Phenological responses of ash (Fraxinus excelsior) and sycamore (Acer pseudoplatanus) to riparian thermal conditions

There is increasing evidence that riparian corridors have modified thermal conditions compared to non-riparian areas. However, the biological significance of this difference is less clear. Here we tested this by investigating the response of tree phenology to riparian thermal conditions. We monitored the timing of bud burst, leaf fall and growing season of riparian and non-riparian ash (Fraxinus excelsior L.) and sycamore (Acer pseudoplatanus L.) in the city of Sheffield over two years. We compared the phenologies between riparian and non-riparian trees and explored the relationship between tree phenologies and thermal environments. Tree phenologies varied between riparian and non-riparian areas and the effect was species specific. Bud burst and leaf fall were earlier in non-riparian than in riparian ash, but no location effects on either bud burst or leaf fall were detected for sycamore, or in the growing season for both species. Bud burst for the two species was highly correlated to spring temperature; warmer temperature resulting in earlier bud burst in ash but later bud burst in sycamore. No significant relationship between leaf fall and temperature was found for either species. A positive correlation between growing season and temperature was observed for ash but not sycamore.