The paradox of compact cities in terms of ecosystem services supply (ESs) and demand (ESd) is evidenced. Most researches established that ESs and ESd are spatially unbalanced, especially a major mismatch pattern showed in central urban area. But some researches showed unusually well balance in central city. Scientists notice that all those researches are based on averaged yearly data which would minimize the impact of extreme values. 

"The mismatch between ESs and ESd would probably overestimated or underestimated, when it is estimated based on averaged yearly data. Trees are the main provider of ecosystem services, which have their own life rhythm, therefore the seasonal variation of ESs, especially in temperate zone. While ESd also has its own seasonal variation, such as air purification." said assistant Professor YAO Jing from the Institute of Applied Ecology of the Chinese Academy of Sciences.  

In a recent study, YAO and other collaborators utilized deficit ratio and supply-demand ratio to quantitatively assess the risk of ESd-ESs mismatch and the extent to which ESd satisfied by ESs for air purification on seasonal and annual timescales in Shenyang. 

They found that the evaluation based on annual data would induce overoptimistic results about the mismatch between ESs and ESd. "Taking SO₂ purification for example, although it showed well balances in spring, summer, fall and for a year, there was only 21.78% ESd in winter satisfied," said YAO Jing.  

"The quantitative assessment utilizing deficit ratio and supply-demand ratio can reflect the ecological risk and stability of an urban ecosystem. Our results demonstrate the urban ecosystem of Shenyang suffers high risk. That the high ESd is well beyond the capacity of the urban ecosystem reflects an unhealthy and unsustainable urban ecosystem," said YAO Jing. 

They pointed out explicit spatiotemporal analysis of ESs and ESd would provide detail information for informed urban ecosystem management. 

This study was published in a paper entitled "Quantitative assessment of demand and supply of urban ecosystem services in different seasons: a case study on air purification in a temperate city" in Landscape Ecology. This study was supported by the National Natural Science Foundation of China. 

Mismatch between ESs and ESd in seasonal pattern (Image by YAO Jing)