Framework for assessing the effects of elevated temperature, CO₂ and water availability on tree growth

Robert Teskey, University of Georgia

Abstract

Objectives: 1) To test a conceptual model designed to predict the response of a tree species to climate change across its geographic range; and 2) To comprehensively examine the relationships between temperature, [CO₂] and water availability on tree growth and physiological processes.

Hypotheses: 1. At temperatures below the optimum for growth, both elevated temperature and elevated CO₂ will contribute to a positive growth response. 2. At temperatures above the optimum for growth, elevated temperature will have a substantial negative effect on growth that will reduce or negate the positive effect of elevated CO₂. 3. Water deficits will modify the response to elevated CO₂ and temperature, having less effect at suboptimal temperatures and more effect at supra-optimal temperatures.

Location: Georgia

Methods: The study will involve field and growth chamber experiments. The field study will be a factorial experiment of ambient and elevated temperature and [CO₂] with subplots of high and low water availability, conducted simultaneously in three locations that are either below, above or near the optimum mean annual temperature for growth of the target species, loblolly pine. The growth chamber experiments are designed to isolate the effects of temperature and water availability on growth and physiological processes under environmentally controlled conditions.

The intent of the research: We will test the concept that temperature has such a large effect on physiological processes that the growth response to climate change (elevated temperature and [CO₂]) can be positive, neutral or negative depending on the temperature regime at a specific location. All three growth outcomes (+, 0, -) are expected to occur because temperatures across a species’ latitudinal and altitudinal distribution will range from sub-optimal to supra-optimal for growth. Therefore the effect of climate change on trees will depend to a very large extent on local temperature conditions. If successful, this project will provide a framework for accurately predicting how tree species will respond to climate change across their entire range.