The Caribou-Poker Creeks Research Watershed (CPCRW) is a relatively pristine, 104 km2, basin reserved for meteorologic, hydrologic, and ecologic research, with no current human influence (other than scientific research). The Institute of Northern Forestry has been collecting climate and hydrology data since 1969, as well as ecological studies on a more sporadic schedule. The data collection infrastructure has recently been upgraded from analog (e.g. paper charts) to digital (e.g. solid-state dataloggers) instrumentation. In addition, access to the watershed has been upgraded by the construction of a bridge across the Chatanika River, completed on 5 August 1995. There is a rustic field camp with accommodations for sleeping and eating, and field laboratory with a generator for line power. See History of CPCRW for more details.
The CPCRW is unique among such research areas in the United States in that it is the only one in the zone of discontinuous permafrost, which comprises a large portion of the state of Alaska, including most of interior Alaska. It is fairly representative of upland headwater stream basins in subarctic Alaska. The hydrology of CPCRW is a major driver of the aquatic ecology and biogeochemistry of the basin, while events in the terrestrial portions of the watersheds set the stage. Hydro-biological research in CPCRW has several major thrusts: to assess the role of disturbance in the terrestrial landscape (e.g. wildfire, herbivory, logging) on subarctic stream ecosystems, to assess the influence of discontinuous permafrost on fresh water ecology, and to assess the validity of the River Continuum concept in a subarctic context.
The mosaic of plant communities found in the subarctic biome is structured by a number of ecological processes. Wildfire is common in the subarctic uplands, and is the primary reset mechanism for forest succession in terrestrial upland ecosystems. In the lowland floodplains, the meandering of large rivers exposes silt bars which are then colonized by shrubs and trees, initiating primary forest succession. Local conditions such as hydrology, topography and microclimate determine the path and rate of forest succession in both floodplains and uplands. Superimposed on this forest mosaic are insect and mammalian herbivores that can influence ecosystem properties such as palatability and decomposability of leaves and leaf litter, and indeed can restructure forest succession (e.g. massive tree mortality caused by spruce bark beetles). CPCRW does not contain the full range of these forest types and ages: stand-initiating fires, and perhaps some logging by early settlers, since the turn of the century have resulted in young (i.e. 60-90 year old) stands of birch and aspen on south facing slopes, while older uneven aged (e.g. up to 200 year) black spruce stands dominate on north facing slopes. White spruce may be under-represented. Stream valley bottoms are generally treeless. Moose and beaver are common in CPCRW, so it is likely that there are patches of herbivore-impacted vegetation. The tops of the peaks and ridges provide near-alpine habitat.
Permafrost is discontinuously distributed within CPCRW, determined by low sun angle at high latitude, local topography, and successional status. The permafrost mosaic of the surrounding taiga forest uplands exerts a powerful influence over hydrological patterns within the watershed. Stream flow is a mixture of highly variable shallow subsurface storm runoff events from permafrost dominated areas and consistent groundwater base flows from permafrost free areas. In addition to physical effects on stream ecology, these two distinct flow regimes have divergent influences on stream biogeochemistry with important ramifications for food webs. Permafrost here may be sensitive to global climate change because of its position close to the southern limit of permafrost in Alaska. In CPCRW, there are first order streams with a range of 4% to 55% of their catchments underlain by permafrost, allowing tests of a number of hypotheses of permafrost effects on stream ecosystems, including patterns of concentrations and export of carbon, nutrients and sediment.