Tactic TR-2: Extending the Growing Season
Extending the period during which soil is thawed increases the amount of microbial degradation of hydrocarbons that can occur in a given year. Extending the growing season can also enhance plant growth, but plant mortality can result if sprouting begins too early in the spring while air temperatures are still well below freezing.
The following techniques can be used to extend the growing season:
Early spring snow removal to degrade hydrocarbons: Scraping snow off the tundra surface (Tactic CR-3) in April or May will initiate soil thawing and promote the onset of microbial activity 30 to 60 days earlier than under natural conditions (Figs. 71–72). Also, solar radiation levels in the Arctic typically are highest during this period, and exposure to sunlight will promote the photochemical degradation of hydrocarbons remaining on the ground surface. Snow can be removed by hand from small areas or with heavy equipment as long as the ground is frozen. Leave enough snow in place to prevent physical damage to the tundra surface.
Early spring snow removal to enhance vegetation growth: Scraping most of the snow off the tundra surface (Tactic CR-3) will speed soil thawing and promote vegetation growth (Fig. 73). If snow is removed too early, however, plants will sprout while air temperatures are still well below freezing, which will likely result in plant mortality. Snow removal is most beneficial to plants at sites covered by large drifts or by snow piles resulting from routine snow removal. If not removed, these areas of deep snow can delay soil thawing until late June or July, strongly limiting plant growth. Snow can be removed by hand from small areas or with heavy equipment as long as the ground is frozen. Leave enough snow in place to prevent physical damage to the tundra surface.
Snow fencing: Snow fencing will keep snowdrifts off sites and speed spring thawing, thus promoting soil microbial activity and plant growth (Figs. 74 and 75). Snow fencing should be approximately 4–8 feet high, and must be placed PPRendicular to the prevailing winds and secured with guy wires. Place one fence within several feet of the site, and stagger 2 or 3 additional rows of fencing behind it at 30- to 50-foot intervals. The length of the fences depends on the size of the site.
Tenting: A tent can be constructed to create a snow-free, heated environment to enhance microbial activity (Fig. 76). Tenting is not necessary for enhancing plant growth. This tactic can be used during spring, summer, and fall. A low tent made with clear polyethylene sheeting and lumber or metal frame can be inflated, heated, and ventilated with a forced-air heater unit.
Considerations and Limitations
- When enhancing microbial activity and plant growth are dual goals, consider the trade-off between promoting early onset of microbial activity and the risk of plant mortality if sprouting occurs too early in the season.
- Snow removal in early spring may limit the water supply on site early in the growing season. Irrigation (Tactic TR-4) may be required during the growing season to compensate.
- Snow fencing left in place for more than a few growing seasons may change the plant communities impacted by the drifts, by repeatedly delaying the onset of the growing season, and by creating wetter conditions resulting from the melting snow.
- Tents and snow fences may require maintenance because of winds.
- Temperature and light levels in tented areas should be similar to natural growing-season conditions.
Equipment, Materials, and Personnel
- Plastic snow fencing (available in 4-foot-wide rolls) (2 to 3 people to install) – stretch sheets between steel poles to block snow drifts.
- Steel poles and means of installation (2 to 3 workers) – to support plastic snow fencing.
- Wire and stakes (2 workers to set up, 1 worker to maintain) – to stabilize snow fences.
- Polyethylene and metal or lumber frame material (3 to 6 workers to build, 1 to 2 workers to maintain) – construction materials for tent.
- Forced-air heater (2 workers to install, 1 worker to maintain) – to provide heat and ventilation, and inflate tent.