Fire‐tolerance mechanisms of common woody plant species in a semiarid savanna in south‐western Zimbabwe

Abstract

The frequency of fire has increased in savannas yet few studies have assessed how plants persist when subjected to long‐term disturbance by fire. We investigated the contributions of bark thickness and resprouting to the persistence of woody plants in two fire trials that were started in 1948 and 1949. The number of resprouts per individual, bark thickness, basal diameter and height of woody plants were measured in unburnt plots and those burnt annually, triennially and quinquennially during the late dry season. Changes in tree density, number of resprouts and individuals in different height classes between 1963 and 2002 were assessed. Bark thickness varied among species and also increased with increases in basal diameter. Generally, plants with thick bark survived fire more than those with thin bark. Resprouting was the major fire survival strategy for most species. The number of resprouts produced per plant ranged from 4 ± 3 (Acacia rehmanniana) to 14 ± 9 (Pseudolachnostylis maprouneifolia). Fire reduced species richness in plots burnt annually and triennially by 47% and 6% respectively. Species richness increased in unburnt plots (5%) and those burnt quinquennially (16%). Most woody species survived fire through a combination of traits.

How do small savanna trees avoid stem mortality by fire? The roles of stem diameter, height and bark thickness

“…In addition to recognising the importance of bark thickness to savanna tree dynamics under regimes of frequent fires ), there is a growing body of evidence that suggests that fire damage to the stem rather than the canopy crown is what kills trees (Gignoux et al 1997, Pinard and Huffman 1997, Balfour and Midgley 2006, Nefabas and Gambiza 2007, Midgley et al 2010). Balfour and Midgley (2006) demonstrated that among small stems in African savannas, the effects of fire on the xylem causes topkill.…”

“…Although bark thickness is implicated in fire resilience, it has received much less attention as an explanation for the general fire resilience of savanna trees than either the escape diameter or escape height hypotheses (cf. Gignoux et al 1997, Pinard and Huffman 1997, Nefabas and Gambiza 2007, but see Hoffmann et al 2009). …”

“…Because there is a positive nonlinear relationship between bark thickness and tree diameter and height (Pinard and Huffman 1997, Werner and Murphy 2001, Nefabas and Gambiza 2007, Williams et al 2007), a relatively thin barked species but faster growing individual may match the fire-proofing of thicker-barked species, within a given inter-fire period, by relatively faster rates of height growth. Although bark thickness is implicated in fire resilience, it has received much less attention as an explanation for the general fire resilience of savanna trees than either the escape diameter or escape height hypotheses (cf.…”

Bark thickness determines fire resistance of selected tree species from fire-prone tropical savanna in north Australia

“…Thus, stem survival after fire is arguably a function of fire intensity, the height, width and growth rate of the stem, and the bud-protective (bark) mechanisms on the stem (Gill and Ashton 1968;Gill 1995;Gignoux et al 1997). Of the plant traits that confer individual fire resistance, bark thickness is the most important so that only trees with thick bark, regardless of their stem height or width, usually survive very severe fires (Vines 1968;Hengst and Dawson 1994;Pinard and Huffman 1997;Nefabas and Gambiza 2007).…”

Participatory monitoring of biodiversity in East African grazing lands

“…Fire plays an important role in savanna dynamics. Every landscape reflects the past history of fire (Sheuyange et al, 2005;Nefabas and Gambiza, 2007). Fire and grazing as natural ecosystem drivers often influence the changes in vegetation structure and composition (Roques et al, 2001).…”