TY - JOUR
T1 - A Canopy Shift in Interior Alaskan Boreal Forests
T2 - Consequences for Above- and Belowground Carbon and Nitrogen Pools during Post-fire Succession
AU - Alexander, Heather D.
AU - Mack, Michelle C.
N1 - Funding Information:
We would like to thank Kamala Earl, Camilo Mojica, Nils Pederson, Leslie Boby, Mindy Sun, Michael Mahala, and Jennifer Stanley for their invaluable help in the field and laboratory. We appreciate the assistance of the US Army for allowing access to fire scars on military sites. Funding for this research was provided by NASA Ecosystems and Carbon Cycle Grant NNX08AG13G, the DOD Strategic Environmental Research and Development Program (SERDP) under project RC-2109, and the Bonanza Creek Long Term Ecological Research Site program, which is funded by NSF DEB-0620579 and USDA Forest Service, Pacific Northwest Research Station, grant PNW01-JV11261952-231.
Publisher Copyright:
© 2015, Springer Science+Business Media New York.
PY - 2016/1/1
Y1 - 2016/1/1
N2 - 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.
AB - 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.
KW - Alaska paper birch
KW - Black spruce
KW - Carbon
KW - Climate warming
KW - Deciduous
KW - Fire
KW - Nitrogen
KW - Succession
KW - Trembling aspen
UR - http://www.scopus.com/inward/record.url?scp=84955735364&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84955735364&partnerID=8YFLogxK
U2 - 10.1007/s10021-015-9920-7
DO - 10.1007/s10021-015-9920-7
M3 - Article
AN - SCOPUS:84955735364
SN - 1432-9840
VL - 19
SP - 98
EP - 114
JO - Ecosystems
JF - Ecosystems
IS - 1
ER -