Fræðaþing landbúnaðarins - 03.02.2006, Síða 353

Kettleholes provide some of the only topographic variation on Skeiðarársandur,
creating a distinct small-scale habitat. They may function as seed traps or seed
sources. In addition, kettleholes may offer protection from wind and abrasive sand,
and may ameliorate temperature íluctuations and soil moisture stress compared to the
surrounding flat areas.
In summer of 2005, a project investigating the kettleholes of Skeiðarársandur was
launched. The aim of the project is to understand the potential facilitative role the
holes may play for vascular plant establishment and succession at three different
scales. First, within the hole we ask whether there are discemable pattems in the
arrangement of plants to suggest the influence of small scale environmental gradients.
Second, we ask if there are differences between the abundance and cover of vascular
plant species inside and outside of the kettleholes, indicating conditions inside the
hole are better suited for plant establishment. Finally, at the scale of the entire sand
plain we investigate whether kettleholes serve as “biogeographical islands” on the
sand plain, functioning as seed traps or sources and helping species to disperse of the
plain. This poster starts at the beginning and examines the habitat of one kettlehole.
The objective is to introduce our study using one kettlehole as an example to give
information on study design and provide results to assist with further hypothesis
testing.
Methods
Twenty kettleholes (>1 m deep) were selected in each of two sites. One site is close to
Skeiðarájökull glacier in an area with scarce vegetation, and the other is more
centrally located in the plain with greater vascular plant cover and species richness.
The hole chosen as an example came from the more vegetated site. Ten holes at each
site were classified “small” (<10 m in diameter) and ten were classified as “big” (>10
m in diameter). For each hole an equal size control plot was marked on the adjacent
flat plain.
A list of vascular plant species was constructed for each hole and flat area. Frequency
data were collected as 100 points on a 0,25 m2 quadrat, replicated five times for each
of three different vertical zones and for aspect (N-S) within each hole and for the
controls. In the hole used for this example, vascular plant cover for each zone was
calculated by counting the number of vascular plant hits for each quadrat and then
averaging the values from all fíve quadrates in the zone. Species density was
measured by counting the number of vascular plant species hit in each quadrat, and
averaging that value (Gotelli and Amett, 2001).
Results
Statistical analysis has not been completed for all kettleholes in the project. However,
an in-depth view of one kettlehole can help us develop null hypothesies to apply to the
entire data set. The sample hole chosen measured 16,4 m across, 3,2 m deep in the
center, and had an inner surface distance of 17,9 m (Figure 2). The total number of
species counted (species richness) inside the hole was 35, total species counted within
the flat adjacent area were 31.
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