Geographic distribution and the reproductive and demographic ecology of two congeneric seeder and resprouter tree species

Schmidberger, J.W. and Ladd, P.G.ORCID: 0000-0002-7730-9685 (2020) Geographic distribution and the reproductive and demographic ecology of two congeneric seeder and resprouter tree species. Forest Ecology and Management, 475 . Art. 118428.

Abstract

The distribution limits of species are mainly related to climate but other environmental factors such as soil and fire may also play an important role in local population dynamics. Species that re-establish from seed after a severe disturbance (seeder species) should have different functional attributes from species that can survive a disturbance by vegetative regeneration (resprouters). The functional attributes will influence the establishment and survival of individuals and for trees, the stem size distributions provide a view of the history of the populations and may indicate the trajectories of the populations as they age. Two congeneric tree species – Allocasuarina fraseriana (a resprouter) and A. huegeliana (a seeder) are dominant to subdominant trees in forest and woodland vegetation of south western Australia and illustrate useful comparisons of functional attributes and population structures. Both species occupy fire prone vegetation, bear seeds in serotinous cones and are considered to regenerate new individuals after fire events. The seeder (Allocasuarina huegeliana) has smaller cones and seeds and more seeds cone-1 than the resprouter (A. fraseriana). The cones of the resprouter provide more protection against heat to the contained seeds than the seeder. It is generally considered that species in fire prone environments often rely on disturbance to provide suitable conditions for regeneration and recruitment between disturbances is poor. For a species killed by disturbance population structures years after the disturbance would be expected to be unimodal while a resprouter would have a multimodal structure, as adults would survive and remain in the population with the new recruits. Unexpectedly population structures for the two species we studied were very similar when compared at an overall landscape scale. We attribute this mainly to the ability of the species to recruit interfire. Best seedling recruitment does occur after fire, as this provides an environment with more nutrients and reduced competition for the seedlings. However interfire recruitment can be abundant in some habitats. The degree to which this occurs may vary in relation to co-occurring tree species and landscape position. In general, fuel reduction fires are being used to reduce the danger of high intensity fires as the climate becomes drier and hotter in parts of southern Australia and mild fires will influence recruitment of both species. Low intensity surface fires will remove interfire recruits of the seeder species, but may increase the density of small plants of the resprouter. Adults are unlikely to be damaged but size class structures will be different from those after stand replacing fires.

Item Type:	Journal Article
Murdoch Affiliation(s):	Environmental and Conservation Sciences
Publisher:	Elsevier BV
Copyright:	© 2020 Elsevier B.V.
URI:	http://researchrepository.murdoch.edu.au/id/eprint/57009

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