FunSpec: detecting long-term functional changes in biodiversity: boosting analyses of herbarium specimens using spectroscopic methods

Agricultural landscapes are potentially species-rich and deliver varied ecosystem services but are increasingly under pressure due to intensified management, leading to declines in diversity. Functional plant traits represent the interface between plant and environment and indicate growth strategies. Herbaria contain a wealth of plant specimens, representing a treasure trove of functional diversity, but functional traits such as leaf nitrogen content require destructive measurements. The aim of this dissertation was to develop near-infrared spectroscopy (NIRS) for the use in herbarium specimens which allows us to non-destructively extract functional traits and track functional trait changes over historical time scales. In Chapter I, the compatibility of NIRS and herbarium specimens was proven through experiments and a new R-based calibration workflow. In Chapter II, a resurvey study was carried out on common plants of agricultural habitats. Predicting functional traits from herbarium specimens through NIRS technology, we found long term trait changes that corresponded to faster growth strategies. In Chapter III, historical species occurrence data was added to the Chapter II dataset. Amid general declines, species with traits corresponding to fast growth strategies were more resilient to intensified management. In this thesis, I was able to prove the suitability of NIRS analysis for the extraction of functional traits from herbarium specimens. I successfully applied this method to assemble a century-spanning functional trait dataset showcasing the impacts of agricultural intensification on plant species of this habitat and then tied this information to occurrence data, thereby connecting region-wide environmental changes to functional traits and ultimately species distributions. The results of this thesis provide a toolset and reference for future studies which want to study long-term impacts of environmental changes on plant communities.