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Bonanza Creek Experimental Forest Introduction

The Bonanza Creek Experimental Forest (BCEF), located approximately 20 km southwest of Fairbanks, Alaska, was established in 1963 with about 3360 ha (8,300 acres) of upland, interior Alaska boreal forest. In 1969, the experimental forest was enlarged to 5053 ha (12,487 acres) to include representative floodplain forests along the Tanana River. The Forest is within the Tanana Valley State Forest, a unit managed by the Division of Forestry, State of Alaska. In 1987 the Bonanza Creek Long-Term Ecological Research program was established, with BCEF as its primary research site.

The area represents a transect of typical vegetation and landforms in interior Alaska, and includes a section of the Tanana River floodplain at an elevation of approximately 120 m and adjacent uplands. These uplands form the southern limit of the Tanana-Yukon uplands, rising to a ridge crest of 470 m (LTER Clickable Image Map).

The vegetation, a mosaic of forest and non-forest types, corresponds to four broad topographic zones: upland hills and ridges, lowland toeslopes and valley bottoms, old Tanana River terraces, and the active floodplain.

Activities within the area interfering with long-term research plots is restricted through the lease agreement. Research development within the area is managed by BNZ staff. Permission to conduct research can be obtained by contacting the lead principal investigators or the site manager.

The LTER research program at Bonanza Creek Experimental Forest is designed to study ecosystem structure and function through examination of controls over successional processes in taiga forests of interior Alaska. This study tests hypotheses under LTER1 and LTER2 in two successional sequences; three replicates each of six successional stages of primary succession on the floodplain of the Tanana River and four stages of succession following wildfire on south-facing slopes in the uplands.

Experimental Forests

Bonanza Creek Experimental Forest is one of 77 experimental forests, watersheds and ranges in the country. Experimental forests provide protected areas to perform long-term research on Forest Service lands. The first experimental forests established in the 1940s were dedicated to research and demonstration in forest and range management, now experimental forest research encompasses watershed management, wildlife, fire, recreation, ecology.

Bonanza Creek Experimental Forest is unique because it is located on land owned by the State of Alaska. Only two experimental forests in the northwest are also Long-Term Ecological Research sites; Bonanza Creek Experimental Forest and H.J. Andrews Experimental Forest in Blue River, Oregon.

Research has been conducted at Bonanza Creek Experimental Forest for over 40 years through partnership with the State of Alaska, University of Alaska Fairbanks, National Science Foundation and the USDA forest service.

Research at Bonanza Creek Experimental Forest

Past and current research

Research activity within the area began even before formal establishment of the Experimental Forest. See the Bonanza Creek LTER bibliography for a complete listing of research publications resulting from work in BCEF. Much of the early research was conducted by scientists from the Institute of Northern Forestry (INF; now Boreal Ecology Cooperative Research Unit), Pacific Northwest Research Station. Early research by Gregory on white spruce seed production began in 1958, and was continued by Zasada from 1969 through 1984. From 1957 until 1966, Gregory and other INF personnel conducted destructive sampling and stem analysis for the development of growth and yield tables for white spruce, aspen, and birch. Both floodplain and upland stands within BCEF were used extensively. Zasada established demonstration plots for different silvicultural systems on an upland white spruce site in 1972, and with others, considered various aspects of natural regeneration including seedfall, seedling survival, density and growth, nutrient status, and competition. 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 by Wolff to include red squirrel response to various silvicultural treatments.

Between 1964 and 1967, Heilman, University of Alaska, conducted studies of nutrient relationships in birch and black spruce stands on north-facing slopes in BCEF. This work was expanded on by Van Cleve, University of Alaska, to include above and below-ground biomass and nutrient cycling in white spruce and birch stands on all aspects. Viereck, Foote, and others have utilized numerous permanent plots to study species composition, successional relationships, and soil temperature fluctuations. BCEF has been used extensively in the study of forest insect biology and management. Research by Werner, Beckwith, and others has focused on the spruce and Ips beetles, large aspen tortrix, spear-marked black moth, and the larch bud moth.

