Print PageClimate variability has complex effects on ecosystems, with monotonic changes representing the exception rather than the rule in ecological responses. Responses of biological communities and ecological processes to climate variation depend upon the sign, magnitude and duration of a particular climate forcer, e.g., temperature or precipitation. Ecosystem processes in climatically extreme environments such as deserts or tundra are often influenced by discrete climate events, traditionally described as pulses. These climate events can be extreme in terms of magnitude (e.g., intense precipitation or ice melt events), but may not have negative impacts on ecosystems in terms of decreases in productivity or species diversity. Rather, temporal climate variability is a characteristic property that contributes to both the structure (i.e., community composition) and functioning (e.g., biogeochemistry and production) of desert ecosystems in particular. Discrete climate events can also be understood to have a disproportional influence over ecosystems relative to the temporal scales over which they occur. This sensitivity to discrete climate events is particularly true for polar deserts because massive water reserves are present as ice in alpine and terminal glaciers. We report on the influence of multiple discrete summer warming events on soil ecosystems observed in the McMurdo Dry Valleys of Antarctica.
Results/Conclusions
The McMurdo LTER program has documented two distinct modes of climate variation over the past 18 years: a decadal scale cooling trend, and 3 discrete summer heat waves characterized by record temperatures and melt. The decadal cooling limited the availability of water and energy to terrestrial and aquatic ecosystems leading to widely documented decreases in ecosystem productivity. In contrast, summer heat waves result in increased glacier melt and stream flow, and subsurface melting of permafrost that contributed to widespread increases in soil water availability, which elicited strong responses from soil invertebrate communities. Populations of a subordinate nematode Eudorylaimus spp. increased in response to elevated soil water availability, whereas the dominant species (Scottnema lindsayae) did not. Continuous measurements of soil microclimate indicate that enhanced levels of soil water persisted through multiple years, resulting in a more favorable habitat for Eudorylaimus and increasing the relative proportion of this species in the invertebrate community. These data suggest that extreme climate events can alter community composition and may contribute to the maintenance of soil biodiversity in dry valley soils. Pulse climate events, long recognized as important drivers of hot deserts, are also significant drivers in Polar desert ecosystems.
