Effects of Climate Change on Tundra Ecosystems Greg Henry, University of British Columbia Philip Wookey, University of Uppsala

Climate Change and Tundra Ecosystems IntroductionIntroduction Conceptual issues: time and space scales, processesConceptual issues: time and space scales, processes Evidence of change: observationsEvidence of change: observations Experimental results: ITEXExperimental results: ITEX Research needsResearch needs

CO 2 ‘fertilization’ effect (‘  -factor’); Regional differences in global warming: greater than average warming at high northern latitudes; Increased deposition of airborne N- containing compounds; Stratospheric O 3 depletion  increased UV- B fluxes at the surface. Environmental change has multiple facets “The past as a key to the future” Yes, but with caution!

Shaver et al., (2000) BioScience Herbivores Climate Change Snow cover

Vegetation Other Soils migration and invasion disturbance regime  herbivores SOM development  species w/in initial community  litter mass, quality  microbes, fauna N availability allocation Leaf Ps, Rs 1 day1 yr10 yr100 yr1000 yr TIME-SCALE OF RESPONSE Key issues – time scales. [ from Shaver et al. (2000) BioScience ] “Typical” study length Need to understand long-term effects

Key issues – time scales Ecosystem C balance Net C uptake by system C E D A B Time Net C loss to atmosphere Harvard forest (A,B) Toolik Lake (C,D) Great Dun Fell (D,E) Colorado subalpine (C) Abisko (C) [from Shaver et al. (2000) BioScience] 0

Vegetation cover Soil organic matter Nutrient stock Unoccupied space Cryo-processes?? Temperature gradient (30º latitude & 10º temp) Warmer Colder Key issues - spatial scales Geological & topographic influences - cross-cutting (regional and local scales) Low ArcticHigh Arctic

Schematic comparison of low- and high-arctic tundra response to warming Permafrost table Water table Organic matter (and nutrient pool) Mineral ‘soil’ or regolith Lateral spread Immigration Vertical development Community shifts LOW ARCTIC TUNDRA Mesic Shrub Tundra HIGH ARCTIC TUNDRA Polar Semi-Desert () = + and -) Deeper active layer

a 3 4b 55 Semi-permanent snow drift Prevailing wind 1. Dry exposed ridges 2. Mesic zonal sites 3. Wet meadows 4. Snowbeds a. well-drained, early-melting b.poorly-drained, late-melting 5. Streamside sites Key issues - spatial scales [From Walker D.A. (2000) GCB] Relations between topography and tundra plant communities

Evidence of changes in tundra vegetation Increased abundance of shrubs – Alaska positive feedback with snow accumulation Increased growth rates of trees at treeline leading to greater seed production and treeline advance (?) Results from experimental manipulations International Tundra Experiment (ITEX)

International Tundra Experiment - Experimental approaches ITEX  12 years progress (ITEX Resolution, 5 th December, 1990) sites in 1992;  Straightforward approach designed to encourage broad international participation;  Manipulation, monitoring, modelling (synthesis), mapping;  Bottom-up (‘ITEX species’)

Toolik Lake, Alaska Alexandra Fiord, Ellesmere Island, Canada Magerøya, Norway ITEX and related experiments

Temperature/ Position in range Process rate NorthSouth Net PS Intensity of competition Experimental approaches – Experiments along gradients

Alexandra Fiord, Ellesmere Island, Canada

ITEX Meta-analysis: leaf bud break Arft et al. 1999

ITEX Meta-analysis of vegetative growth Arft et al Short-term effects differ by growth form

ITEX synthesis II - Community responses Walker M.D. et al. (2004) Meta-analysis

ITEX results – synthesis I  Warming  Warming experiments confirm sensitivity of cold region vegetation in general (e.g. Rustad et al. 2001): ITEX provides detail for tundra plants;  Growth increased  Growth increased in general - variation among growth forms;  Phenological shifts  Phenological shifts consistent – earlier flowering;  Geography is important  Geography is important; (e.g. low vs high arctic)

detectable responses3-4 years;  Plant communities exhibit detectable responses to warming in only 3-4 years;  The most significant changes are: increasesdeciduous shrub  increases in deciduous shrub cover & height decreasescryptogam  decreases in cryptogam cover decreasesspecies richness  decreases in (apparent) species richness; ITEX results – synthesis II

effects on soil microorganism diversity and processes? effects on soil microorganism diversity and processes? negative feedback of increasing C:N ratio (low quality litter) and stimulation by warmth? negative feedback of increasing C:N ratio (low quality litter) and stimulation by warmth? use of organic vs mineral N sources by plants and microbes: how will this change? use of organic vs mineral N sources by plants and microbes: how will this change? effects of combined factors: CO 2, heat, moisture, nutrients, light, season length effects of combined factors: CO 2, heat, moisture, nutrients, light, season length Long-term changes in NEP and Carbon balance? Long-term changes in NEP and Carbon balance? Continuing questions: