Robinson, Randall ORCID: 0000-0001-8425-0709 (2007) Regeneration mechanisms in Swamp Paperbark (Melaleuca ericifolia Sm.) and their implications for wetland rehabilitation. PhD thesis, Victoria University.

Abstract

This study investigated three aspects of the life history of Swamp Paperbark (Melaleuca ericifolia Sm.) that have implications for the ecology, management and restoration of wetlands occupied by the species: i) seed germination responses and tolerances; ii) clonal growth characteristics; and iii) safe sites for recruitment. Laboratory studies included the responses and tolerances of seed to three key environmental factors: light; temperature; salinity; and the potential interactions they may have on germination. Germination percentages were used as indicators of success. Darkness, moderate temperatures (~ 200C) and low salinity levels (< 2 gL-1) were found to be the most ideal germination conditions. Additional studies were carried out on secondary structures, hypocotyl hairs, which were shown to influence establishment success of seedlings. The conditions found ideal for germination proved to be suitable for hypocotyl hair formation. Field and laboratory studies were carried out to determine the allocation of resources to reproductive effort and seed production in M. ericifolia. Comparative studies were carried out between two sympatric Melaleuca species with contrasting life histories and reproductive strategies (clonal vs. non-clonal) to determine if there were differences in reproductive capacity and commitment of resources to either sexual or asexual reproductive effort. There was low germinability of the clonal species M. ericifolia (< 40%) when compared to the non-clonal M. parvistaminea (< 70%). Germinability of M. ericifolia was reduced as population size decreased and distance to nearest population and degree of disturbance increased. Laboratory and field studies were undertaken to investigate the growth characteristics and ecological significance of the clonal growth form. Genetic methods were used to determine the genetic diversity and clonal intermingling in existing populations. Individual genets were found to contain thousands of stems and cover areas greater than 3,000 m2. Intermingling of the genets was not found. Air-photograph interpretation and structural analysis of individual clones were used to determine colonisation rates, longevity and time since recruitment. Lateral growth rates were generally found to be rapid, up to 0.5m per year. The largest plants found (3,274 m2), were determined to be approximately 52 years old. Safe sites for germination and recruitment were determined using historical aerial photographs and climate data combined with on-ground confirmation and characterisation of conditions. Microtopographical relief provided by hummocks within the wetland provided suitable safe sites for recruitment by modifying light, salinity and moisture levels to a range suitable for germination and hypocotyl hair production. Recruitment was however, restricted to a limited range of climatic conditions that diluted salinity levels but did not inundate newly germinated seedlings: flood conditions in spring followed by average rainfall in summer. Recommendations for landscape-scale rehabilitation of wetlands using M. ericifolia were formulated. The implications of the findings of this study on current ecological restoration theory and practice are discussed. Germination from seed in the highly modified conditions found in many wetlands in South-eastern Australia is problematic due to the specific climatic and on-ground conditions needed for successful recruitment. The findings of the growth and genetic studies of M. ericifolia indicate that planting of nursery grown stock is possible and even preferable if the growth characteristics of the plant are taken into consideration. Present planting methods used for non-clonal terrestrial species, hand planting large numbers of seedlings at close spacings, is inappropriate for M. ericifolia. A planting method that carefully selects planting sites, uses smaller numbers of plants and factors in clonality and lateral growth rates (time) would reduce restoration costs and improve long-term survival of planted stock.

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