The work yet to be done on casuarinas challenges researchers in many parts of the world and in disciplines such as botany, forestry, soil science, microbiology, ecology, and etanobotany. For philanthropic institutions, foundations, and international development agencies concerned with problems of fuel, fiber, and other resources, casuarina research presents an area worthy of financial support.
Specific research needs and recommendations follow.
ASSESSMENT OF GENETIC RESOURCES
In the past, the introduction of casuarinas has been made haphazardly, without regard to relationships between species, provenances, and site requirements. Yet there is much genetic diversity within the broad group of casuarinas and within individual species. It is now important to learn about this diversity and to broaden the genetic base of casuarina plantations. The time has come to make extensive field collections, with a view to selecting species and individual plants with the greatest potential for specific sites and purposes.
In particular, it is important to establish seed collections and to study populations from many and diverse provenances. Almost all seeds so far distributed have come from southern Australia. Species from the Pacific Islands and more tropical areas have been little used, nor have their populations been studied. Few of the many species of Western Australia have been collected, studied, or tested elsewhere. Because so many casuarinas are native to Australia, it is clear that much of the research on the genetic resources will be done there and will be crucial for casuarina development in the rest of the world.
Assessment of genetic resources should include:
· Accurate mapping of worldwide distribution;
· Seed collections of known species from identified provenances;
· Assessment of the importance of hybridization, both natural and experimental; and
· Seed distribution and genetic-information exchange.
COOPERATIVE WORLDWIDE PLANTATION TRIALS
Commercial experience with casuarinas is restricted to a small number of species planted randomly throughout the tropics. It is now imperative to establish a series of carefully planned and replicated plantation trials at selected sites throughout the tropical and subtropical world to allow comparisons of growth and performance. A common methodology should be used at each trial location. Sites for the trials should be selected that test the responses of various species to different soils, altitudes, latitudes, temperatures, moisture levels, and pests. Information from the trials, brought together for assessment and comparison, will provide the technical foundation to enable rational choices about the establishment of large casuarina plantations under the most favorable conditions.
This effort in international scientific cooperation will require a coordinator with sufficient funding to collect and distribute seeds, to establish contact and maintain correspondence with research groups, and, ultimately, to collect data and publish results of the trials.
Information available in the published literature, though suggesting a promising future for casuarinas, is insufficient to support recommendations for the immediate establishment of large plantations throughout the tropics and subtropics. Much of the information still needed must come from carefully planned and coordinated silvicultural trials. However, basic research in a number of areas can make future forestation efforts more effective, less expensive, and more widely applicable.
Silvicultural research on casuarina species is needed in the following areas:
· Phenology of flowering and fruiting;
· Methods of seed storage, especially of tropical species;
· Nutrient requirements, including microbial interactions;
· Methods of establishing plantations, including planting densities and cluster planting;
· Methods of vegetative propagation from mature superior trees, including the influence of tree age, sex, and type of cuttings, the use of hormone treatments, potential of tissue culture and of air-layering;
· Intercropping with other tree crops such as Eucalyptus for biomass, timber, or pulp and of interplanting with agricultural field crops;
· Coppice cropping and root suckering;
· Fire tolerance and regeneration after fire;
· Photosynthetic effectiveness, including effects of stress;
· Investigation of potential plant pathogens, nematodes, and other plant pests; and
· Accurate measurements of growth and productivity of casuarinas.
Casuarinas are pioneer species with the ability to establish and persist on poor sites. They exhibit capacities to flourish under stressed environments that include extremes of soil acidity and salinity, water stress (both flooding or drought), high temperatures, and other adverse conditions. Physiological studies of these tolerances will make possible the best use of the genetic capacities within the group.
Specific research needs into the casuarinas' symbioses include the following:
· Isolation and culture of Frankia strains, optimum methods
of inoculation and nodule establishment, and combinations that most effectively
boost symbiotic nitrogen fixation;
· Vegetative propagation of trees selected on the basis of their ability to nodulate and fix nitrogen; and
· Identification of mycorrhizal fungi, as well as development of inoculation methods and analysis of phosphorus and micronutrient requirements of casuarinas.
Examples of research areas needed on casuarina utilization include:
· The design and planning of shelterbelts;
· Methods of improving land stabilization and controlling erosion;
· Use of casuarinas for biomass plantations;
· Methods for making pulp and particle board from casuarina wood; and
· Conversion of casuarina wood to firewood and charcoal.
RESEARCH ON OTHER SPECIES
This report has highlighted 18 of the 67 species of casuarina. Among the remainder are species certain to be just as valuable as those we describe here - they are merely less we's known. These species offer interesting research challenges to botanists and foresters.
Species worth particular study include the following:
· Casuarina collina A little-known tree native to New
Caledonia. It seems to have properties similar to those of Casuarina glauca, but
it occurs in more humid and tropical areas. It is well worth more-widespread
· Casuarina grandis Often larger than Casuarina cunninghamiana (to 50-60 m), but commonly 35-40 m. This tree is closely related to Casuarina cunninghamiana and Casuarina junghuhniana. It is known only from southeastern Papua New Guinea from near Tufi in the Northern Province to the Gwariu River in the Milne Bay Province. It forms dense stands along rivers, regenerating on gravel banks and other open sites, possibly partly from root suckers.
