Phenological data on the First Flowering Date (FFD) of woody plants in Beijing from 1963-2007 are analyzed. The correlation between each species' yearly FFD and the mean monthly temperatures for every year over a 45-year period is used to identify the month in which temperature has the most effect on FFD. Through further analysis, the FFDs of 48 woody plant species are shown to have advanced an average of 5.4 days from 1990-2007 compared to 1963-1989. The results indicate that 70.8% of species flowered significantly earlier (7 days on average) during the period 1990-2007, while only one species (2.1%) flowered significantly later. Moreover, the responses of FIFD to climate change are shown to be different, in two climatic stages, defined by an abrupt climate change point. Thirty-three species which first flower in March and April are sensitive to temperature are examined. The correlation coefficients between FFD and temperature for 20 species during the latter period (1990-2007) are shown to be larger than during the former period (1963 1989), with a difference of around -0.87 days per 1 degrees C on average. The paper concludes that with the warming of climate, the linear trend of FFD variation, as well as its responsiveness to temperature, became more prominent during 1990-2007 than 1963-1989. The data analyzed in this study present a strong biological indicator of climate change in Beijing, and provide further confirmation of previous results from regional and local studies across the Northern Hemisphere. Phenophase variations indicate that the climate is changing rapidly.