In the Alaskan boreal forest, climate change is causing more frequent and more severe wildfires that consume trees and burn deeply into the organic layer. Black spruce (Picea mariana) is the most common tree species in Interior Alaska and is typically associated with slow decomposition rates, a thick organic layer comprised primarily of moss, and shallow depth to permafrost (frozen soil). Severe fires leave a thin organic layer or expose the mineral soil, which commonly leads to post-fire colonization by deciduous tree species including Alaska paper birch (Betula neoalaskana) and quaking aspen (Populus tremuloides). These tree species can cycle nutrients more quickly, which may result in long-term changes in carbon and nitrogen cycling and reduced organic matter accumulation. As a Postdoctoral Research Associate, I worked with Michelle Mack, where I investigated interactions among fire, forest succession, and ecosystem nutrient dynamics. Research projects included studies of the influence of tree species composition on nutrient pools and fluxes, effects of land management practices on ecosystem carbon storage, and monitoring of permafrost degradation following forest fire.
We investigated plant-soil-microbial feedbacks in adjacent mid-successional stands of black spruce and Alaska paper birch that established following a 1960 fire near Fairbanks, Alaska. Using both field and laboratory methods, we quantified above- and belowground nutrient stocks and fluxes of carbon, nitrogen, phosphorus, and base cations to understand how these species influence ecosystem nutrient dynamics. Our published findings are available here:
Melvin, A.M., Mack, M.C., Johnstone, J.F., McGuire, A.D., Genet, H., Schuur, E.A.G. 2015. Differences in ecosystem carbon distribution and nutrient cycling linked to forest tree species composition in a mid-successional boreal forest. Ecosystems 18: 1472-1488
Forest management effects on plants, soils, and permafrost
To reduce the likelihood of fire spread in inhabited areas, fuel loads are commonly reduced by tree cutting and on-site burning of removed tree biomass. We quantified how this management practice influences soil and aboveground carbon and nitrogen pools, tree seedling establishment, and permafrost thaw. This work was conducted at numerous sites across Interior Alaska in areas treated with two of the most common management types: shearblading (i.e. clearcutting), and thinning. Our published results can be found here:
Melvin A.M., Celis, G., Johnstone, J.F., McGuire, A.D., Genet, H., Schuur, E.A.G., Rupp, T.S., Mack, M.C. 2018. Fuel-reduction management alters plant composition, carbon and nitrogen pools, and soil thaw in Alaskan boreal forest. Ecological Applications 28(1): 149-161
Monitoring permafrost post-fire
The soil organic layer insulates mineral soils and reduces thawing of permafrost. Following severe fires where the organic layer is removed, permafrost degradation can occur. To improve our understanding of this process, we installed soil temperature sensors to a depth of 1.5 meters and are collecting hourly measurements of soil temperature in areas that have recently burned and in nearby unburned areas.