ALBERT

Description: Forest biomass, rates of production, and carbon dynamics are a function of climate, plant species present, and the structure of the soil organic and mineral layers. Inventory data from the U.S. Forest Service (USFS) Inventory Analysis Unit was used to develop estimates of the land area represented by the major overstory species at various age-classes. The CENTURY model was then used to develop an estimate of carbon dynamics throughout the age sequence of forest development for the major ecosystem types. The estimated boreal forest area in Alaska, based on USFS inventory data is 17 244 098 ha. The total aboveground biomass within the Alaska boreal forest was estimated to be 815 330 000 Mg. The CENTURY model estimated maximum net ecosystem production (NEP) at 137, 88, 152, 99, and 65 g·m2·year1 for quaking aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh.), balsam poplar (Populus balsamifera L.), white spruce (Picea glauca (Moench) Voss), and black spruce (Picea mariana (Mill.) BSP) forest stands, respectively. These values were predicted at stand ages of 80, 60, 41, 68, and 100 years, respectively. The minimum values of NEP for aspen, paper birch, balsam poplar, white spruce, and black spruce were 171, 166, 240, 300, and 61 g·m2·year1 at the ages of 1, 1, 1, 1, and 12, respectively. NEP became positive at the ages of 14, 19, 16, 13, and 34 for aspen, birch, balsam poplar, white spruce, and black spruce ecosystems, respectively. A 5°C increase in mean annual temperature resulted in a higher amount of predicted production and decomposition in all ecosystems, resulting in an increase of NEP. We estimate that the current vegetation absorbs approximately 9.65 Tg of carbon per year within the boreal forest of the state. If there is a 5°C increase in the mean annual temperature with no change in precipitation we estimated that NEP for the boreal forest in Alaska would increase to 16.95 Tg of carbon per year.

Description: Evidence suggests that climate change dynamics have been occurring in the northern latitudes for the past two and a half decades. The CENTURY ecosystem model was used for a set of simulations related to the carbon dynamics of interior Alaska taiga forest types. The functional dynamics of three age-classes (young, middle, and mature) of three ecosystem types (white spruce (Picea glauca (Moench) Voss), black spruce (Picea mariana (Mill.) BSP), and hardwoods) were compared using an average climate that was present prior to 1980 and the climate record from 1980 to 2000. Estimates for total ecosystem production indicate a decrease in tree carbon capture for hardwood stands for all three age-classes summed across a 20-year climate change period. White spruce displayed increases in carbon capture for the three age-classes. Young and mid-aged black spruce stands showed a decrease in ecosystem productivity. The old-growth black spruce stand showed a small increase in carbon capture. Dynamics displayed for the entire ecosystem (soil organic matter, tree dynamics, dead wood, and forest litter) followed the same trends as vegetation productivity. For the same 20-year climate period and across all three age-classes, carbon capture decreased for hardwood ecosystems and increased for white spruce ecosystems. The young black spruce system showed a change from a positive carbon balance to a negative carbon balance. Based on the landscape area covered by each vegetation type, we suggest that the net effect of climate warming over the past 20 years has been a substantial decrease in carbon capture in the forests of interior Alaska.

Description: Modeling the biology of forest ecosystems has been devoted to a combination of theoretical and empirical approaches representing the function of a forest ecosystem generally within an undefined spatial context. Moving to a large spatial context will require the use of theoretical representations of critical ecosystem functions that can be represented on an individual cell basis. A Spatial Alaskan Forest Ecosystem Dynamics (SAFED) model was developed that is based on the nitrogen productivity concept for forest growth, litter fall quality, and microbial efficiency for forest floor decomposition. Climate and ecosystem disturbances were handled as restricted stochastic processes. The restriction was based on known state-factor relationships. The state factors are used to describe a broad-scale classification of the landscape to define basic limitations for the randomly derived driving variables used in the model. The model has been programed as ARC/INFO macro language within the GRID package. The current version of the model has been verified as functional from an individual tree basis (1-m2 cell size) within an old-growth white spruce (Picea glauca (Moench) Voss) forest found in interior Alaska.

Description: The negative exponential and Wiebull distributions were used to estimate stand survivorship curves for forested sites in the Porcupine River drainage of interior Alaska. The survivorship curve of Piceaglauca (Moench) Voss sites was best described by a Wiebull function, while both functions adequately described the Piceamariana (Mill.) Britton, Sterns & Poggenburg hardwood and all sites stand survivorship curve. Fire cycles calculated from the Wiebull distribution were 43, 113, 36, and 26 years for the entire study area, P. glauca, P. mariana, and hardwood sites, respectively. Fire frequencies estimated from a life table analysis were 48, 105, 43, and 30 years, respectively. The relationship between fire cycle and fire frequency calculations is discussed and various management implications are given.

Description: The Spatial Alaskan Forest Ecosystem Dynamics (SAFED) model was validated across four of the most common vegetation types found in interior Alaska. The vegetation types were an alder (Alnus spp.) - balsam poplar (Populus balsamifera L.) site (FP2), an old-growth balsam poplar and white spruce (Picea glauca (Moench) Voss) site (FP3), a mixed deciduous (primarily birch (Betula papyrifera Marsh.) and aspen (Populus tremuloides Michx.)) and white spruce site (UP2), and a mature white spruce site (UP3). The FP site types are common on the floodplain along the Tanana River and the UP site types are common in the uplands in interior Alaska. SAFED is based on nitrogen productivity for vegetation growth, litter fall quantity and quality, and microbial efficiency for forest floor decomposition. The state factors (climate, topography, and disturbance) are used to describe a broad-scale classification of the landscape to define basic limitations for the driving variables. Climate and ecosystem-level disturbances are handled as restricted stochastic processes. The model has been programed in a spatial framework as an ARC/INFO AML within the GRID package. The current version of the model has been validated as functional from an individual tree basis (1-m2 cell size) in a number of forest types found in interior Alaska. The growth, litter fall, and forest floor decomposition were compared with data from the sites. An estimate of yearly carbon balance for the four sites was calculated.

