The Effect of Ecophysiological Traits on Live Fuel Moisture Content

Abstract

Live fuel moisture content (LFMC) is an important metric for fire danger ratings. However, there is limited understanding of the physiological control of LFMC or how it varies among co-occurring species. This is a problem for biodiverse yet fire-prone regions such as southern California. We monitored LFMC and water potential for 11 native woody species, and measured ecophysiological traits related to access to water, plant water status, water use regulation, and drought adaptation to answer: (1) What are the physiological mechanisms associated with changes in LFMC? and (2) How do seasonal patterns of LFMC differ among a variety of shrub species? We found that LFMC varied widely among species during the wet winter months, but converged during the dry summer months. Traits associated with LFMC patterns were those related to access to water, such as predawn and minimum seasonal water potentials (Ψ), and water use regulation, such as transpiration. The relationship between LFMC and Ψ displayed a distinct inflection point. For most species, this inflection point was also associated with the turgor loss point, an important drought-adaptation trait. Other systems will benefit from studies that incorporate physiological mechanisms into determining critical LFMC thresholds to expand the discipline of pyro-ecophysiology.