· Casuarina papuana One of the most attractive species. It makes an excellent ornamental in Hawaii and has pleasing foliage display and red adventitious root masses on the trunk. A medium-sized tree native to Papua New Guinea, it is found at low altitudes and is also scattered in the Highlands. It grows mostly on rocky creek banks or in secondary forests on ridges. The species is useful because it can grow on poorer soils than Casuarina oligodon and tolerates a wide range of rainfall and temperatures in the country. It is used mostly as firewood but can also be used for heavy construction (usually in the round), tool handles, shuttles, charcoal, and pilings permanently submerged in fresh water. The tree grows to 30 m with dark open crown composed of tufted branches; its branchlets are not obviously drooping. It grows commonly in hill and mountain upland areas, notably on poor or variously nutrient-imbalanced soils, but it may also occur along rocky river banks and on top of limestone hills and pinnacles. It is restricted to the Moluccas and New Guinea. The tree is often cultivated, both in villages and in towns; it is known in New Guinea Pidgin as "Hat Yar."
· Casuarina nobilis Tree reaches at least 25 m, with slender bole, growing in various types of forest and bush, usually on nutrient-poor or unbalanced soils. It has been reported by Whitmore and others working on Borneo vegetation as occurring in heath forest (kerangas), peat-swamp forest, forest on ultramafic rocks, and on limestone hills and pinnacles. It has, when young, a bushier habit that Casuarina papuana. It is found in Borneo and New Guinea and is cultivated in towns and settlements (for instance, Kepong, West Malaysia, and Lae, Papua New Guinea).
· Casuarina rumphiana Found in Moluccas, Celebes, and Philippines, in mountain forests, 10-14 m high. It is a slow-growing species. The tree grows to 20-25 m with large open crowns when mature. The "needles" have a tendency to drop somewhat and not to form tufts as bushy as those of Casuarina papuana and Casuarina sumatrana. It grows on dry fire-prone slopes, limestone hills, and volcanic blast areas from low elevations to about 1,000 m. It is a common local tree and is perhaps "encouraged" in villages. On the karstic Lelet Plateau in New Ireland all trees of this species form a striking feature of the landscape, sometimes giving a park-like aspect on the limestone hills. It is the characteristic upland casuarina of New Britain, as well as New Ireland, the Philippines, Moluccas, and the Bismarck Archipelago. It was originally described by Rumphius in the 17th century.
· Casuarina sumatrana A moderately large tree up to 30 m tall with a clear cylindrical bole. It occurs in heath forest in Borneo on very poor, acid soils from sea level to 1,000 m. It grows quickly and has been planted as a fuelwood crop in Sarawak. It produces a very high grade of charcoal and is a popular ornamental tree. The wood seasons well with little degrade. Nodules were found on all 72 trees examined in Bogor. It is slow growing. The tree grows to 30 m with crowns similar to those of Casuarina papuana, but its cones are about twice the size. In Papua New Guinea it is only known from one locality where it grows in swamps mixed with sago palms, but records from Irian Jaya suggest it also grows in nutrient-poor upland areas. The trunk has better form than that of Casuarina papuana; in swamps it may be stilt-rooted. It is found in Burma, Sumatra, Java, Borneo, Celebes, Philippines, western Irian Jaya, and New Britain. It is also cultivated in towns and settlements (for example, Kepong, West Malaysia).
· Casuarina deplancheana An efficient colonizer of ferrallitic soils in New Caledonia. It is resistant to fire. Both endomycorrhizae and nitrogen-fixing nodules with Frankia have been identified on its roots.
· Casuarina spicigera Grows to perhaps 20 m along rocky banks of lowland rivers, like Casuarina grandis (see above). The crowns are fairly open. It is restricted to the northern side of the north coast ranges of Papua New Guinea and also to the Van Rees range of Irian Jaya. The tree is locally cultivated, for example, at Vanimo in Papua New Guinea.
DISSEMINATION OF INFORMATION
The panel recommends that casuarina researchers undertake to publish three documents:
1. A field guide to the identification of members of the family
Casuarina and hybrids between them. This is an urgent task if confusion and
wasted effort are to be avoided as researchers in various parts of the world
begin work with the different species.
2. Planting guides. Handbooks should be published with practical, step-by-step information on propagating, planting, managing, and utilizing the plants.
3. A newsletter. In exploring the potential of casuarinas as useful crops, it will be important to maintain communication among researchers working with the plants. Since these researchers are likely to be situated in far-flung research stations, universities, missions, and villages, their findings may not be widely noted in technical journals. A newsletter would bring together results from botany and forestry science, would provide rapid exchange of information, and would be a forum for informal opinions, observations, and preliminary experimental data that are usually not accepted by journals.