2.1. Ecosystem’s Health Potential (EHP)
According to findings from literature, we suggest that the Ecosystem’s Health Potential (EHP) should be developed on an ecological scale and supported through components that have a potential specific link through any of the four different channels of human experience (knowing; perceiving; interacting in a physical and multi-sensory manner; living within). This was proposed by a previous study [1
], which stated that people’s behavior can provide demonstrable health benefits in the context of NCDs. Therefore, the EHP should include the identification of where the HR is most conducive to physical and mental health benefits. In other words, the EHP should identify where some types of potential environmental exposures with positive health effects are located and determine their potential magnitude. This implies the potential to perform certain types of interactions with nature that may benefit health and wellbeing.
For instance, from that standpoint, health and wellbeing may benefit from certain sounds of the natural world [40
], such as those from flowing water [41
], birds [40
] and wind [41
Potentially healthful views should also be considered, such as those with the presence of flowers in different colors [40
], aesthetically beautiful landscapes [44
], places where the sea waves can be admired [40
], streets with trees [47
], the degree of naturalness of the landscape [12
], views of agricultural landscape [45
] and green spaces [13
The potential health and wellbeing benefits provided by sensory experiences from the smells of nature must be taken into account, especially the smell of fresh air [44
], wet earth [41
], trees [54
] and wild fruits [44
]. There are potentially healthful flora settings that should be identified, considering the presence of native flowers [56
], the degree of plant biodiversity [49
] and the presence of grassland [60
] and trees [44
Water is one of the most important physical and aesthetic landscape elements where salutogenic health benefits can be identified, such as through the presence of lakes and rivers [43
]. Nevertheless, natural white spaces, such as snow-capped mountains, can both promote and reduce physical, mental and social well-being, depending on experiences and personal understanding of severe winter weather conditions [63
]. Similar to the presence of a certain degree of plant biodiversity, the degree of animal biodiversity can influence health benefits [40
] and must be identified in the ecosystem.
Therefore, in general terms, the EHP should include the identification of where the ecosystem settings are, which will focus on the structural and functional complexity of the abiotic and biotic components of the ecosystems that are most conducive to physical and mental health benefits.
Besides the relevant human–nature interactions, theories from the environmental psychology perspective, such as somatic interactions with nature, should also be taken into account in order to help to meet the physiological and biomechanical needs of more than 37 trillion individual and identifiable cells that ultimately define the structure and functions of an adult human body [64
]. These types of interactions imply physical activity levels that most closely approximate the Paleolithic standard, for which our genetic makeup was originally selected [65
]. Our genes were selected in a strenuous, demanding and diverse natural environment in order to enable our ancestors to survive and prosper. This was the result of a very vigorous lifestyle and the change from a very physically demanding lifestyle in a natural outdoor setting to an inactive indoor lifestyle forms the origin of many widespread non-communicable diseases that are endemic in our contemporary society [15
]. Furthermore, because humans evolved to be active for the purpose of play or through necessity, efforts to promote physical activity will require diverse natural environments to nudge or even compel people to be active and that make physical activity fun [66
Taking into account that the diversity of stimuli from the ecosystem settings depends on the structural and functional complexity of the abiotic and biotic components of the ecosystems, a prospective Health Potential Indicator (HPI) should be developed and supported through components based on the findings from surveys and from literature to connect the diversity of ecosystem settings with human senses. These settings can be divided into five components (Figure 2
): geodiversity; biodiversity; weather and climate diversity; waterscape diversity; and biomechanical exposure diversity.
Geodiversity can be defined as the natural range (diversity) of geological (rocks, minerals, fossils), geomorphological (landform, processes) and soil features [38
]. It includes their assemblages, relationships, properties, interpretations and systems [67
]. Even if the quantitative evaluation of geodiversity is a scientific topic in development, predictive models should be supported by means of quantitative analysis of geological and geomorphological components in order to contribute to a geodiversity index that is inferable by GIS analysis. Sites of Geological Interest and Areas of Special Landscape Interest should also be considered in the geological component. For instance, these models should take into account the theoretical contribution to the aesthetics literature and the practical implications for destination planning, branding and management created by Kirillova et al. [68
]. Furthermore, they should consider the aesthetics-based classification of geological structures in outcrops developed by Mikhailenko et al. [69
] that could augment restorative properties of recreational activities and thus, improve quality of life and health.
According to Hill et al. [70
], biodiversity evaluation is the process of measuring the value of biodiversity components, such as the number of species present, the population of a species, a habitat or the sum of all such components within a given area or site. Quantitatively, biodiversity can be measured by a biodiversity index (such as the Shannon index and/or the Simpson index), which is a mathematical measure of species diversity in a given community based on the species richness (the number of species present) and species abundance (the number of individuals per species).
Considering that the weather and climate indicates the behavior of the atmosphere over different temporal and spatial scales with respect to its effects upon life and human activities, it appears to be reasonable to take into account climate characterization and a weather diversity index. This could possibly incorporate temperature, humidity, precipitation, cloudiness, brightness, visibility, wind, atmospheric pressure and so on.
A landscape in which a view of water bodies is a dominant feature (waterscape) has an added attractiveness conferred by those water bodies on the surrounding areas. However, there are several factors, such as coastal morphology and water quality, that can reduce attractiveness and therefore, the waterscape diversity [28
]. Therefore, apart from the bathing water quality, a waterscape diversity index should take into account the multifunctional emerged and submerged structures (artificial and natural) that could provide coastal protection as well as the enhancement of water recreation features.
Biomechanical exposure diversity can be defined as the extent to which mechanical exposure entities differ [71
]. Therefore, the biomechanical exposure diversity in an ecosystem can be defined as the extent to which the prospective ways of interacting physically or mechanically with the natural outdoor setting differ. As human bipedal locomotion is the natural way to access the natural environment, a biomechanical exposure diversity index should consider the gradient, tread texture (hard-packed dirt trails, soft dirt trails, loose surfaces, sandy trails, muddy trails, rocky trails, snow trails, etc.) and shape (presence of trees, stream, stones, and other obstacles) of the prospective natural surface trails.
To calculate the final result of the EHP, the approach suggested by some authors [72
] for calculating the final result of the RPI can be adapted in order to consider the five components suggested by us. These components (geodiversity, biodiversity, weather and climate diversity, waterscape diversity and biomechanical exposure diversity) should be considered to have the same importance and could be aggregated using the procedure for building composite indicators [32