Page - 254 - in Biodiversity and Health in the Face of Climate Change

254 Biological Diversity 1992). Consequently, biodiversity can be categorised in many ways. Genetic diversity, although often not apparent visually, is arguably the funda- mental level of biodiversity that underpins all the others. Where genetic variation is low, wildlife and agricultural populations tend to be less resilient to environmental changes including disease, pollution and the impacts of climate change. Within a single species, underlying genetic variation can be crucial in providing phenotypic (i.e. observable) differences. For example, the single species Canis lupus familiaris (domestic dog) provides a range of valuable attributes  to benefit humans, includ- ing  support for hearing, seeing, disease detection and companionship. Within spe- cies, there are less visible genetic differences; for example, individual street trees have differing levels of tolerance to pollution. Genetic diversity can also be impor- tant in providing sustainable crops and in moderating disease pathogens. For most people, morpho-species (organisms that look different from others) provide the basis for perceived species richness. The number, type and mixture of species (com- munity structures) provide useful measures of richness at a fairly basic level. At a broader level of diversity, organisms live in habitats that may form distinct entities, usually described in terms of their vegetation or physical characteristics (e.g. woodlands, grasslands, ponds, rivers). Habitats may be complex, featuring gradual horizontal transitions between different types (tall herbaceous vegetation merging into scrub and then becoming denser and taller woodland; open areas of water, becoming vegetated at the edges, merging into marshy areas and then wet grassland). Complexity is also increased by the vertical layers found within them (woodlands may feature ground vegetation, herbaceous layers, scrub, lower cano- pies of saplings, full canopies of mature trees and emergent trees that poke beyond the canopy). 11.1.1 Chapter Overview Having introduced some key concepts, we summarise the linkages between public health and biodiversity then discuss two spheres of public health influence. First, we discuss the role (and duty) of those working in public health to lobby for measures to tackle climate change and other threats to biodiversity. The second sphere of influence exploits the local links between access to biodiverse environments and public health, and the chapter examines how people (especially urban dwellers) can be encouraged to engage with such environments. This includes a critical look at the evidence for interventions that bring humans into health-promoting biodiverse envi- ronments, and we summarise the literature in a model. We explicate how a range of nature-based activities (including ‘green care’) within the nature, health and well- being sector can be used as environmentally biodiverse interventions to promote well-being, and we include two case studies on how organisations can enable com- munities to access and sustain biodiverse environments for the benefit of human and planetary health. Finally, we evaluate how access to biodiverse greenspace can fulfil the public health objective of reducing inequalities in health that are linked to socio- economic status. P. A. Cook et al.