Chapter 6. Arctic Tundra and Polar Desert Ecosystems

Transcription

1 Chapter 6 Arctic Tundra and Polar Desert Ecosystems Figure 6.1 Schematic timescale of ecological processes in relation to disturbances in the Arctic. The schematic does not show responses expected due to anthropogenic climate change (based on Oechel and Billings, 1992; Shaver et al., 2000; Walker and Walker, 1991) Figure 6.2 Present day natural vegetation of the Arctic and neighboring regions from floristic surveys. Vegetation types 1-5 are classified as Arctic, whereas types 6-8 are classified as

2 Figure 6.3 Growth forms of Arctic plants (modified from Webber et al., 1980).

3 Figure 6.4 Northern vegetation in the Mid- Holocene a) simulated by the IPSL-CM1 AOJCM model, b) simulated by the HADCM2 AOJCM model, c) observed vegetation reconstructed from pollen data (Bigelow et al. 2003; Kaplan et al., 2003).

4 Figure 6.5 Top: the relationship between the number of nesting bird species and July mean temperature in western and middle Siberia. Middle: correlation between July mean temperature and number of ground beetle species in local faunas of the Taymyr Peninsula. Bottom: Correlation between July mean temperature and number of day butterflies in the middle Siberian and Beringian sectors of the Arctic (Chernov, 1989; Chernov, 1995; Matveyeva and Chernov, 2000). The middle figure illustrates how current bioclimatic distributions are related to climate change scenarios by plotting the likely changes in the number of ground beetles for three time slices of mean July temperature derived from the mean of the five ACIA scenarios.

5 Figure 6.6 The relationship between July mean temperature and the number of vascular plant species in local floras of the Taymyr Peninsula and the Canadian Arctic Archipelago. 1. The whole flora 2. Poaceae 3. Cyperaceae 4. Brassicaceae 5. Saxifragaceae (Rannie, 1986; Matveyeva and Chernov, 2000) Figure 6.7 Latitudinal distribution of soil fungi (top) and bacilla (bottom). Recalculated from data in Mirchink (1988).

6 Figure 6.8 Schematic showing relationship between timing of the growing season and the seasonal pattern of irradiance together with an indication of where transient switches from carbon sink to carbon source could occur (modified from Chapin and Shaver, 1985b). Figure 6.9 Dwarf shrub distributions (labeled boxes) in relation to latitude and solar UV-B radiation incident at the Earth's surface (Hultén, 1962; Gwynn-Jones et al., 1999; Phoenix, 2000).

7 Figure 6.10 Population dynamics of Svalbard reindeer (solid line) at Brøggerhalvøya and sibling voles (broken line) at Fuglefjella on Svalbard (Aanes et al., 2000; Yoccoz and Ims, 1999). Also included are data from Robinson et al. (1998) and Callaghan et al. (1999) showing observed (circles) and projected (squares) changes in vegetation. Figure 6.11 Yearly winter survival rate (with 95% confidence intervals) of experimental tundra vole Microtus oeconomus populations plotted against the number of days with temperatures above 0 oc during mid winter (December-February). Mean winter temperature and the year are denoted above the survival rate estimates (Aars and Ims, 2002).

8 Figure 6.12 Evidence from the beginning of the 1990s for change in the population dynamics in the formerly cyclic and numerically dominant grey-sided vole and other vole species (combined) at Kilpisjärvi, N-Finland (Henttonen and Wallgren, 2001). Figure 6.13 Simulation of changes in a tundra microbial community (Barrow, Alaska) induced by climate warming. Left: population dynamics of dominant soil bacteria; note that L-selected species (Bacillus) display only sporadic occurrence under normally cold conditions of the tundra, which is in agreement with observations, and attains high population density after soil warming. Right: carbon budget including net primary production (NPP), soil respiration and litter dynamics. It was assumed that average air temperature was instantly (see y-axes break) shifted by 10 oc (Panikov, 1994).

9 Figure 6.14 a) The number of leaves produced per year in shoots of Cassiope tetragona as a function of the average July temperature b) Correlation between a growth parameter in Hylocomium splendens and mean annual temperature at seven Arctic/sub-Arctic sites. The boxes on the regression lines contain scenarios of growth for ACIA time slices resulting from temperature increases according to the five ACIA scenarios. The dotted line in a) depicts predicted growth probably outside the capability of the species. The expanded boxes to the right depict uncertainty ranges associated with each of the predictions. Filled circles denote populations for which scenarios have been applied.