More recently BCEF has been the site of studies of floodplain soil moisture dynamics and formation of salt crust on freshly-deposited alluvium (Salt Affected Soils), forest reestablishment following wildfire (Rosie Creek Burn), insect and disease dynamics following wildfire, and tree species provenence tests. In 1987, BCEF joined the network of Long-term Ecological Research (LTER) sites, studying successional processes in the well represented taiga forests at the Experimental Forest (LTER1 and LTER2). In 1996, the Institute of Northern Forestry was closed and the Boreal Ecology Cooperative Research Unit (BECRU), PNW Research Station, established.

Many of these projects are described more fully in the Bonanza Creek LTER data catalog. Project details and datasets are archived and generally are available for secondary use.

Research accomplishments

Research at the BNZ LTER site has contributed substantively to understanding the relationship between "independent" state factors and internal ecosystem dynamics in causing successional change in the boreal forest of Alaska. Major findings of the program are: Species effects are strong in the boreal forest; Successional changes in species composition are not a simple consequence of changes in competitive balance but involve species-driven changes in biogeochemistry and the physical environment; Vertebrate herbivores are a powerful force driving successional change through their effects on plant competitive interactions and biogeochemistry; Succession influences exchanges of CH4, CO2, water, and energy in ways that could feed back to climate. This research on succession raises important questions about the broader regional context in which succession occurs. The current phase of LTER addresses the question: How do changes in climate and disturbance regime alter the functioning of the Alaskan boreal forest?

Vegetation of Bonanza Creek Experimental Forest

The taiga forest of Alaska, part of the circumpolar band of boreal forest, consists of a mosaic of forest, grassland, shrubs, bogs, and alpine tundra that have formed primarily as a result of slope, aspect, elevation, parent material, and succession following disturbance. In interior Alaska the forest is dominated by young stands in various stages of succession; mature stands of over 200 years in age are rare due to frequent fire. In areas relatively protected from fires such as the river floodplains, 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. Unlike many areas of the world, successional sequences developing after human disturbances are relatively rare and recent.

Upland forest types vary from highly productive aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh), and white spruce (Picea glauca (Moench.) Voss) stands on south-facing, well-drained slopes to permafrost and moss-dominated black spruce (Picea mariana (Mill.) B.S.P.) forests of low productivity on north-facing slopes, lowlands, and lower slopes. Floodplain forests of balsam poplar (Populus balsamifera L.) 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. Approximately 32%, or 42,800,000 ha, of the total 137,000,000 ha that make up interior Alaska is forested. Forest land that is considered of commercial value totals about 9,600,000 ha.

• Vegetation cover map   


• Bonanza Creek LTER Species Lists

Successional stages and turning points

We selected "turning points" in the succession sequences where, within a relatively short interval, critical changes in ecosystem structure are accompanied by functional changes which have far-reaching effects on ecosystem development. At six turning points in the floodplain succession and three turning points in the upland succession three replicates of experimental plots were established for experimental projects and to follow the natural changes occurring in ecosystem structure and function.

The trajectory of succession is sensitive to environment, propagule availability, legacies associated with prefire vegetation, and disturbance severity. Primary succession predominates in the active floodplain. After initial establishment, competition, facilitation, and herbivory interact to drive successional. Ecosystem controls change at key turning points (thresholds), where a shift in dominance of plant functional types radically alters the physical and chemical environment that govern ecosystem processes and disturbance probability. In the floodplain, intense herbivory by moose initially constrains canopy development, creating an ecosystem dominated by physical controls over soil water movement, surface evaporation and gypsum accumulation at the soil surface. Colonization by alder shifts the system from physical to biological control, adds 60-70% of the nitrogen that accumulates during succession, and causes herbivory to change from a deterrent to an accelerator of succession by eliminating palatable early successional species. Other key turning points include (1) a shift to balsam poplar dominance, where changes in productive potential and litter chemistry enhance NPP and nitrogen cycling rates and (2) the shift to white spruce dominance, where mosses grow rapidly in the absence of smothering broadleaved litter, reduce nutrient cycling rates by sequestering nutrients in low-quality litter, and increase fire probability by producing resinous fuels that dry quickly. In late-successional black spruce stands, root turnover governs nutrient supply.

