last past immediate exposure. This study aims to advance the field by assessing the effects of a 2-week intervention in which participants spent 2 h in a nature setting (or engaging in a comparison group) each week, with measurements taken before and after the 2-week period rather than immediately following time in nature.

Second, experiments with strong theoretically relevant comparison groups are needed. Although experimental work is becoming more common in the field, many of these studies employ a waitlist control group or a similar nonactive comparison group, making it unclear whether the effects found were truly due to being in nature or due to placebo effects or various confounding factors (e.g., activity). To address this concern, some studies have thoughtfully used an urban exposure group to compare with a nature exposure group and have shown that spending time in nature is more beneficial for health, well-being, and cognition than spending time in urban environments (Bratman et al., 2015). However, although urban settings provide a well-designed comparison for nature settings, evidence for the effects of nature would be even stronger if compared with established positive interventions such as exercises from positive psychology.^† To test whether the effects of spending time in nature achieves health and well-being improvements comparable with those seen in positive psychology interventions, we adapted exercises from positive psychology (Nelson, Layous, Cole, & Lyubomirsky, 2016) to create two comparison groups for the nature exposure group.

Finally, many studies rely on postintervention measurements that limit the precision of assessment and introduce the possibility of selection artifacts (Campbell & Stanley, 1963). Although post-test-only designs can be robust if random assignment is used with large samples, baseline measures add statistical power and allow for more precise estimates of change. In this study, we collected baseline and post-test measures from participants, examining differential change over time based on condition assignment.

In summary, given that the literature to date paints a promising picture of the benefits of nature, we can move forward with more rigorous tests of the effects of nature on health and well-being. This study aims to address some of the limitations outlined previously. Specifically, we randomly assigned participants to one of three groups (an experimental nature condition or one of two active comparison groups) and implemented the intervention for a 2-week period with measurements taken before and after. In short, our goal was to conduct an ecologically valid test of the lasting effects of nature on physical health (i.e., physical symptoms and fatigue), psychological health (i.e., well-being and diligence), as well as identification with nature.

Methods and Materials

Design

Participants first completed a survey in the laboratory and were then randomly assigned to one of three groups: a nature exposure group (nature), an acts-of-kindness-for-others group (other), or an acts-of-kindness-for-the-self group (self). After engaging in their assigned behavior for 2 weeks, participants again completed a survey in the laboratory. The study was preregistered^‡ and also approved by the principal investigator's institution's human subjects institutional review board before data collection. Data and code for the project can be found at the footnote below.^§

Participants

Participants (N = 104)^** were members of the college community where the study took place, and were 78.8% female, of ages 18–72 years (mean [M] = 29.05, standard deviation [SD] = 13.77). In the sample, 91 participants identified as white or Caucasian, 6 as Hispanic or Latino, 2 as black or African American, 2 as Asian or Pacific Islander, and 3 as other.

Excluded participants

Nine participants did not return for a post-test assessment and were excluded from analyses, including the participant demographics already reported (Participants section). One participant was mistakenly provided two different sets of instructions based on different condition assignments and was thus also dropped from analyses. Welch's (1938) two sample t-tests were used to identify any pretest differences between those who did and did not complete the post-test. p-Values were >0.31 for all demographic and dependent variables other than the diligence composite (p = 0.013; those who did not complete the post-test were higher on this construct) and gender (p = 0.024; six of the nine participants who did not complete the post-test were male).

Participant recruitment and compensation

Participants were recruited using flyers and e-mails to the campus community. The communications included a link to a survey, where participants were screened for eligibility. To be eligible, participants had to be 18 years or older; be comfortable “reflecting on yourself, your life, and your behaviors”; be able to attend two hour-long research sessions at the college; be able to spend 2 weeks engaging in behaviors “that may or may not include spending time with others, exercising, eating a healthy diet, practicing self-care, watching videos, or spending time in nature”; and be able to be “moderately physically active.” Eligible participants then signed up for an appointment to come to the laboratory through an online scheduling tool. Upon completion of the full study, participants were compensated with a $50 gift card and were entered into a drawing to win one of four $100 gift cards.

