Scientists at the Forest Service’s Northern Research Station mentored and supported a PhD study at the University of Pennsylvania examining data collected a decade ago by a Forest Service-led multi-agency program known as the Collaborative Environmental Monitoring and Research Initiative (CEMRI). CEMRI designed three intensive study sites in three watersheds within the Delaware River Basin and established more than 60 plots using Forest Inventory and Analysis protocols but with more intensive measurements of forest variables. In 2012-2013, a group of students and the scientists revisited and remeasured these plots. These data reflect changes of forest carbon and tree demography that were subject to local land-use changes and regional climate change. The study found that the biomass carbon (C) stock of the Delaware River Basin forest increased and was thus a carbon sink over the past decade. It also revealed an increased mortality, which counted for 20 percent of the total biomass C change. The data also show the significant changes in tree demography among species. All oaks including chestnut, white, and black oak, experienced a decrease in living biomass because of the greater mortality rates, while white pine, American beech, and sweet birch increased in both biomass and stem density.