The purpose of this review was to explore the relationship between NC and EWB by means of a meta-analysis and to compare this with the relationship between NC and HWB. The data showed a small positive correlation between NC and EWB, indicating that individuals who are connected to nature are more likely to be flourishing and functioning well psychologically. However, the hypothesis that NC would be more strongly associated with EWB than it is with HWB was not supported, and there may be a number of possible explanations for this. Firstly, it is worth considering that the way EWB has been defined for the purposes of this study (i.e. based on Ryff’s definition (1989)) may not be sufficiently comprehensive. For example, Huta (2015) identified a number of aspects of eudaimonic functioning—including self-regulation, ethics, contribution, and thoughtfulness—that are not included in the definition used by Ryff (1989). It may be that future studies, exploring the relationship between NC and these other aspects of EWB, can add to our understanding. Secondly, Huta and Waterman (2014) highlight the distinction between well-being measures based on cognitive-affective experiences and those based on ways of functioning. They suggest that using measures from different categories may lead to difficulties in making direct comparisons between eudaimonia and hedonia (Huta and Waterman 2014). The fact that, in this review, the EWB measures tended to fall into the ’functioning’ category, whereas the HWB measures tended to be based more on experiences, may have resulted in any true differences being obscured. Perhaps future research addressing these conceptual and definitional issues may help clarify the findings of this review.

Although the difference between the respective effect sizes for EWB and HWB was not significant, there were effect size differences between the EWB subscales. All the well-being subscales had small positive correlations with NC, with the exception of personal growth which had a moderately positive relationship. In addition, the effect size for personal growth was significantly larger than all the other eudaimonic subscales, except for vitality, and was also significantly larger than the effect size for life satisfaction. These findings suggest that, in order to further explore the relationship between NC and EWB, it may be fruitful to focus on specific aspects of EWB rather than on composite measures.

There is evidence that NC mediates the relationship between exposure to nature and EWB (Mayer et al. 2009; Pensini et al. 2016; Webber et al. 2015), which would be consistent with a causal mechanism whereby nature exposure leads to increased NC, which in turn leads to improved EWB. However, another study has found that NC does not moderate the effect of nature exposure on EWB (as measured by elevating experience) (Passmore and Howell 2014), which implies that NC may not play a part in promoting EWB. It is also possible that, if a causal association does exist, it is in the other direction, with EWB leading to increased NC; or it may be that the relationship between NC and EWB is bi-directional.

A number of authors have suggested that NC may benefit EWB because it provides a route through which basic psychological needs can be met (e.g. Cleary et al. 2017; Howell and Passmore 2013; Nisbet et al. 2009). As described in Ryan and Deci’s self-determination theory, three basic psychological needs—autonomy, competence and relatedness—are considered essential for psychological growth, integrity and well-being (Ryan and Deci 2000). It is plausible that NC provides a route through which these basic needs are met and so leads to increased EWB. For example, the basic psychological need for relatedness could be met by being exposed to nature which in turn is known to increase feelings of connectedness to nature (e.g. Weinstein et al. 2009). Howell and Passmore (2013) suggested that the relationship between nature affiliation and well-being could be mediated by a greater sense of social connectedness, and nature connection has been found to promote pro-social behaviour such as altruism and generosity (Weinstein et al. 2009). It also seems likely that nature connection promotes a form of relatedness distinct from social (human) connectedness and important in its own right (Cleary et al. 2017). This is supported by research from Zelenski and Nisbet (2014), who found that the concept of nature relatedness was distinct from other forms of relatedness—including connectedness with family and friends—and was a significant and distinct predictor of happiness.

In relation to increasing autonomy, nature could be a route through which individuals are enabled to express their personal distinctiveness, and not feel constrained by external influences such as the values imposed by society (Howell and Passmore 2013; Ridder 2005). Ridder’s (2005) concept of a ‘nature-inspired autonomy’ describes the importance of recognising the value of naturalness as a means of gaining a personal sense of freedom and escaping from the dissatisfaction caused by extrinsic influences of society. The freedom and autonomy felt in wild nature enables individuals to reinforce their own intrinsic beliefs and values, to gain perspective on the things that really matter, and to feel inspired (Ridder 2005). There is some empirical support for this idea: Weinstein et al. (2009) found that, when asked to view scenes from nature or from ‘non-nature’ (such as cityscapes), participants who were more immersed in the nature scenes felt a greater sense of autonomy; by contrast, participants who were immersed in the non-nature scenes felt reduced autonomy.

Competence needs could be met through learning about natural environments and ecosystems, as well as through enhanced self-knowledge and self-development gained from being connected to nature. Outdoor learning, outdoor play and wilderness expeditions have all been linked with improved well-being, cognition, personal, social and emotional development, as well as higher achievement and increased motivation to learn (Lovell 2016a).

The association of vitality with NC can also be linked with the fulfilment of psychological needs. Ryan and Frederick (1997) considered that vitality is a part of the ‘fully-functioning’ person and should therefore be linked with agency and growth, and with the need for autonomy, competence and relatedness. They found supporting evidence that vitality is associated with self-actualisation and self-determination, as well as mental health and self-esteem (Ryan and Frederick 1997).

