© 1995 Heron Publishing—Victoria, Canada
Water relations and growth of loblolly pine seedlings planted under a shelterwood and in a clear-cut
Craig T. Dalton (1) and Michael G. Messina (2)
1. Wisconsin Department of Natural Resources, Box 411, Wausaukee, WI 54177, USA / 2. Department of Forest Science, Texas A&M University, College Station, TX 77843-2135, USA / Received November 30, 1993
Summary
We investigated the influence of shelterwood conditions on water relations and growth of loblolly pine (Pinus taeda L.) seedlings on two harsh sites in eastern Texas. Site I was harvested to provide four overstory density treatments (0,
2.3, 4.6 and 9.2 m2 of residual basal area per ha). To quantify the effects of overstory competition, trenched and nontrenched subplots, each
containing 25 one-year-old seedlings, were established within each overstory treatment plot, and predawn and midday water
potentials (Ψw), seedling growth and survival were measured during the growing season. Leaf area and seedling biomass partitioning were
measured at the end of the growing season. Site II was harvested to provide two overstory density treatments (0 and 6.9 m2 ha–1) and planted with one-year-old loblolly pine seedlings. Seedling Ψw, stomatal conductance (gwv), transpiration flux density (E), leaf area, height and survival were determined.
On Site I, seedling Ψw increased with increasing overstory basal area, whereas trenching only substantially affected Ψw of seedlings in the 9.2 m2 ha–1 overstory treatment. Growth was not affected by overstory treatment or trenching. On Site II, Ψw and gwv were highest during the morning hours and lowest in the afternoon, whereas E peaked in the afternoon. Vapor pressure deficits and photosynthetic photon flux density were major factors in determining
gwv differences between treatments. On individual days, the presence of an overstory increased Ψw and reduced both gwv and E. On Site II, leaf area was affected by overstory treatment throughout most of the study. We conclude that the presence of
an overstory can have ameliorative effects on harsh sites at the western fringe of the loblolly pine natural range.
Keywords:
leaf area, plant water stress, stomatal conductance, transpiration, xylem water potential.
