CUR - The Council on Undergraduate Research

How Plant Physiological Characteristics Can Be Used to Better Manage Wildfires

Nicolas Bakken-French, Cheryl Swift, Biology, Whittier College, 13406 E, Philadelphia St, Whittier, CA 90602

Currently in wildfire management, fuel loads are estimated by taking the ratio of wet to dry mass; however, the relationship of physiological water stress to fuel loads is not well understood. Conventional fire management policy assumes that older stands of vegetation have increased fuel loads. This study addressed two questions: 1) To what extent are measures of plant moisture content correlated with water potential? 2) Does plant water stress increase with time since fire and does this in turn decrease plant moisture content? We sampled three different aged burns in the Angeles and Los Padres National Forest in southern California and three different aged burns in the Stanislaus and Sierra National Forest in the Sierra Nevada. We controlled for elevation and time between fires. At each location we marked individuals of scrub oak, (Quercus sp) and manzanita, (Arctostaphylos sp.) Mean Leaf Moisture Content, Relative Water Content and Stem Water Content increased with increased pre-dawn water potential suggesting that water stress plays a factor in fuel moisture content. Surprisingly individuals in more recent burns had lower pre-dawn and midday water potentials, and slightly lower measures of plant water content.  Our results suggest that, at least in chaparral, plant water stress is related to plant moisture content, but that time since fire did not increase water stress or reduce plant water content. There are a number of possible explanations for our results. First, our oldest burns were ten years old, so perhaps more time is needed for post fire water stress and accompanying fuel increases to develop. It is also possible that micro-climate unrelated to elevation plays an important role in water stress. Regardless, our results suggest that a focus on time since fire as a way of predicting fuel loads may not be an accurate way of predicting fire risk.

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