Leveraging community-science to examine plant phenological responses to thermal gradients in Chicago, IL

Background/Question/Methods

: Plant phenology is a key biodiversity variable that can be monitored at different ecological scales – from the individual to the plant community and regional level – to track stress, plant-animal interactions, and ecosystem functions. Its rapid response to fluctuations in abiotic conditions make it a powerful indicator of the effect of climate change and landscape transformations on plant communities. Urbanization is an important driver of landscape transformation and previous studies have demonstrated its impact on phenological events (e.g., spring greening, flowering). Cities offer unique environmental conditions – including high temperatures, albedo, and night-time light exposure – that modulate cues used to trigger phenological events and mimic our potential climatic future. Yet most studies to date have focused on the aggregated response of plant communities to the urban-rural interface, leaving gaps in our understanding of how individual species respond to climatic gradients within cities. Our study leverages community observations of phenological events from the platform Budburst and surface temperature data captured by Landsat to assess how plants respond to thermal gradients across Chicago. We used linear regressions to assess how the timing of greening, flowering, fruiting, and senescence varies with a thermal gradient of surface temperature and its annual variation.

Results/Conclusions

: We focused on the 15 species most frequently observed by Budburst users between 2011 and 2021 and spanning different status (e.g., native, introduced) and growth forms (e.g., shrubs, grasses, herbs). Preliminary results suggest a significant impact of surface temperatures on phenological events, with species experiencing earlier flowering times and later fall senescence with higher temperatures. The effect is more pronounced in trees and shrubs than understory species, for which microclimatic conditions might be protected by proximity to taller species. This study shows the potential of community science to advance our understanding of the impact of climate change on plant phenology and resilience, and how it varies with species identities and characteristics.