Seite - 170 - in Biodiversity and Health in the Face of Climate Change

170 8.3 Concluding Remarks In this chapter, we focused on definitional and measurement issues with regard to access to and contact with nature, more specifically the biodiversity of that nature. We stated that biodiversity is originally an ecological concept, developed in the context of nature conservation. As we have illustrated, the concept has been adapted (‘tweaked’) to make it more relevant in the context of mental health. To begin with, frequently its functional aspect with regard to the sustainability and resilience of ecosystems is ignored. In addition to this, in several studies the measurement of biodiversity is limited to the parts that are perceivable and/or appreciated by lay persons. At the same time, such adaptations are likely to make the concept less rel- evant from a nature conservation perspective. So, much depends on the research question at hand. We envision two lines of research. The first line has its focus on mental health promotion. In this line of research it makes perfect sense to look for qualities of nature that are likely to be conducive to produce (more or greater) mental health benefits. The concept of biodiversity may be adapted at will (preferably though based on theoretical arguments), but confusion may be reduced by (a) making clear that the concept has been adapted and (b) consistently labelling it differently (e.g. perceived species richness rather than biodiversity, without equating the both). The second line of research is about whether or which ecologically sound systems, requiring a certain amount of functional biodiversity, may go together with mental health promotion. Within this second line of research, focusing on multi-functional land use, adapting the concept of biodiversity seems less fruitful. To evaluate whether nature conservation and mental health promotion by contact with nature go well together, the success of each function, ecological and human health, needs to be assessed according to its own criteria. Up till now, the first line of research seems to be more popular. That is, while there is a broad array of studies that refer to biodiversity and (mental) health, few of these studies address biodiversity in its ecological sense of functional species diversity. In fact, Dean et  al. (2011) identified only one study, that of Fuller et  al. (2007). We agree that the latter study provides one of the best examples of a rigorous measurement of species richness in the context of ‘biodiversity  – mental health’ research. At the same time, even this study does not seem to put species richness in the context of the functional species diversity that is needed for a healthy ecosystem. The same argument can be made for the additional studies addressing species richness in the context of biodiversity and health that have been identified in more recent reviews (Lovell et  al. 2014; Korpela et  al. 2018; Marselle et  al. Chap. 9, this volume). Also, in ecological science, where it is more likely that a stricter definition of biodiversity is adhered to, the compatibility of ecosystem health and human health also does not seem to be high on the agenda. Von Döhren and Haase (2015) conclude that in ecosystem services research possible negative S. de  Vries and R. Snep