Relative Bark Thickness is Correlated with Tree Species Distributions along a Fire Frequency Gradient

Jennifer L Schafer,Matthew G Hohmann,Bradley P Breslow,William A Hoffmann

doi:10.4996/fireecology.1101074

Jennifer L Schafer, Matthew G Hohmann + Show 2 more

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https://doi.org/10.4996/fireecology.1101074

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Abstract

AbstractThe probability of stem survival after fire is strongly influenced by energy allocation to bark because bark thickness affects heat transfer during fire. Greater relative investment in inner bark versus outer bark should also enhance survival because of greater moisture content of inner bark. We measured stem diameter, bark thickness, and habitat preference of five species typical of long-leaf pine savannas, and six species characteristic of adjacent wetlands (pocosins), and calculated relative bark thickness, the inner bark proportion, radial growth, and bark accumulation of each species. We hypothesized that savanna species have thicker bark and greater relative investment in inner bark than pocosin species, because fires occur more frequently in savannas than pocosins. As hypothesized, savanna species have relatively thicker bark than pocosin species. Relative bark thickness and the rate of bark accumulation were correlated with the mean location of a species along the pocosin-to-savanna gradient. However, the inner bark proportion did not differ between savanna and pocosin species. Our results indicate that relative bark thickness is likely the primary bark trait affecting fire-induced topkill and influencing the distribution of species along the pocosin-to-savanna gradient.

Highlights

In pyrogenic ecosystems, thick bark allows trees to minimize or escape fire damage by protecting the vascular cambium (Gignoux et al 1997, Hoffmann et al 2009, Midgley et al 2010, Lawes et al 2011a) and xylem (Michaletz et al 2012)
Frequent anthropogenic fires may favor trees with thicker bark (Stephens and Libby 2006), while fire suppression may allow for increased survival of species with thinner bark that are less resistant to fire (VanderWeide and Hartnett 2011)
The relationship was curvilinear for most species (Table 1), indicating that relative bark thickness does not remain constant as trees grow

Summary

Introduction

Thick bark allows trees to minimize or escape fire damage by protecting the vascular cambium (Gignoux et al 1997, Hoffmann et al 2009, Midgley et al 2010, Lawes et al 2011a) and xylem (Michaletz et al 2012). Fire frequency and intensity can select for higher investment in bark thickness (Pausas 2014) due to the importance of thick bark for post-fire survival. In both Brazil and Australia, savannas burn more frequently than adjacent forests, and savanna tree species have relatively thicker bark than forest tree species (Hoffmann et al 2003, Hoffmann et al 2009, Lawes et al 2011a). Frequent anthropogenic fires may favor trees with thicker bark (Stephens and Libby 2006), while fire suppression may allow for increased survival of species with thinner bark that are less resistant to fire (VanderWeide and Hartnett 2011)

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