Not in the eye of the beholder: climate change effects on alpine plant communities

Prepared by Andreas Futschik, Manuela Winkler, Klaus Steinbauer, Andrea Lamprecht, Sabine B. Rumpf, Peter Barančok, Andrej Palaj, Michael Gottfried & Harald Pauli

The monitoring of plant biodiversity patterns always implies a degree of observer error, such as overlooking or misidentifying species. This can occur if, for example, a species is exceptionally small and inconspicuous, flowers are absent, or co-occurring species have similar shapes.

Observer errors may increase at long-term efforts, where observer teams inevitably change over the course of decades. This study of the international monitoring programme GLORIA (GLobal Observation Research Initiative in Alpine Environments; www.gloria.ac.at) deals with climate change impacts on species richness, species abundance and plant community composition of high-mountain vegetation. The study included different types of alpine vegetation on siliceous and limestone bedrock in three mountain regions in the European Alps and Carpathians.

Our main objectives were (1) to disentangle systematic and random error in species abundance estimation, and (2) to assess if pseudo-changes (due to observer errors) in species richness, abundance and species composition are smaller or larger than changes observed over time. A systematic error can occur if one observer notoriously over-estimates species abundance whereas another observer is an under-estimator. Random errors, in contrast, have no pattern and are unpredictable. To address our questions, vegetation data from observer error trials, where the same plots were recorded successively by 13-14 observers in the same year, were compared with data from long-term monitoring plots recorded in different years.

Our results show that the percentage of the systematic error was less than 5% and that changes over time significantly exceeded pseudo-changes in all cases where the observation period was at least 10 years. We therefore conclude that a turnover of observer teams is not a fundamental difficulty for long-term vegetation monitoring, as long as all observers are well-trained persons and, second, that already after a decade the climate change signal is “louder” than observer error noise, even in vegetation composed of slow-growing alpine plants.

This is a plain language summary for the paper of Futschik et al. published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.12822).