Prevalent vegetation growth enhancement in urban environment

Significance Cities experiencing elevated temperature (i.e., urban “heat island” warming), CO2, and nitrogen deposition decades ahead of the projected average global change are regarded as the “harbingers” of the future global change. It is for this reason that cities have been regarded as ideal natural laboratories for global change studies and particularly valuable to elucidate the potential responses of other nonurban ecosystems to future climate and environmental changes. However, the impacts of urbanization on vegetation growth are not well understood. We demonstrate, conceptually and empirically, that urbanization generates direct and indirect effects on vegetation growth at the landscape to regional scales. Urbanization, a dominant global demographic trend, leads to various changes in environments (e.g., atmospheric CO2 increase, urban heat island). Cities experience global change decades ahead of other systems so that they are natural laboratories for studying responses of other nonurban biological ecosystems to future global change. However, the impacts of urbanization on vegetation growth are not well understood. Here, we developed a general conceptual framework for quantifying the impacts of urbanization on vegetation growth and applied it in 32 Chinese cities. Results indicated that vegetation growth, as surrogated by satellite-observed vegetation index, decreased along urban intensity across all cities. At the same time, vegetation growth was enhanced at 85% of the places along the intensity gradient, and the relative enhancement increased with urban intensity. This growth enhancement offset about 40% of direct loss of vegetation productivity caused by replacing productive vegetated surfaces with nonproductive impervious surfaces. In light of current and previous field studies, we conclude that vegetation growth enhancement is prevalent in urban settings. Urban environments do provide ideal natural laboratories to observe biological responses to environmental changes that are difficult to mimic in manipulative experiments. However, one should be careful in extrapolating the finding to nonurban environments because urban vegetation is usually intensively managed, and attribution of the responses to diverse driving forces will be challenging but must be pursued.

[1]  T. Vesala,et al.  Deriving a light use efficiency model from eddy covariance flux data for predicting daily gross primary production across biomes , 2007 .

[2]  N. Golubiewski.  Urbanization increases grassland carbon pools: effects of landscaping in Colorado's front range. , 2006, Ecological applications : a publication of the Ecological Society of America.

[3]  M. Quigley.  Street trees and rural conspecifics: Will long-lived trees reach full size in urban conditions? , 2004, Urban Ecosystems.

[4]  Aakriti Grover,et al.  Analysis of Urban Heat Island (UHI) in Relation to Normalized Difference Vegetation Index (NDVI): A Comparative Study of Delhi and Mumbai , 2015 .

[5]  Josep Peñuelas,et al.  Urban plant physiology: adaptation-mitigation strategies under permanent stress. , 2015, Trends in plant science.

[6]  Christopher E. Holden,et al.  Tree Productivity Enhanced with Conversion from Forest to Urban Land Covers , 2015, PloS one.

[7]  Martijn Gough.  Climate change , 2009, Canadian Medical Association Journal.

[8]  Valasia Iakovoglou,et al.  Factors related to tree growth across urban-rural gradients in the Midwest, USA , 2004, Urban Ecosystems.

[9]  R Core Team,et al.  R: A language and environment for statistical computing. , 2014 .

[10]  M. Takagi,et al.  Light and atmospheric pollution affect photosynthesis of street trees in urban environments , 2004 .

[11]  A. Richardson,et al.  Landscape controls on the timing of spring, autumn, and growing season length in mid‐Atlantic forests , 2012 .

[12]  A. Huete,et al.  Overview of the radiometric and biophysical performance of the MODIS vegetation indices , 2002 .

[13]  Dennis D. Baldocchi,et al.  Response of a Deciduous Forest to the Mount Pinatubo Eruption: Enhanced Photosynthesis , 2003, Science.

[14]  N. Grimm,et al.  Global Change and the Ecology of Cities , 2008, Science.

[15]  J. Monteith,et al.  The Micrometeorology of the Urban Forest [and Discussion] , 1989 .

