Ecology of Allocasuarina littoralis (Salisb.) L. Johnson and A. torulosa (Ait) L. Johnson in North Queensland

Crowley, Gabriel Mary (1986) Ecology of Allocasuarina littoralis (Salisb.) L. Johnson and A. torulosa (Ait) L. Johnson in North Queensland. PhD thesis, James Cook University.

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Abstract

Allocasuarina littoralis and A. torulosa occur in the woodlands of North Queensland in areas receiving between 1,000 and 2,000 mm annual rainfall. This thesis examines factors influencing their distibutional patterns, and discusses the implications of their comparative ecology for life history modelling, tropical revegetation programs and reconstruction of North Queensland’s environmental history.

The life-cycle is divided into several stages: seed dispersal and losses, germination and early seedling recruitment, the first year juvenile stage, and established juvenile stage to reproduction. Factors limiting survival in each stage of the life-cycle and progression to subsequent stages are identified.

Seed-fall, post-dispersal seed losses, seedling germination and recruitment, growth rate and mortality of juvenile and adult plants, and reproductive output were measured in contiguous stands in Kirrama State Forest. Seed germination, population structure and recovery from fire were measured for other North Queensland sites. The effects of fire, light and moisture conditions on germination and seedling survivorship, growth and competition were examined in the laboratory.

A.littoralis is found to be adapted to low or intermittent moisture availability and high light levels. This is contributed to by erect cladodes, high root: shoot ratio, maintenance of a high transpiration rate relative to A. torulosa at all soil moisture levels, maintenance of seed variability through wetting and drying cycles and protracted germination.

Life history characteristics appear to be influenced by the environments suitable to growth. A.littoralis, typically found in more open vegetation than A.torulosa, has an earlier onset of reproductive maturity and greater reproductive effort, and consequently a shorter life span; in A. torulosa, reproduction does not generally occur until individuals reach sub-canopy height. Recruitment in A. torulosa is aided by larger seeds and lignotuber reserves.

A.littoralis produces more seed per individual, but, with greater seed fall and smaller seeds, experiences a greater level of seed loss due to predation that does A.torulosa. This ultimately results in A.littoralis having lower seed viability and a smaller soil stored seed bank.

While lignotuber reserves may result in a greater ability of established A torulosa than A. littoralis plants to recover after fire, before these reserves are developed. A. littoralis shows the greater recovery rates, possibly aided by a higher root: shoot ratio. A. littoralis seeds appear to be more sensitive to heating by fire than those of A. torulosa, and germination in the former species is delayed by ash, but in neither species is affected by charcoal. Post-dispersal seed losses of both species are substantially lower from charcoal and ash beds, than from bare ground. The observed effects of ash and charcoal on seed harvesting are likely to operate with other species and therefore have important implications for forestry.

Assessment of published models of life history characteristics are found to be inadequate to explain the data collected in this thesis.

Item ID: 11413
Item Type: Thesis (PhD)
Keywords: Allocasuarina littoralis, Allocasuarina torulosa, North Queensland, life histories, seed dispersal, life cycles, fire survival, survival strategies, she-oaks
Date Deposited: 01 Jun 2010 21:43
FoR Codes: 06 BIOLOGICAL SCIENCES > 0607 Plant Biology > 060703 Plant Developmental and Reproductive Biology @ 34%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060308 Life Histories @ 33%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060303 Biological Adaptation @ 33%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960806 Forest and Woodlands Flora, Fauna and Biodiversity @ 50%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 50%
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