In this review, NC had a significantly stronger association with personal growth than most of the other aspects of EWB, which raises the possibility that our relationship with nature may have a particularly important role in furthering psychological growth and development. Ryff described personal growth as perhaps the nearest of all her six subscales to EWB because it is specifically concerned with self-realisation and is akin to Maslow’s concepts of self-actualisation and self-transcendence (Koltko-Rivera 2006; Ryff and Singer 2008). Huta and Ryan (2010) expected that, since eudaimonia is oriented towards excellence and growth, it would be related to uplifting experiences (such as contact with the natural world) which stretched people beyond their usual boundaries. Such ‘elevating experiences’ are ‘where a person feels awe, elevation to a higher level of awareness and a connection with some greater whole’ (Huta and Ryan 2010, p. 740). NC has been found to correlate strongly with the value of self-transcendence (Tam 2013) and also to predict transcendent and awe-inspiring experiences, particularly in wild nature (Davis and Gatersleben 2013). The ‘higher order’ emotions such as awe and wonder, which are often associated with transcendent experiences, could be a key mediating influence in the relationship between NC and personal growth. Awe has been defined as ‘an emotional response to perceptually vast stimuli that overwhelm current mental structures, yet facilitate attempts as accommodation’ (Shiota et al. 2007, p. 944). Thus, the sense of awe felt in nature could lead to an expansion in individuals’ mental structures and frames of reference, as well as an expanded sense of self, and so foster personal growth. This would be consistent with Frederickson’s broaden and build theory of positive emotions (Fredrickson 2004). Likewise, the association that NC has with meaning and purpose in life is also in accord with the idea that self-change is brought about when people accommodate new experiences after having contact with nature: people often describe awe-inspiring experiences in nature as giving them a sense of perspective on their life, goals, and purpose (Silvia et al. 2015).

Future Research

In general, more well-controlled studies are needed which explore the direction of the relationship between NC and well-being. Furthermore, much NC research has used composite measures of well-being which may mask potential differences among the well-being subscales. More nuanced studies exploring the links between NC and specific aspects of EWB, such as personal growth, would help tease any differences apart.

There is a general lack of research on children’s well-being and nature connection—in this review all but one of the included studies was of adults. Childhood experience may be an important route by which individuals become connected to nature in the first place (e.g. Lovell 2016b), and experiences in nature may enhance optimal child development (Kellert 2002). The association found in this review of NC and personal growth in adults would suggest that nature’s effect on childhood development may be equally—if not more—important. Orr (1993) speculated that there could be a window of opportunity in childhood for connecting to nature, similar to the window of opportunity for language development. If this is the case, the consequences for nature disconnection in childhood could be long-term, and not easily repaired by experiences in adulthood. Conducting longitudinal studies which follow individuals over their life-course would help address this gap.

Additional research is needed to explore which particular qualities of nature may affect HWB and EWB. It is possible that different types of nature elicit different emotions and, by implication, could affect different types of psychological functioning. For example, familiar nature may be more likely to lead to feelings of calm and contentment and thus be more restorative (Richardson et al. 2016b), whereas unfamiliar objects in nature—those that transcend previous knowledge—may be more likely to produce awe and wonder than familiar objects (Keltner and Haidt 2003) and thus stimulate new ideas and experiences. Nature-induced awe may be triggered by large natural objects, such as mountains or vistas, by natural events such as storms, or by objects with infinite repetition such as fractals, waves and patterns in nature (Keltner and Haidt 2003). Factors such as the degree of naturalness of an environment (the extent to which it is free of human intervention) may also be important in the relationship with EWB (Ridder 2007). Furthermore, there is evidence that levels of actual or perceived biodiversity (Dallimer et al. 2010; Fuller et al. 2007; Luck et al. 2011), or the degree of landscape heterogeneity (Fuller et al. 2007; Jorgensen and Gobster 2010), are linked with well-being and these aspects are therefore worthy of further investigation.

It is also worth exploring how different patterns of nature exposure may affect the relationship between NC and well-being. For example, there is evidence of a dose-response effect between frequency of visits to nature and EWB, but not HWB (White et al. 2017). By contrast, the same study found that self-reported HWB (as felt on the previous day) was significantly related to a visit to nature that day, but that EWB was not. Thus, two possible nature exposure mechanisms may be at work—a short-term restorative effect linked to HWB, and a longer-term (additive) effect of increased visit frequency linked to EWB, possibly due to greater NC developing over that time. Dose-response and short and long-term effects of nature exposure are important variables to be explored in further research.

Finally, most of the research on NC and its association with well-being has been undertaken in westernised societies. Although there is some evidence that the association of NC and well-being persists across non-westernised cultures (e.g. Capaldi et al. 2017; Tam 2013), there are cultural differences in the way in which humans perceive and value nature (Olivos and Clayton 2016), and so our understanding remains limited.

Limitations

A common aspect of correlational studies is that the direction of effect and causality remains unclear. Furthermore, a lack of representativeness of the study population could have resulted in bias—most studies comprised non-random and/or self-selected adult subjects. Males were generally under-represented, and a high proportion of the studies were of students. However, the moderator analyses indicated that neither age nor percent female were significant predictors of effect size indicating that the results were not affected by these factors. In addition, a number of the included studies involved participants who were either park visitors, exercised in natural settings, or were gardeners, and it is conceivable that these participants may have had higher than average NC. This may have resulted in range restriction and thus attenuation of reported effect sizes.

Conclusion

This review has shown that NC is associated with EWB, and one aspect of EWB—personal growth—appears to have a significantly stronger relationship with NC than most other EWB subscales. These results signal the important role NC may play in contributing to positive psychological functioning and highlight the possibility that different aspects of EWB may relate to NC to varying extents. Multiple pathways—perhaps mediated by a range of emotions and elicited by different aspects of nature—may be involved in the relationship between NC and EWB.