HR: 10:35h
AN: B21H-02    [PDF]
TI: The Influence of Stand Development on Annual Carbon Exchange in Ponderosa Pine in Eastern Oregon
AU: * Kurpius, M R
EM: meredith.kurpius@oregonstate.edu
AF: Atmospheric Science, Oregon State University, 104 Ocean Admin. Bldg., Corvallis, OR 97331-5503 United States
AU: Irvine, J
EM: james.irvine@orst.edu
AF: Forest Science, Oregon State University, 121 Richardson Hall, Corvallis, OR 97331-5752 United States
AU: Law, B E
EM: bev.law@oregonstate.edu
AF: Forest Science, Oregon State University, 121 Richardson Hall, Corvallis, OR 97331-5752 United States
AU: Unsworth, M H
EM: unswortm@coas.oregonstate.edu
AF: Atmospheric Science, Oregon State University, 104 Ocean Admin. Bldg., Corvallis, OR 97331-5503 United States
AB: It is commonly assumed that productivity, and therefore total carbon sequestration, is higher in young, actively growing stands than in old-growth stands. We show that ponderosa pine stands in Oregon did not fit this pattern. Carbon and water fluxes were measured continuously by eddy covariance above young-, mature-, and old-aged ponderosa pine (Pinus ponderosa Dougl. Ex P. \& C. Laws.) stands located within 10 km of each other in central Oregon. The general study area is on the east side of the Cascade Mountains and is classified as high desert: winters are cool and wet while summers are hot and dry, resulting in seasonal drought stress. The old site is composed of patches of multiple age classes: 27% (by ground area) old trees ($>$ 250 years old), 25% young trees ($<$ 50 years old), and 48% mixed - with both age classes. The forest has a very open canopy with summer maximum LAI of 2.1 (0.1 in understory shrubs). The mature site (approx. 90 yrs. old) is naturally regenerating after clear-cutting and summer maximum LAI is 3.0 (0.1 in understory shrubs). The young site (approx. 16 yrs. old) was previously an old-growth forest that was clearcut in 1978 and allowed to regenerate naturally, and the maximum summer LAI was 1.2 (0.4 in understory shrubs). The mature site had the highest gross ecosystem productivity (GEP) (1350 gC m$^{-2}$ y$^{-1}$) but also the highest ecosystem respiration (Re) (940 gC m$^{-2}$ y$^{-1}$). The old site had moderately high GEP (1200 gC m-2 y-1) and lower Re (690 gC m$^{-2}$ y$^{-1}$). The young site had the lowest GEP (730 gC m$^{-2}$ y$^{-1}$ in 2000-2001 and 790 gC m$^{-2}$ y$^{-1}$ in 2002) and the lowest Re (550 gC m$^{-2}$ y$^{-1}$ in 2000-2001 and 600 gC m$^{-2}$ y$^{-1}$ in 2002). Despite having the highest LAI, the mature site did not have the highest net ecosystem exchange (NEE). The balance of GEP and Re resulted in the highest NEE occurring at the old site (-580 $\pm$75 gC m$^{-2}$ y$^{-1}$), which experiences the least severe drought stress according to water potential and sapflow data. NEE at the mature site was moderately high (-435 $\pm$60 gC m$^{-2}$ y$^{-1}$) and was lowest at the young site (-170 $\pm$20 gC m$^{-2}$ y$^{-1}$ in 2000-2001 and -160 $\pm$20 gC m$^{-2}$ y$^{-1}$ in 2002) which experiences the most severe drought stress. The ratio of Re:GEP was 0.6, 0.7, and 0.75 for the old, mature, and young stands, respectively, indicating that as the stands age they respire less per unit carbon fixed. We conclude that more established ponderosa pine stands in this region are likely to sequester more carbon than recently disturbed stands, likely due to a low Re:GEP and a more established rooting system which enables older trees to better withstand drought.
DE: 0315 Biosphere/atmosphere interactions
DE: 0400 Biogeosciences
DE: 1600 GLOBAL CHANGE (New category)
DE: 1615 Biogeochemical processes (4805)
DE: 1620 Climate dynamics (3309)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting