Abstract

1. Introduction

Approximately half of the world's people live in urban areas (United Nations 2004). Rapid urbanization has increasingly isolated people from experiences of nature (Wilson 1984; Miller 2005). Indeed, for much of the population, remnant or managed public urban greenspaces provide one of the few avenues for direct contact with the natural environment. This is of profound concern, because such interaction leads to a variety of measurable benefits, at both individual and societal levels. In a now classic paper, Ulrich (1984) reported that post-surgical patients whose hospital windows overlooked trees, rather than a brick wall, recovered more rapidly and required less pain relief. Subsequent research revealed that a range of human well-being measures responds positively to greenspace availability, including general health (de Vries et al. 2003), degree of social interaction (Sullivan et al. 2004) and mental fatigue (Kuo 2001), and opportunities for reflection (Herzog et al. 1997).

While the effects of ‘green’ environments are increasingly well understood, little is known about the importance of variation in the quality of greenspace for benefits to human well-being. Here, we show that the psychological benefits gained by greenspace users increase with levels of species richness, and moreover those visitors to urban greenspaces can perceive differences in the species richness of some well-known higher taxa.

2. Material and methods

3. Results

Total plant richness varied by an order of magnitude among the 15 greenspaces, while butterfly and bird richness varied three- and fivefold, respectively (table 1). Given the theoretical basis for positive species–area relationships, the effect of area as a predictor of the well-being measures was considered in all analyses. While we recognize that care is needed when interpreting results of multiple comparisons, we did not apply a correction, as our contrasts were planned and we are studying a complex response (Moran 2003). Park area was positively correlated with the number of habitat types (r=0.65, n=15, p=0.009), but unrelated to plant richness (r=0.29, n=15, p=0.296). The number of habitat types was positively correlated with plant richness (r=0.7, n=15, p=0.003).

Table 1

Greenspace characteristics, psychological well-being and perceptions of species richness in urban greenspaces. See text for details of measures. Perceived species richness is the mean of the scale values of the richness categories (1–4; see footnotes). ...

Psychological well-being measures also varied across greenspaces (table 1). reflection, distinct identity and continuity with past increased with greenspace area (table 2). Plant richness was positively associated with reflection and distinct identity (figure 1a,b), both effects stronger than those of area (table 2). Butterfly richness was not associated with any well-being measure (table 2). Bird richness was positively related to continuity with past and attachment, although the former effect was weaker than that of area (table 2). The number of habitat types was positively associated with reflection, distinct identity and continuity with past (figure 1c; table 2), although tree cover was unrelated to any well-being measure (table 2).

Figure 1

Relationship between log plant species richness and (a) reflection, (b) distinct identity and (c) the relationship between number of habitat types present in a greenspace and reflection. See text and table 1 for explanation of units.

Table 2

Linear regressions exploring relationships between biodiversity value (habitat heterogeneity, tree cover and species richness), area and psychological well-being. Each pairwise combination of variables was tested separately and the resulting model, where ...

Perceived plant richness increased strongly with sampled plant richness (r=0.84, n=15, p<0.001; figure 2a). No apparent relationship existed between perceived and measured butterfly richness (r=0.25, p=0.366; figure 2b), although for birds there was a marginally non-significant positive relationship (r=0.49, p=0.066; figure 2c). Perceived plant richness was positively correlated with the number of habitats (r=0.58, n=15, p=0.023).

Figure 2

Relationship between perceived and sampled species richness of (a) plants, (b) butterflies and (c) birds. The relationship in the plant data remains highly significant on removal of right-hand data point. See text and table 1 for explanation of units. ...

4. Discussion

Our data demonstrate measurable positive associations between the species richness of urban greenspaces in Sheffield and the well-being of greenspace visitors. The degree of psychological benefit was positively related to species richness of plants and to a lesser extent of birds, both taxa where perceived richness corresponded with sampled richness. While benefits did increase with greenspace area, the relationships with plant and bird richness were generally stronger. Our species richness measures encompass effects of taxon density and heterogeneity, and we do not distinguish the two effects here. The number of different habitats was correlated with reflection and personal identity, plant variety with the ability to reflect and bird variety with participants' emotional attachment.

Our results indicate that the respondents, surrounded by urban built form, are not completely disconnected from an experience of biodiversity, but that their ability to perceive ambient species richness varies across taxonomic groups. People assessed most accurately the visible static components of biodiversity namely, plant species richness. Perceptions of bird and butterfly richness, arguably more cryptic components of urban ecosystems in terms of behaviour and ease of species differentiation, respectively, were less accurate.

Although these associations emerge quite clearly, untangling causality is not easy. First, it is unlikely that people were randomly distributed among parks, perhaps preferring those that enhance their psychological well-being. Selection by individuals of environments that enhance personal well-being makes interpretation of the causal structure of these relationships difficult, but is an important effect in its own right. Increased well-being may result from a variety of different kinds of greenspace, allowing individuals to access greenspaces from which they benefit most. Second, the increase in psychological well-being with species richness and the accurate assessment of richness levels presumably operate through some proxy mechanism. Positive relationships between the number of habitats in the greenspace and (i) psychological benefits gained by users and (ii) perceived levels of plant diversity hint that gross structural habitat heterogeneity might cue the perceptions and benefits of biodiversity. If this is the case, management emphasizing a mosaic of habitat patches (Thwaites et al. 2005) may enhance biodiversity levels, ecosystem service provision and the well-being of the human urban population.

Our results indicate that simply providing greenspace overlooks the fact that greenspaces can vary dramatically in their contribution to human health and biodiversity provision. Consideration of the quality of that space can ensure that it serves the multiple purposes of enhancing biodiversity, providing ecosystem services (Arnold & Gibbons 1996), creating opportunities for contact with nature (Miller 2005) and enhancing psychological well-being. Given the cultural differences in perceptions of wildlife (Jim & Chen 2006), an interesting extension of our study could test the generality of our results in other cultural settings.

Acknowledgments

References