Secondary succession is the rule in the uplands. Self-replacement, in which the prefire tree species returns to dominance shortly after fire, generally occurs in extreme environments, whereas succession with multiple stages is more common in intermediate sites. Late-successional conifers establish during the initial 1-2 decades after fire, but their establishment success is sensitive to the depth of the organic mat remaining after fire, understory species composition, and seed availability from on-site serotinous cones (black spruce) or off-site seed sources (white spruce). Variations in fire frequency or severity can alter plant regeneration feedbacks that stabilize community composition and cause rapid shifts in forest cover types. Changes in any of these processes could alter vegetation composition and successional trajectory.

Plot Layout

At each of the sites in Bonanza Creek Experimental Forest a 50x60 meter permanent "control plot" was established to provide a control for experiments and to monitor vegetation change. Within each control plot 20 vegetation plots are measured.

Each vegetation plot consists of a 1 m2 plot for measurement of herb, lichen, moss, and low shrub cover estimates, and a 4 m2 plot for measurement of shrubs and tree seedlings (vegplot.ai). In addition all trees and shrubs having a breast height diameter of 2.5 cm or larger are tagged and mapped. Ten trees of each species within the reference stand are also equipped with band dendrometers for measuring annual diameter growth at breast height. In young successional stands the vegetation plots are monitored every two years; in mature types they are monitored every five years. In addition, litter trays have been placed in each reference stand and seed traps in one of each of the eight successional stages. At four points around the perimeter of each reference stand the forest floor and mineral soil profile was described and sampled using standard procedures. Bulk samples of both materials were obtained for physical and chemical analysis. These assessments are repeated at 10-year intervals.

Climate at Bonanza Creek Experimental Forest

Interior Alaskan forests are part of the circumpolar band of boreal forests. Interior Alaska is bounded on the south by the Alaska Range and on the north by the Brooks Range, mountains that provide an effective barrier to coastal air masses. As a result, the climate is strongly continental with cold winters and warm relatively dry summers. These forests are also unique for their association with an environment characterized by drastic seasonal fluctuation in day length (more than 21 hours on June 21 and less than 3 hours on December 21). Temperature ranges from extremes of -50°C in January to over +33°C in July, with a short growing season (100 days or less). The average annual precipitation is only 269 mm, 30% of which falls as snow. Snow covers the ground from mid-October until mid- to late April, and maximum accumulation averages 75-100 cm. Soil temperatures are consistently low.

One characteristic of the continental climate of interior Alaska is the wide range of air temperatures that occur between summer and winter and the large fluctuations around the means. Mean annual temperatures in the Tanana valley area average between -2 oC and -5 oC with the long-term average at the Fairbanks International Airport being -3.1 oC. The warmest month, July, averages 16.3 oC whereas in January the average is a cold -23.5 oC. Periods of extreme cold ranging in the vicinity of -40 oC to -45 °C can occur at any time from late November through February. In contrast, daily maximum temperatures may occasionally reach into 35 oC to 37 oC in June and July, often with only modest night cooling because of the persisting daylight.

Annual precipitation in interior Alaska is low, from 250 to 500 mm, with a 50-year average for Fairbanks of 287 mm. About 35 percent of precipitation falls as snow between October and April. Summer and winter precipitation is generated from major frontal systems that cross the State, but convection storms that produce abundant lightning add significantly to the summer precipitation. Although precipitation amounts during the growing season may below, evaporation rates are also low because of the relative short growing season and cool temperatures. Even so, as much as 76 to 100 percent of the summer precipitation may be lost as evapotranspiration.

Study site naming scheme and descriptions

Study sites at Bonanza Creek Experimental Forest are named according to the habitat, successional stage the site was at when the site was established, and the replicate. There are two main naming schemes. In the first the site is described numerically. An example would be site 231 where the 2 indicates a floodplain site, 3 indicates the third successional stage and 1 indicates the first of three replicates. 112 would represent an upland site in the first successional stage and the second of three replicates.

In the second naming scheme the sites are coded according to the following scheme: Habitat (FP=Floodplain, UP=Upland), successional stage (numeric), replicate (A-C). An example using this scheme would be UP3B representing an upland, mid successional site and the second of three replicates. FP5C would represent a floodplain site, advanced in successional sequence and the third of three replicates. A table of the sites is shown below. Clicking on a site name will link you to our study sites database.

Core study sites at Bonanza Creek Experimental Forest are named according to the following scheme: habitat (UP=Upland, FP=Floodplain), the successional stage at time of site establishment (0-5), the replicate (A-C). A numerical scheme has also been used to name these sites. Shown below is a table of the sites, using both naming schemes. Click on a site name to see a detailed description of each site from our study sites database.

