Regeneration biology and silviculture of Tasmanian Soft Tree Fern Dicksonia antarctica

Summary of the final Report on the Australian Flora Foundation funded project:

Gregory L. Unwin1 and Mark A. Hunt2.
University of Tasmania, PO Box 1214, Launceston, Australia 7250.
1Present address: Southern Cross University, PO Box 157, Lismore NSW 2480.
2Present address: Old. Forest Research Institute, QDPI, Bruce Hwy, Gympie Old. 4570.

Australian Flora Foundation Final Report 1997.

Grant details    Final report

In recent years, commercial horticulture has provided an incentive to harvest mature Dicksonia stems from private and crown forests in Tasmania in order to supply Soft Tree Ferns at low prices domestically in Australia and to develop a very small market at high specially prices for export to Europe. Extraction and marketing of Dicksonia antarctica for export raised new issues of conservation and management of the native fern flora in Australia. At the same time, such an opportunity provided new avenues for research on the application of propagated growing stock and commercial silviculture of the tree fern within managed understoreys of fast growing Eucalyptus plantations.

Project Objectives
(i) Preliminary investigation of regeneration biology and microclimate requirements for growth of Soft Tree Fern in native moist forest and in clearfelled plantation sites, notably to establish silvicultural requirements of the tree fern as a commercial understorey crop in Eucalyptusplantations, presently being widely established by large scale private forest companies in northern Tasmania.
(ii) Development of suitable techniques for nursery propagation, micropropagation, species provenance and site tolerance trials, suitable to complement and progressively to replace existing salvage of mature Dicksonia from field harvest, prior to reduction of the private forest clearance programme for plantation establishment.
(iii) Initial silvicultural trials of Dicksonia as an undercrop, specifically to place nursery stock of spore propagated Dicksonia in young Eucalyptus nitens plantations of northern Tasmania

Achievements in continuity of the work
The project was proposed as a three year investigation with the above objectives. The Flora Foundation, RIRDC and Ausfern Pty Ltd. have supported this project financially and in kind for the first two years (1995 and 1996) with results as reported herein. The work continued as a limited holding operation during 1997 without funding. Continuation of comparative studies in Australian tree fern species, including Dicksonia antarctica, has now been approved by way of a commencement research grant with Southern Cross University, Lismore NSW, with an offer of $5000 which will allow silvicultural trials of this and similar species to proceed during 1998 and beyond.

Flora Foundation support for the investigation to date has also resulted in interest being expressed by forest ecologists in State Forestry Commissions. Research scientists consider the tree ferns may have application as possible indicator species in developing suitable criteria for maintaining and monitoring ecologically sustainable forest management practices (ESFM). The following report is based on progress reports, publications and commercial information produced by the authors during the course of this investigation. The report accounts for two years of investigation, as supported by the Flora Foundation and RIRDC.

Achievements: listed against the original objectives shown above.

Objective 1. Regeneration biology and microclimate requirements
(a) Completion of ecophysiological studies of Dicksonia antarctica (particularly in relation to photosynthesis and frond water relations);
(b) Analysis and preparation of these results for further publication and communication in scientific journals, international research groups and the popular horticultural press;

Objective 2. Propagation techniques
(a) Training of a graduate student in developing techniques for micropropagation of Dicksonia from field collected spores and experimental callus culture;

Objective 3. Initial silvicultural trials of Dicksonia as an undercrop
(a) Establishing a working relationship with local nursery and plantation industries, purchasing, managing fern stock for outplanting; and
(b) Designing trials for silvicultural underplanting of the tree fern beneath a young Eucalyptus nitens canopy in a moist plantation site of northeast Tasmania (for
underplanting mid 1998).

With due credit to the Flora Foundation, the results of this work have also been communicated among our research peers in Europe (Univ. of Edinburgh and British Pteridologists Society) and in the popular horticultural press in Australia (Australian Horticulture, Nov. 1996 and The Examiner newspaper, Launceston, April 1996). As well as hosting a fern visit by European tree fern specialist A. Wardlaw (Univ. of Glasgow) and the renowned plant physiologist RGS Bidwell in April 1996, the researchers have been invited to return to the British Pteridologists Society, London in the year 2000 to present the results of continuing silvicultural investigations of the tree fern species in proposed underplanting trials beneath fast growing eucalypt plantations.

The Flora Foundation / RIRDC support of these investigations during 1995 and 1996 has been instrumental in developing international interest in a continuing tree fern research programme for future years (proposed and now accepted by way of Internal Research Grant, Southern Cross University for 1998). Even though financially limited in scale, the work has allowed the investigators to bring international attention to the prospect of cultivating and managing propagated tree fern populations silviculturally for an expanding world horticultural interest in Australian native ferns. The concept of actually raising and managing tree fern stocks for horticulture beneath rapidly expanding eucalypt plantations or disturbed farm forests, rather than simply exploiting or salvaging native populations for domestic or export sales, is somewhat new to Australian tree fern management (or our lack thereof). The Flora Foundation support for this research has enabled the investigators to focus international attention on tree fern conservation management with a degree of scientific authority hitherto lacking in the domestic horticultural trade among such species.

As outlined in the Project Proposal (16.5.94), our investigation of regeneration biology and microclimate requirements of the species is ultimately directed towards improved conservation of the Soft Tree Fern in eastern Australia, including assessment of opportunities for its silvicultural management in disturbed native forests and eucalypt plantations. Hence during 1995 and 1996, our Dicksonia studies have developed along two lines of investigation, both of which have involved a training component among graduates of Applied Biology at University of Tasmania:
(a) The ecophysiology of the species regenerating in eucalypt plantation forest understoreys (following from a successful invitation made to a B.App.Sci. (Hons.) student in 1994), and
(b) The development and training of techniques for micropropagation of the tree fern in controlled sterile conditions (undertaken by another student as part of a Grad. Dip. in Agricultural Science (Horticulture)).

The two lines of investigation were linked by the common objective of future propagation of the species for commercial horticulture, taking advantage of shaded understorey environments in forest plantations, in moist uplands of northeast Tasmania. Accordingly, the principal investigators have now established a secure partnership with a large prominent forest nursery in northern Tasmania (Mr J. Nicholson of Woodlea Forest Nursery via Scottsdale, Tas.) who is now providing in kind assistance in the form of shadehouse maintenance of planting stock and well managed field sites for continuing stage 3 of the project (above), i.e. underplanting of Dicksonia antarctica, beneath young eucalypt plantations, during 1998.

In moist forest sites of northern Tasmania. present rate of Eucalyptus plantation establishment by large private corporations varies from 3500 4500 ha per year, depending on seasonal and operational conditions. This rate of conversion is set to treble as national goals of the proposed 2020 Vision programme are delivered in Tasmania. Additionally, tree growers on smaller family owned farm properties are becoming increasingly well organised towards sustainable harvest and export of forest products from their collective forest estate. Tree Growers Cooperatives and the T17GA Farmwood Association in northern Tasmania are committed to optimal and sustainable long term use of forest products from their farms, as a means to diversify and balance their agricultural operations, both financially and ecologically. The scale of farm forest development is ideally suited to improving productivity through small scale plantations and enrichment of disturbed native forest woodlots. Accordingly, there is particular interest in the next stage of the project, namely the design and development of experimental dual crop silvicultural systems for Dicksonia beneath young eucalypt plantations, planned to continue with the support of Southern Cross University research funding during 1998.

Results to date suggest that light, moisture and nutrient requirements of Dicksonia antarcticacan be provided adequately in plantation forest understoreys or beneath disturbed native forests, without compromising either the productivity of the plantation or the ecological succession of native forest gaps. As follows in this report, plant microclimate analysis and canopy/understorey comparisons indicate that declining vapour pressure deficit exerts a stringent control on foliar gas exchange in Dicksonia, such that the species has very conservative water use during seasonal and diurnal dry spells. The analysis suggests that atmospheric water relations and intolerance of direct sunlight determine the adult growth behaviour of Dicksonia in plantation forest understories, as opposed to microsite condition and availability of free water which limits field germination and initial establishment from spores. This has important implications for dual crop silviculture as the conservative tree fern species appears ideally suited to understorey conditions, by and large avoiding adverse competitive effects on the fast growing canopy eucalypt.

Techniques for sporophyte propagation of Dicksonia from prolific yields of wild spores are well established (M.Garrett, pers. comm.; Goudey & Hill, 1986). In vitro propagation of sporophyte tissues also offers promise in relation to cloning and multiplication of isolated or threatened genetic material. In the present study, protocols and media requirements for the in vitro propagation of sporelings of this important native fern species were derived experimentally, with replicated factorial trials for sterilisation, germination and culture on agar. Development of a suitable methodology included techniques for measurement of prothallus size (maximal diameter) in situ on sealed agar plates, to avoid the risk of contamination. Growth responses of gametophyte plants to auxin and cytokinin additions to the media were interactive with sugar concentration. Development work also included culture trials using explants of sporophyte tissue taken from fern fronds, both from young crozier material and using pieces of adult frond. As anticipated, sterilisation proved a critical problem with adult explant material. Cultures using young frond material remained healthy for several months but did not produce differentiated frond or root tissues from cultured explant material.

Results of the project have sustained. our cautious prospects for sustainable silvicultural production of advanced adult tree ferns in moist plantation understoreys. Difficulties associated with the absence of funding during 1997 and the interstate transfer of both authors during the same year, have now been overcome. Silvicultural establishment trials will continue with S.C. University support for outplanting present stocks of nursery propagated sporelings in the plantation understorey, during 1998. This field application of results will ultimately put to the test our explanation of plant-environment relations derived experimentally through ecophysiological investigation of Dicksonia antarctica, as outlined in the following report.

Publications and reports generated as a result of this study are listed as follows:
1996. Unwin, G.L. and M.A.Hunt. Conservation and management of soft tree fern Dicksonia antarctica in relation to commercial forestry & horticulture. In: J.M. Camus, M. Gibby and R.J. Johns (Eds.), Pteridology in Perspective. pp. 125-137, Royal Botanic Gardens, Kew, London.
1996. Unwin, G.L. and Hunt, M.A. Towards a functional definition of understorey: Canopy and understorey processes in relation to farm forestry. Keynote address, Understorey in Farm Forests, Understorey Network and Univ. of Tasmania, Nov. 1996, Launceston, Tas.
1995. Unwin, G.L. and Hunt, M.A. Regeneration biology and silviculture of Tasmanian Soft Tree Fern Dicksonia antarctica. Ausfern P/L., Tree Fern Associaton of Australia and Australian Flora Foundation. Progress Report, 30pp.
1994. M.A. Hunt, N.J. Davidson & G.L.Unwin. Carbon and water relations of Dicksonia antarctica: A preliminary investigation. Aust. Soc. Pl. Phys., Qld. September 1994.
(1998). Hunt, M.A., Davidson, N.J. and G.L. Unwin. Ecophysiology of Soft Tree Fern Dicksonia antarctica. Aust. J. Botany. 12pp. (Submitted).