  Phenological timing -- i.e. the course of annually recurring development
stages in nature -- is of particular interest since it can be understood as a
proxy for the climate at a specific region; moreover changes in the so called
phenological phases can be a direct consequence of climate change. We analyze
records of botanical phenology and study their fluctuations which we find to
depend on the seasons. In contrast to previous studies, where typically trends
in the phenology of individual species are estimated, we consider the ensemble
of all available phases and propose a phenological index that characterizes the
influence of climate on the multitude of botanical species.
