© 2000 Heron Publishing—Victoria, Canada
European larch and eastern white pine respond similarly during three years of partial defoliation
Dirk W. Vanderklein (1) and Peter B. Reich (2)
1. Montclair State University, Department of Biology and Molecular Biology, Science Hall 116, Montclair, NJ 07043, USA (vanderkleid@mail.montclair.edu) / 2. University of Minnesota, Department of Forest Resources, 1530 N. Cleveland Avenue, St. Paul, MN 55108, USA / Received November 18, 1998
Summary
To test whether trees with different leaf life spans respond differently to defoliation, eastern white pine (Pinus strobus L.) and European larch (Larix decidua Mill.) trees (9 years old in 1991) were partially defoliated by hand between July 1 and 10 in 1989, 1990 and 1991. At the
end of 1991, trees of both species had received either 0, 1, 2 or 3 years of defoliation. Trees that received only 1 year
of defoliation were defoliated in 1989. Variables measured included photosynthesis, twig water potential, leaf mass per area
and leaf nitrogen concentration. There were few significant responses to defoliation in any of the three years of treatment
in either species, and only the current-year defoliation treatments caused significant responses. Both species had reduced
photosynthetic rates and less negative twig water potentials in response to defoliation in 1989. In 1990 and 1991, the defoliation
treatments had no significant effect on any of the parameters measured in European larch. In 1990, there was a significant
reduction in foliar nitrogen concentration in eastern white pine in response to defoliation in 1990. In 1991, eastern white
pine had significantly less negative twig water potentials in response to defoliation in 1991. Leaf mass per area was not
affected by defoliation in either species. We conclude that, for European larch and eastern white pine, differences in leaf
life span have no effect on leaf- and twig-level responses to defoliation.
Keywords:
foliar nitrogen, Larix decidua, leaf life span, leaf mass per area, photosynthesis, Pinus strobus, twig water potential.
