Beating the blaze: Fire survival in the fan aloe (Kumara plicatilis), a succulent monocotyledonous tree endemic to the Cape fynbos, South Africa

Abstract

Fire is central to the ecology of Mediterranean-type climate ecosystems, but little is known about the fire ecology of succulent plants therein. This study investigated the fire ecology of an arborescent succulent monocot, Kumara plicatilis (L.) G. D. Rowley (Asphodelaceae), a Cape fynbos endemic. Habitat suitability was assessed to determine whether the species tolerates or 'avoids' fire, and fire survival traits (bark thickness and tissue water content) were measured. The population size structure and density of three K. plicatilis populations were assessed after natural fires, and resprouting potential was investigated. Kumara plicatilis adopts a dual fire survival strategy, occupying rocky sites to 'avoid' fire and possessing morphological features that afford fire tolerance, e.g. well-protected apical meristems and thick corky bark. Bark thickness of burned individuals in situ was similar to unburned plants, suggesting that K. plicatilis bark provides effective insulation against fire. Mortality rates were 64%, 40% and 11%, and decreased as rock cover at the population level increased. All three populations showed reduced plant density post-fire, with greater density reductions associated with lower rock cover. Small plants appear most vulnerable to fire damage due to lower absolute bark thickness and plant heights within the flame zone. Kumara plicatilis is an apical sprouter, recovering after fire or mechanical stem damage by onward growth from surviving stem apices, rather than resprouting. Post-fire population recovery therefore likely depends on inter-fire recruitment.

Bark thickness and fire regime: another twist

“…). In an ecosystem with long fire intervals, a thick bark may still be relevant but for only the long‐lived plants; this may explain the occurrence of bark protected plants in some arid ecosystems (Cousins et al ., ; Schubert et al ., ), and the high variability of bark thickness in these ecosystems (Table ). However, the variability in bark thickness of most species in arid ecosystems may be shaped by factors other than fire (such as water control or structural stability; see Paine et al ., ; Rosell et al ., ; Pausas, ; Richardson et al ., ).…”

Flammability as an ecological and evolutionary driver

“…a; Dantas, Batalha & Pausas ). Extreme examples of non‐flammable plants may include several succulent plants from fire‐prone ecosystems (Givnish, McDiarmid & Buck ; Thomas ); in some cases, succulent leaves or leaf bases protect meristems in a similar manner to thick corky bark in trees (Bond ; Thomas ; Cousins, Witkowski & Pfab ). The persistence of slow‐growing non‐resprouting conifers ( Callitris , Juniperus ) in highly flammable landscapes (eucalypt forests, grasslands) has also been explained by the low flammability of their canopy (Trauernicht et al .…”

“…1c), fire-promoting grasses Post-fire seeders (Fig. 1b), including serotionus plants Thomas 1991;Cousins, Witkowski & Pfab 2016). The persistence of slow-growing non-resprouting conifers (Callitris, Juniperus) in highly flammable landscapes (eucalypt forests, grasslands) has also been explained by the low flammability of their canopy (Trauernicht et al 2012) or litter (Twidwell et al 2013a,b).…”

Plant responses to fire in a Mexican arid shrubland

“…stem is negatively related to post-fire mortality due to leaves' insulating properties. Likewise, the protection of apical meristems, and thick and highly suberised bark confer fire tolerance in some succulent plants (e.g., Kumara plicatis [L.] G. Rowley in South Africa; Cousins et al 2016). The low flammability of succulent plants has also been proposed as an adaptive mechanism for surviving low-intensity fire regimes (Pausas et al 2017).…”