Thomas J. Givnish

 

Henry Allan Gleason Professor of Botany and Environmental Studies

Ph.D. (1976) Princeton University • 315 Birge Hall • 608-262-5718 • givnish@wisc.edu

Plant ecology and evolution; adaptive radiation and molecular systematics;
phylogeography; physiological ecology; landscape dynamics

Physiological ecology and biomechanics are major areas of interest. 


My colleagues and I recently published a new conceptual framework for constraints on maximum tree height. Data from a steep rainfall gradient in Victoria, Australia shows a tight relationship between maximum height of Eucalyptus species and relative moisture supply, as measured by the ratio of rainfall to pan evaporation. Variation in the stable carbon isotope ratios of trees along this gradient implicate both hydraulic constraints and biomechanical limitations as setting maximum tree height. I am looking to recruit a student or post-doc interested in examining the rate of height growth and several physiological and allocational parameters in 10 species of Eucalyptus in a series of common gardens, in order to understand why different species dominate different portions of the Victoria rainfall gradient.


Rebecca Montgomery and I are studying the ecology and evolution of photosynthetic light adaptations in the Hawaiian lobeliads (see Adaptive Radiation).


Omar Lopez, Rebecca Montgomery, and I are analyzing how time of leafing and hydraulic conductance influence shade tolerance in trees of the southern Appalachians. Early leafers obtain a “spring subsidy” of carbon by photosynthesizing a few extra days or weeks under an open canopy, which may allow them to persist in microsites that are shadier in midsummer. To do so, however, they must have narrow xylem elements to weather late frosts. Such elements resist cavitation but are hydraulically inefficient. Late leafers with more efficient vessels may be able to sustain higher rates of transpiration (and hence photosynthesis) in sunnier microsites, even if they have higher whole-plant compensation points. We are testing these hypotheses through a series of field measurements and common-garden experiments on 17 tree species in Great Smoky Mountains National Park and Nantahala National Forest.


Recent Ph.D. Emily Sessa investigated hydraulic and photosynthetic adaptations in several North American species of Dryopteris, as part of her research on adaptive radiation in this group. Recent Ph.D. Bob Wernerehl studied the bases for the differential distribution of dominant prairie grasses across the local dry-wet continuum of microsites.

 


Photographs:  TOP - Portrait of the scientist as a young man among Nymphaea; Cyanea floribunda (Lobeliaceae), a highly shade-adapted lobeliad from windward Hawai`i, in wet forests of the Ola`a Tract of Hawaii Volcanoes National Park; Pinus lambertiana (Pinaceae), a common associate of the giant redwood in the Sierra Nevada and among the tallest trees on earth; shade-tolerant saplings of Ostrya virginica leafing out under the as-yet-unopened canopies of Quercus rubra and other late-leafing, shade-intolerant trees at Clifty Falls Park, Indiana; Eucalyptus diversicolor (karri) temperate rain forest in southwestern Australia, dominated by the second tallest species of flowering plants in the world.


© 2011 University of Wisconsin Department of Botany

Last updated: 27 November 2011