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Effects of Climate Change on Tundra Ecosystems Greg Henry, University of British Columbia Philip Wookey, University of Uppsala Climate Change and Tundra Ecosystems • Introduction • Conceptual issues: time and space scales, processes • Evidence of change: observations • Experimental results: ITEX • Research needs Environmental change has multiple facets • CO2 ‘fertilization’ effect (‘-factor’); • Regional differences in global warming: greater than average warming at high northern latitudes; • Increased deposition of airborne Ncontaining compounds; • Stratospheric O3 depletion increased UVB fluxes at the surface. • “The past as a key to the future” Yes, but with caution! Herbivores Snow cover Climate Change Shaver et al., (2000) BioScience Key issues – time scales Need to study understand “Typical” lengthlong-term effects Other migration and invasion disturbance regime herbivores Vegetation Soils SOM development litter mass, quality microbes, fauna N availability species w/in initial community allocation Leaf Ps, Rs 1 day 1 yr 10 yr 100 yr TIME-SCALE OF RESPONSE [from Shaver et al. (2000) BioScience] 1000 yr Key issues – time scales Ecosystem C balance Net C uptake by system C A 0 Harvard forest (A,B) Toolik Lake (C,D) Great Dun Fell (D,E) Colorado subalpine (C) Abisko (C) B D Net C loss to atmosphere E Time [from Shaver et al. (2000) BioScience] Key issues - spatial scales Low Arctic High Arctic Warmer Colder Temperature gradient (30º latitude & 10º temp) Vegetation cover Soil organic matter Nutrient stock Unoccupied space Cryo-processes?? Geological & topographic influences cross-cutting (regional and local scales) Schematic comparison of low- and high-arctic tundra response to warming • Vertical development • Community shifts • Lateral spread • Immigration • Vertical development Organic matter (and nutrient pool) () = + and -) Water table () = + and -) Mineral ‘soil’ or regolith Permafrost table Deeper active layer LOW ARCTIC TUNDRA HIGH ARCTIC TUNDRA Mesic Shrub Tundra Polar Semi-Desert Key issues - spatial scales Relations between topography and tundra plant communities 1 2 4a Prevailing wind 4b Semi-permanent snow drift [From Walker D.A. (2000) GCB] 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 2 3 5 5 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) Experimental approaches ITEX 12 years progress (ITEX Resolution, 5th December, 1990) sites in 1992; Straightforward approach designed to encourage broad international participation; Manipulation, monitoring, modelling (synthesis), mapping; Bottom-up (‘ITEX species’) International Tundra Experiment - www.itex-science.net Toolik Lake, Alaska Magerøya, Norway Alexandra Fiord, Ellesmere Island, Canada ITEX and related experiments Experimental approaches – Experiments along gradients Process rate Intensity of competition Net PS North Temperature/ Position in range South Alexandra Fiord, Ellesmere Island, Canada ITEX Meta-analysis: leaf bud break Arft et al. 1999 ITEX Meta-analysis of vegetative growth Short-term effects differ by growth form Arft et al. 1999 COVER ITEX synthesis II Community responses All shrubs Effect-size (d) 1.0 CANOPY HEIGHT 3 4 0.5 0 -0.5 -1.0 4 4 Deciduous shrubs 6 Meta-analysis 2 Graminoids 4 DIVERSITY (Shannon) Bryophytes 2 4 3 Lichens 2 Walker M.D. et al. (2004) Litter Walker et al. Figure 3 ITEX results – synthesis I Warming experiments confirm sensitivity of cold region vegetation in general (e.g. Rustad et al. 2001): ITEX provides detail for tundra plants; Growth increased in general - variation among growth forms; Phenological shifts consistent – earlier flowering; Geography is important; (e.g. low vs high arctic) ITEX results – synthesis II Plant communities exhibit detectable responses to warming in only 3-4 years; The most significant changes are: increases in deciduous shrub cover & height decreases in cryptogam cover decreases in (apparent) species richness; Continuing questions: • effects on soil microorganism diversity and processes? • 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? • effects of combined factors: CO2, heat, moisture, nutrients, light, season length • Long-term changes in NEP and Carbon balance?