Ecological Homogenization of Residential Macrosystems Peter M

PUBLISHED: 22 JUNE 2017 | VOLUME: 1 | ARTICLE NUMBER: 0191 comment Ecological homogenization of residential macrosystems Peter M. Groffman, Meghan Avolio, Jeannine Cavender-Bares, Neil D. Bettez, J. Morgan Grove, Sharon J. Hall, Sarah E. Hobbie, Kelli L. Larson, Susannah B. Lerman, Dexter H. Locke, James B. Heffernan, Jennifer L. Morse, Christopher Neill, Kristen C. Nelson, Jarlath O’Neil-Dunne, Diane E. Pataki, Colin Polsky, Rinku Roy Chowdhury and Tara L. E. Trammell Similarities in planning, development and culture within urban areas may lead to the convergence of ecological processes on continental scales. Transdisciplinary, multi-scale research is now needed to understand and predict the impact of human-dominated landscapes on ecosystem structure and function.

rban, suburban and exurban land uses will the homogenous American residential land-use in six cities across the US (Boston, cover an increasingly large area of the macrosystem persist in the next century Baltimore, Miami, Minneapolis–Saint Paul, UUnited States1, and the consequences or is it dynamic? How will alternative Phoenix and Los Angeles)4,9–11. We have of human residential landscapes have approaches to managing these systems observed remarkable homogenization received heightened attention in ecology influence the ecological system? And what of soil variables, whereby parameters and evolution over the past 30 years. are the social benefits and dis-amentities ranging from moisture content to soil This emergence has been driven by the of these alternative futures? We make the nitrogen cycling to microbial biomass recognition that human populations are case that the large and expanding extent of all vary less among residential sites than increasingly concentrated in cities, where this system at the interface with agricultural among natural reference sites across the human activities and social processes, high and less human-dominated systems will continent. Moreover, while we assumed that impervious cover that creates novel climate have broader, continental-scale impacts urban and suburban land-use change and and hydrology, and highly fragmented on community assembly, evolution and homogenization would markedly decrease habitats all interact to uniquely alter ecosystem response to global environmental carbon sequestration at parcel, landscape, ecological and evolutionary processes2,3. change over the next 50–100 years. We regional and continental scales, effects are In recent years, the spatial scope of urban predict that societal desires for biodiversity, much more complex and variable. In arid ecology has expanded, driven by ideas about water conservation, reduced delivery of regions, both soil and vegetation carbon urban ‘homogenization’ or ‘convergence,’ pollutants to receiving waters and aesthetic stocks are increased by urbanization due to wherein cities with very different climates ecological amenities will lead to marked addition of water and planting of shrubs and and histories have been hypothesized changes in residential macrosystems across trees, while in humid regions, carbon stocks to have similar mixes of trees, shrubs, the globe and a reduction in ecological in unpaved soils (the largest reservoir) grasslands and impervious surfaces that lead homogenization. Alternatively, factors such are either increased or unchanged by to similar ecosystem structure, function and as a desire for neatness, low maintenance, urbanization. The net effect of urbanization services4,5. The focus on homogenization neighbourhood norms and covenants, and on carbon sequestration in humid regions has coincided with the emergence of real estate markets that function as agents of depends on just how much aboveground interest in ‘macrosystems’ biology, defined6 stability may overcome these factors driving carbon is lost, which varies greatly within as “regional to continental extents with change. We also predict that the increases and between cities and is amenable distances spanning hundreds to thousands in biodiversity caused by residential land to management. of kilometres with biological, geophysical management will increase the dynamism of and social components that interact with natural ecosystems in and around residential More species but less diversity one another and with phenomena at other macrosystems as new species alter the nature Residential landscapes contain turf grass, spatial or temporal scales ranging from and extent of ecosystem response to global weeds and numerous exotic and native days to millennia.” In North America, environmental change. herbaceous species, and a variety of trees in an analysis focused on single-family and shrubs. These plant assemblages residential parcels, we have characterized Urbanization and carbon sequestration contribute to the overall managed and a large, ecologically homogenous In ongoing research funded by the US emergent diversity of urban landscapes and ‘American residential macrosystem’ that National Science Foundation (NSF) reflect social and structural drivers (such as has continental-scale impacts on water, Macrosystems Biology programme, we have aesthetic preferences and norms as well as energy, carbon and nutrient dynamics, characterized and evaluated continental- the availability of certain plant species) of despite some variation in social priorities7 scale effects of urban homogenization landscaping decisions. Urbanization reduces and practices8 at different scales. In this on plant biodiversity, soil carbon and differences in plant community composition comment, we describe these effects and nitrogen pools and processes, microclimate, and aboveground biomass among address current research gaps. Specifically, hydrography and land cover in residential biophysically dissimilar regions because