The Tanana River

A river of change

The Tanana River floodplain ecosystem is a major focus of the Bonanza Creek Experimental Forest (BCEF) LTER studies. Located in central Alaska (63°-65° N) about 150 to 250 km south of the Arctic Circle, the Tanana River flows northwest from headwaters near the Canadian Border. With a length of nearly 1000 km, the Tanana River is the largest tributary of the Yukon River. Bordered by the Alaska Range to the south and the Yukon-Tanana Upland physiographic province to the north (Wahrhaftig 1965), the Tanana River valley lowland covers 17,400 km2. The Tanana River occupies a structurally-controlled basin extending below sea level and is filled by Tertiary and Quaternary fluvial/glaciofluvial deposits as much as 100 to 250 m thick (Pewe and Reger 1983).

Geomorphic Development

Early geological history of the Tanana River was summarized by Collins (1990). During the Delta Glaciation of the late Pleistocene, the increased discharge and sediment load from the glaciers of the Alaska Range caused the Tanana River and its tributaries to aggrade rapidly, damming the lower reaches of several valleys of the Yukon-Tanana Uplands. A period of downcutting by the Tanana followed the end of the Delta Glaciation, forming an upper terrace. During the Donnelly Glaciation, the Tanana River once again aggraded; the resulting floodplain was not built up as high as during the Delta Glaciation. Following the end of the Donnelly Glaciation, the Tanana cut down again, forming a second, lower terrace, whose age has been estimated at 10,000 years before presetn (Blackwell 1965).

The recent geological history of the Tanana River is only partially documented. Fluctuating periods of minor aggradation and downcutting are probable; these periods possibly correspond to minor Holocene climatic changes or alpine glaciations (Collins 1990). Documentation of late Quaternary alluviation along the Tanana River is outlined by Mason and Beget (1991) . Illinoian(?) and Wisconsin-aged terraces and meander scars along the Tanana were described by Pewe et al. (1966). Fernald (1965) first suggested that Tanana River alluviation varied throughout the Holocene from studies of terraces in the upper Tanana basin. The Bitters Creek section near Northway recorded high sedimentation rates (1.7 m/1000 yr) during the middle Holocene between 6200+300 BP to 5380+260 BP and lower sedimentation rates after 1600 BP (less than 0.2 m/1000 yr). Stratified archaeological sites along Tanana River tributaries suggest high rates of deposition between 4000-2000 BP and before 1100 BP (Leehan, 1981). Sediment input is related, ultimately, to production in glacial sources in the Alaska Range. Such changes in sedimentation rates presumably reflect changes in the frequency of floods large enough to overtop terraces.

Active and recently abandoned floodplain terraces adjacent to the Bonanza Creek Experimental Forest are only around 3000 years old, based on a series of radiocarbon ages on stratigraphic sections in Luke's Slough (Mason and Beget 1991). Similar ages were found by Mann et al. (199The stratigraphic succession preserves a record of late Holocene alluvial flooding. Two periods witnessed considerably more frequent and larger floods, 3000-2300 yrs ago and from 1600 to 1900 AD. Both are correlative with glacial expansions. The intervening period from 2300 to 400 yrs ago of comparable surface stability on the floodplain recorded frequent fires and soil formation on the terrace which reflects warmer and dryer conditions. Preliminary mapping in the BCEF area of the floodplain confirms this basic chronology and shows that the islands contain floodplain deposits 1000 yrs old. However, most of the islands are considerably younger, less than 400 yrs old.

River Discharge and Floods

About 85% of the discharge of the Tanana River is derived from north-flowing, glacier-fed rivers originating in the Alaska Range. Four large rivers provide about half the total Tanana Discharge, and two of these, the Nabesna and the Delta, lie upstream from the study locale. The south-flowing tributaries from the Yukon-Tanana upland provide only about 15% of the total discharge and all lie upstream from the study locale (Anderson 1970). Baseline data for studies of environmental change along the Tanana River are available from historic records of river activity. Unfortunately the duration of gauged discharge record for the Tanana River and its tributaries is quite short, extending only over portions of the last forty years (Bigelow et al. 1989). On the Tanana River itself, gauging stations were maintained only at Tanacross (1953-present), Big Delta (1948-52, 1953-57), Tok (1950-53, and Nenana (1962 to present). Gauging stations have also been maintained sporadically at eight other locations on tributaries of the Tanana River, with the longest period of record at the Chena River station at Fairbanks (1948 to present).

