High-resolution analysis of stem increment and sap flow for loblolly pine trees attacked by southern pine beetle

Manual and automated dendrometers, and thermal dissipation probes were used to measure stem increment and sap flow for loblolly pine (Pinus taeda L.) trees attacked by southern pine beetle (Dendroctonus frontalis Zimm.) in east Tennessee, USA. Seasonal-long measurements with manual dendrometers indicated linear increases in stem circumference from April through June. Changes in stem circumference slowed after this time, and further increases were either modest or not observed. These effects coincided with a massive midsummer infestation of trees with southern pine beetles. High-resolution measurements with automated dendrometers confirmed that, while early-season increases in radial increment were positive, daily rates of radial increment for slow- and fast-growing trees were largely negative in early to late July. Sap velocity also declined despite favorable weather conditions, but these reductions were not observed until mid-August. Thus, effects on radial increment and stem circumference preceded those on sap velocity by several weeks. The timing of these events, combined with the known developmental rate of southern pine beetles, suggest that disruption of whole-tree water balance is not a prerequisite for the success of attacking beetles or for oviposition by colonizing females and larval development, all of which were completed by early August. Additional field experiments that use high-resolution techniques to measure stem increment and sap flow are needed to more rigorously characterize temporal changes in host physiology during initial invasion and colonization of trees by southern pine beetle.