by Sue Bishop
Originally published by the Society for Ecological Restoration—Northwest Chapter, November 2021.
Oil and gas exploration in northern Alaska began in the 1960’s, and the first discovery of oil in the Prudhoe Bay field was announced in March 1968. The Trans-Alaska Pipeline System was constructed during 1975–1977, to bring the oil to the tidewater port at Valdez, 800 miles south on the coast of Alaska. The first oil flowed through the pipeline in June 1977 and took about 30 days to reach Valdez.
ABR, Inc.—Environmental Research & Services has been involved in research, planning, and implementation for land rehabilitation in Prudhoe Bay and other North Slope oilfields since the early 1980s. For most of the sites we’ve worked at, complete restoration to pre-disturbance conditions is not a realistic goal, due to the nature of the disturbances and the harsh environmental conditions. We tend to focus more on rehabilitation, i.e., promoting the development of a stable, self-sustaining community of indigenous plants, although typically not the same community that existed before the disturbance.
Disturbance types within the oilfields that may require rehabilitation include gravel roads and pads (intact, partially, or completely removed), excavations (intact or backfilled), spills (petroleum, seawater, chemicals), off-road vehicle traffic (intentional or accidental), and tundra affected by the removal of ice roads and pads. In some cases (e.g., intact gravel pads), the original tundra vegetation has been completely lost, and the new substrate provides very different conditions. In other cases (e.g., disturbance by off-road traffic), the surviving tundra vegetation may be capable of recovery.
Northern Alaska is a challenging environment for land rehabilitation or restoration, for several reasons:
The North Slope is in the zone of continuous permafrost, meaning that any disturbance may result in thawing of the frozen soil and loss of surface stability. In some areas the soil may contain well over 50% ice by volume, so thawing can lead to dramatic changes in site conditions.
The growing season is short (about 2 months) and cool, resulting in slow plant growth. The short, cool summer also limits the rate at which dead plant matter decomposes, leading to low soil nutrient levels.
There are no commercial sources for plant materials native to the region.
Heavy grazing, primarily by flocks of temporarily flightless geese, limits plant growth at some rehabilitated sites.
Until recently, northern Alaska has been largely free of non-native, potentially invasive plant species. As the climate warms, there is increased concern that invasive species may be more likely to survive in the Arctic if they are inadvertently introduced.
The logistics of land rehabilitation projects in the Arctic can be difficult for a number of reasons, including; Lack of road access to many sites, limited communication (e.g., no internet and/or cell phone coverage), short season for fieldwork, weather (frosts or snow can occur even in summer), and wildlife (bear safety is a concern at many locations).
Early revegetation projects in the oilfields relied on cultivars of native grasses that were developed for the purpose, but we no longer recommend this approach in most situations, for several reasons:
The grass cultivars require relatively high nutrient levels, so live cover typically begins to decline after 5–7 years unless fertilizer application is repeated. At most sites, periodic fertilization is not a realistic option.
Most natural tundra communities are dominated by sedges and/or shrubs, rather than grasses.
There is some evidence that a heavy cover of grass (living and/or dead) may inhibit natural colonization by indigenous tundra plants, by preventing seeds from reaching the soil surface, intercepting precipitation, or competing for water or nutrients in the soil.
Commercial seed mixes may be contaminated with seed of non-native, potentially invasive species.
Much of our work in the past several decades has focused on developing plant cultivation techniques for sites in the North Slope oilfield that promote the recovery or establishment of communities dominated by indigenous tundra plants. Several of these techniques are described below.
Natural Colonization—Natural colonization (with or without the addition of fertilizer) may be appropriate for sites with considerable surviving vegetation (e.g. minor damage from off-road traffic or a spill site where impacts are not severe). We also typically recommend natural colonization for narrow, linear disturbances (e.g. backfilled trenches) where there is good potential for both seed input and vegetative spread from the adjacent tundra.
Fertilize Adjacent Tundra—This treatment may promote seed production in the adjacent tundra, resulting in higher seed input to the disturbed site. It is only recommended for sites where the adjacent tundra contains species that are both 1) adapted to the conditions in the disturbed area and 2) likely to increase seed production in response to the added nutrients (e.g. wetland sedges adjacent to a moist or wet site). Fertilizer is not added to flooded areas where it might enter ponds or streams.
Seed or Transplant Wetland Sedges—Wetland sedges are dominants in many tundra plant communities, so re-establishing them is a priority on sites with suitable hydrology and soil conditions. Seed must be hand collected, typically in the season before sowing, to allow time for cleaning and germination testing. Alternatively, tundra plugs can be harvested from nearby natural stands and transplanted onto the rehabilitation site. This technique is somewhat labor intensive, but we have had good success with it where conditions are favorable. The impact to the source population is minimal in wet tundra, if the harvest rate is limited to one plug per square meter or less. The plugs are typically dominated by Carex aquatilis and/or Eriophorum angustifolium, with a few forbs and the occasional willow.
Seed Native Forbs—Some sites (e.g. gravel pads, road embankments) provide soil and hydrologic conditions that are completely different from the surrounding tundra. Plants that are adapted to similar habitats include legumes and other forbs that occur naturally on riparian gravel bars. The legumes have the additional advantage of potentially contributing nitrogen to the soil that may benefit natural colonizers. Occasionally, seed of some of these species is available from the Alaska Plant Materials Center, but for the most part we hand collect seed from nearby natural populations. Over the winter we send the seed to the PMC to be cleaned and germination tested, in preparation for sowing the following summer. Species we’ve successfully seeded on rehabilitated sites include Artemisia arctica, A. borealis, Chamerion latifolium, and the legumes Astragalus alpinum, Oxytropis borealis, and O. deflexa.
Seed salt-tolerant species—Some sites within the oilfields that need rehabilitation have elevated soil salinity, due to either the residual effects of a spill or naturally occurring salts. This is a coastal area, so there are natural populations of species that are adapted to moderately high soil salinity. We have had some success with seeding several of them, including the sedge Carex maritima, the grass Puccinellia angustata, and the forb Cochlearia officinalis.
Transplant willow cuttings—Shrubs are a desirable addition at many rehabilitated sites to increase species diversity, enhance habitat value for wildlife, and/or help to stabilize slopes or shorelines. We have primarily focused on willows, as they are relatively easy to harvest and transplant and can survive well as long as soil moisture is adequate. Cuttings may be harvested either in the spring before they break dormancy or in the fall after the leaves have dropped. However, the cuttings cannot be planted in the spring as the soil remains frozen well into June. We prefer to harvest and transplant in the fall to avoid storing the cuttings over the winter.
Transplant aquatic plants—At locations where shallow flooding is expected, often due to thawing of permafrost, the rehabilitation objective may be to establish emergent aquatic vegetation. Early revegetation researchers in Alaska selected the emergent grass Arctophila fulva for this purpose and developed a technique that involves separating individual tillers before planting. We have continued to use Arctophila but have found that transplanting clumps (or plugs) is less labor-intensive and more successful. This species is capable of spreading rapidly once it’s established; we often find that after a few years, Arctophila is still present at the site but is no longer exactly where we planted it.
Tundra sod—Harvesting and transplanting blocks of intact tundra is labor-intensive and costly, but highly effective rehabilitation; this technique is typically reserved for use at high-priority sites. It provides both instant vegetation cover with a natural tundra community and thermal protection for the underlying permafrost. This technique is an option only if a source of sod is available that would otherwise be destroyed (e.g., expansion of a gravel mine). This innovative approach to tundra restoration is discussed in detail in the accompanying article “Restoration of Disturbed Sites in Northern Alaska using Tundra Sod."