title: Effects on the structure of Arctic ecosystems in the short- and long-term perspectives.
abstract: Species individualistic responses to warming and increased UV-B radiation are moderated by the responses of neighbors within communities, and trophic interactions within ecosystems. All of these responses lead to changes in ecosystem structure. Experimental manipulation of environmental factors expected to change at high latitudes showed that summer warming of tundra vegetation has generally led to smaller changes than fertilizer addition. Some of the factors manipulated have strong effects on the structure of Arctic ecosystems but the effects vary regionally, with the greatest response of plant and invertebrate communities being observed at the coldest locations. Arctic invertebrate communities are very likely to respond rapidly to warming whereas microbial biomass and nutrient stocks are more stable. Experimentally enhanced UV-B radiation altered the community composition of gram-negative bacteria and fungi, but not that of plants. Increased plant productivity due to warmer summers may dominate food-web dynamics. Trophic interactions of tundra and sub-Arctic forest plant-based food webs are centered on a few dominant animal species which often have cyclic population fluctuations that lead to extremely high peak abundances in some years. Population cycles of small rodents and insect defoliators such as the autumn moth affect the structure and diversity of tundra and forest-tundra vegetation and the viability of a number of specialist predators and parasites. Ice crusting in warmer winters is likely to reduce the accessibility of plant food to lemmings, while deep snow may protect them from snow-surface predators. In Fennoscandia, there is evidence already for a pronounced shift in small rodent community structure and dynamics that have resulted in a decline of predators that specialize in feeding on small rodents. Climate is also likely to alter the role of insect pests in the birch forest system: warmer winters may increase survival of eggs and expand the range of the insects. Insects that harass reindeer in the summer are also likely to become more widespread, abundant and active during warmer summers while refuges for reindeer/caribou on glaciers and late snow patches will probably disappear.
authors.affiliation: Abisko Scientific Research Station, Sweden. terry.callaghan@ans.kiruna.se
authors.forename: Terry V
authors.initials: TV
authors.lastname: Callaghan
authors.forename: Lars Olof
authors.initials: LO
authors.lastname: Björn
authors.forename: Yuri
authors.initials: Y
authors.lastname: Chernov
authors.forename: Terry
authors.initials: T
authors.lastname: Chapin
authors.forename: Torben R
authors.initials: TR
authors.lastname: Christensen
authors.forename: Brian
authors.initials: B
authors.lastname: Huntley
authors.forename: Rolf A
authors.initials: RA
authors.lastname: Ims
authors.forename: Margareta
authors.initials: M
authors.lastname: Johansson
authors.forename: Dyanna
authors.initials: D
authors.lastname: Jolly
authors.forename: Sven
authors.initials: S
authors.lastname: Jonasson
authors.forename: Nadya
authors.initials: N
authors.lastname: Matveyeva
authors.forename: Nicolai
authors.initials: N
authors.lastname: Panikov
authors.forename: Walter
authors.initials: W
authors.lastname: Oechel
authors.forename: Gus
authors.initials: G
authors.lastname: Shaver
authors.forename: Heikki
authors.initials: H
authors.lastname: Henttonen
mesh_terms: D000818:Animals; D001110:Arctic Regions; D044822:Biodiversity; D003081:Cold Climate; D017753:Ecosystem; D004784:Environmental Monitoring; D007313:Insecta; D010944:Plants; D012988:Soil Microbiology; D014466:Ultraviolet Rays