Page - 168 - in Biodiversity and Health in the Face of Climate Change

168 8.2.7 Access Versus Exposure, and  Type of  Contact Earlier in this chapter, it was stated that most theories regarding pathways by which nature affects mental health assume that contact with that nature is required (see e.g. Hartig et  al. 2014, on stress and social contact as mediators). Therefore, it is impor- tant to make a clear distinction between access to nature and actual contact with nature. According to these theories, only if access to nature leads to exposure to nature, will it be accompanied by mental health benefits. Although in some studies access is equated to exposure, the first is a proxy for the latter at best. Given the focus on biodiversity, exposure should be about the biodiversity with which an indi- vidual comes into contact. The level of biodiversity of a natural area might be hypothesised to increase the mental health effect of a visit to that area. It might also be hypothesised to make the area more attractive to visit (initially and subsequently), and thereby increase the frequency and/or duration of visits to that area. It may be noted that a visit is a specific form of contact. People may also encoun- ter nature, especially small natural elements such as street trees and those present in front gardens, while they are travelling to and from all kinds of destinations. Moreover, they may also have a window view of nature, allowing visual contact with outdoor nature while indoors. And even the latter has been shown to be related to mental health (Honold et  al. 2016). It depends on the definition of biodiversity that is used whether or not such contacts should be included in the measure of the amount of biodiversity that a person comes into contact with over a certain period of time. A focus on exposure implies that not only the residential environment is of inter- est, but also natural areas and elements that are encountered elsewhere, as in the work or school environment, as well as between such settings of ordinary activity. Nowadays, exposure measurement seems to head in the direction of the exposome: a comprehensive description of lifelong exposure history (Wild 2012; Kondo et  al. 2018). The concept of ‘exposome’ is introduced as the environmental counterpart of the genome. Measuring actual total exposure is not easily achieved. For example, even when looking only at the number of visits to a specific type of nature, such as forests, retrospective self-reports tend to be rather inaccurate (Jensen 1999), though this presumably depends on the time frame for recall. To complicate matters further, the type of contact itself, ranging from indirect contact (e.g. looking at a nature documentary or looking at actual nature through a window), to being in a natural environment and actually interacting with nature (e.g. gardening or picking berries), may also have consequences for its mental health effects (Keniger et  al. 2013). S. de  Vries and R. Snep