Reported annual maximum discharge for the Tanana River shows a predictable downriver increase, with upstream discharge recorded at 1107 m3 s-1 (39,100 cfs) near Tanacross building to 3310 m3/s (117,000 cfs) near Nenana in the middle reaches of the river. As is common in arctic rivers (Church 1988), the Tanana varies widely in mean monthly discharge, with minimum values occurring during the lengthy period of low discharge under the winter snow and ice cover and much higher discharges characterizing break-up periods in spring. Stream flow at Nenana in January falls to only 280 m3/s (10,000 cfs) while June discharges are often over 1415 m3/s (50,000 cfs). Ice jams and localized overbank floods are fairly common along tributaries and at some localities along the Tanana River during spring breakup and are associated with a rapid warming over several days (Smith 1978).

The most detailed flood records in the Tanana basin derive from Fairbanks, the largest and oldest settlement in the region. Flood records at Fairbanks refer primarily to the Chena River, a comparatively short south-flowing tributary of the Tanana. Flood stage has reached over 4.5 m above datum in Fairbanks at five times during the last 90 years: in May of 1905, 1911, and 1937, and in August of 1930 and 1967 (Bigelow et al. 1989) The May floods in 1905, 1911 and 1937 were caused by local ice jams (Bigelow et al. 1989, Pewe 1982). Much larger floods have been produced by unusual meteorological events. The 1967 event is the flood of record and peaked at a discharge of almost 10 times greater than the average summer maximum of 212 m3/s (7500 cfs). Downriver, at the Nenana gaging station on the Tanana River, the August 1967 flood had a discharge of 5260 m3/s (186,000 cfs) and a gauge height of 5.76 m. This flood was produced by a series of large rainstorms in August which affected much of the Tanana River basin (Childers et al. 1972). The Tanana and Chena Rivers both flooded and submerged all of Fairbanks and large areas of the floodplain along much of the length of the Tanana River, causing substantial damage along virtually the entire floodplain (Childers et al. 1967). In addition, high precipitation in the Tanana upland produced debris landslide in the Chena River area.

A flood due to rainstorms in May 1948 on the Chena and Tanana Rivers had a discharge at Nenana of 3820 m3/s (135,000 cfs) and a gauge height of 4.85 m, and an estimated discharge of about 680 m3/s (24,200 cfs) on the Chena River (Pewe 1982). Up river from Fairbanks on the Tanana River, small floods occurred at Tanacross during June 1962 and July 1975, elevating discharge about 25% over annual extreme values (Bigelow et al. 1989).

The frequency of large floods has been estimated from the relatively short gauge records of discharge. Collins (1990) used 15 yr of gauging data (1973-1987) from the Tanana River at Fairbanks to calculate a recurrence interval of 333 yr for the 1967 flood. Pewe (1982) suggested that floods as large as that in 1967 have a recurrence interval greater than a century, while the 1948 flood had a recurrence interval of 25 years. Mason and Beget (1991) estimated that large floods occurred every 57 years during the last 400 years; an increase over the timing of floods in the previous millennia that witnessed a large flood every 120 years.

Several generalizations can be made about Tanana valley flooding. While floods are caused by both ice dams during break-up and by high rainfall storms, floods following break-up are usually more restricted in area and size. By far the largest floods are produced by unusual meteorological conditions, i.e., very high rainfall over several days. The two types of flood differ in their ability to transform the landscape because of the occurrence of frozen ground (both annual and permafrost) which protects river banks from erosion during break-up floods. Maximum riverbank erosion in June or July, during periods of high water, is dependent on warmer water temperatures, as at Galena, on the Yukon River (Ashton and Bredthauer 1986).

