Lay summary of the following paper: Bigler C. and Vitasse Y. 2021. Premature leaf discoloration of European deciduous trees is caused by drought and heat in late spring and cold spells in early fall. Agricultural and Forest Meteorology 307.
While leaf discoloration of many tree species has been delayed in response to climate warming, climatic stress such as severe drought can cause premature leaf discoloration. The recent study by Bigler and Vitasse analyzed almost 17’000 observations of leaf discoloration from nine deciduous tree species in Switzerland. Leaf discoloration of most species has been significantly delayed by 1.5 to 3.3 days per decade from 1996 to 2018. For most species, premature leaf discoloration occurred in years with very warm and dry spring-summer conditions or with very cool fall temperatures. Growing degree days in May and June were higher and the climatic water balance in June was lower in years with premature leaf discoloration compared to years with regular leaf discoloration, especially for drought sensitive species such as beech. Similarly, minimum temperatures in September were consistently lower in years with premature leaf discoloration. The future increase in the frequency and severity of droughts in Europe will likely increase the risk of premature leaf discoloration.