Procedure

Upon reporting to the laboratory, participants provided informed consent and completed a survey on a computer alone in a laboratory room. While the participants were completing the survey, which took ∼30 min, the researcher randomly assigned the participant to a condition and prepared the instructions for the participant based on group assignment. After survey completion, participants were given instructions for the 2-week intervention period (described in the Materials section) to which participants verbally confirmed that they wanted to continue with the study (all participants chose to continue) and scheduled a time to return to the laboratory to complete the post-test. When participants returned to the laboratory 2 weeks later, they completed the post-test questionnaire, and were compensated and debriefed.

Group assignment

Participants were randomly assigned to conditions using a random number generator after they completed the in-laboratory pre-test questionnaire. A total of 34 participants were assigned to the nature condition, 36 were assigned to the other-kindness condition, and 34 were assigned to the self-kindness condition.

Materials

Condition prompts

After completing the baseline questionnaire, participants were read and received a printed copy of following prompts. Prompts for the other-kindness and self-kindness conditions were adapted from Nelson et al. (2016). To preserve ecological validity, participants were not informed about comparison groups and were also not asked to refrain from partaking in activities other groups were assigned to do. That is, the goal of this study was to provide a real-world test of the effects of a “nature prescription” compared with active comparison groups, and our procedures were developed to maintain ecological validity.

Nature prompt

Thank you for completing the first component of this study. The second component of this study asks that you spend time in nature. Psychological theory suggests that spending time in nature may be good for health, and our laboratory is further evaluating this connection.

For the next 2 weeks, we ask that you spend 2 h in nature each week. You should spread this time across 3 days each week. For example, you may spend 20 min in nature one day, 40 min second day, and 60 min on the third day. You may choose the specific days that you spend in nature. You may also choose the specific nature sites. For example, you may enjoy strolling along the D&L trail, sitting and relaxing along Monacacy Creek, riding your bicycle on mountain trails, or fishing in your favorite place. The specific activity and space are up to you; we only ask that the space you select feels as though you are surrounded by nature.

Other-kindness prompt

Thank you for completing the first component of this study. The second component of this study asks that you perform acts of kindness for others. Psychological theory suggests that performing acts of kindness for others may be good for health, and our laboratory is further evaluating this connection.

For the next 2 weeks, we ask that you select 3 days to perform two acts of kindness each week. That is, each week you should perform six acts of kindness toward others in total. These acts can be big (e.g., helping a neighbor in need clean their house) or small (e.g., telling a person you know that you appreciate them), but they should be something out of the ordinary that you do for somebody else. Examples include cooking dinner for friends or family, doing a chore for a family member, paying for a stranger's coffee in line behind you, or writing a thank you letter. These acts of kindness do not need to be for the same person, the person may or may not be aware of the act, and the act does not need to be one of the acts already listed.

Self-kindness prompt

Thank you for completing the first component of this study. The second component of this study asks that you perform acts of kindness for yourself. Psychological theory suggests that performing acts of kindness for the self may be good for health, and our laboratory is further evaluating this connection.

For the next 2 weeks, we ask that you select 3 days to perform two acts of kindness each week. That is, each week you should perform six acts of kindness toward yourself in total. These nice things that you do for yourself could be large (e.g., enjoying a day trip to your favorite lunch) or they could be small (e.g., taking a 5-min break when feeling stressed), but they should be something out of the ordinary that you do for yourself with a little extra effort. Examples include treating yourself to a massage, watching a favorite TV show, or spending time on your favorite hobby. These nice things for yourself do not need to be the same as the examples already listed, and although they may involve other people, they should be things that you do explicitly for yourself, not others.

Measures

Because experimental work exploring the effects of nature on health and well-being is still limited, we took an exploratory approach to data collection. That is, we wanted robust measures that could capture the many plausible direct effects of nature on health, well-being, and nature identity. Although some measures may seem unconventional, there was good support for including them. For example, conscientiousness is a strong predictor of physical health and some past work has shown that not only can this personality trait change in response to interventions (Roberts et al., 2017), but it may also change in response to similar types of nature-based interventions (Heilmayr & Friedman, 2018). All the scales used in this study are validated measures that have been used in the published literature around health, well-being, and nature identity.

Demographics

Participants were asked to provide their date of birth, ethnicity, gender, and level of education.

