Spatial structure of private gardens, which plays an important role in urban ecosystem biodiversity and life quality of people, might be associated with socioeconomic conditions. Private gardens are a key component of urban green areas, with an important role in the connection between urban green areas and the life quality of people (Rudd et al. 2002). Gardens can represent the majority of urban green areas, and their management is challenging due to the diversity of actors involved (Gaston et al. 2013). Gardens comprise one of the main scenarios for interactions with wildlife in cities, offering opportunities for the enjoyment of the natural environment (Power, 2005; Freeman et al., 2012) in a context in which human population is undergoing rapid changes towards a dominantly urban way of life (Grimm et al. 2008). Further, projections estimate that by 2050 75% of the world population will live in urban areas (Mills 2007). Most of this increase will occur in intermediate-sized urban areas (i.e., between one and three million inhabitants) of developing countries (Crossette, 2011). Private gardens are an important component of cities, and their governance and management have a substantial impact on ecosystem services provision and urban biodiversity maintenance (Loram et al., 2008; González-García & Sal, 2008; Peroni et al., 2016).
The role of private gardens on urban biodiversity is complementary to that of public green areas (e.g., parks, street woodlands). Private gardens are generally small but numerous, and thus they are an important component of urban nature conservation strategies (Loram et al., 2007; Goddard et.al., 2010). Most research focuses on public spaces and the benefits they provide both to the health of people and to biodiversity in cities (Chiesura, 2004; Boone et al., 2009; Dobbs et al., 2017). Studies addressing private gardens (Loram et al., 2008; González-García & Gómez Sal, 2008; Peroni et al., 2016) are underrepresented in the research of urban green areas, although in many growing cities the area they occupy and their biodiversity are larger than those of other urban areas (Thompson et al. 2003). Additionally, the social implications of each may be different: green public areas are special due to being surrounded by households, as providers of experiences with nature, and for their positive contribution to the environment, while domestic private gardens also provide privacy, freedom, and opportunities for gardening (Coolen & Meesters, 2011). Regarding species composition, humans import a wide variety of non-native plants to cities, for landscaping and other horticultural objectives (Reichard & White, 2001); thus, import of non-native plants is also an important cause of increasing plant species richness in urban habitats. The proportion of exotic species in urban environments is generally much larger among plants compared to other taxonomic groups, such as birds, mammals, reptiles or amphibians (McKinney, 2006).
In Argentina, it has been observed that when green spaces are a scarce commodity, their distribution is mainly related to socioeconomic variables; in which sectors with higher socio-economic level have higher access to urban vegetation (Spescha et al 2020). Since most urban green spaces are private (Gaston et al 2013), it is likely that much of this pattern is explained by the contribution of domestic gardens. It is important to highlight the importance of each type of green urban space to biodiversity: public spaces are managed by only one administrative unit, while private gardens have a more diverse management (Gaston et al. 2013) for which the contribution of private green spaces to biodiversity might be more relevant than that of public spaces.
Cities have socio-economic segregation related to the urban form, the provision of infrastructure, and the value based on location (Lima, 2001). Several studies have shown that a higher financial income in households is related to higher vegetation cover, and to higher access to the benefits provided by ecosystem services (Flocks et al., 2011); and that education level is also positively correlated with vegetation cover (Heynen & Lindsey, 2003). The social, economic and cultural differences of the population are reflected in the urbanized landscape, and explain the access to social and infrastructure services, affecting the spatial pattern of vegetation in urban ecosystems (Pedlowski et al., 2002; Hope et al., 2003; Pickett et al., 2008; Luck et al., 2009; Clarke et al., 2013, Spescha et al., 2020). Thus, since socioeconomic factors affect vegetation complexity, social and cultural factors could be expected to affect species richness and abundance (Kinzig et al. 2005).
Socio-economic level is one of the main factors which spatially structure cities, and it is expected to influence on many attributes of gardens. Several studies have found correlations between socioeconomic status and diversity of urban birds (Melles, 2005; Bradley & Altizer, 2007), and some ecologists have tried to quantify the scope of wildlife-friendly gardening (e.g., Gaston et al. 2007). The analysis of these patterns can be difficult due to the effect of “mimicry” or contagious processes in the structure of gardens, which increase spatial autocorrelation of the considered attributes. For example, in Vancouver, Canadá, vegetation and landscaping of neighboring gardens were observed to be more similar compared to those of different streets or neighborhoods (Zmyslony & Gagnon, 1998). It is important to identify whether the contagion process is due to the spatial distance or the socioeconomic distance, since it modifies the spatial structure of urban biodiversity, and the spatial replacement of species.
In our study, we analyze private gardens as socio-ecological components, and we seek to understand the interactions between socio-economic structure and urban vegetation diversity in private gardens of one of the main urban agglomerates of Argentina: Gran San Miguel de Tucumán. We seek to determine which variables control ecological attributes of gardens, considering that socio-economic characteristics can directly influence garden management, which is reflected in the heterogeneity of urban landscapes (Martin et al., 2004: Grove et al., 2006; Mennis 2006; Troy et al., 2007).
Our hypothesis is that people with higher income might dedicate more time and economic resources, and might have more access to information and resources for gardening, for which we expect a positive association between socio-economic level and species richness. However, it is likely that other attributes of the garden, such as age and area also have an influence on richness. Another hypothesis is that due to a “mimicry” process and to the exchange of genetic material, socioeconomic level also determines the identity of the species present in gardens, for which we expect to find an association between socio-economic level and garden species composition.
We analyzed the spatial and non-spatial relation of species composition and socio-economic level in a subtropical agglomerate of Argentina: Gran San Miguel de Tucumán. We characterized plant species diversity through sampling in 50 private gardens and a short survey to owners. We evaluated the relation between plant diversity with a socioeconomic index and the different variables obtained in the surveys to explain the pattern of species distribution. We used multivariate analyses to visualize the similarity patterns of species composition among gardens, and we evaluated whether the emerging pattern of these analyses responds to geographic distance or socioeconomic aspects.