Phoenix, Arizona Regional flora Twin Cities, Minnesota species pools. These cultivated landscapes Natural areas also have implications for bird and insect Climate, communities since these animals have strong history, associations with local plant communities dispersal, 16,17 stress at both the yard and landscape scales . tolerance Lastly, the filtering processes of managed landscapes may create novel selective Interstitial pressures that alter organismal phenotypes, spaces Urban yard flora change the composition of biodiversity, and give rise to different evolutionary trajectories Preferences, 18,19 management, in managed and unmanaged areas . dispersal, One hypothesis is that the environmental pollination, conditions of urban areas select for species environment that are well adapted to the warmer, more variable climatic conditions predicted to Horticultural flora dominate the planet in coming decades. If so, then the diffusion of these species will Accessibility, influence the dynamics of unmanaged areas preferences, propagation as these changes occur. constraints, transportability, Futures for residential macrosystems regulations We have focused on the complex and dynamic human actions at multiple spatial Figure 1 | An example of urban homogenization of yard vegetation between Phoenix and Minneapolis– and temporal scales, for example, parcel, Saint Paul. Flora in urban yards assemble from spontaneous and cultivated species of the regional flora neighbourhood and region (metropolitan 7,8,20,21 (both native and non-native species, including weeds) and flora provided by the horticulture industry statistical area) , that influence the (largely non-native species), subject to different filters (middle column). Despite dissimilar climates that development and maintenance of the give rise to very different flora in natural areas (desert in Phoenix, oak savannah in Minneapolis–Saint American residential macrosystem. The Paul), urban yards in these two cities have similar structure and the spontaneous species in them come dynamism of these actions suggests that from relatively few evolutionary lineages, while the cultivated species come from a diversity of lineages. the diversity, composition and structure, Species that escape cultivation, and spontaneous species fostered by the urban environment can disperse as well as ecosystem functions and back to natural areas through interstitial spaces to become a greater component of the regional flora. services, of this macrosystem are subject to change over time frames of 50–100 years with potentially significant continental- residential areas have similar landscaping. varies with spatial scale and likely by scale effects on ecological processes and Thus, relative to the composition of native geographical region. The horticultural environmental quality. ecosystems in these regions, the plant flora is influenced by accessibility of plant Future research needs to determine how community composition is more similar. material, propagation constraints, and drivers of change, such as shifts in human When comparing residential lawns and human preferences, and is further filtered population and ethnicity, increasing desire native herbaceous communities, there was by regulation and management processes. In for biodiversity and water conservation, strong evidence for homogenization of plant contrast, the continental flora is influenced and regulations governing water use and communities in analyses that both included by historical biogeographic processes and quality, will interact with stabilizing factors, or excluded turf grass species. filtered by dispersal limits and climatic and such as social norms, property values, Analysis of the flora of entire residential edaphic constraints13,14. Similarly, cultivated neighbourhood and city covenants and yards and native reference systems showed and spontaneous pools within the regional laws, and commercial interests, to produce that the urban flora have lower turnover in and urban flora are subject to contrasting marked differences in ecological processes species and phylogenetic composition across dispersal and filtering processes within in residential macrosystems. For instance, climatic regions than the native flora12. As the urban environment. For example, will widespread management that promotes a result, the urban flora has higher species cultivated species are likely filtered by nutrient- and water-use efficient and richness but relatively lower phylogenetic human preferences and management and wildlife-supporting plants as well as lower diversity than the flora in natural areas due often receive additional resources (for inputs of water and nutrients give rise to to the high number of exotic urban species example, water, fertilizer, weed control). greater regional biodiversity across trophic from relatively few phylogenetic lineages. Spontaneously regenerating species are levels, higher nutrient retention, lower water also likely filtered by human preferences use, and reduced runoff and losses of soil Impacts beyond residential yards and management (for example, mowing carbon and nitrogen from residential yards The analysis of whole yards leads to and fertilizing), as well as by dispersal and at the regional scale? Or do the constraints new ideas about assembly of vegetation broader urban environmental conditions. imposed on ecological processes by the communities in the American residential Cultivated species may ‘escape’ cultivation unique structural attributes of cities (that macrosystem and in the less human- to become part of the spontaneous flora of is, their high degree of imperviousness and dominated systems that are intermixed urban and surrounding natural areas and their high habitat fragmentation) override with, adjacent to, and affected by these wider regional species pools12,15. Natural the effects of management decisions? There communities (Fig. 1). The major sources areas within and surrounding cities are thus is also a great need to determine how these of urban flora are subject to contrasting likely to be mixed assemblages derived from coupled biophysical and social dynamics filtering processes, each of which the interactions between these contrasting vary within and between cities. For example,

2 NATURE ECOLOGY & EVOLUTION 1, 0191 (2017) | DOI: 10.1038/s41559-017-0191 | www.nature.com/natecolevol ©2017 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved. ©2017 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved.

