Are space-for-time substitution approaches appropriate in phenology research? Results from a macroecological approach

Knowing and understanding variation in plant phenology is important for three main reasons. 1. Plant phenology is sensitive to climate change, 2. Plant phenology influences the dynamics and interactions between species, and 3. It drives important ecosystem functions. Still, large-scale, macroecological analyses spanning several phenological databases from various continents and environmental conditions are scarce. Here we present the first results of a global analysis of the relationship between phenological events and functional traits in herbaceous plant species as a basis for predicting variations in ecosystem functions. More specifically, we analyzed phenological data from three different data sources: the PEP725 database from Europe, the NPN database from the US, and the PhenObs database from a global network of botanical gardens (www.idiv.de/en/phenobs). We evaluate spatio-temporal variations of three phenological stages: leaf emergence, open flowers, and onset of senescence. We linked phenological variations in space as well as phenological variations in time with variations in temperature (extracted from CRU TS database v4.07) of the observation periods and observation sites, respectively. Deduced associations between phenology and temperature across time and space were compared between Europe and North America, and between controlled environments in botanical gardens and natural environments. First results indicate that the direction of phenological responses to changes in temperature is consistent across time and space. However, the variability of this response is higher across time compared to space. This higher variation phenology is not explained by differences in variations of temperature, but we assume that other environmental and climatic factors could vary more strongly across the spatial compared to the temporal gradient. The phenological responses of plants growing in botanical gardens to increasing temperature, were less variable compared to plants growing in uncontrolled environments. We attribute these differences to botanic garden management, such as irrigation, which mitigates the effects of increased temperature and drought on herbaceous species phenology. On our poster, we will further determine the climatic factors and functional traits that explain inter- and intraspecific phenological variability.