CANCELLED - Phenological shifts in a decade – evidence of climate change from urban trees

Background/Question/Methods

With an estimated increase in global temperature of at least 1.5 °C in the coming decade, climate change will affect more strongly plant communities and ecosystems. Phenology, in this scenario, has emerged as an important tool to understand the influence of changing climate on plant organisms and their ecological relationships. Urban phenology has been pointed as key for monitoring plant responses to climate as it may indicate the exacerbated effects of global warming in the cities. We analyzed a phenological time series of thirteen years (2003 to 2015) of weekly observations collected for nine tree species located at the campus of São Paulo State University (Rio Claro, São Paulo, Brazil). Vegetative (leaf flush and leaf fall) and reproductive phenophases (flower buds, anthesis, and unripe and ripe fruits) were scored applying five classes of intensity. First, we tested whether the phenophases showed single peaks, indicating seasonality. Second, we tested whether the phenophases were related to precipitation and temperature, also assessed weakly, applying circular-linear regression models. Finally, we grouped the first and the last three years (2003-2005 and 2013-2015) and applied corrected Watson tests to compare the distribution of each phenophase of each species between the two time-groups.

Results/Conclusions

Regression models showed significant relationships of leaf and fruiting phenology with both precipitation and maximum temperature, for most species. Relationships between phenophases and climatic variables were either positive or negative, but always with small slope values (below 1), indicating a smooth effect for the whole time frame. To highlight the differences along the decade, Watson tests corrected for multiple testing showed at least one difference in the phenological patterns of every species with a decade apart, observed to leaf and fruiting phenophases. Vegetative phenology changed in eight, whilst fruiting changed in five out of nine species. Flowering phenophases generally did not change. Phenological events were generally anticipated or lost their peak. Through the application of circular statistics, filling a gap in the lack of long-term phenological field records in the tropics, we present evidence of climate change effects on urban tropical phenology. The impact of global change on plant phenology was not uniform across species, as expected. The effects at species level may potentially extend to the community level, affecting the availability of the resources in urban ecosystems and causing a mismatch in the mutualistic networks.