HR: 11:05h
AN: B42A-03    [Abstracts]
TI: Are the High Latitudes Greening or Browning? Evidence for Nonlinear Responses in Tree Growth and the Satellite Record
AU: * Bunn, A G
EM: abunn@whrc.org
AF: Woods Hole Research center, Box 296, Woods Hole, MA 02543 United States
AU: Goetz, S J
EM: sgoetz@whrc.org
AF: Woods Hole Research center, Box 296, Woods Hole, MA 02543 United States
AU: Lloyd, A H
EM: LLOYD@MIDDLEBURY.EDU
AF: Middlebury College, Department of Biology, Middlebury, VT 05443 United States
AB: There have been substantial temperature increases in the northern high latitudes in recent decades. Changes in climate have affected the productivity and physiology of plants and been associated with changes in the global carbon cycle. Crucial studies over the past decade have indicated "greening" of the high latitudes - plants growing earlier in the growing season and more intensely during the summer. Analyses based on the most recent AVHRR-NDVI time series data in boreal North America suggest, however, that: (1) widespread greening is not ubiquitous, but varies with land cover and disturbance history, (2) an interplay between temperature and precipitation affects the NDVI signal according to plant type. These findings are in conjunction with recent tree-ring research that has documented "browning" in some boreal locales in response to physiological temperature thresholds and temperature-induced drought stress. Documenting and interpreting trends in plant growth at high latitudes is critical for understanding the associations and feedbacks between temperature, precipitation, land cover, and atmospheric CO2. We discuss recent analysis from remote sensing and dendroclimatology and present new analysis that integrates the satellite and tree-ring based measures of growth across the high latitudes, and investigate drivers of the observed trends. First, we analyze AVHRR-NDVI time series in a circumpolar study, refined through incorporation of MODIS products, in order to better understand how NDVI has changed over the last two decades. Second, we merge hundreds of tree-ring chronologies from the high latitudes with the AVHRR-NDVI record to understand the associations between tree-growth and NDVI by cover type, latitude, forest density, and landscape setting. These models illuminate the relationship between the satellite NDVI and an integrative measure of tree growth. When merged with climate data, this provides a circumpolar assessment of how tree growth in the high latitudes is changing. The embedded temporal variability in the tree-ring chronologies (decades to centuries) allows current trends to be placed in a longer -term context.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 1630 Impacts of global change (1225)
DE: 1640 Remote sensing (1855)
DE: 4920 Dendrochronology
SC: Biogeosciences [B]
MN: Fall Meeting 2005