Composites

To minimize the likelihood of a type I error, we reduced the scales into broad composites using a data-drive bottom-up approach. Scales were averaged into composites when the individual scales demonstrated adequate internal consistency (α's presented for pre- and post-test), the scales were unidimensional, and had approximately equal loadings on a single factor when pre- and post-test scores were tested independently. Before aggregation, each scale was put on the same scale by dividing it by the maximum value on that scale to create percent of maximum possible scores (Cohen, Cohen, Aiken, & West, 1999). This method creates scores that range from 0 to 1 for each scale, a score of 0.6, for example, would be interpreted as that person scored 60 of the maximum 100 points on that scale. The correlation between composites within and between time points is displayed in Table 1.

Table 1.

Correlation Among Composites

		1	2	3	4	5	6	7	8	9
	Pretest
1	Physical health
2	Well-being	0.44^***
3	Nature identity	0.24^*	0.32^***
4	Diligence	0.29^**	0.63^***	0.34^**
5	Fatigue	−0.62^***	−0.74^***	−0.28^**	−0.48^***
	Post-test
6	Physical health	0.68^***	0.27^**	0.28^**	0.27^**	−0.43^**
7	Well-being	0.32^***	0.82^***	0.29^**	0.55^***	−0.60^***	0.29^**
8	Nature identity	0.17	0.35^***	0.84^***	0.35^***	−0.29^**	0.33^***	0.45^***
9	Diligence	0.22^*	0.60^***	0.34^***	0.83^***	−0.44^***	0.25^**	0.70^***	0.47^***
10	Fatigue	−0.48^***	−0.56^***	−0.21^*	−0.35^***	0.77^***	−0.46^***	−0.68^***	−0.29^**	−0.45^***

Note: N = 104.

p < 0.05, ^**p < 0.01, ^***p < 0.001.

Physical health composite

A composite for physical health was created from the following scales.

Short form-36

The short form-36 (SF-36; Ware & Sherbourne, 1992) is a 36-item measure of physical health. Subscales of the SF-36 used in the physical health composite were the 9-item physical functioning (α's 0.83 and 0.90), 4-item role limitations due to physical health (α's 0.80 and 0.85), 2-item pain (α's 0.81 and 0.81), and 5-item general health (α's 0.78 and 0.83).

Well-being composite

A composite for well-being was created from the following scales.

Comprehensive inventory of thriving: meaning and purpose, optimism, and life satisfaction

Subscales from the comprehensive inventory of thriving (CIT; Su, Tay, & Diener, 2014) were used to measure core areas of psychological well-being: meaning and purpose (with three items; α's 0.91 and 0.90), optimism (with three items; α's 0.79 and 0.72), and subjective well-being (with nine items; α's 0.94 and 0.94). Participants indicate their agreement on a 5-point Likert scale from strongly disagree to strongly agree.

Satisfaction with life scale

The satisfaction with life scale (α's 0.92 and 0.91; Diener, Emmons, Larsen, & Griffin, 1985) is a 5-item scale on which participants indicate their agreement on a 7-point Likert scale from strongly disagree to strongly agree.

Happiness

The subjective happiness scale (Lyubomirsky & Lepper, 1999) is a 4-item scale that asks participants to respond on 7-point scales comparing their level of happiness with that of others (α's 0.83 and 0.87).

Mood states

Participants indicated their mood using an adapted mood states questionnaire (Zevon & Tellegen, 1982). Participants indicated the extent to which they felt 28 emotions over the past week on a 5-point scale from not at all to extremely. Positive mood was indicated by 13 of the items (α's 0.93 and 0.92), and negative mood was indicated by 15 items (α's 0.92 and 0.93).

Stress

Participants indicated their stress using the perceived stress scale (Cohen, Kamarck, & Mermelstein, 1983). Participants completed the 14-item scale, indicating how often they felt specific stressors in the past month from never to very often (α's 0.88 and 0.87).

Psychosomatic symptoms

Participants were asked eight questions about how they felt in the past week, to which they responded on a 3-point scale often, sometimes, or never (α's 0.80 and 0.79; Crown & Crisp, 1966).

Meaning and purpose

Participants indicated how much they agree on a 5-point scale from strongly disagree to strongly agree to the 7-item meaning and purpose scale (α's 0.88 and 0.92; Salsman et al., 2013).

