HR: 14:25h
AN: B53E-04    [Abstracts]
TI: Thresholds controlling shifts in forest cover types in the boreal region of Interior Alaska: inter- actions between climate, fire and edaphic factors
AU: * Kasischke, E S
EM: ekasisch@umd.edu
AF: University of Maryland, Department of Geography, College Park, MD 20742, United States
AU: Johnstone, J F
EM: jill.johnstone@usask.ca
AF: University of Saskatchewan, Department of Biology, Saskatoon, SK S7N 5E2, Canada
AU: Rupp, S
EM: ffsr@uaf.edu
AF: University of Alaska, Department of Forest Sciences, Fairbanks, AK 99775, United States
AU: Duffy, P A
EM: ffpad.uaf.edu
AF: University of Alaska, Department of Forest Sciences, Fairbanks, AK 99775, United States
AU: Kielland, K
EM: ffkk@uaf.edu
AF: University of Alaska, Institute of Arctic Biology, Fairbanks, AK 99775, United States
AU: Chapin, F S
EM: fffsc@uaf.edu
AF: University of Alaska, Institute of Arctic Biology, Fairbanks, AK 99775, United States
AB: There is a general consensus that future warming in the North American Boreal Region will cause a reduction in coniferous species common to cool, wet sites and an increase in deciduous/coniferous species found on warmer drier sites. In addition, it is believed that much of the change in forest cover will occur during secondary succession following disturbance and that the frequency of disturbance is likely to increase in response to climate warming; however, neither the rate at forest cover will change, nor the mechanisms thereof are well understood. Here, we summarize results from recent studies in Alaska that are being carried out as part of the Bonanza Creek Long Term Ecological Research Project and research being funded by the Joint Fire Science Program and NASA. We have examined factors important in regulating the change in the extent of black spruce (Picea mariana), a dominant forest type across the North American boreal region. Depth of burning of the surface organic layer is a fire severity measure that is important in regulating the post-fire environment in black spruce forests. In particular, seeds from deciduous trees have extremely low germination rates in post-fire organic soils that are greater than 3 cm deep. In addition, we found the growth of deciduous species in burned stands is inversely proportional to the depth of the remaining organic soil, with the highest growth observed on sites with exposed mineral soils. Other factors controlling seedling survival and growth include soil temperature and moisture, nutrient availability, and the fact that deciduous and coniferous species have different capabilities in absorbing different forms of soil nitrogen. These additional factors are also controlled by the amount of organic soil remaining after the fire. Finally, our research has shown that the depth of the remaining organic soil after fires is controlled both by topography and climate, with the frequency of sites with organic layers shallower than 3 cm being significantly greater during fires that occurred late in the growing season (after 20 July) compared to fires that occurred early in the growing season, a result of the influences of seasonal thawing of the ground layer on ground moisture. In addition, we found that the drier ground conditions that occur during extremely large fire years lead to a higher fraction of deep burning fires than occurs during small fire years. Thus, changes in climate can be directly related to factors regulating an important threshold for change in Alaskan black spruce forests. As the boreal forest provides a wide range of ecosystems services, particularly to Native Peoples, being able to predict the rate of change in forest cover is particularly important in developing policies that account for the effects of climate in relationship to fire management policies.
DE: 0400 BIOGEOSCIENCES
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0439 Ecosystems, structure and dynamics (4815)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting