Establishment of Salix alaxensis on a gravel pad in Arctic Alaska

Published source details Bishop S.C. & Chapin F.C. (1989) Establishment of Salix alaxensis on a gravel pad in Arctic Alaska. Journal of Applied Ecology, 26, 575-583.
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Summary

During construction of the arctic section of the Trans Alaska Pipeline System, roads, worksites and camps were placed on raised gravel pads to prevent thermal erosion of the underlying permafrost. Gravel extraction was mostly from the Atigun and Sagavanirktok river floodplains, where the pipeline, camps, work pads and roads were also located. This resulted in destruction of riparian shrub communities important to wildlife, including caribou Rangifer tarandus, musk ox Ovibos moschatus and moose Alces alces. Of particular concern was the destruction of over 80 ha of felt-leaved willow Salix alaxensis dominated thickets, this willow being the primary winter browse species for moose.

In a restoration attempt to re-establish felt-leaf willow, the effects of water and nutrient availability on germination, survival and growth of S.alaxensis on an abandoned gravel pad were examined in a series of experiments. The experiment described here investigated germination of willow seeds in the laboratory.

In July 1985, S.alaxensis catkins were collected from 20 plants in the Toolik Lake area (68º40'N, 149º40'W) in the vicinity of an abandoned workers camp.

Compressed air and sieves were used to remove the seeds from the catkins and pappus. Seeds were frozen for 10 months prior to sowing in spring 1986. Seeds were sown in Petri dishes (10/dish) on filter paper moistened with polyethylene glycol solutions of 0, -0.1, -0.2, -0.5, -1.0, and -1.5 MegaPascals (MPa). The dishes were placed in plastic bags and kept in a growth chamber at 20°C in constant light. Dishes were weighed every 2 days, and distilled water added to replace any water lost. Germinated seeds were counted and removed every 2 days.

Seeds failed to germinate at osmotic potentials of -0.5 MPa and lower. Total percentage germination after 10 days did not differ significantly between the control, -0.1 and -0.2 MPa treatments, with about 10% of seeds germinating in each. However, the seeds used in this experiment had been frozen for 10 months, so germination success was much lower than the 90-95% typical for fresh seeds.

Conclusions: These results, in combination with information concerning water availability at gravel pads in the study area (i.e. water content of the top 10 cm of soil of gravel pads ranged from 3.6 to 15.4% of dry weight with a water potential of approximately -0.01 to -0.3 MPa) suggests that moisture availability is a limiting factor for germination of willow seeds.

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