Stem demography and post-fire recruitment of a resprouting serotinous conifer

Citation
Je. Keeley et al., Stem demography and post-fire recruitment of a resprouting serotinous conifer, J VEG SCI, 10(1), 1999, pp. 69-76
Citations number
21
Categorie Soggetti
Plant Sciences
Journal title
JOURNAL OF VEGETATION SCIENCE
ISSN journal
11009233 → ACNP
Volume
10
Issue
1
Year of publication
1999
Pages
69 - 76
Database
ISI
SICI code
1100-9233(199902)10:1<69:SDAPRO>2.0.ZU;2-X
Abstract
The contribution of resprouts and seedling recruitment to post-fire regener ation of the South African fynbos conifer Widdringtonia nodiflora was compa red eight months after wildfires in 1990. Stems on all trees were killed by fire but resprouting success was > 90 % at all but one site. A demographic study of burned skeletons revealed that prior to these fires, nearly all p lants were multi-stemmed (4 - 9 stems/plant) and multi-aged, indicating con tinuous sprout production between fires. All stems were killed by these 199 0 fires and at most sites > 90 % of the stems were burned to ground level. All diameter stems were susceptible to such incineration as, at most sites, there was no difference in average diameter of stems burned to ground leve l and those left standing. Individual genets usually had all ramets inciner ated to ground level or all ramets charred, but intact, suggesting certain micro-sites burned hotter, whereas other sites were somewhat protected. Alt hough not true of the 1990 fires, there was evidence that occasionally Widd ringtonia stems may survive fire. At one site, four of the 16 plants sample d had a burned stem twice as old as the oldest burned stem on the other 12 plants at the site, suggesting some stems had survived the previous fire (c a. 1970) and this conclusion was supported by fire-scars on these four stem s that dated to ca. 1970. Based on the highly significant correlation betwe en stem diameter and cone density left standing after the 1990 fires, we ca lculated that for most sites > 80 % of the initial cone crop was incinerate d by fire. This is important because we observed a strong relationship betw een size of the canopy cone crop surviving fire and post-fire seedling recr uitment. Under these conditions we hypothesize that sprouting confers a sel ective advantage to genets when fires cause heavy losses of seed. The infre quent occurrence of sprouting in the Cupressaceae suggests the hypothesis t hat resprouting is an apomorphic or derived trait in Widdringtonia. Data fr om this study suggests resprouting provides a selective advantage under sev ere fynbos fires, which are not only 'stand-replacing fires,' but also are intense enough to incinerate cone-bearing stems.