Alaska Boreal Interior
Alaska Boreal Interior
The Alaska Boreal Interior ecoregion occupies Interior Alaska between the Brooks Range in the north and the Alaska Range in the south. The ecoregion extends from the Yukon-Kuskokwim Delta and the eastern and northern shores of Norton Sound to the Old Crow Basin in northwestern Yukon Territory. The ecoregion includes lands southeast to include the lowlands of the Tanana River, and northwest to the lower reaches of the Kobuk River. The upper reaches of rivers draining the northern part of the watershed for Bristol Bay in southwestern Alaska are included in the Alaska Boreal Interior ecoregion. The major rivers of interior Alaska drain into or are fully within (Kuskokwim) this ecoregion.
The ecoregion has a continental climate, with short, warm summers and long, very cold winters. Because the ecoregion is so large, there is much variation in temperature and precipitation from west to east. Total annual rain and snow generally increase with elevation. Temperature, while affected by elevation, is also influenced by distance from the ocean; maximum summer temperatures increase from west to east, and minimum winter temperatures decrease in the same pattern. Accordingly, variation in diurnal temperature increases from west to east.
Mean annual precipitation over most of the region ranges from 250 mm to 550 mm, with contribution from snowfall averaging from 125 cm to 205 cm. Most precipita- tion occurs during summer, mainly as a result of convective storms. Snow covers the landscape for half the year, lingering at higher altitudes, on north-facing slopes, and on shaded aspects. Average minimum winter temperatures vary from -18°C in the west to -35°C in the east; average maximum winter temperatures vary from -11°C in the west to -22°C in the east. Strong, stable temperature inversions are common in winter due to low sun angle and corresponding long-wave radiation cooling. Summer temperatures, averaging a minimum of 8°C to 11°C and a maximum of 17°C to 22°C, have less regional variation than winter temperatures. At lower elevations, temperatures usually remain above freezing from June through mid-September.
The Interior Forested Lowlands and Uplands Ecoregion consists of rolling lowlands, dissected plateaus, and rounded low to high hills. Most of the region lies between elevations from sea level to 500 m, but some hills rise over 700 m. Slope gradients are generally from 0° to 5°. The predominant geologic formations are derived from Mesozoic and Paleozoic sedimentary rocks, but extensive areas of volcanic deposits also occur. The region is surficially mantled by undifferentiated alluvium and slope deposits. There is little exposure of bedrock. Streams originating from within the ecoregion tend to be short, with the larger and longer streams originating from adjacent glaciated mountainous regions. Although thaw lakes and oxbow lakes occur throughout the ecoregion, lakes are not a predominant landscape feature. The western portion of the ecoregion is underlain by thin to moderately thick permafrost, and the eastern portion has a discontinuous distribution of permafrost. The region was not glaciated during the Pleistocene epoch.
Dominant soils of this ecoregion are Histic Pergelic Cryaquepts, Pergelic Cryaquepts, Aquic Cryochrepts, Pergelic Cryochrepts, Typic Cryochrepts, Typic Cryorthents, and Pergelic Cryumbrepts. Many upland soils were formed in silty, micaceous loess and colluvial material. Where mantles of loess are lacking, upland soils formed in stone and gravel weathered from local rock. Lowland soils were formed in silty alluvium and loess derived from the floodplains of large rivers. Soils are generally shallow, often overlying ice-rich permafrost. Those soils with permafrost, especially in the eastern portion of the ecoregion, are very susceptible to alteration upon disturbance of the organic mat. This is due to the relatively warm (>-1.5°C) permafrost tem- perature. Organic mat disturbance, as by wildfire, can result in warmer soil temperatures, lowered permafrost tables, and significant changes in soil physical properties and hydrology.