Projects

Vegetation shifts between black and white spruce forests after fire (DFG)

Scientist(s): Christian Wirth Funding: Max-Planck-Society, DFG Duration: Fieldwork during summer 2004

Project description: Introduction: Black spruce and white spruce are the two dominant tree species in the boreal forest of Interior Alaska. Their current distributions are strongly controlled by the soil thermal regime. Black spruce is found on permafrost soils (north slopes and floodplains), whereas white spruce occurs on warm and well drained upland soils. However, Alaska's climate is warming rapidly (0.4 °C per decade) and extreme fire seasons occur more often. As a consequence the permafrost is melting, many upland soils are becoming warmer and drier, and ecological opportunities for vegetation transformation are enhanced by the elevated fire regime.

Question: Climate change may alter the suitability of soil environments for post-fire regeneration of the two species, and thus may lead to shifts in dominance of the two species. We studied post-fire regeneration in a heterogeneous landscape containing typical black spruce and white spruce habitats. The overall question was: To what extent is the current distribution controlled by dispersal limitation versus edaphic constraints on establishment and growth. More specific questions were: Do post-fire densities of saplings of the two species mirror the adult distributions, or do the distributions of the saplings broadly overlap? How do the saplings of the two species perform inside and outside their pre-fire habitats?

Results: The distribution of black spruce regeneration mirrored the pre-fire distribution of adults, while abundant regeneration of white spruce was found far away from the seed source and outside the adult habitat. White spruce recruits exhibited highest establishment rates in typical black spruce habitats, but here their growth was reduced. We conclude that even in a large burn white spruce is not strongly limited by seed dispersal. Permafrost and burn severity are the major controls on abundance and performance. This suggests that the vegetation may respond to warming without a pronounced time-lag.

Collaborators: Frank Stuart (Terry) Chapin III, Jeremy Lichstein, Jonathan Dushoff, Anping Chen, Steve Pacala

Project publications: Wirth C, Chapin III FS, Lichstein JW, Chen A, Pacala SW: Abundance and performance of post-fire regeneration of Black and White spruce in relation to seed source, burn severity and edaphic conditions (in prep for Journal of Ecology)