not-yet-known not-yet-known not-yet-known unknown The Arctic experiences rapid climate change, but our ability to predict how this will influence plant communities is hampered by a lack of data on the extent to which different species are associated with particular environmental conditions, how these conditions are interlinked, and how they will change in coming years. Increasing temperatures may negatively affect plants associated with cold areas due to increased competition with warm-adapted species, but less so if local temperature variability is larger than the expected increase. Here we studied the potential drivers of change in vegetation composition and species richness along coast to inland and altitudinal gradients by the Nuuk fjord in western Greenland using Hierarchical Modelling of Species Communities (HMSC) and linear mixed models. Community composition was more strongly associated with random variability at intermediate spatial scales (among plot groups 500 m apart) than with large-scale variability in summer temperature, altitude or soil moisture, and the variation in community composition along the fjord was small. Species richness was related to plant cover, altitude and slope steepness, which explained 42% of the variation, but not to temperature. Jointly, this suggests that the direct effect of climate change will be weak, and that many species are associated with topographically defined microhabitats. However, both species richness and the occurrence of several species with inferior competitive capabilities peaked at intermediate cover, indicating that increasing dominance of competitive warm-adapted species can result in decreasing diversity under warmer climatic conditions.

Recreational boats are common in many coastal waters, yet their effects on cetaceans and other sensitive marine species remain poorly understood. To address this knowledge gap, we used drone videos to quantify how harbour porpoises (Phocoena phocoena) responded to a small motorboat approaching at different speeds (10 or 20 knots). The experiment was carried out in shallow waters near Funen, Denmark (55.51° N, 10.79° E) between July and September 2022. Porpoises moved further away from the boat path during approaches at both boat speeds. In addition, porpoises swam faster when approached at 20 knots but not when approached at 10 knots, and they had a higher likelihood of moving away from the boat path when approached at 10 knots but not at 20 knots. Importantly, the received sound level did not depend on how fast the boat approached, suggesting that differences in porpoise responses were related to the speed of the boat’s approach rather than to sound itself. The porpoises’ behaviour during the minute where the boat was closest did not differ from their behaviour before boat exposure, indicating that the direct impact of small vessels on porpoise behaviour was most likely small. Nevertheless, repeated exposure to noise from small vessels could influence porpoises’ foraging efforts and cause them to relocate from disturbed areas. The approach used in this study increases our understanding of recreational boats’ impact on harbour porpoises and can be used to inform efficient mitigation measures to help conservation efforts.