Emotional well-being

The SF-36 emotional well-being subscale with five items was used (α's 0.84 and 0.82; Ware & Sherbourne, 1992).

Nature identity composite

A composite for nature identity was created from the following scales.

Environmental identity

The 24-item environmental identity scale (Clayton, 2003) captures the extent to which individuals feel that they are connected with the nonhuman natural environment (α's 0.92 and 0.94). Participants respond on a 5-point Likert scale from strongly disagree to strongly agree.

Connectedness to nature

Participants responded on a 7-point Likert scale from very low to very high to the single-item connectedness to nature scale that asks “My connectedness to nature is”: Mayer and Frantz (2004).

Diligence composite

A composite for diligence was created from the following scales.

CIT: engagement and mastery

Subscales from the CIT (Su et al., 2014) were used to measure engagement (with 3 items; α's 0.85 and 0.84) and mastery (with 15 items; α's 0.88 and 0.92). Participants responded to three items on a 5-point Likert scale from strongly disagree to strongly agree.

Self-efficacy

Participants responded to the 5-item patient-reported outcomes measurement information system (PROMIS) general self-efficacy short form (Salsman et al., 2013) on a 5-point Likert scale from I am not at all confident to I am very confident (α's 0.82 and 0.86).

Conscientiousness

The big five personality inventory (John, Donahue, & Kentle, 1991; John, Naumann, & Soto, 2008) was used to assess participants' conscientiousness. Participants responded to the nine items on a 5-point Likert scale from strongly disagree to strongly agree (α's 0.75 and 0.82).

Fatigue composite

A composite for the fatigue factor was created from the following scales.

Fatigue

The PROMIS 4-item fatigue short form 4a (Lai et al., 2011) asks participants to indicate on a 5-point Likert scale from not at all to very much how fatigued they have felt in the past 7 days (α's 0.94 and 0.93).

Sleep impact

The 5-item sleep impact short form (Keller, Yang, Treadwell, Werner, & Hassell, 2014) asks participants to indicate how often in the past 7 days they experienced different kinds of sleep loss on a 5-point Likert scale from never to always (α's 0.93 and 0.93).

Energy

The SF-36 energy subscale with four items was used (α's 0.83 and 0.81; Ware & Sherbourne, 1992).

Additional measures

Participants in all conditions were asked to keep a log of their activities; logs could be kept online or on paper depending on participant preference. Participants in the nature condition were also asked to take photos of the nature locations they visited. These data were used as a manipulation check to ensure that participants were following instructions. At post-test, participants were also asked to report, on a scale of 0–100, the degree to which they “adhered to the instructions provided” over the past 2 weeks. In addition, participants responded to several scales that were not included in composites due to poor fit with other measures. The elevating experiences scale (Huta & Ryan, 2010) was excluded from the nature identity composite, and the Epworth sleepiness scale (Johns, 1991) was excluded from the fatigue composite due to relatively small loadings onto a single factor through exploratory factor analysis. The Paffenbarger physical activity questionnaire (Paffenbarger, Wing, & Hyde, 1978), which is used to estimate the number of calories each participant tends to burn in a day, was not used as participant responses were not deemed accurate with the calories burned being reported ranging from 2352 to 319,090.

Results

Manipulation check

Activity logs and photos were reviewed to ensure that participants followed instructions for the 2-week experimental period. With the exception of one participant noted in the Excluded Participants section, all participants understood and followed instructions. A typical log entry for the nature group was “I watched the sunset from a new location” or “Walked through [—] Park and watched ducks swim along the river.” For the other-kindness group, a typical entry read: “I treated my sister to coffee and left a tip for the barista” or “I picked up recycling around communal mailbox.” Finally, for the self-kindness group, typical entries read: “I let myself order whatever I wanted for lunch” or “[I used a] cooling face mask.” There were no differences at post-test between conditions with regard to self-reported adherence (possible range of 0–100, M = 89.52, SD = 11.04) to instructions F(2,101) = 0.091, p = 0.913, providing support that participants across all groups followed instructions relatively well.

Descriptive statistics

Table 2 displays the means and SDs for each condition at each time point.

Table 2.

