Gymnosperm Resprouting-A Review

Abstract

Gymnosperms are generally regarded as poor resprouters, especially when compared to angiosperms and particularly following major disturbance. However, is it this clear-cut? This review investigates two main aspects of gymnosperm resprouting: (i) various papers have provided exceptions to the above generalization-how frequent are these exceptions and are there any taxonomic trends?; and (ii) assuming gymnosperms are poor resprouters are there any anatomical or physiological reasons why this is the case? Five of six non-coniferous gymnosperm genera and 24 of 80 conifer genera had at least one species with a well-developed resprouting capability. This was a wider range than would be expected from the usual observation 'gymnosperms are poor resprouters'. All conifer families had at least three resprouting genera, except the monospecific Sciadopityaceae. Apart from the aboveground stem, buds were also recorded arising from more specialised structures (e.g., lignotubers, tubers, burls and underground stems). In some larger genera it appeared that only a relatively small proportion of species were resprouters and often only when young. The poor resprouting performance of mature plants may stem from a high proportion of apparently 'blank' leaf axils. Axillary meristems have been recorded in a wide range of conifer species, but they often did not form an apical dome, leaf primordia or vascular connections. Buds or meristems that did form often abscised at an early stage. While this review has confirmed that conifers do not resprout to the same degree as angiosperms, it was found that a wide diversity of gymnosperm genera can recover vegetatively after substantial disturbance. Further structural studies are needed, especially of: (i) apparently blank leaf axils and the initial development of axillary meristems; (ii) specialised regeneration structures; and (iii) why high variability can occur in the resprouting capacity within species of a single genus and within genera of the same family.

Keywords: axillary meristems; buds; conifer; coppice; epicormic; layering; leaf axil; lignotubers; meristems; pine; sprouts; suckers; vegetative.

Figure 1

Epicormic and coppice shoots for various species in the Araucariaceae. (a) Araucaria cunninghamii, (b) Araucaria bidwillii, (c) Agathis robusta, (d) Araucaria heterophylla, (e,f) Wollemia nobilis. In (a–d) the shoots had formed on relatively intact specimen trees that may have been subject to damage from landscape maintenance. While different to resprouting after substantial damage it does show that these conifer species retain a resprouting capacity in mature trees. (e,f) Wollemia nobilis in the Wollemi National Park. (e) clump of coppice shoots from what is possibly a single individual. (f) large diameter trunk with numerous epicormic shoots growing from the distinctive bubble bark.

Figure 2

Epicormic resprouting in two species of the Cupressaceae. (a) Cryptomeria japonica. This species is used for bonsai and topiary and this example in a Japanese botanical garden had been pruned to form several leaders of equal dominance. (b,c) Sequoiadendron giganteum. This species is known to resprout from the stumps of younger trees, as is shown here for trees in an arboretum.

Figure 3

Phylogeny of extant conifer families (adapted from Figure 5 of Lu et al. [23]). Numbers in brackets represent number of resprouting genera/number of genera in the family; number of species resprouting after 100% leaf scorch/total number of species in the family.

Figure 4

Radial longitudinal sections of the leaf axils of Wollemia nobilis. (a) Leaf axil from a plagiotropic first order branch of juvenile morphology. Note the location of the axillary meristem (arrowed) and the xylem of the central vascular cylinder (x). Scale 200 μm. (b) Detail of a) showing the small axillary meristem (note the large nuclei and dense cytoplasm) and the bark patch (arrow), the activity of which resulted in the axillary meristem being located below stem level. Scale 100 μm. (c) Leaf axil from the orthotropic leader of a mature tree. Note the xylem (x) of the central vascular cylinder, the sclereid (s) bands in the cortex and the relatively deeply buried axillary meristem (arrowed). Scale 200 μm. (d) detail of (c) showing the axillary meristem has a distinct outer layer, while it gradually merges into the cortex to the rear. Note the absence of leaf primordia or vascular connections. Scale 100 μm.