Anthropogenic fire and bark thickness in coastal and island pine populations from Alta and Baja California

Fire is a common ecosystem process in many landscapes of western North America. Each landscape has a unique set of properties such as fuel arrangement, load, weather, ignitions, cultural history and topography that will influence fire behaviour and effects. These characteristics will have an impact on the probability that a particular area will be subjected to low-moderate intensity fires, stand-replacement fires, mixed-severity fires, or no fires (Stephens & Ruth, 2005). The type and frequency of fire will have a profound influence on the evolutionary strategies for a given landscape (Keeley & Zedler, 1998). Plants exhibit adaptive responses to fire, and there may also be selection for specific physiological or life-history strategies in the post-fire environment (Mutch, 1970; Sannikov, 1981; McCune, 1988; Jackson et al., 1999; Schwilk & Ackerly, 2001). Fire-induced injury of plants can be separated into three categories: (1) injury to roots, (2) crown injury, and (3) cambium injury (Ryan et al., 1988; Brown & Smith, 2000). Trees and shrubs can be killed to ground level by stem girdling, independently of crown or root injury (Ryan et al., 1988; Stephens & Finney, 2002). Fire resistance of tree stems is most closely related to bark thickness (Martin, 1963; Jones et al., 2004).