Mean and Standard Deviation by Condition at Each Time Point

COMPOSITE	CONDITION	PRETEST	POST-TEST
Physical health	Self	0.81 (0.15)	0.86 (0.15)
	Other	0.80 (0.15)	0.86 (0.15)
	Nature	0.77 (0.19)	0.82 (0.18)
Well-being	Self	0.74 (0.13)	0.80 (0.11)
	Other	0.70 (0.11)	0.74 (0.13)
	Nature	0.71 (0.13)	0.77 (0.10)
Nature identity	Self	0.71 (0.15)	0.73 (0.17)
	Other	0.64 (0.16)	0.64 (0.18)
	Nature	0.67 (0.15)	0.73 (0.12)
Diligence	Self	0.81 (0.11)	0.83 (0.11)
	Other	0.79 (0.08)	0.80 (0.09)
	Nature	0.80 (0.09)	0.81 (0.09)
Fatigue	Self	0.44 (0.19)	0.38 (0.13)
	Other	0.47 (0.18)	0.40 (0.17)
	Nature	0.46 (0.17)	0.37 (0.14)

Note. N = 104; Scores expressed as percent of maximum possible scores.

Test of changes over time across conditions

Table 3 displays the results from the 3 (condition: nature, other, self) × 2 (time: pretest, post-test) analyses of variance, where condition is a between-subjects factor and time is a within-subjects factor.

Table 3.

Mixed Factorial Analysis of Variance Results

COMPOSITE		F	p	η²
Physical health	Condition	0.67	0.512	0.01
	Time	18.06	<0.001	0.03
	Condition × time	0.05	0.956	0.00
Well-being	Condition	1.68	0.192	0.03
	Time	54.93	<0.001	0.05
	Condition × time	0.29	0.749	0.00
Nature identity	Condition	2.95	0.057	0.05
	Time	8.00	0.006	0.01
	Condition × time	5.75	0.004	0.01
Diligence	Condition	0.80	0.453	0.01
	Time	11.49	0.001	0.01
	Condition × time	0.18	0.836	0.00
Fatigue	Condition	0.27	0.763	0.00
	Time	45.67	<0.001	0.05
	Condition × time	0.39	0.677	0.00

Note: Degrees of freedom for condition: 2101, for time: 1101, condition × time: 2101; condition (self, other, nature) is a between-subjects factor, time (pretest vs. post-test) is a within-subjects factor, condition × time is a within-subjects factor.

For nature identity, there was an interaction between condition and time, F(2,101) = 5.75, p = 0.004, η² = 0.01. Simple effects (paired samples t-test) suggest that participants in the nature condition increased in nature identity from pretest to post-test t(33) = 4.61, p < 0.001, d = 0.79, whereas the self and other conditions did not change in nature identity over the same time t(35) = 0.66, p = 0.514, d = 0.11 and t(33) = 1.40, p = 0.170, d = 0.24, respectively.

For all composites other than nature identity, there were no differences between conditions (p's > 0.192) and no significant interactions (p's > 0.677; Table 3). There was a difference between the pre- and post-test scores for every dependent variable (p's < 0.006), such that participants increased in nature identity, physical health, well-being, and diligence, and decreased in fatigue from pre- to post-test (Tables 2 and 3).^††

Discussion

This study was designed to rigorously assess the effects of nature on health and well-being compared with active comparison groups. The most intriguing result that emerged is that spending time in nature increased participants' identification with nature. This finding lends experimental support to past research, which has found that positive experiences in nature predict a stronger nature connectedness (Chawla, 1999; Gifford & Nilsson, 2014; Wells & Lekies, 2006). Given that there is some evidence that nature connectedness is linked with environmental stewardship, promoting nature experiences may be a promising avenue for developing environmental stewards (Heilmayr & Friedman, 2018; Kuo, Barnes, Jordan, & Snell, 2019; Mayer & Frantz, 2004; Otto & Pensini, 2017). Although the study to date looks promising in this regard, further research—in particular, experimental work that measures actual behavior over time—is needed before nature interventions to promote environmentally sustainable behaviors are developed and implemented.

