© 1998 Heron Publishing—Victoria, Canada
Regulation of ponderosa pine foliar physiology and insect resistance mechanisms by basal area treatments
Thomas E. Kolb (1), Kristina M. Holmberg (1), Michael R. Wagner (1) and Joseph E. Stone (1)
1. School of Forestry, College of Ecosystem Science and Management, Northern Arizona University, Flagstaff, AZ 86011-5018, USA / Received April 25, 1997
Summary
We compared foliar physiology and several measures of tree resistance to insect attack among ponderosa pine (Pinus ponderosa var. scopulorum Engelm.) trees growing in thinned stands. Measurements were made in a second-growth ponderosa pine forest in northern Arizona
where the basal area treatments (6.9, 18.4, 27.6, 78.2 m2 ha–1) have been experimentally maintained by frequent thinnings for 32 years before our measurements began in 1994. Most of the
physiological characteristics measured were affected by the basal area treatments. As stand basal area increased from 6.9
to 78.2 m2 ha–1, predawn water potential, midday water potential, net photosynthetic rate, resin production, phloem thickness, and foliar
toughness decreased. Foliar nitrogen concentration was greatest in trees in the intermediate basal area treatments. Our results
show that the physiological condition of second-growth ponderosa pine can be manipulated by silvicultural control of stand
basal area, and support the hypothesis that high stand basal area increases tree stress and decreases tree resistance to insect
attack.
Keywords:
Arizona, foliar toughness, herbivory, phloem thickness, photosynthesis, Pinus ponderosa, resin, thinning, water relations.