The sediment yield accompanying particular types of flood also differs considerably. In upland areas around Fairbanks runoff is highest during break-up, April-May, when the ground is still largely frozen (Gieck and Kane 1986). This nival run-off pattern connected to the spring melting of the cumulative snowpack adds very little sediment to the Tanana River, and probably adds little to alluvial terraces. Similarly, flooding induced by ice jams is unlikely to contribute significantly to overbank sedimentation (Smith 1978:335). The catastrophic summer flood is more likely to erode banks, incorporate sediment into suspension and produce overbank deposits. Glacial streams also undergo an annual cycle of flooding connected with the warmth of the summer season which results in the transport of sediment downstream. Infrequent large-scale glacial floods occurring in summer probably contribute a considerable amount of sediment into the Tanana River and its tributaries.

Soils of Bonanza Creek Experimental Forest

Soils description

Parent material, slope, aspect, time and climate have been used to describe the mosaic of soils found in interior Alaska. Soils are uniformly immature reflecting the characteristics of the parent material. They range from poorly-drained cold soils with shallow permafrost to warm well-drained soils in the uplands that support mature white spruce communities. Parent material in the Fairbanks falls into three main categories: (1) bedrock composed of precambrian schist, (2) thick loess deposits originating from glacial periods, and (3) alluvium deposits in floodplain areas. Slope and aspect are critical in the formation of permafrost. North-facing slopes are usually underlain by permafrost, and contrast sharply with the warm, well-drained soils of south-facing slopes. Poorly-drained black spruce flats of interior Alaska are also largely underlain by permafrost formed by a combination of biota, cold climate and topography.

Permafrost

Permafrost is ground that is continuously frozen through at least two successive cold seasons and the intervening summer. Globally, permafrost is found in higher latitudes and elevations, where mean annual soil temperature is below freezing (Brown and Andrews 1982; Young 1989). Nearly one-fourth of the earth's surface is influenced by permafrost (Brown and Andrews 1982). Ice-rich permafrost is commonly impervious to infiltration of water (Young 1989), providing the basis for the "paradox of the arctic," i.e. the abundance of saturated soils and impressive biological productivity of vegetation despite very low annual precipitation. In colder regions such as the North Slope of Alaska, permafrost is "continuous," underlying virtually the entire landscape except beneath large water bodies. In the somewhat warmer subarctic regions such as the taiga of central Alaska, permafrost is discontinuous and is found in locally cold settings (e.g. north-facing slopes and low-lying, poorly drained locales). In interior Alaska, where permafrost is present, temperatures of the upper layers of the permafrost are in the range of -0.5C to -2.0C.

Permafrost presence and the depth of summer thaw (the "active layer") are major controls on vegetation distribution and productivity. In central Alaska, discontinuous permafrost, topographic variations and varying surficial geology result in a mosaic of plant communities, typified by white spruce (Picea glauca), birch (Betula papyrifera) and aspen (Populus tremuloides) stands on south-facing slopes with dry mineral soils with a thin organic horizon (2-10 cm organic layer), and black spruce (Picea mariana) stands on north-facing slopes and in low-lying areas with thick (50-100 cm) organic soils (Viereck et al. 1986). Soil carbon density is high in boreal ecosystems compared to other, warmer systems (Schlesinger 1977; Post et al. 1982). Soil carbon densities reflect the balance between input (organic matter production) and decomposition. In the cold and often water-saturated soils common at high latitudes, decomposition is much reduced and, while primary production is low, soil carbon still accumulates over very long time periods. Thus, there is a positive relationship between the amount of soil organic matter and the amount of permafrost in a watershed.

Permafrost also affects the hydrological regimes of subarctic streams: streams dominated by permafrost are more "flashy," i.e. more extreme, than those relatively permafrost-free (Carlson 1974; Dingman 1973). Snowmelt runoff is later and higher in a permafrost-dominated basin than snowmelt runoff from a permafrost-free basin. Likewise, peak stormflow discharge from a permafrost-dominated basin is much higher than in a non-permafrost stream (Figure 1), but during rain-free periods and in winter, flow is much lower (Haugen et al, 1982). This pattern is a result of the flow-paths of precipitation as it travels to the stream. On permafrost dominated north-facing slopes, precipitation enters the thick organic layer and flows above the permafrost to the stream. On permafrost-free south-facing slopes, precipitation enters the bedrock groundwater, and is released much more slowly to the stream. Differences in discharge result in different patterns of carbon and sediment flux from basins with differing amounts of permafrost, and likely result in different patterns of channel geomorphology and nutrient flux (see below). Thus, the synergistic effects of altered flowpath and organic carbon accumulation combine to make permafrost soils true wetland soils.

