Leaf Axil Anatomy and Bud Reserves in 21 Myrtaceae Species from Northern Australia

Abstract

Dormant axillary buds allow plants to repair minor damage to their canopies. In woody plants, these buds subsequently develop into epicormic structures that may allow vegetative recovery after major disturbances. They are an essential but little-studied part of the persistence niche. We wondered what bud reserves were present in the leaf axils of northern Australian myrtaceous species, what levels of protection they have, and how this relates to the ecology of these species. Axillary buds of 21 species from 10 genera of northern Australian Myrtaceae were examined anatomically. All species possessed axillary buds in all axils examined, and accessory buds were recorded in 86% of species. The species exhibited an extremely wide range of variation-from axillary buds that consisted of only an apical dome with no leaf primordia (Calytrix exstipulata) to axils with a complex array of accessory buds and meristems located beneath the axil surface (Corymbia and Eucalyptus). The axils of the Eucalyptus and Corymbia species had a greater number of and better protected axillary buds and meristems than the other species studied, including some of their closest relatives, Arillastrum, Allosyncarpia, and Stockwellia. All investigated species had an excellent meristem reserve for recovery of photosynthetic capacity after minor canopy damage and for developing epicormic structures for sprouting after more severe damage. The complex and well-protected axillary bud or meristem structures of Corymbia and Eucalyptus may be an important component of the success of these genera in Australia.

Experimental evidence that fire causes a tree recruitment bottleneck in an Australian tropical savanna

“…For example, when there are few large trees and no fire, the Myrtaceae will be at a relative advantage, but under a regime of early fire and when there are many small adults, the pantropicals will be favoured. These results also lend support to suggestions that the success of eucalypts in Australian savannas is related to their fire tolerance relative to other eco-taxonomic groups (Bowman & Prior 2005, Burrows et al 2008). …”

“…Existing publications based on the Kapalga dataset address this issue, and are drawn on in the discussion. In addition, it has been suggested that the success of the eucalypts in Australian savannas is related to their fire tolerance (Bowman & Prior 2005, Burrows et al 2008, an idea we investigated by asking (5) how does the fire tolerance of eucalypts compare with that of other savanna species?…”

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

“…Thus, epicormic resprouting is inextricably linked to those plant functional traits that protect buds, conferring resilience to fire and topkill, and make escape from the fire-trap possible. In particular, the role of bark thickness in protecting trees and epicormic buds from fire has been underappreciated (Burrows 2002, Burrows et al 2008). Here we examine the role of bark thickness in enabling savanna trees to escape the fire-trap.…”

“…Currently, two hypotheses exist for how juveniles of many savanna trees develop resilience to fire and may escape topkill: (1) heightresponse, growing quickly and tall (escape height), which allows apical buds to escape being scorched (Higgins et al 2000, Bond 2008, Burrows et al 2008; and (2) diameter-response, growing a thicker stem (escape diameter) and thus being buffered against the heat of the fire (Uhl andKauffman 1990, Balfour andMidgley 2006), which can be achieved by having thick bark (bark thickness) and/or other bud protection such as deeply embedded meristems (Gill and Ashton 1968, Vines 1968, Gill 1995, Gignoux et al 1997, Burrows 2002, Midgley et al 2010. 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.…”

Epicormic ontogeny on Quercus petraea trunks and thinning effects quantified with the epicormic composition

“…Epicormic shoots, sometimes called reiterates (Barthélémy and Caraglio, 2007), have been the most studied epicormics in both angiosperms (Colin et al, 2008;Fontaine et al, 2004;Nicolini et al, 2001;Spiecker, 1991) and gymnosperms (Bryan and Lanner, 1981;Edelin, 1977;Ishii et al, 2002;O'Hara and Berrill, 2009), in temperate (Del Tredici, 2001;Fink, 1980;Spiecker, 1991;Nicolini et al, 2001) as well as in tropical regions (Ashton et al, 1990;Fink, 1983;Nicolini et al, 2003). Epicormic shoots develop from latent buds (Hartig, 1878), also called epicormic buds, of proven-* Corresponding author: colin@nancy.inra.fr titious (Burrows et al, 2008) or adventitious origin (Fink, 1983;Kauppi and Rinne, 1987). Besides buds and shoots, epicormics include epicormic meristems (Burrows et al, 2003;Fink, 1984), epicormic strands (Burrows, 2002), "embedded latitudinal suppressed buds" (Aloni and Wolf, 1984), bud clusters and burls (Fontaine et al, 2004;Kauppi et al, 1987;Stone and Cornwell, 1968), picots (Fontaine et al, 2004), spheroblasts (Fink, 1980) and lignotubers (Del Tredici, 2001).…”