© 1988 Heron Publishing—Victoria, Canada
Water stress integral—a link between short-term stress and long-term growth
Brian J. Myers
CSIRO Division of Forestry and Forest Products, Box 4008, Canberra, ACT 2600, Australia / Received April 29, 1988
Summary
Water stress integral (SΨ), the cumulative integral of pre-dawn leaf water potential over any chosen period of time, was estimated from measurements
of pre-dawn water potential made every two weeks in a Pinus radiata D. Don plantation near Canberra, Australia. Also measured were final length of current-season needles and annual stem basal
area increment. Data were gathered over a 4-year period from a control plot, a fertilized plot, an irrigated plot, and two
plots that were both fertilized and irrigated. Among years and treatments, annual basal area increment varied over a threefold
range. Of this variation, 91% was accounted for by variation in SΨ for the entire year, during every month of which stem diameter growth occurred. Of variation in annual needle elongation,
90% was accounted for by variation in SΨ from late August to late February, which was the period of needle growth. In dry years, the annual value of SΨ in non-irrigated plots was mainly determined by soil water content, but in wet years in non-irrigated plots, and in all years
in irrigated plots, it was closely correlated with tree nutrient status (r2 = 0.81).