As mentioned above, central Alaska is the region of discontinuous permafrost. General circulation models all predict that global warming from increased concentrations of radiatively active gasses will occur earlier and to a larger extent at high latitudes. Because the temperature of permafrost in this area is so close to the melting point, we are at what might be called the "thermal ecotone," that is, the region in which small changes in temperature will have large consequences to ecosystems. Colder regions (i.e. colder than interior Alaska) must experience larger warming increments before permafrost melting occurs. Thus, we believe that interior Alaska is an ideal area to investigate and monitor the potential effects of climate change.

History of Bonanza Creek Experimental Forest

The Bonanza Creek Experimental Forest (BCEF) is a 5053 ha (12,487 acre) research area located approximately 20 km southwest of Fairbanks along the Parks Highway (map). The Forest is within the Tanana Valley State Forest, a unit managed by the Division of Forestry, State of Alaska. The Experimental Forest is leased to the USDA Forest Service, Pacific Northwest Research Station, Boreal Ecology Cooperative Research Unit (formerly Institute of Northern Forestry) for the exclusive purpose of conducting research in forestry. The original 55-year lease on July 1, 1963 established about 3360 ha (8,300 acres) representative of upland forest types. On January 6, 1969, the lease was amended to include representative floodplain forests along the Tanana River.

Existing vegetation types within BCEF strongly reflect three wildfire periods. In the early 1780's, there was one or more major fires that burned through most of what is now BCEF. Evidence for this fire is the relatively uniform stand ages of most mature spruce and spruce-birch stands in the uplands, and ages of black spruce in small patches on the old river terraces. In about 1914 another extensive fire burned through black spruce on old terraces of the Tanana River. East of BCEF the fire burned through large areas in the uplands as well as the flats. Evidence for this fire include the stand origins of about 1914 within the burned areas and fire scars from scattered black spruce that survived the fire. The 8,600 acre 1983 Rosie Creek wildfire burned extensively in the lowlands to the east of BCEF and made a wide run through the uplands within the Experimental Forest, burning through large continous stands of white spruce and paper birch on about 3,400 acres. It reburned through most of the area burned in the 1914 fire.

Research activity within the area began even before formal establishment of the Experimental Forest. Descriptive studies of upland soil profiles were conducted in 1958-1959 by S.A. Wilde and H.H. Krause (See the BNZ bibliography for a complete listing of research publications resulting from work in BCEF). Early research by R.A. Gregory on white spruce seed production began in 1958, and was continued by J.C. Zasada from 1969 through 1984. From 1957 until 1966, Gregory and other INF personnel conducted destructive sampling and stem analysis for the development of growth and yield tables for white spruce, aspen, and birch. Both floodplain and upland stands within BCEF were used extensively. Gregory also studied seasonal cambial activity in white spruce in the late 1960's. Zasada established demonstration plots for different silvicultural systems on an upland white spruce site in 1972, and with others, considered various aspects of natural regeneration including seedfall, seedling survival, density and growth, nutrient status, and competition. 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 by J.O. Wolff to include red squirrel response to various silvicultural treatments. Between 1964 and 1967, P.E. Heilman, University of Alaska, conducted studies of nutrient relationships in birch and black spruce stands on north-facing slopes in BCEF. This work was expanded on by K. Van Cleve, University of Alaska, to include above and below-ground biomass and nutrient cycling in white spruce and birch stands on all aspects. L.A. Viereck, M.J. Foote, and others have utilized numerous permanent plots to study species composition, successional relationships, and soil temperature fluctuations. BCEF has been used extensively in the study of forest insect biology and management. Research by R.A. Werner, R.C. Beckwith, and others has focused on the spruce and Ips beetles, large aspen tortrix, spear-marked black moth, and the larch bud moth.

More recently BCEF has been used for studies of floodplain soil moisture dynamics and formation of salt crust on freshly-deposited alluvium (Salt Affected Soils), forest reestablishment following wildfire (Rosie Creek Burn), insect and disease dynamics following wildfire, and tree species provenence tests. In 1987 BCEF joined the network of Long-term Ecological Research (LTER) sites, studying successional processes in the well represented taiga forests at the Experimental Forest (LTER1 and LTER2).

** References cited can be found in the Bonanza Creek LTER bibliography