Steven Bressan, Joseph McWilliams, Erika Díaz-Almeyda, Brad Oberle

Urbanization displaces agriculture and natural ecosystems, constraining food security and carbon (C) sinks. A proposed solution, Urban Food Forestry (UFF), promises local food from trees that can sequester C faster than other land cover types as long as soil function improves. We compared fine-scale variation in soil physical, chemical and biological properties within and between UFF and traditional lawn for evidence of changes in belowground ecosystem services. Both land covers sequestered C, but UFF did so nearly an order of magnitude faster, especially in upper soil strata where soil bulk density fell by 50% and microbial activity increased by an order of magnitude. Species richness of both soil fungi and bacteria increased along with nutrient concentrations. Contrary to expectations, that different tree traits would drive increasing fine scale variability in C density, soils beneath the UFF became more uniform, which is consistent with the rapid emergence of system-level regulation. Soil C mass balance may distinguish forests from collections of trees and determine how long UFF helps cities store their carbon and eat it too.