10 Figure Results of long term (generally 10 years or more) experiments in a range of habitats at Toolik Lake, Alaska and Abisko, Sweden. The figure shows the responsiveness of aboveground biomass ordered by treatment and size of responsiveness. Data are given for total vascular plant biomass and lichen biomass. Numbers in the graphs are the mean effect size (L*) for each treatment and between parentheses the 90% confidence interval value. Codes relate to the geographical region (To=Toolik, Ab=Abisko), the site name and the duration of the experiment (van Wijk et al., 2003).

11 Figure 6.16 Effect of long term fertilizer addition and experimental warming and shading during the growing season on aboveground net primary production (NPP) of different plant functional types at Toolik Lake, Alaska (Chapin et al. 1995). The left hand panel shows NPP by functional type and treatment in 1983, after three years of treatment, and the right hand panel shows NPP by functional type and treatment in 1989, after nine years of treatment. C=control (unmanipulated) plots; F=annual N+P fertilizer addition; G=warming in a plastic greenhouse during the growing season; FG=fertilizer plus greenhouse treatment; S=50% light reduction (by shading) during the growing season.

12 Figure 6.17 Changes in greeness (depicted by NDVI) of northern vegetation between 1981 to 1991 (Myneni et al., 1997).

13 Figure Long term trends in summer net CO2 flux, temperature, and precipitation for Alaskan coastal wet sedge tundra (Oechel et al., 1993; 2000b). Figure Nitrogen budget for wet sedge tundra at Barrow Alaska (Shaver et al., 1992; adapted from Chapin et al., 1980). Numbers in boxes are N stocks in g m-2; numbers in parentheses are N fluxes in g m-2 y-1.

14 Figure Response of plants to environmental perturbations. Values are means +- SD, depicted as percentage of untreated controls. Black and grey symbols indicate that means differ significantly from 100% (P <0.05 and 0.1>P>0.05, respectively two-tailed t-test). Treatments are: elevated CO2, fertilization (FERT), light attenuation (SHADE), elevated temperature (TEMP), elevated UV-B radiation, and irrigation (WATER). The y axis is scaled logarithmically. Numbers at the bottom refer to corrected sample size (df+1) (Dormann and Woodin, 2002).

15 Figure 6.21 Seasonal mean methane emission from a high Arctic fen in NE Greenland (Zackenberg) plotted against leaf biomass of Eriophorum scheuchzeri, Dupontia psilosantha, Carex subspathacea and total leaf biomass of the three species. The regression lines represent linear fits. The figure shows that the minor constituents of the total vascular plant biomass (Carex and Eriophorum) seem to be "driving" net methane emissions from the site suggesting that shifts in vascular plant species composition alone could lead to significant effects on trace gas exchange (Joabsson and Christensen, 2001).

16 Figure 6.22 Controls on methanogenesis (redrawn from Davidson and Schimel, 1995). Figure Accumulated carbon and greenhouse warming potential from CO2 and CH4 exchanges calculated as CO2 equivalents throughout the summer of 1997 at Zackenberg, Northeast Greenland (data from Friborg et al., 2000; Søgaard et al., 2000).

17 Figure 6.24 Simulated potential vegetation for with the HADCM2-SUL GCM using the IS92a greenhouse-gas scenarios (Kaplan et al., 2003). (See Figures 6.2 and 6.4 for the legend) Figure 6.25 Carbon storage anomalies (kg C/m2) between predicted by LPJ- DJVM using emissions from the SRES B2 within four GCM (Sitch et al., 2003).

18 Figure Threats to current conservation using protected areas from climate change. A map of current protected areas in the Arctic (CAFF, 2001) has been overlain by a map of changes in vegetation derived from Kaplan et al. (2003) and Figures 6.2 and 6.24.

19 Plate 6.1 Forest tundra vegetation represented by the Fennoscandian mountain birch forest, Abisko, northern Sweden. Plate 6.2 Zonal tussock tundra near Toolik Lake, Alaska, with large shrubs/small trees of Salix in moist sheltered depressions.

20 Plate 6.3 Polar semidesert dominated by Dryas octopetala, Ny Ålesund, Svalbard. Plate 6.4 Polardesert, Cornwallis Island, Northwest Territories, Canada.

21 Plate 6.5 Polygonal wet tundra near Prudhoe Bay, Alaska. Plate 6.6 Racomitrium/Empetrum heath in Iceland showing erosion.

22 Plate 6.7 Snow bank vegetation showing increasing vegetation development with increasing length of the growing season represented Plate 6.8 Thermokarst scenery in the Russian Tundra, New Siberian Islands.