Ewers, John , Jacobsen, Anna L. , Lopez-Portillo, Jorge , Telewski, Frank W. , Ewers, Frank W. .
Vessel redundancy: modeling safety in numbers.
Ecological wood anatomists have long suggested, but never modeled, the concept that high vessel number per transverse area provides safety by virtue of redundancy. Here we assumed that embolism formation occurred due to independent random events and that when any stem reached a particular embolism threshold, runaway embolism resulted in stem mortality. The independent variable was the number of vessels per stem, i.e., redundancy. The dependent variable was probability of branch mortality and we selected three thresholds for catastrophic runaway embolism (50%, 75% and 90%). When the modeled levels of embolism were below the thresholds, the safety benefits (percent stem survival) increased dramatically in going from one to ten vessels and approached their maximum in stems with 100 to 1000 vessels, with greater advantage of redundancy as the thresholds for runaway embolism were approached. However, after the thresholds were reached, the redundancy relationships were reversed and the survival probability was greater in stems with lower vessel numbers. The results could explain redundancy benefits conferred by many vessels in a central trunk of a tree, and the isolation benefits of short stems of desert annuals, and of the many narrow twigs of desert and chaparral shrubs. We are also using various poplar clones as models of trees that vary in both mechanical and hydraulic safety.
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1 - Michigan State University, Department of Plant Biology, 166 Plant Biology, East Lansing, Michigan, 48824, USA
2 - Instituto de Ecología, A. C., Departamento Ecología Vegetal, km 2.5 antigua carretera a Coatepec No. 351, Congregación El Haya, Xalapa, Veracruz, 91070, Mexico
safety versus efficiency
Presentation Type: Oral Paper
Date: Monday, August 15th, 2005
Time: 11:30 AM