The effects of urbanization on aboveground carbon storage and woody species composition in the Boston metropolitan region

Background/Question/Methods

Urban areas are rapidly expanding to house the world’s growing population, and the development of non-urban land for residential use has many ecological consequences.  Because carbon storage is one of the most important services provided by ecosystems, it is important to understand how levels of urbanization alter terrestrial carbon pools.  The objectives of this paper are to quantify changes in forest structure, tree species composition, and aboveground carbon storage along a gradient of urban intensity in metropolitan Boston.  Field data were collected from 31 urban, suburban, and exurban sites and 3 reference forests.  Data from this study were also compared to two large supplemental forest data sets from Massachusetts. 

Results/Conclusions

Reference forests had higher canopy cover, tree density, and proportion of native species than residential sites.  However, no significant differences in carbon storage and sequestration were observed among land use types.  Residential areas have maintained comparable carbon storage values to forested ecosystems through their relatively high proportions of large trees.  In residential yards over 25% of carbon was stored in 1.4% of trees that had diameters greater than or equal to 60 cm. Furthermore, while nearly 100% of carbon is stored in native species in forested and exurban sites, both native and non-native species were important for carbon storage in more densely developed areas.  Because a small number of large trees accounted for such a high proportion of the carbon stored in residential areas, the capacity of Boston’s urban forest to store and sequester high quantities of carbon is vulnerable to future change.