Trees and shrubs in residential areas: Effects of density, housing age, and land use history on C stocks and fluxes

Background/Question/Methods

Residential vegetation represents the majority of the biomass C stock
in urbanized landscapes, and is responsible for a large fraction of
biomass C fluxes.  The factors that influence the size of these stocks
and fluxes are not well understood.  We hypothesized that legacy
effects of prior land use would remain detectable, although they would
be modulated by time since development (housing age), and that
structural aspects of development (e.g. housing density) would play a
confounding role.  In order to test for these effects, we surveyed
vegetation on 32 residential lots in Baltimore County with similar
soils that differed by housing density, prior land use, and time since
development and used the i-Tree Eco model to generate estimates of C
stocks and fluxes.

Results/Conclusions

C stocks and fluxes both generally increased with housing age,
reflecting both more and larger trees on older lots; the effect was
more pronounced on lots that were in agricultural use prior to
development.  Interestingly, C fluxes per unit C stock also increased
with age, which may reflect reports of increased soil N pools with
urbanization.  As expected, both C stocks and fluxes were higher on
lots that were forested prior to development, although the difference
decreased with housing age and was smaller on higher-density lots.
These results confirm our hypotheses, for the most part, although the
specifics are more nuanced than we anticipated.