Bonanza Creek Experimental Forest & Caribou-Poker Creeks Research Watershed

Climate

The climate in interior Alaska is strongly continental, with cold winters and warm, relatively dry summers; it is characterized by drastic seasonal fluctuation in day length (> 21 hours on June 21 and < 3 hours on December 21). Mean annual temperatures in the Tanana Valley area average between -2 and -5 °C. July temperatures average 16.3 °C, whereas in January the average is -23.5 °C. Periods of extreme cold in the vicinity of -40 to -45 °C can occur at any time from late November through February. Daily maximum temperatures occasionally reach 35 to 37 °C in June and July, often with only modest night cooling because of the persisting daylight. The growing season is short (100 days or less).

Annual precipitation in interior Alaska is 250 to 500 mm. About 35 percent of this precipitation falls between October and April as snow. Although precipitation amounts during the growing season may be low, evaporation rates are also low because of the relatively short growing season and cool temperatures. Even so, as much as 75 to 100 percent of the summer precipitation may be lost as evapotranspiration. Snow covers the ground from mid-October until mid- to late April, and maximum accumulation averages 75 to100 cm. Soil temperatures are consistently low.

Soils

In this area of Alaska, soils are uniformly immature and range from cold poorly drained soils with shallow permafrost to warm well-drained soils in the uplands that support mature white spruce communities. Parent material falls into three main categories: (1) bedrock composed of Precambrian schist, (2) thick loess deposits originating from glacial periods, and (3) alluvial deposits in flood plains. Slope and aspect are critical in the formation of permafrost. North-facing slopes are usually underlain by permafrost, contrasting sharply with south-Bonanza Creek Experimental Forest/Caribou-Poker Creeks Research Watershed (Alaska) facing slopes and their warm, well-drained soils. Poorly drained black spruce flats of interior Alaska are also largely underlain by permafrost.

Vegetation

The taiga forest of Alaska consists of a mosaic of forest, grassland, shrubs, bogs, and alpine tundra. The forest is dominated by young stands in various stages of succession; mature stands more than 200 years old are rare due to frequent fires. In areas relatively protected from fires, such as the river flood plains, the active erosion and meandering of the silt-laden, glacially fed rivers results in the active production of newly vegetated silt bars and the rapid erosion of older, mature stands.

Upland forest types range from highly productive aspen, paper birch, and white spruce stands on well-drained, south-facing slopes to permafrost and moss-dominated black spruce forests of low productivity on north-facing slopes, lowlands, and lower slopes. Flood plain forests of balsam poplar and white spruce are productive on recently formed river alluvium where permafrost is absent, but slow-growing black spruce and bogs occupy the older terraces that are underlain by permafrost.

Bonanza Creek Experimental Forest

USDA Forest Service Pacific Northwest Research Station

University of Fairbanks Alaska

P.O. Box 756780

Fairbanks, AK 99775-6780

Research, Historical & Present

Much of the early Forest Service research in Alaska was conducted by scientists from the Pacific Northwest Forest and Range Experiment Station’s Institute of Northern Forestry (INF). Early research on white spruce seed production began in 1958 and continued through 1992. From 1957 until 1966, INF personnel conducted destructive sampling and stem analysis for the development of growth and yield tables for white spruce, aspen, and birch. Both flood plain and upland stands within Bonanza Creek were used extensively. Demonstration plots were established for different silvicultural systems on an upland white spruce site in 1972, and various aspects of natural regeneration (including seedfall, seedling survival, density and growth, nutrient status, and competition) also were evaluated. Sprout and sap production in birch stands has also been studied. Beginning in 1962, INF and the University of Alaska cooperated in studies of the effects of red squirrel foraging on white spruce cone and seed production. This work was later expanded to include the red squirrel response to various silvicultural treatments.

Between 1964 and 1967, nutrient relationships in birch and black spruce stands on north-facing slopes were studied at Bonanza Creek. This work was expanded to include above- and below-ground biomass and nutrient cycling in white spruce and birch stands on slopes of all aspects. Numerous permanent plots have been used to study species composition, successional relationships, and soil temperature fluctuations. Research has also focused on the spruce and Ips beetles, large aspen tortrix, spear-marked black moth, and the larch bud moth. More recently, Bonanza Creek has been the site of studies of flood plain soil moisture dynamics and formation of salt crust on freshly deposited alluvium, forest reestablishment and insect and disease dynamics following wildfire, and tree-species provenance tests.

Research at Caribou-Poker Creeks in recent years has examined the performance of electrical resistivity, ground penetrating radar, and transient electromagnetic surveys to determine subsurface conditions. Hydrologic monitoring has been essential in developing a computer model capable of predicting runoff rates and volumes from watersheds with permafrost distribution ranging from 2 to 53 percent. An experimental oil spill conducted in the mid-1970s has provided critically valuable data demonstrating natural degradation processes following oil spills on thick organic soils and continues to provide information on vegetation recovery and the natural resilience of subarctic forests.

Research Opportunities

Research topics at the Bonanza Creek LTER site vary widely, with 30 principal investigators listed in the current proposal.

Lat. 64° 8' N, long. 148° 0' W (BNEF)

Lat. 65° 16' N, long. 147° 5' W (CPCRW)

There are climate data for both Bonanza Creek and Caribou-Poker Creeks. The Bonanza Creek LTER also has a long-term vegetation data base. There are data for all LTER successional control sites, including tree-growth measurements, litter collections, seedfall counts, seedling establishment; thaw depth (permafrost), and 15- and 30- year records for thaw depth after fire, as well as archived soil samples and archived herbarium specimens and snow-course measurements. All data from the LTER site are cataloged at www.lter.uaf.edu.