Summary To evaluate indicators of whole-tree physiologi- cal responses to climate stress, we determined seasonal, daily and diurnal patterns of growth and water use in 10 yellow pop- lar (Liriodendron tulipifera L.) trees in a stand recently re- leased from competition. Precise measurements of stem increment and sap flow made with automated electronic dendrometers and thermal dissipation probes, respectively, in- dicated close temporal linkages between water use and patterns of stem shrinkage and swelling during daily cycles of water de- pletion and recharge of extensible outer-stem tissues. These cycles also determined net daily basal area increment. Multivariate regression models based on a 123-day data series showed that daily diameter increments were related negatively to vapor pressure deficit (VPD), but positively to precipitation and temperature. The same model form with slight changes in coefficients yielded coefficients of determination of about 0.62 (0.57–0.66) across data subsets that included widely variable growth rates and VPDs. Model R 2 was improved to 0.75 by us- ing 3-day running mean daily growth data. Rapid recovery of stem diameter growth following short-term, diurnal reductions in VPD indicated that water stored in extensible stem tissues was part of a fast recharge system that limited hydration changes in the cambial zone during periods of water stress. There were substantial differences in the seasonal dynamics of growth among individual trees, and analyses indicated that faster-growing trees were more positively affected by precipi- tation, solar irradiance and temperature and more negatively affected by high VPD than slower-growing trees. There were no negative effects of ozone on daily growth rates in a year of low ozone concentrations. Keywords: climate, dendrometers, growth, regression, sap flow. Introduction Physiological differences in response to environmental stress within and among tree species and across spatial and temporal scales significantly limit efforts to understand and predict for- est responses to future global climate change. It is increasingly apparent that responses of seedling and sapling trees to envi- ronmental stresses may not provide a valid basis for estimating growth rates and stand dynamics of mature trees subjected to the same stresses. This generalization is supported by studies of the adverse effects of tropospheric ozone on forest trees (Chappelka and Samuelson 1998, Samuelson and Kelly 2001), the positive effects of atmospheric elevated CO 2 con- centrations (Norby et al. 2001, Oren et al. 2001), as well as tree responses to climatic stress, including drought (Orwig and Adams 1997, Hanson and Weltzin 2000). These differences can be related to the effects of tree size and geometry on photo- synthesis and water transport pathways and resistances (Yoder et al. 1994), to the effects of tree size on carbohydrate alloca- tion pathways (McLaughlin and Shriner 1980, Waring 1987) as well as to changes in the depth, extent and vigor of rooting systems (Joslin et al. 2000) as trees mature. Dendroecological studies suggest that there have been sys- tematic shifts in the growth responses of mature trees to com- ponents of both physical and chemical climate in widespread regions over recent decades. These include reduced latewood density (Schweingruber et al. 1979) and growth (Briffa et al. 1998, Smith et al. 1999) of conifers associated with increasing temperatures in central Europe and increased sensitivity of red spruce to temperature (McLaughlin et al. 1987, Cook and Zedaker 1992) and rainfall (McLaughlin et al. 1997) at high- elevation sites in the eastern USA, where acid deposition is high. In addition, there is evidence of increased sensitivity of mature loblolly pine (Zahner et al. 1989, McLaughlin and Downing 1995, 1996) and big cone Douglas-fir (Peterson et al. 1995) to drought in areas with high ozone concentrations. Ozone has also been identified as one of the most important climatic variables affecting growth of white pine in Maine (Bartholomay et al. 1997). Although the future distribution and amount of rainfall are uncertain, predictions of increased temperatures and greater climatic variability suggest that drought will increasingly af- Tree Physiology 23, 1125–1136 © 2003 Heron Publishing—Victoria, Canada Diurnal and seasonal changes in stem increment and water use by yellow poplar trees in response to environmental stress † SAMUEL B. MCLAUGHLIN, 1–3 STAN D. WULLSCHLEGER 1 and MILOSLAV NOSAL 4 1 Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831-6422, USA 2 Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37931, USA 3 Author to whom correspondence should be addressed (mclaughlinsb@ornl.gov) 4 Department of Mathematics and Statistics, University of Calgary, Alberta, Canada Received October 17, 2002; accepted April 5, 2003; published online October 1, 2003 † This paper was among those presented at the 17th North American Forest Biology Workshop “Rocky Mountain ecosystems: Diversity, com- plexity and interactions,” sponsored by the Tree Physiology and Forest Genetics working groups of the Society of American Foresters and held at Washington State University, Pullman, WA. Downloaded from https://academic.oup.com/treephys/article-abstract/23/16/1125/1659313 by guest on 19 June 2020