Our knowledge of climate variability in the densely populated Northeastern United States is limited to instrumental data of the last century. Most regional paleoclimate proxies reflect a mix of climate responses, which makes reconstructing historical climate a challenge. Here we analyze tree-ring chronologies from Atlantic white cedar (Chamaecyparis thyoides) as a potential regional paleotemperature proxy. We evaluate our tree-ring network for spatiotemporal climate signal strength and reconstruction skill across New England. Atlantic white cedar sites in the northern section of the species' range exhibit positive significant annual growth relationships with local and regional temperatures. Chronologies constructed from northern sites yield skillful reconstructions of temperature that reproduce centennial, multidecadal, and interannual variability in the instrumental record, providing a novel paleotemperature record for New England.

Forest ecosystems are being altered by climate change, invasive species, and additional stressors. Our ability to detect these changes and quantify their impacts relies on detailed data across spatial and temporal scales. This dissertation expands the ecological utility of long-term satellite imagery by developing high quality forest mapping products and examining spatiotemporal changes in tree species abundance and phenology across the northeastern United States (US; the ‘Northeast’). Species/genus-level forest composition maps were developed by integrating field data and Landsat images to model abundance at a sub-pixel scale. These abundance maps were then used to 1) produce a more detailed, accurate forest classification compared to similar products and 2) construct a 30-year time-series of abundance for eight common species/genera. Analyzing the time-series data revealed significant abundance trends in notable species, including increases in American beech (Fagus grandifolia) at the expense of sugar maple (Acer saccharum). Climate was the dominant predictor of abundance trends, indicating climate change may be altering competitive relationships. Spatiotemporal trends in deciduous forest phenology – start and end of the growing season (SOS/EOS) – were examined based on MODIS imagery from 2001-2015. SOS exhibited a slight advancing trend across the Northeast, but with a distinct spatial pattern: eastern ecoregions showed advance and western ecoregions delay. EOS trended substantially later almost everywhere. SOS trends were linked to winter-spring temperature and precipitation trends; areas with higher elevation and fall precipitation anomalies had negative associations with EOS trends. Together, this work demonstrates the value of remote sensing in furthering our understanding of long-term forest responses to changing environmental conditions. By highlighting potential changes in forest composition and function, the research presented here can be used to develop forest conservation and management strategies in the Northeast.