We were also intrigued to find that the nature, self, and other groups all showed improvements from pretest to post-test on all composite measures of health and well-being. Given positive psychology's strong experimental support for interventions (for meta-analysis see Bolier et al., 2013), this study shows that spending time in nature is just as good for health and well-being as previously established interventions. Past experimental work has found that acts of kindness for the self (Rowland & Curry, 2019) and others (Chancellor, Margolis, Bao, & Lyubomirsky, 2018) is beneficial for health and well-being, and this study is suggestive that nature experiences are as beneficial as positive psychology interventions while also having the potential to increase nature identity. Indeed, spending time in nature may be more feasible for individuals seeking to improve their well-being, given that it is generally free, does not rely on proximity to close others, and may be culturally or spiritually congruent.

Although promising, there are still many questions to explore. For example, this study prioritized ecological validity in an attempt to understand the potential effects of a nature intervention conducted outside of a controlled laboratory setting. Although this is a key for implementation of nature-based interventions, it also means that we did not isolate and identify the “active ingredient” of nature experiences. Future study should explore the mechanisms through which nature promotes health to ensure that interventions include these mechanisms.

Limitations

The purpose of this study was to compare nature experiences to established positive psychology interventions in an ecologically valid way. This resulted in some participants spending time in their backyards or walking through neighborhoods, while others reported spending the day at a beach or hiking. Although strides have been made to understand the types of nature features that are most beneficial (White et al., 2010), future study should explore these potential moderators more carefully. Relatedly, this study took place over the course of ∼4 months, when some days were pleasant and sunny, and others were hot and humid. An empirical question that arises is whether participants who spent time outdoors on pleasant days benefited more compared with participants who were outdoors on muggy days. Although some research (Pretty et al., 2005) has sought to assess the effects of threatening or unpleasant nature stimuli, more study is needed.

The prompts used to assign participants to conditions were modeled after commonly used prompts for positive psychology interventions (Nelson et al., 2016). The wording of these prompts was meant to ensure equivalent motivation across conditions but may have also introduced demand characteristics. Although demand characteristics may be present—groups showed similar changes across time—there is some evidence that this may not be the case: first, participants were told that the intervention was “good for health,” yet participants showed improvements in measures other than health. Second, we detected differential effects in the hypothesized direction for nature identity: the nature condition changed in a theoretically relevant and different way from the active comparison groups. That there were differential changes by group suggests that more than just demand characteristics were at play.

Finally, the positive psychology interventions used here have been closely examined and compared with waitlist and no-treatment control groups (Chancellor et al., 2018). As such we opted to compare the experimental nature group with active comparison groups (comparing a new treatment with other known effective treatments, as is typical in medical trials). Comparing the experimental nature group with active comparison groups also has the advantage of ensuring that intensity and positive expectations are similar across groups. However, given that all groups improved, we cannot rule out the possibility of cohort effects. Although it is possible that the summer weeks had a positive effect on all participants, for example, we have reason to believe this is unlikely. Participants completed the study for 2 weeks sometime for a 4-month timeframe; that is, not all participants completed the study during the same 2 weeks.

Concluding remarks

This study helps to advance the literature on nature and health by addressing some of the field's areas of weakness. First, we assessed the effects of spending time in nature after a 2-week period of receiving the “treatment.” To date, only few studies have measured experimental change beyond the immediate exposure effects. Second, participants completed baseline measurements, allowing for better estimates of change. Finally, we randomly assigned participants to spend time in nature, or to one of two active comparison groups—a design that provides a rigorous test of the effects of nature. Although the study presented here was not designed to test for the mechanisms of why nature might promote health, it is a realistic and ecologically valid inquiry that is suggestive of how “nature prescriptions” may play out in nonlaboratory settings. The body of research as a whole provides good evidence nature is beneficial for humans, and the results reported here suggest that these effects may hold up in real-world contexts and are comparable with the effects found in best practice interventions from positive psychology. Still, for implementation to be successful, it will be important for future study to explore the precise mechanisms as well as possible moderators of the effects of nature on health and well-being.

In summary, quasi-experiments and correlational studies have built a compelling case for the health benefits of nature experiences, but experimental studies are necessary for a path forward for real-world application and implementation. The study reported here rillustrates the promise of nature-based interventions while also motivating researchers to further disentangle the complexities of such interventions. By continuing to execute ecologically valid experiments while also exploring mechanisms and moderators, we will become better positioned to create nature-based interventions that are efficient and effective for a variety of populations.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this article.

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