PARENT SESSION
Poster Session # 15: Plant Ecology.
Wednesday, August 6 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Seasonal sap flux density in young versus old loblolly pine stands.
Farris, Marianne *,1, Samuelson, Lisa1, Stokes, Thomas1, Coleman, Mark2, Blake, John 2, 1 Auburn University, Auburn, AL2 USDA Forest Service, Aiken, SC
ABSTRACT- Sap flux density is being monitored over two years in young and old loblolly pine (Pinus taeda L.) stands receiving irrigation to better understand tree physiological differences in response to increasing trees size and age, and environmental factors controlling stand level water use. Thermal dissipation probes were installed in three-year-old loblolly pine stands of an average diameter of 7 cm and winter LAI of 1.0 m2 m-2, respectively. Probes were also installed at different depths and aspects in dominant, approximately 70-year-old pines ranging in diameter from 32 to 56 cm and with a winter LAI of 2.0 m2 m-2. Both plantations are located on the Savannah River Site in New Ellenton, S.C. Irrigation is based on PET and is similar between sites. During the winter months of 2003, average maximum sap flux density was 35 and 25 g m-2 s-1 in saplings and mature trees, respectively. However, winter sap flux density was as high as 100 g m-2 s-1 in saplings compared to a maximum of 30 g m-2 s-1 in mature trees, indicating potentially lower hydraulic conductance in mature trees. In mature trees, radial patterns in sap velocity were examined at sapwood depths of 0-10, 0-20, 20-40, 40-60, 60-80 and 80-100 mm. Surprisingly, winter sap velocity was highest at 40 mm but significant above the 40-60 mm depth. Sap flow was approximately six times higher in mature trees compared to saplings. Environmental factors controlling stand level transpiration will be compared between seasons and stand ages.
Key words: sap flow, loblolly pine, scaling, radial variation