Survival and growth of transplanted felt-leaf willow Salix alaxensis seedlings on an abandoned gravel pad at Toolik Lake, Alaska, USA

  • 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


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 the survival and growth of transplanted willow seedlings.

Study site: The study was undertaken in the vicinity of an abandoned gravel pad (site of a former construction site) in the Toolik Lake area (68º40'N, 149º40'W) in Artic Alaska, USA.

Seedling cultivation and transplanting: S.alaxensis catkins were collected near Toolik Lake in late June 1984. Seeds were separated from the catkins, sealed in plastic containers and frozen for c. 8 months. Seedlings were grown at the Alaska State Forest Nursery (Eagle River) and transplanted to the gravel pad after 4 months, each planted in a hole about 20 cm in diameter and 15 cm deep. Seedlings were watered (1 L each) at planting and approximately every 3 days for 2 weeks subsequently.

Experimental design: Fertilizer and water treatments were applied. Both fertilized and control plants were grown in three water treatments. In the wet treatment, the hole was lined with plastic sheeting before the soil was replaced at planting. In the control (mesic) treatment, the original soil was replaced around the seedlings. In the dry treatment, coarse sand was substituted for the original soil. Each fertilized seedling received 5 g NPK fertilizer (18% N, 18% P2O5, 18% K20) at the time of planting.

Treatments were assigned in a randomized block, with 20 replicate blocks. Numbers of surviving seeds were compared among treatments.

Seedling growth: To record the effects of treatments on seedling growth, seedlings were harvested near the end of the second growing season in August 1986. Roots were washed of soil, and seedlings divided into root, stem and leaf tissue. Leaves were counted, and length of the longest leaf measured. Tissues were oven-dried at 60°C and weighed, samples were analysed for N and P.

Survival of willow seedlings to the end of the second growing season varied from 50 to 85%, but treatment differences were not statistically significant. The unaltered gravel pad soil supplied sufficient water and nutrients for seedling survival.

Leaf and stem biomass were higher in fertilized seedlings than in controls, but root biomass was not. This larger leaf biomass was due to the production of larger, rather than more, leaves. Longest leaf length was significantly increased by fertilizer addition (e.g. 41-42 mm in dry and mesic plots, compared to 33-36 mm in corresponding controls), but number of leaves per seedling was not. The lack of response to fertilizer by roots may be an artifact of large amounts of root tissue produced before transplanting.

Concentrations of N and P in leaves were significantly higher in fertilized seedlings indicating that nutrient uptake increased more in response to added nutrients than did growth. Leaf biomass and number of leaves were significantly lower in the wet than in the dry treatment, while values for the mesic treatment did not differ from either of the others.

Maximum leaf length was higher in the mesic than in the wet treatment, with intermediate values in the dry treatment. Overall, there was little difference between the dry and mesic treatments, but both size and number of leaves were significantly reduced in the wet treatment. Possibly the wetter soil remained frozen later in the spring, reducing the effective length of the growing season.

Conclusions: The availability of water and nutrients in the gravel pad soil did not limit the survival of established seedlings of S. alaxensis. The addition of NPK fertilizer increased growth of transplanted seedlings to the end of the second growing season.

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