PARENT SESSION
Poster Session # 11: Disturbance Ecology.
Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Population dynamics of black spruce at its northern limit in Alaska.
Lloyd, Andrea*,1, Wilson, Alexis1, Fastie, Christopher1, 1 Middlebury College, Middlebury, VT
ABSTRACT- Black spruce (Picea mariana) forests dominate much of interior Alaska, but black spruce is absent or extremely rare at arctic and alpine treeline locations. In the Brooks Range in northern Alaska, the northern limit of black spruce is several kilometers south of the northern range of white spruce. Although white spruce have successfully advanced into tundra as it has warmed in Alaska over the last several decades, the effects of climate on the distribution of black spruce remains largely unknown. We investigated the dynamics of black spruce populations at the species northern limit in the Brooks Range, Alaska, exploring the relative importance of fire and climate as limits on black spruce population viability at its northern limit. We reconstructed fire history and recruitment dynamics in three replicate sites at the species northern limit, and developed a matrix population model to explore black spruce population dynamics. All sites were affected by a nearly stand-replacing fire slightly more than 100 years ago. Black spruce experienced high recruitment rates in the 20 years following the fire, but recruitment declined precipitously after that point. Black spruce currently recruits primarily by layering, and although low densities of seedlings were present in all sites, seed germination rates in greenhouse conditions were extremely low (<1-8%). White spruce recruitment rates have been much more consistent over time, and white spruce are now significantly over-represented in the seedling size classes. Black spruce are likely to become increasingly uncommon in these stands as time-since-fire increases, and the persistence of black spruce on the landscape in the absence of fire will depend almost entirely on asexual reproduction. The low success of black spruce recruiting in the absence of fire suggests that the species limit is unlikely to advance unless warmer conditions are accompanied by an increase in fire frequency.
Key words: treeline, Picea mariana, fire, boreal forest