Hyperspectral leaf spectroscopy reveals the drought response of Fagus sylvatica seedlings from across the species’ range.

Europe is expected to experience increased numbers and intensified summer droughts due to climate change. The common European beech (Fagus sylvatica) is an important native tree species with a high ecological and economical value, which is sensitive to prolonged duration of droughts and anticipated to change its natural distribution range. Here, we conducted a common garden experiment with potted 180 two-year-old seedlings from 16 beech provenances across the species’ range and simulated two drought periods by discontinuing irrigation (treatment). We combined empirical approaches (spectral indices) and a physically-based radiative transfer model (PROSPECT-D) on hyperspectral leaf spectroscopy data covering visible to short-wave infrared electromagnetic radiation to determine drought induced changes in leaf biochemical and functional traits and to assess the intraspecific response diversity. Findings from this experiment suggest that (i) spectroscopy is able to discern changes of a variety of leaf traits in drought treated seedlings, that (ii) spectral variation is higher in drought treated seedlings and associated uncertainties are negligible, and that (iii) there is no evidence of intraspecific variation in the response to drought in F. sylvatica leaf traits as it may be masked by variation on the individual level. We demonstrated that hyperspectral leaf spectroscopy is a useful tool to assess drought responses in leaf traits but must be complemented with further analysis on population structure to study intraspecific diversity and the persistance of F. sylvatica.