PARENT SESSION
Oral Session #15: Paleoecology and Climate Change.
Presiding: J. Betancourt
Monday, August 5. 1:00 PM to 3:45 PM. Graham Meeting Room, TCC.
History of Sphagnum palustre in Hawaiian montane forests: disturbance, invasion, community and ecosystem change.
Hotchkiss, Sara*,1, Vitousek, Peter2, Ku, Richard3, Luo, Shangde3, 1 Department of Botany, Madison, WI2 Department of Biological Sciences, Stanford, CA3 Department of Earth Sciences, Los Angeles, CA
ABSTRACT- Invasion of forested ecosystems by Sphagnum moss presents an opportunity for integrated analysis of disturbance, invasion, community change, and ecosystem functioning over time. Sphagnum palustre is abundant in wet forests and bogs on Kohala Mountain, Hawaii, but not elsewhere in the Hawaiian Islands. Although the same species of Sphagnum is present in 21,000 yr-old peat from Kohala Mountain, a widespread increase in abundance appears to have occurred within the last century. We used 210Pb and 137Cs to date Sphagnum accumulation at 11 sites on Kohala Mountain. With some exceptions, Sphagnum accumulation appears to have begun earlier toward the center of the current distribution, and later toward the modern distribution limits. With pollen analysis we documented changes in community composition coincident with accumulation of Sphagnum-dominated peat. Most sites show some evidence of canopy disturbance coincident with Sphagnum arrival. Two sites near the center of current Sphagnum distribution lack clear evidence of disturbance, but nonetheless show major changes in community composition following the initial accumulation of Sphagnum peat. Changes include a decrease in the abundance of pollen or spores of wet forest understory species such as Ilex anomala, Melicope spp. and many ferns, and an increase in pollen or spores of species that thrive in high light conditions, such as Palhinhaea cernua, Asplenium florentinum-type, and Poaceae. Comparison of surface pollen assemblages with vegetation within 50-100m establishes a relevant pollen source distance of about 30-50m for closed-canopy forest pollen records, and >80m for samples from shorter, more open vegetation.
KEY WORDS: Sphagnum, Hawaii, paleoecology, invasion