Page - 142 - in Biodiversity and Health in the Face of Climate Change

142 ferred up to a limit (see Sects. 7.2.1 and 7.2.2 for further discussion on why inter- mediate levels of biodiversity might be most preferred). 7.3 Theories of  Restorative Environments Restoration refers to the recovery of physiological or psychological resources that have been diminished through the demands of dealing with everyday life (Hartig et  al. 2011). Physiological resources are the ability to mobilise energy toward a specific demand, such as running to catch a train home or working hard to meet a deadline. Psychological resources include the ability to focus attention in order to concentrate on a particular task. Without restoration of these resources, a person is unable to cope with new demands (imagine working to meet a new deadline with depleted physiological and psychological resources immediately after meeting the last deadline). Over time, lack of restoration of these resources can lead to mental and physical ill health (Hartig et  al. 2011; von Lindern et  al. 2016). Environments that facilitate the recovery and restoration of these depleted resources are called restorative environments. This section describes the two theories of restorative environments. 7.3.1 Stress Reduction Theory (SRT) The Stress Reduction Theory (SRT) (Ulrich 1983; Ulrich et  al. 1991) considers the physiological impact from viewing natural environments. Box 7.2 summarises the defining features of SRT.  According to the theory, natural environments facilitate restoration from stress. Outcomes of restoration are reduced physiological arousal, psychological stress, and negative affect, and enhanced positive affect (Ulrich et  al. 1991). Individuals who are stressed are most likely to experience reduced physio- logical arousal through contact with nature, whilst unstressed individuals are most likely to experience improved affect (Hartig and Evans 1993). Box 7.2: Defining Features of the Stress Reduction Theory • Natural environments benefit health by faciliating  recovery from stress • Stress recovery is manifest as reduced physiological arousal, psychologi- cal stress and negative affect, and enhanced positive affect • Visual characteristics of restorative environments are: moderate complex- ity; moderate depth; a focal point; deflected vistas (e.g. path bending away); a ground surface conducive for movement; lack of threat; and water • Biodiversity is considered to be a measure of an environment’s complexity M. R. Marselle