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Accueil du site → Doctorat → Australie → 2007 → Demographic and ecological indicators of rarity in a suite of obligate-seeding Persoonia (Proteaceae) shrubs

University of Wollongong (2007)

Demographic and ecological indicators of rarity in a suite of obligate-seeding Persoonia (Proteaceae) shrubs

McKenna, David Jeffrey

Titre : Demographic and ecological indicators of rarity in a suite of obligate-seeding Persoonia (Proteaceae) shrubs

Auteur : McKenna, David Jeffrey

Grade : Doctor of Philosophy PhD (2007)

Université de soutenance : University of Wollongong. Biological Sciences

Résumé partiel
An understanding of the demography and population dynamics of rare species, and the mechanisms maintaining this rarity, is vital if we are to manage threatened species effectively. However, in long-lived plants this is no easy task, due to indeterminate growth and complex stage transitions in the lifecycle and cryptic life history stages such as soil-stored seed banks. In this study, I used a combination of classical demography, experimentation and matrix transition modelling to investigate commonness and rarity in obligate seeding species from the plant genus Persoonia. I made comparisons between two closely related species pairs, Persoonia lanceolata (common) and P. glaucescens (rare), and also Persoonia mollis subsp. nectens (common) and P. mollis subsp. maxima (rare), and included a third rare species, Persoonia bargoensis. If we are to predict and mitigate the effects of changing fire regimes on obligate-seeding vegetation, we need to understand the response of seed banks to fire. I quantified the dynamics of the cryptic seed bank stage by conducting a seed burial experiment where I monitored in situ seed survival and germination in both inter- and post-fire periods. I found high levels of seed dormancy and low levels of seed mortality in the absence of fire in both common and rare species. Germination only occurred in sites that burned in late 2001, and was significantly higher in the medium intensity fire than for either the low intensity or partial-burn fires. None of these seedlings survived to October 2002, possibly as a result of well below average winter rainfall for the region. Fire effects were patchy at small scales regardless of intensity, but became more uniform across the larger site scale as intensity increased. How seed banks respond to multiple fires is also poorly understood, yet this information is important if we wish to assess the ability of obligate seeding species to persist through such disturbance regimes. I quantified the response of the single seed bank of Persoonia mollis subsp. nectens to two closely spaced fires (1997 and 2001) by comparing the magnitudes of the post-fire germination responses and by using Ripley’s L function to examine differences in the spatial pattern of the seedlings in each cohort at 3.5 years post-fire. There was strong germination from the seed bank after both fires (473 and 287 individuals at 3.5 years post-fire) indicating the ability of viable seeds to persist through at least two fires, although there were significantly fewer seedlings following the second fire. The spatial pattern of germination in both seedling cohorts was significantly clustered at small scales around deceased adults, suggesting limited dispersal. The second fire also resulted in tighter clustering around deceased adults and in fewer seedlings dispersed away from adults. My results suggest that Persoonia mollis at this site has a persistent seed bank that can buffer the population against unfavourable fire frequencies and post-fire conditions, and may allow it to retain higher levels of genetic diversity in the form of seeds from previous cohorts of adult plants. Matrix transition models that allow the calculation of the population growth rate, � and identification of the vital rates most influential in directing � are a useful tool for comparing the viability of different populations and examining potential management options.

Mots clés : Biogeography • Phytogeography • Plant populations — Mathematical models • Proteaceae — New South Wales • Proteaceae — Geographical distribution • Rare plants — Population viability analysis • Seeds — Viability • Seeds — Effect of fires on • Germination — Post fire • Population dynamics — Plant — Post fire • Conservation management • Persoonia

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Page publiée le 29 février 2008, mise à jour le 30 juin 2017