The phenological events of trees, such as leaf emergence and senescence, are sensitive to the temperature and precipitation changes associated with climate change, thus they serve as an important indicator of a forested ecosystem’s response to climatic shifts. Research at Harvard Forest performed a decade ago indicated trends of earlier emergence and later senescence; this is expected due to increasing temperatures triggering photosynthetic changes. This increase in growing season length could have substantial implications in carbon sequestration, as the leaves have more time to perform photosynthesis. However, a shorter study period limits this research, and two anomalous years with very early leaf emergence implies an advancing spring beyond what has been recently observed. We hypothesize that by extending the study years, spring advancement will be less pronounced. In this study, we analyze 33 years of ground data and 39 years of satellite imagery, using linear regression to assess if these trends have continued. We utilize ground observation data of leaf phenology, which researchers have collected at Harvard Forest since 1990. We also process 30-meter Landsat satellite data using a Bayesian phenology model. We use this data to assess long-term phenological trends, compare results by the acquisition method, and quantify the sensitivity of tree phenology to temperature and precipitation. Finally, we explore potential implications on forest carbon storage via the LANDIS-II landscape change model and its PnET-Succession extension. We model species cohorts in a simulated environment of the study area over a range of climatic conditions to quantify changes in aboveground biomass. Our results indicate that most individuals studied do not indicate significant vernal advancement; however, nearly half of the individuals indicate slight autumnal delay. Model simulation results indicated correlation in some species between growing season length and foliage dry weight - a potentially promising result for projecting carbon sequestration based on phenological observation.