Description: Two mature floodplain white spruce (Piceaglauca (Moench) Voss) ecosystems (stage VIII) located on islands in the Tanana River, approximately 20 km southwest of Fairbanks, Alaska, were clear-cut during the winter of 1985–1986 to quantify the effects of clear-cutting on selected environmental characteristics. Clearings in earlier successional stages (poplar–alder (Populus–Alnus), stage V; and open willow (Salix), stage III) were used to contrast the environmental parameters with the earlier stages found in the primary successional sequence. After clear-cutting, total radiation at the soil surface increased to early successional stage III levels. Potential evaporation from the soil surface increased 5-fold as a result of clearing in the stage VIII sites and was substantially greater than that found in the stage III sites by other researchers. Clearing had relatively little effect on air temperature. The concentration of P and K was significantly lower in the forest floor of both clearcuts, and the concentration of C was significantly higher at VIII-A-T (stage VIII–site A–treated (cleared) plot) when compared with the control stands. There was a decrease in total forest floor biomass at both clear-cut plots. Organic matter, total N, available NH4 and P, and extractable Mg and K all decreased after cutting, whereas pH increased. Decomposition of spruce foliage on the forest floor surface was slower in the clearcuts. Nitrogen immobilization occurred during the first 2 years of decomposition. During the third year it appeared that some mineralization was beginning to occur but the levels were very low, averaging only 3 mg N per bag in the clear-cut areas. Plant growth analysis indicated that growth was limited by high mineral soil salt content in the early successional stages (III) and that this limitation was species specific. Balsam poplar (Populusbalsamifera L.) appears to be more tolerant of the high cation content of the stage III sites compared with trembling aspen (Populustremuloides Michx.). By the time successional development has progressed to stage V, the soil has been sufficiently augmented by the inclusion of organic matter from the developing vegetation and the fixation of N by alder to result in higher seedling growth rates in the cleared areas.

Description: The chemical composition of soil solution reflects the demand of soil biological processes and the solubility and ion-exchange equilibria between physical and biological components of the soil. The objectives of this study were to document soil-solution chemistry for representative phases of the primary successional sequence on the Tanana River floodplain near Fairbanks, Alaska, and to assess the effect of physical versus biological control on solution chemistry in these sites. Soil-solution samples were collected weekly using porous-cup soil-solution samplers located 20, 50, and 150 cm below the soil surface. In addition, groundwater and river water samples were collected at several sites that represented the successional stages typical of the Tanana River floodplain of interior Alaska. Magnesium, HCO3, Cl, Na, K, NO3, and PO4 showed the highest concentrations in the 50-cm layer at each site. Manganese, Fe, and Zn showed the highest concentrations at the groundwater level. Aluminum and Ca showed decreasing concentrations with depth from the surface. Silicon displayed no specific depth trends. Ammonium was the only ion that was more concentrated in river water than in soil solution. Soil-solution pH showed no specific depth trends. Conductivity of the soil solution was generally lower at greater depths and was much lower in the river water. Sulfate, K, Ca, and Mn decreased in concentration from the early successional stages to the later successional stages, although some year to year variability did occur. All measured concentrations except Zn displayed at least one significant change in concentration due to vegetation clearing. These differences can be summarized broadly as effects on nonbiologically cycled nutrients in the open willow stage (III) and changes in the biological cycling of nutrients in the poplar–alder and mature white spruce stages (V and VIII, respectively). Significant increases in concentration of Fe and Mn were found at III-B-T (stage III–site B–treated (i.e., cleared) plot) while Na, Mn, Fe, Ca, Mg, Si, and SO4 increased at III-A-T. At V-A-T significant increases were found in concentrations of NH4, NO3, PO4, SO4, K, Na, Ca, Mg, Mn, Fe, Al, Si, HCO3, and conductivity in 987. These same trends were repeated in 1988 with the exception of NO3, Fe, and Si, which showed no significant differences. As a result of clearing both V-A-T and V-B-T, Fe and Si significantly decreased in concentration at 50 cm, which was the opposite trend found at 150 cm. The Cl concentration at 50 cm decreased at V-A-T in 1987 but increased in 1988 as a result of clearing. V-B-T showed no effect of clearing in 1988 and only NO3, SO4, Ca, Mg, and conductivity increased in 1987. Chloride, Al, and Si decreased in concentration as a result of clearing in 1987 at V-B-T. Nitrate, NH4, Cl, and pH increased, while PO4, K, Na, Ca, Mg, Si, HCO3, and conductivity decreased, as a result of clearing in VIII-A-T. At VIII-B-T, NO3, K, Ca, Mg, Cl, HCO3, and conductivity increased as a result of clearing in 1987, while only NO3 increased in 1988. Bicarbonate, Cl, and pH showed significant decreases in 1987 and 1988 at VIII-B-T. The results of this study, combined with the results of other studies of these salt-affected floodplain soils, detailing the soil environment and control of evaporative movement of water to the soil surface support the hypotheses that: (i) the genesis and maintenance of surface salt crusts are controlled by the soil physical and chemical environments encountered on early-successional mineral soils and (ii) the disappearance of salt crusts and reduction in mineral soil salt concentrations are controlled by forest succession, which mediates the changing soil physical, chemical, and biological environment.