Seedling Recruitment Strategies in Obligate‐Seeding and Resprouting Banksia Shrubs

Abstract

Banksia ericifolia is killed by fire and so depends upon seeds for persistence. In contrast, B. oblongifolia can persist after fire by resprouting from protected buds, as well as by recruiting seedlings. These serotinous species coexist in the fire-prone scrublands of the Sydney Basin. Here we report experiments that compared seed release from cones retained in the canopy, seed germination, and seedling establishment in these two species. B. oblongifolia seeds were released more quickly than B. ericifolia seeds after a fire, and B. oblongifolia follicles opened and shed seeds after exposure to lower temperatures than those of B. ericifolia. B. oblongifolia seeds germinated more quickly than those of B. ericifolia. The relative growth rates and leaf mass ratios (mean ratio of leaf dry mass to plant dry mass over sequential harvests) of the two species did not differ. Root : shoot ratios were significantly large and biomass allocation to roots was faster in B. oblongifolia seedlings. B. ericifolia seedlings survived low and intermediate levels of droughting better than B. oblongifolia under greenhouse conditions. In a field experiment in which water was not limiting, large B. oblongifolia seedlings had the highest survival rate. These results suggest that selection has acted on B. ericifolia to minimize the chance of zero seedling survival by distributing the risks over more than one germination episode. There was no consistent evidence to support the hypothesis that selection on this species has increased its probability of seedling survival during any one germination opportunity relative to its congener.

Seed-Germination Patterns in Fire-Prone Mediterranean-Climate Regions

“…1976, Sonia and Heslehurst 1978, Abbott 1985a, Zammit and Westoby 1987b, Richardson et a1. 1987, Lamont and Barker 1988, Lamont et a1.…”

Fire season and intensity affect shrub recruitment in temperate sclerophyllous woodlands

“…Fire intensity regulates the dormant proportions of seed banks for species with heat-related germination cues (Auld 1986;Bell et al 1987a, b;Bond and Van Wilgen 1996), and influences seed release of species with canopy-held seed banks (Bradstock and Myerscough 1981;Zammit and Westoby 1987;Enright and Lamont 1989;Bradstock et al 1994;Setterfield 1997). Fire intensity also affects the amount of standing vegetation that is consumed by a fire, thereby influencing the degree to which post-fire competition from persisting vegetation affects seedling mortality (Bond 1984).…”

Factors influencing seedling recruitment in a critically endangered pitcher plant, Sarracenia rubra ssp. alabamensis

“…Many fire-dependent plant species exhibit increased seedling recruitment following fire (Zammit & Westoby 1987, Keeley 1991, Menges 1995, Brewer 1999, Carrington 1999, Lesica 1999. Such increases can result from increased seed or seedling supply due to increased flowering or reduced predation or herbivory (O'Dowd & Gill 1984, Brewer & Platt 1994, Kirkman et al 1998) and/or improved environmental conditions for seedlings after fire (Christensen & Muller 1975, Zammit & Westoby 1987, Brewer 1999.…”

“…Many fire-dependent plant species exhibit increased seedling recruitment following fire (Zammit & Westoby 1987, Keeley 1991, Menges 1995, Brewer 1999, Carrington 1999, Lesica 1999. Such increases can result from increased seed or seedling supply due to increased flowering or reduced predation or herbivory (O'Dowd & Gill 1984, Brewer & Platt 1994, Kirkman et al 1998) and/or improved environmental conditions for seedlings after fire (Christensen & Muller 1975, Zammit & Westoby 1987, Brewer 1999. However, the benefits of post-fire increases in seedling recruitment depend strongly on life history (Zammit & Westoby 1987, Keeley 1991, Brewer 2001, Brewer et al 2009, and can in some cases be abrogated by increased seed predation or other environmental factors that negatively affect seeds or seedlings (Lamont et al 1993, Denham 2008.…”

“…Such increases can result from increased seed or seedling supply due to increased flowering or reduced predation or herbivory (O'Dowd & Gill 1984, Brewer & Platt 1994, Kirkman et al 1998) and/or improved environmental conditions for seedlings after fire (Christensen & Muller 1975, Zammit & Westoby 1987, Brewer 1999. However, the benefits of post-fire increases in seedling recruitment depend strongly on life history (Zammit & Westoby 1987, Keeley 1991, Brewer 2001, Brewer et al 2009, and can in some cases be abrogated by increased seed predation or other environmental factors that negatively affect seeds or seedlings (Lamont et al 1993, Denham 2008. Hence, elucidating the causes of differences in seedling recruitment between burned and unburned sites requires taking into account a species' life history and site-related differences other than fire, such as seed predation and the availability of safe sites for germination and seedling survival.…”