A model of premature decline of temperate overstorey eucalypts in temperate Australian eucalypt forests. 1. A long absence of fire (this timeframe varies between forest types, e.g. ca. 30 years in coastal Eucalyptus gomphocephala in the Mediterranean climate of south west Western Australia to 150 years in cool, wet, high altitude Eucalyptus delegatensis forests of Tasmania) leads to the development of dense midstorey vegetation. 2. The developed midstorey competes for soil available water with the overstorey eucalypts. Competition for soil water, coupled with periodic drought, causes water stress, leaf abscission, altered canopy structure, altered plant carbon balance and increased epicormic shoot development in overstorey eucalypts. 3. The absence of fire leads to a build up of soil surface litter that moderates soil surface temperatures leading to wetter, cooler soil surface conditions (mesophication; Nowacki & Abrams, 2008) that may be less favourable to mycorrhizae of eucalypts that are particularly important for P acquisition. 4. Soil nitrogen accumulates via fixation and atmospheric deposition, and P, Zn, Mn, Fe and Mg become immobilised in soil surface litter (Hart et al., 2005). Overstorey eucalypts become deficient in P or soil-pH dependent micronutrients, limiting photosynthesis and causing leaf abscission that leads to further epicormic shoot development. The foliage of epicormic shoots is more susceptible to herbivory (Landsberg et al., 1990) due to decreased lignin and increased digestive value of foliage. Greater occurrence of herbivory further reduces crown leaf area and contributes to decline
We propose a model of the ecophysiological processes that underpin
premature decline of temperate overstorey eucalypts in Australia in
the long absence of fire (Fig. 1 ), and describe the
implications of these changes for forest, fire and biodiversity
decreased availability of plant nutrients (Fig. 1 )..
The main conclusions drawn from this review underpin our model of
premature decline of temperate Australian overstorey eucalypts
(Fig. 1 ).
Our integrated model of premature tree decline in the absence of
fire (Fig. 1 ) provides a valuable synthesis of current
research on forest dynamics and ecosystem functions, and provides a
framework to guide research on this issue.
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