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 pots and plots on the gravel pad under field conditions.

Study site: In July 1985, S.alaxensis catkins were collected from 20 plants in the Toolik Lake area (68º40'N, 149º40'W). The effects of watering, fertilizer addition and substrate amendments were examined in outdoor pots and field plots on an abandoned gravel pad (location of a former construction site):

Pot experiment: Freshly collected seeds were sown in 13 x 13 cm square pots (10 seeds/pot) filled with river sand, and placed outdoors at Toolik Lake. Approximately 0.9 g of commercial NPK fertilizer (18% N, 18% P₂O₅, 18% K₂0) was added to the surface of each fertilized pot at the time of sowing. Watered pots were watered whenever the soil became dry. A combined treatment and an untreated control were also included. There were 10 replicate pots for each treatment. Germinated seeds were counted and removed daily.

Field plot experiment: Germination was examined in five replicate blocks, each 1 x 1 m, on the gravel pad. Each block was divided into 16, 25 x 25 cm plots. Within each block, treatments (see below) were randomly assigned to alternate plots, so that they were separated by unused buffer plots. Approximately 200 seeds were sown by hand in each plot. All plots were watered at the time of sowing, but no additional water was given except in the watered treatments. The fertilizer used was the same as that described above. Germination was checked after 5 days. The eight treatments were:

Water - watered whenever surface soil became dry, to increase availability of water.

Peat - commercial Sphagnum moss mixed with surface layer (1-2 cm) of soil (approximately equal volumes of peat and soil), to improve water retention.

Sand - sand mixed with surface layer of soil (approximately equal volumes of sand and soil), to increase drainage and reduce soil moisture.

Stones - stones (up to 4 cm diameter) placed on the soil surface, covering approximately 75% of the area to provide shaded, moister microsites.

Fertilized - approximately 3.4 g of NPK fertilizer added to each subplot (555 kg/ha) to increase nutrient availability and simulate conditions on sites seeded with non-native grasses.

Fertilizer/sand - fertilizer and sand treatments combined.

Fertilizer/water fertilizer and water treatments combined.

Control - no treatments applied.

Germination in pots: Fertilizer added to pots reduced average germination from 15 to 10%, whether or not the pots were watered, suggesting that the effect was toxic rather than osmotic. The amount of fertilizer used (equivalent to 555 Kg/ha), was slightly less than was added when gravel pads were revegetated with non-native grasses by the pipeline construction company. These fertilizer additions may have inhibited natural germination and hence establishment of willow seeds on the gravel pads. Watering had no significant effect on germination, perhaps as the weather was rainy during the week of the experiment.

Field plots: The highest germination in field plots (not significantly different from each other) occurred in regularly watered plots (3.2%) and in those with stones added (1.2%). Germination percentages in all other treatments approached zero. In all treatments where germination occurred, most seeds germinated near stones, which provided sites protected from the drying effects of wind and sun.

Conclusions: Germination of S. alaxensis was strongly limited by moisture availability. Watering or surface addition of stones in the field enhanced germination. The addition of fertilizer in pots appeared to have a toxic affect and reduced germination.

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