Abstract
A mechanistic understanding of fire-driven seedling recruitment is essential for effective conservation management of fire-prone vegetation, such as South African fynbos, especially with rare and threatened taxa. The genus Leucadendron (Proteaceae) is an ideal candidate for comparative germination studies, comprising 85 species with a mixture of contrasting life-history traits (killed by fire vs able to resprout; serotinous vs geosporous) and seed morphologies (nutlets vs winged achenes). Individual and combined effects of heat and smoke on seed germination of 40 species were quantified in the laboratory, and Bayesian inference applied to distinguish biologically meaningful treatment effects from non-zero, but biologically trivial, effects. Three germination syndromes were identified based on whether germination was dependent on, enhanced by, or independent of direct fire cues (heat and smoke). Seed storage location was the most reliable predictor of germination syndromes, with soil-stored seeds c. 80% more likely to respond to direct fire cues (primarily smoke) than canopy-stored seeds. Notable exceptions were L. linifolium, with an absolute requirement for smoke to germinate (the third serotinous species so reported), and two other serotinous species with smoke-enhanced germination. Nutlet-bearing species, whether serotinous or geosporous, were c. 70% more likely to respond to fire cues than winged seeds, but there was no evidence for an effect of phylogeny or persistence strategy on germination. This comprehensive account of seed germination characteristics and identification of germination syndromes and their predictors, supports propagation, conservation and restoration initiatives in this iconic fynbos genus and other fire-prone shrubs with canopy or soil-stored seeds.
Highlights
Sclerophyll shrublands, called fynbos, are the predominant vegetation type in the biodiverse Cape Floristic Region of South Africa (Bergh et al 2014)
We investigated the individual and combined effects of heat and smoke on germination of 40 species comprising a mixture of life-history and functional traits, including 22 species for which no previously published germination data were available
We focused on simulating conditions that seeds would be exposed to under field conditions in the postfire environment and asked the following: (1) What are the individual and combined effects of heat and smoke on germination? (2) What types of germination syndromes can be identified? (3) How well do phylogeny and life-history traits such as persistence strategy, seed morphology and seed storage location correlate with these syndromes?
Summary
Sclerophyll shrublands, called fynbos, are the predominant vegetation type in the biodiverse Cape Floristic Region of South Africa (Bergh et al 2014). As is the case for vegetation types in other Mediterranean-type regions of the world, fynbos is highly fire-prone (Rundel et al 2016). Wildfires usually occur during the dry summer-autumn period and have a mean return interval of 10–20 years (Kraaij and van Wilgen 2014). In addition to periodic disturbance by fire, fynbos is characterised by nutrient-poor soils and a Mediterranean-type climate with wet winters and dry summers (Rundel et al 2016). Fynbos species possess a variety of life-history traits that enable fire survival and consequent persistence in the landscape (Kraaij and van Wilgen 2014), and the origin of fire-adapted traits here can be traced back to at least 90 million years (Lamont and He 2012; He et al 2016).
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