Journal
ECOSYSTEMS
Volume 19, Issue 1, Pages 98-114Publisher
SPRINGER
DOI: 10.1007/s10021-015-9920-7
Keywords
Climate warming; Fire; Carbon; Nitrogen; Succession; Black spruce; Trembling aspen; Alaska paper birch; Deciduous
Categories
Funding
- NASA Ecosystems and Carbon Cycle Grant [NNX08 AG13G]
- DOD Strategic Environmental Research and Development Program (SERDP) [RC-2109]
- Bonanza Creek Long Term Ecological Research Site program - NSF [DEB-0620579]
- USDA Forest Service, Pacific Northwest Research Station [PNW01-JV11261952-231]
- Division Of Environmental Biology [1026415] Funding Source: National Science Foundation
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Global change models predict that high-latitude boreal forests will become increasingly susceptible to fire activity as climate warms, possibly causing a positive feedback to warming through fire-driven emissions of CO2 into the atmosphere. However, fire-climate feedbacks depend on forest regrowth and carbon (C) accumulation over the post-fire successional interval, which is influenced by nitrogen (N) availability. To improve our understanding of post-fire C and N accumulation patterns in boreal forests, we evaluated above-and belowground C and N pools within 70 stands throughout interior Alaska, a region predicted to undergo a shift in canopy dominance as fire severity increases. Stands represented gradients in age and successional trajectory, from black spruce (Picea mariana) self-replacement to species replacement by deciduous species of trembling aspen (Populus tremuloides) and Alaska paper birch (Betula neoalaskana). Stands undergoing deciduous trajectories stored proportionally more of their C and N in aboveground stemwood and had 5-7 times faster rates of aboveground net primary productivity of trees compared to stands undergoing a black spruce trajectory, which stored more of their C and N in the soil organic layer (SOL), a thick layer of mostly undecomposed mosses. Thus, as successional trajectories shift, total C and N pool sizes will remain relatively unchanged, but there will be a trade-off in pool location and a potential increase in C and N longevity due to decreased flammability and decomposition rates of deciduous stemwood. Despite often warmer, drier conditions in deciduous compared to black spruce stands, deciduous stemwood has a C: N around 10 times higher than the black spruce SOL and often remains standing for many years with reduced exposure to fungal decomposers. Thus, a fire-driven shift in successional trajectories could cause a negative feedback to climate warming because of increased pool longevity in deciduous trajectories.
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