Hydrologically Triggered Regime Shifts in Terrestrial Arctic Ecosystems: A Cross-Scale Perspective

Recently observed changes in soil moisture, runoff, snow cover, and precipitation, as well as in specific hydrological indicators of permafrost thawing show that the climate warming is altering hydrological processes in the Arctic. These changes may push some terrestrial Arctic ecosystems from one ecological regime to another. We present three types of such regime shifts, ecosystem change from one set of mutually reinforcing feedbacks to another, and focus on the temporal and spatial cross-scale interactions on which the drivers and feedbacks of these shifts operate. The three regime shifts are: 1) Conversion of aquatic to terrestrial ecosystems (e.g., draining of lakes), 2) Conversion of terrestrial to aquatic ecosystems (e.g., development of wetlands); and 3) Shifts in terrestrial ecosystems (e.g., transition from tundra to forest). The key driver behind all these regime shifts is a warming climate in the Arctic, but the shifts are also all locally mediated by local soil conditions, topography and hydrology. Even if all these regime shifts occur at a landscape scale, they do not only have consequences for local people and animals, but may also alter the regional supply of ecosystem services (benefits that people receive from nature). Furthermore, they may also have implications for the Earth system as a whole, through the different feedbacks that different Arctic ecosystems and their ice/permafrost-land-freshwater conditions yield to carbon exchange and climate. Understanding how complex Arctic terrestrial ecosystems will respond to climate and hydrological change is essential in order to identify the processes and locations that have the potential to experience abrupt threshold changes and regime shifts.