Key Concepts:

Figure 1. Riparian habitats in Arctic tundra can be found along a continuum of states, from a state dominated by large willow shrub patches (a) to a state without such shrub cover (b). These states have different structure – species dependent on willow shrubs such as willow grouse disappear in state (b) – as well as different functions – for example, increasing shrub cover will decrease albedo ((c) contrast the dark shrubs and the white snow cover) and therefore will affect climate. Climate change represents an important driver of a transition from (b) to (a) – warmer temperatures favour shrub growth – but herbivores, and in particular reindeer, may slow down or even reverse shrub cover increase ((a)–(b)). Furthermore, climate change may negatively influence small mammalian herbivores, such as lemmings ((d) dead Norwegian lemming on hard snow), with consequences for emblematic, predatory species (Snowy owl; (c)). Ecological Monitoring starts with a simple model of the interactions between climate, shrub cover, herbivores and their predators, and incorporates the human dimension, particularly reindeer herding and indigenous people. Because Arctic terrestrial ecosystems cover huge areas, with large variation in present state, history (e.g. presence of ice during the last Glacial Maximum), diversity, climate regime, socio‐economic condition and governance, monitoring needs to integrate local (‘context’) and global components. Reproduced from Nigel Yoccoz (a) and Rolf A Ims ((b)–(d)).