Proposal summary

Environmental effects on pine tree carbon budgets and resistance to bark beetles
Southern Global Change Program and Southern Research Station of U.S. Forest Service: Two years, 1995-97.
Background
Environmental conditions such as nutrient availability, soil moisture, and temperature strongly influence carbon gain and patterns of allocation in individual trees. Growth and yield at the level of whole stands is ultimately determined by these physiological processes in combination with ecosystem management practices such as regulating stand density through thinning. This largely unexplored linkage between tree physiology and stand properties is the basis of projects underway in RWU-SO-4101. In cooperation with RWU-SO-4101, we propose to expand the research objectives to include considerations of pest resistance. Our experiments over the last 8 years with loblolly pine demonstrate that even apparently mild environmental changes can alter the partitioning of carbon between growth and anti-herbivore defense, thereby impacting the success of attacking southern pine beetles. Correlative evidence suggests that stand density and thinning regime also influence the risk of bark beetle outbreaks, probably through long term effects of competition on tree carbon budgets. Optimal forest management strategies, especially in a changing environment, should account for the risk of catastrophic losses to pests as well as expected yield in the absence of pests.

General Objective

  • Evaluate the consequences of environmental effects on tree physiology for resistance of loblolly pine plantations to the southern pine beetle and associated pathogens.

Specific Hypotheses

  • In the short term (1-2 years), thinning will result in greater proportional allocation of carbon to cambial growth, subtracting from carbon available for resin-based defenses, and resulting in lowered resistance to southern pine beetles.
  • In the long term (>3 years), trees in thinned stands will have a larger carbon budget, invest more carbon in resin-based defenses, and have increased resistance to southern pine beetles.
  • In the short term (1-2 years), fertilization will ease nutrient limitations on tree growth, result in greater proportional allocation of carbon to growth processes, subtract from carbon commitments to secondary metabolism, and lower resistance to southern pine beetles.
  • Effects of stand density and nutrient availability on carbon allocation and pest resistance interact with stand age due to ontogenetic changes in tree allocation patterns.
  • Unthinned stands of mature trees on productive sites will be particularly vulnerable to southern pine beetles and likely to promote bark beetle outbreaks.
Investigators: Matthew P. Ayres, Kier Klepzig, Peter L. Lorio, Fina Lombardero, Richard Hofstetter, Matthew Ungerer
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