An estimate of carbon emissions from 2004 wildfires across Alaskan Yukon River Basin

© 2007 Tan et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution Licens

Climate, soil organic layer, and nitrogen jointly drive forest development after fire in the North American boreal zone

Previous empirical work has shown that feedbacks between fire severity, soil organic layer thickness, tree recruitment, and forest growth are important factors controlling carbon accumulation after fire disturbance. However, current boreal forest models inadequately simulate this feedback. We address this deficiency by updating the ED2 model to include a dynamic feedback between soil organic layer thickness, tree recruitment, and forest growth. The model is validated against observations spanning monthly to centennial time scales and ranging from Alaska to Quebec. We then quantify differences in forest development after fire disturbance resulting from changes in soil organic layer accumulation, temperature, nitrogen availability, and atmospheric CO2. First, we find that ED2 accurately reproduces observations when a dynamic soil organic layer is included. Second, simulations indicate that the presence of a thick soil organic layer after a mild fire disturbance decreases decomposition and productivity. The combination of the biological and physical effects increases or decreases total ecosystem carbon depending on local conditions. Third, with a 48C temperature increase, some forests transition from undergoing succession to needleleaf forests to recruiting multiple cohorts of broadleaf trees, decreasing total ecosystem carbon by �40% after 300 years. However, the presence of a thick soil organic layer due to a persistently mild fire regime can prevent this transition and mediate carbon losses even under warmer temperatures. Fourth, nitrogen availability regulates successional dynamics; broadleaf species are less competitive with needleleaf trees under low nitrogen regimes. Fifth, the boreal forest shows additional short-term capacity for carbon sequestration as atmospheric CO2 increases

Effects of carbon, fertilizer, and drought on foliar chemistry of tree species in interior Alaska

Changes in foliarchemistryresultingfromchanges in forest-flooarnd min- eral-soilmoistureavailability,forest-floomricrobialenergysupply,andnitrogenavailability wereinvestigatedacross thesuccessional sequences in bothuplandand floodplainlandscape positions.Three amendments,sugar,sawdust,and nitrogenfertilizer(NH4NO3),were ap- plied to a series of threeupland and fourfloodplainsuccessional sites. The sugar and sawdusttreatmentwseredesignedtoincreasethecarbon:nitrogenratio(C/N)oftheforest floorto values typicalof black spruce sites (C/N = 50). The nitrogenfertilizertreatment was designed to equal estimatedyearlyN mineralizationin an attempto double available nitrogenin the forestfloor.A moistureexclusion treatmentwas designed to remove all summerrainfallfromthe treatmenptlots. Foliarphosphorusconcentrationwserehigherintheuplandsitesthanonthefloodplain. No consistentdifferenceswerereportedamongsuccessionalstageswithina landscapeunit. Theeffectofeithersugarorsawdusttreatmenwtastodecreasefoliarphosphorusconcen- trations.Sugar produced more significantdifferencesthan did sawdust. Sugar treatments decreased foliarnitrogenin all treespecies except forwhitespruce,while fertilizertended to increasefoliarnitrogenI.n thesecond yearfollowingtreatmentherewas notan increase in foliarnitrogenconcentrationresultingfromfertilizertreatment

Log Decomposition Dynamics in Interior Alaska

Logs on and in the forest floor represent a potential large pool of carbon in forest ecosystems. The decomposition of the logs results in the release of stored carbon back into the atmosphere. It is currently thought that this release will take a substantial period of time however; these changes have not been measured in a large number of species in forested regions. From 1994 to 1996, a log decomposition monitoring study was started in a series of sites established in the successional turning points, using ecosystems dominated by alder, balsam poplar and white spruce on floodplain locations and aspen, birch and white spruce in upland locations. This study was set up using green logs from within the forest ecosystems. Fifteen logs were placed on the forest floor in each of six replicate sites to be sampled at years 0, 2, 5, 10, 15, 20, 25, 30 and subsequent 10 year intervals till year 100. The initial ten year results show large differences in the decomposition rates between the species. Currently the species with the highest decomposition rate is alder on floodplain sites, which has lost 62.5% of its total mass (wood and bark) in 10 years. The lowest rate was for white spruce on floodplain sites that lost 29.5%, or birch in upland sites which has lost 30.6% of its total mass in 10 years. This represents a loss of 59.4%, 29.5% and 28.2% of the carbon in the floodplain alder, white spruce and upland birch, respectively

P-band radar mapping of forest biomass in boreal forests of interior Alaska

Biomass values are predicted from the radar at various frequencies and polarizations and are compared to the actual biomass values. Predicted biomass levels are most accurate at P-band. Multiple incidence angle data also reveal that the incidence angle of the radar illumination affects the retrieval of biomass from the radar data even at HV polarizations. One consequence is that topographic information is required for mapping the biomass in areas of moderate topography. Also the inversion curve for biomass retrieval varies with season and environmental conditions

P-band radar mapping of forest biomass in boreal forests of interior Alaska

Biomass values are predicted from the radar at various frequencies and polarizations and are compared to the actual biomass values. Predicted biomass levels are most accurate at P-band. Multiple incidence angle data also reveal that the incidence angle of the radar illumination affects the retrieval of biomass from the radar data even at HV polarizations. One consequence is that topographic information is required for mapping the biomass in areas of moderate topography. Also the inversion curve for biomass retrieval varies with season and environmental conditions