e-mail: eugster@giub.unibe.ch
The question is: how many landscape or vegetation types have to be distinguished in the arctic tundra, to be able to represent this environment adequately in mesoscale meteorological or global scale climate models (MM4; GCM)?
We present first results from the field season 1995. Please see also poster H32C-3 for 1994 results.
soil properties (description, organic matter, water content, ...)
active layer depths
microtopography (including microrelief, slope and aspect)
plant species composition
leaf area index and stem area index
canopy heights
The two towers were set up simultaneousely at different sites for approximately 10 days, and then were moved to another pair of sites. Ten tundra sites plus one lake surface, Toolik lake, (Figure 1) covered the major vegetation types of the North Slope and the range of soil moistures (Figure 2).
For comparisons between different pairs of sites (non-simultaneous measurements) data from three permanent eddy correlation towers run by G. Vourlitis and W. Oechel (San Diego State Univ.) will be used.
Figure 3 shows a comparison between a non acidic tussock tundra vegetation type that occurs on loess soils of pH 7.5-8 versus an acidic tussock tundra vegetation type on soils of pH 3-4. These are the two major vegetation types covering 38.9% and 30.8% of the Kuparuk River basin which stretches from the Brooks Range roughly 240 km towards the Arctic Ocean. These two sites are a few km apart. The altitude differs by 100 m.
Figure 4 shows flat-centered (moist) and low-centered (wet) polygons on the coastal plain. The sites are separated by 750 m. Polygons are periglacial structures of permafrost typical in the coastal zone.
Figure 5 shows two different types of shrublands. The willows on a sandy riverbar in the Sagavanirktok River were slightly more productive (more CO2 uptake during daytime) than the watertrack shrubs (dwarf birches and willows).
Figure 1: Mobile tower and permanent tower locations (flux measurements) on the North Slope. The 11 sites cover a roughly 200 km north-south transect between the Arctic Ocean and the Brooks Range. The latitude is approximately 70° N.
Figure 2: Volumetric water content of the top 5 to 10 cm soil slab at the 11 sites. Four samples per site at same locations as ground heat flux and soil temperature measurements. The shaded lines indicate the range of small-scale variability at the individual sites. Large labels indicate the sites shown on this poster.
Figure 3: Sensible heat (H), latent heat (LE) and CO2 fluxes for the two vegetation types which are most important on the North Slope. LE does not differ significantly, although leaf area index is higher in acidic tundra. High values of H in the afternoon are probably due to local upslope winds, otherwise H values are similar. The CO2 flux shows the difference according to the difference in leaf area index.
Figure 4: Sensible heat (H), latent heat (LE) and CO2 fluxes for two important landscape types near the arctic coast. Leaf area at these two sites is comparable. Low-centered polygons have a shallow open water surface in the center, which makes them clearly colder than flat-centered polygons, which do not have a wet surface. This has a significant impact on H and a smaller impact on LE. CO2 fluxes do not differ significantly.
Figure 5: Sensible heat (H), latent heat (LE) and CO2 fluxes of shrub tundra. River bar shrubs are the most productive vegetation type in the tundra (highest CO2 uptake). However, the cold river water and cold up-valley winds reduce sensible heat flux H under certain conditions (14 July), but less on other days (16 July). LE consistently shows higher evapotranspiration from the riverbar, where water availability never is a limiting factor.