19.3.1  Introduction

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Figure 19.8  (A) A typical burnt habitat (right side) in heathlands of the northern sandplains of southwestern Australia. Note that grass trees (Xanthorrhoea spp.) are the only species whose above-ground biomass has survived fire. (B) Example of a fire weed (Gyrostemon ramulosus) in full fruit. (C) A seeder species of Banksia showing mature unburnt individuals with seed reserves carried in woody cones. Seed release occurs mostly after fire and a cohort of seedlings then establishes to replace the adults killed by the fire. (D) Typical resprouter tree species (Allocasuarina fraserina) showing new shoots developing from epicormic buds under the bark of the burnt trunk. Only a few of these shoots will survive to reconstitute the branching profile of the tree. (E) Transverse section through the root of a typical resprouter (Conospermum stoechadis) showing storage of starch (stained black with iodine) in the cortex, rays and interray xylem parenchyma of the root. (F) Transverse section through the root of a typical seeder (Banksia prionotes) showing virtual absence of starch. (Photographs courtesy J.S. Pate)

 

Much of the Australian flora recovers rapidly after fire, in spite of many individuals perishing through heat and combustion (Section 19.1). Plant communities that regenerate post-fire capitalise on reduced competition for nutrients, water and light, therefore environmental changes imposed by fire (see fire regimes outlined in Section 19.1) are a potent selective force in many Australian plant communities. However, it is still debatable whether the range of genetically programmed responses that we see in fire-tolerant species represents adaptations to burning or arises incidentally in response to features of fire regimes such as drought and nutrient release through an ash-bed effect (Section 19.2). Evidence below demonstrates that nutrient and carbon economies of many species are modified according to fire regimes. Life cycles of species able to tolerate fire contrast dramatically, depending on investment of resources in the parent storage organs relative to seed stocks. Intervention of fire in the Australian landscape, especially in sclerophyllous heathlands (Figure 19.8A), has therefore selected directly or indirectly for a suite of genetic changes.

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