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although landscape preferences and Finally, a major question is if a distinct Management, Portland State University, Portland, decisions may vary across households at the socio-ecological theory of urban ecology Oregon 97201, USA. Christopher Neill is at Woods parcel scale, the dominant reasons for yard is needed, or if current theories from Hole Research Center, Falmouth, Massachusetts management — that is, aesthetics, ease-of- biophysical and social domains can be used 02540, USA. Jarlath O’Neil-Dunne is at University maintenance, and norms of neatness — are in combination or in complementary ways of Vermont, Burlington, Vermont 05405 USA. largely similar across regions7. Yet some to address the research challenges outlined Diane E. Pataki is at University of Utah, Salt Lake within-region and cross-region distinctions above. We argue that transdisciplinary, City, Utah 84112, USA. Colin Polsky is at Florida exist, such as variation across individual multi-scale research in urban ecology Atlantic University, Davie, Florida 33314, USA. preferences (for example, for neat, orderly presents both theoretical and practical Tara L. E. Trammell is at University of Delaware, lawns versus more naturalistic, non-grass challenges that should be a focal area Delaware 19716, USA. landscapes) as well as across cities in in ecology and evolution over the next e-mail: [email protected] northern, cold regions relative to those in few decades. ❐ the warm Sun Belt, where cooling vegetation References is more of a priority. Understanding the Peter M. Groffman is at Advanced Science 1. Brown, D. G. et al. Ecol. Appl. 15, 1851–1863 (2005). 2. Tanner, C. J. et al. Front. Ecol. Environ. 12, 574–581 (2014). outcomes of residential landscapes “may Research Center at the Graduate Center of the 3. Grimm, N. B. et al. Front. Ecol. Environ. 6, 264–272 (2008). require a multiscale, differentiated approach City University of New York, New York, New York 4. Groffman, P. M. et al. Front. Ecol. Environ. 12, 74–81 (2014). because the underlying social practices 10031, USA. Meghan Avolio is at the National 5. Pouyat, R. V. et al. in Urban Ecosystem Ecology 8 (eds Aitkenhead-Peterson, J. & Volder, A.) 119–152 (American appear relatively varied” . Socio-Environmental Synthesis Center, Annapolis Society of Agronomy, 2010). It is important to recognize that while Maryland 21401, USA. Jeannine Cavender- 6. Heffernan, J. B. et al. Front. Ecol. Environ. 12, 5–14 (2014). dense urban land use occupies a relatively Bares, Sarah E. Hobbie and Kristen C. Nelson 7. Larson, K. L. et al. Urban Ecosyst. 19, 95–113 (2015). are at University of Minnesota, Saint Paul, 8. Polsky, C. et al. Proc. Natl Acad. Sci. USA 111, 4432–4437 (2014). small area of the Earth’s surface, suburban 9. Hall, S. et al. Landscape Ecol. 31, 101–117 (2015). and exurban land use is much more Minnesota 55108, USA. Neil D. Bettez is at the 10. Trammell, T. L. E. et al. Oecologia 181, 271–285 (2016). common. More importantly, we suggest that Cary Institute of Ecosystem Studies, Millbrook, 11. Steele, M. K. et al. Ecosystems 17, 685–697 (2014). the effects of urbanization on biodiversity, New York 12545, USA. J. Morgan Grove is at 12. Pearse, W. D. et al. Preprint at bioRxiv http://doi.org/b68x (2016). 13. Wiens, J. J. et al. Ecol. Lett. 13, 1310–1324 (2010). hydrology and biogeochemistry will have USDA Forest Service, Baltimore, Maryland 21228, 14. Cavender-Bares, J. et al. Annu. Rev. Ecol. Evol. System. impacts on community assembly and USA. Susannah B. Lerman is at USDA Forest 47, 4330462 (2016). ecosystem function well beyond residential Service, USDA Forest Service Northern Research 15. Knapp, S. et al. Ecol. Lett. 11, 1054–1064 (2008). 16. Frankie, G. W. et al. J. Kansas Entomol. Soc. 78, 227–246 (2005). parcels and landscapes, affecting water Station Amherst, Massachusetts 01003, USA. 17. Lerman, S. B. & Warren, P. S. Ecol. Appl. 21, 1327–1339 (2011). quality and the nature and extent of Kelli L. Larson and Sharon J. Hall are at Arizona 18. Alberti, M. Trends Ecol. Evol. 30, 114–126 (2014). ecosystem response to global environmental State University, Tempe, Arizona 85281, USA. 19. Cheptou, P.-O. et al. Proc. Natl Acad. Sci. USA 105, 3796–3799 (2008). change at regional and continental scales. Dexter H. Locke and Rinku Roy Chowdhury are 20. Groffman, P. M. et al. Environ. Res. Lett. 11, 034004 (2016). Urban land-use change is clearly a global at Clark University, Worcester, Massachusetts 21. Epp Schmidt, D. J. et al. Nat. Ecol. Evol. 1, 0123 (2017). challenge of similar intensity and extent 01610, USA. James B. Heffernan is at Duke to agricultural land-use change and other University, Durham, North Carolina 27708, USA. Competing interests components of global environmental change. Jennifer L. Morse is at Environmental Science and The authors declare no competing financial interests.

NATURE ECOLOGY & EVOLUTION 1, 0191 (2017) | DOI: 10.1038/s41559-017-0191 | www.nature.com/natecolevol 3 ©2017 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved. ©2017 Mac millan Publishers Li mited, part of Spri nger Nature. All ri ghts reserved.