[16]  C. Tucker,et al.  Climate-Driven Increases in Global Terrestrial Net Primary Production from 1982 to 1999 , 2003, Science.

[17]  A. Troy,et al.  Urban ecological systems: scientific foundations and a decade of progress. , 2011, Journal of environmental management.

[18]  F. Dijkstra,et al.  Simple additive effects are rare: a quantitative review of plant biomass and soil process responses to combined manipulations of CO2 and temperature , 2012, Global change biology.

[19]  Jianguo Wu,et al.  Urbanization alters spatiotemporal patterns of ecosystem primary production: a case study of the Phoenix metropolitan region, USA. , 2009 .

[20]  N. Grimm,et al.  A distinct urban biogeochemistry? , 2006, Trends in ecology & evolution.

[21]  N. McIntyre,et al.  From patterns to emerging processes in mechanistic urban ecology. , 2006, Trends in ecology & evolution.

[22]  T. Dawson,et al.  Urbanization effects on tree growth in the vicinity of New York City , 2003, Nature.

[23]  Kevin R. Gurney,et al.  Urbanization and the carbon cycle: Current capabilities and research outlook from the natural sciences perspective , 2014 .

[24]  J. HilleRisLambers,et al.  Conifer growth and reproduction in urban forest fragments: Predictors of future responses to global change? , 2012, Urban Ecosystems.

[25]  M. Carreiro,et al.  Forest Remnants Along Urban-Rural Gradients: Examining Their Potential for Global Change Research , 2005, Ecosystems.

[26]  Fengsong Pei,et al.  Assessing the differences in net primary productivity between pre- and post-urban land development in China , 2013 .

[27]  W. Yue,et al.  The relationship between land surface temperature and NDVI with remote sensing : application to Shanghai Landsat 7 ETM + data , 2009 .

[28]  S. Searle,et al.  Urban environment of New York City promotes growth in northern red oak seedlings. , 2012, Tree physiology.

[29]  S. Running,et al.  Assessing the impact of urban land development on net primary productivity in the southeastern United States , 2003 .

[30]  J. Bagley,et al.  The influence of photosynthetic acclimation to rising CO2 and warmer temperatures on leaf and canopy photosynthesis models , 2015 .

[31]  Taylor H. Ricketts,et al.  The consequences of urban land transformation on net primary productivity in the United States , 2004 .

[32]  Yan Sun,et al.  Spatial and Temporal Dimensions of Urban Expansion in China. , 2015, Environmental science & technology.

[33]  Shi Pei-jun,et al.  How does the conversion of land cover to urban use affect net primary productivity? A case study in Shenzhen city, China , 2009 .

[34]  I. Burke,et al.  Carbon fluxes, nitrogen cycling, and soil microbial communities in adjacent urban, native and agricultural ecosystems , 2005 .

[35]  B. G. Lockaby,et al.  Urbanization effects on leaf litter decomposition, foliar nutrient dynamics and aboveground net primary productivity in the subtropics , 2015, Urban Ecosystems.

[36]  Decheng Zhou,et al.  Rates and patterns of urban expansion in China’s 32 major cities over the past three decades , 2015, Landscape Ecology.

[37]  Shuguang Liu,et al.  Remotely sensed assessment of urbanization effects on vegetation phenology in China's 32 major cities. , 2016 .

[38]  S. Frank,et al.  Do cities simulate climate change? A comparison of herbivore response to urban and global warming , 2015, Global change biology.

[39]  M. Quigley.  Franklin Park: 150 years of changing design, disturbance, and impact on tree growth , 2002, Urban Ecosystems.

[40]  L. Ziska,et al.  Characterization of an urban-rural CO2/temperature gradient and associated changes in initial plant productivity during secondary succession , 2004, Oecologia.

[41]  S. Running,et al.  Satellite Evidence of Phenological Differences Between Urbanized and Rural Areas of the Eastern United States Deciduous Broadleaf Forest , 2002, Ecosystems.