PARENT SESSION
Oral Session # 70: Landscape Ecology.
Presiding: S Hannon
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 201.

Landscape development and ecosystem function: Results from the Hawaiian Islands.

Porder, Stephen^*,1, Vitousek, Peter ¹, Paytan, Adina ², Bullen, Thomas ², ¹ Dept. of Biological Sciences, Stanford, CA² Dept. of Geological and Environmental Sciences, Stanford, CA

ABSTRACT- Most landscapes are shaped by erosion and deposition, but the effects of these processes on ecosystem function are not well understood. This limits our ability to elucidate ecological and biogeochemical processes at a landscape scale. We examined the ecosystem effects of erosion along two toposequences in the Kohala Mountains, Hawaii, analyzing Sr and Ca isotopes and N, P and cation concentrations in vegetation. By comparing the results to a well-studied, minimally eroded chronosequence, we conclude that some, but not all, ecosystem properties along the slope were rejuvenated by erosion. For example, on 150 ky uneroded surfaces in the Kohala mountains, 80% of Sr in vegetation is obtained from atmospheric sources, while on slopes 80% of plant Sr is derived from local bedrock, similar to the percentage on a 300 year old, uneroded site. This new supply of rock-derived cations correlates with consistent changes in leaf Ca, but not N or P. Sr to Ca ratios, which are positively correlated with Sr and Ca isotopes along the chronosequence, are negatively correlated with isotopic measurements from the toposequences. 44Ca correlates positively with Sr isotopes along the chronosequence and on one slope, but not the other. We conclude that the effects of erosion on ecosystem function are more complex than rejuvenation, and that eroding surfaces may be functionally different than stable surfaces of any age.

Key words: erosion, calcium isotopes, landscape development, strontium isotopes