by
T.K. Vercoe & M.W. McDonald
Australian Tree Seed Centre
CSIRO Division of Forestry
P.O. Box 4008, Queen Victoria Terrace
Canberra ACT 2600, Australia
ABSTRACT
A brief description of previously unknown populations of E. pellita and some Acacia species on the island of New Guinea is given including geological, climate and vegetation information. The seedlots collected are now available for trial.
INTRODUCTION
The Australian Tree Seed Centre (ATSC), part of CSIRO's Division of Forestry, has been undertaking seed collection expeditions to Papua New Guinea (PNG) since the late 1970's carried out in collaboration with local authorities. The purpose of these visits is to broaden access to the genetic diversity of promising tropical hardwood species through seed collections. The collections mostly complement collections from throughout their range in Australia. Early expeditions concentrated on several of the nine Eucalyptus species that have distributions extending into PNG. In recent years the focus has been on sampling four large tree-form Acacia species that are known to occur there.
The species covered in the present collection are among the priority species identified by the FAO Panel of Experts on Forest Gene Resources for research on taxonomy, germplasm acquisition, provenance trials and tree breeding.
The 1990 collections in Irian Jaya were the first made by the ATSC and resulted from previous collaboration with the Indonesian Department of Forestry (Gunn and McDonald, 1991). The expedition concentrated on the lowlands of the Merauke region (Figure 1). This area warranted investigation as it was known to possess a flora similar to that of Western Province, PNG (van Royen, 1963 and Turnbull, 1982).
The expedition to Lake Murray in PNG sampled the most northern known occurrences of A. mangium and A. aulacocarpa in New Guinea as part of the on-going exploration of acacia populations in collaboration with the Forestry Research Institute of PNG.
SEED COLLECTIONS IN IRIAN JAYA
Access to the hinterland of Merauke is primarily by air or water transport. Merpati Airlines provide one-way weekly flights to seven settlements in the region and passage inland via the river systems is possible. One major road exists - the Trans Irian Highway - extending about 250 kilometres from Merauke to Muting.
Eucalyptus pellita
Extensive stands of this species are located in Irian Jaya and seed collections were made from stands near Bupul and Muting (Figure 1). The populations were observed to extend from Erambu (120 km NE of Merauke along the Trans Irian Highway) to Muting, a traverse that stretches some 130 km. The populations are characterised by the uniform habit of individual trees and their predominance over associated species such as Acacia aulacocarpa, A. mangium, Xanthostemon sp., Stenocarpus sp., Syzygium sp. and Grevillea baileyana. Individuals with clear bole-lengths to 20 metres were quite frequently observed. Seventeen individual parent trees were sampled from three discrete stands.
These previously unsampled populations appear to constitute a core area of occurrence for the species. E. pellita was first recorded in New Guinea during a 1986 seed collection expedition made by the ATSC and the PNG Department of Forests. Seed as collected from relatively small sporadic occurrences associated with monsoon vine forests or drainage systems in the Western Province of Papua New Guinea (Thomson and Cole, 1986). The species historically recognised as E. pellita in Australia (N.B. this taxon is currently under review) has a distribution that extends from Iron Range in far north Queensland (lat. 12°45') south along coastal lowlands to Batemans Bay (lat. 36°45') in New South Wales (Boland et al, 1984). Throughout its extensive range it occurs as a component of mixed, mesic forest types attaining 25–40 metres in height however some ecotypes are known (Boland et al, 1984, House et al, 1991).
In Irian Jaya, the populations appear restricted to the landform known as the “Fly-Digoel shelf” (CSIRO, 1971) in an area which has an annual rainfall of over 2000 mm. The terrain is characterised by low, undulating rises incised by the upper tributaries of the Bian, Kumbe and Merauke Rivers. Soils are deep, well-drained, acidic (pH5), clayey podsols derived from laterite.
The taxonomic link between E. pellita and E. urophylla, which is endemic to islands in East Nussa Tengarra group in Indonesia, has been documented in Pryor and Johnson (1981). Further information on the distribution of E. pellita in Indonesia may make significant contributions to understanding the biogeographical derivations of E. urophylla.
Acacia mangium, A. crassicarpa and A. aulacocarpa
Two landform types determine the distribution of Acacia species in the region. From Merauke to Erambu the terrain is flat and poorly drained typical of the Oriomo plateau while north of Erambu there are low, well-drained undulating rises quintessential of the Fly-Digoel shelf. It would appear that A. crassicarpa is restricted to the Oriomo plateau landform (i.e. south of Erambu) while A. mangium and A. aulacocarpa have distributions that extend to Muting. A. aulacocarpa tended to be more widely distributed than A. mangium and was closely associated with the E. pellita tall open-forests. Tree heights of 30 m were frequently observed for A. aulacocarpa while A. mangium reached 20 m in height.
Due to the scarcity of seed production in populations, small bulked seed collections of A. mangium were made from Bupul and Mutting and small quantities of bulked seed was obtained from A. aulacocarpa stands near Erambu and A. crassicarpa from Samlleberr.
SEED COLLECTIONS IN PNG
Lake Murray
Background
Lake Murray lies at 7°00'S 141°30'E in the central western part of Papua New Guinea (see Figure 1). It is formed by a constriction of the Herbert River above the confluence with the Strickland River. It is fed by several other rivers including the June, the Boi, the Ewe and the Kaim. The complete system empties into the Fly River near Obo and Lake Daviumbu. The lake is quite shallow over most of its area (mostly less than 10 m) and it has dried out several times in living memory (most recently about 1980).
The lake and surrounding area is on the southern part of the Fly-Digoel shelf. It is on the boundary of a major vegetation shift from savanna and monsoon vine forests in the south to increasing Indo-Malayan rainforest elements in the north.
Geology and soils
The Fly-Digoel shelf is made up almost exclusively of highly leached quaternary (approx. 2.5 million years B.P) sediments overlying crystalline granite at greater than 2,500 m depth. These sediments are made up of about 1,500 m of sand and mudstone, 1,000 m of limestone, sand and mudstone, 100 m of mudstone and up to 10 m of clay. The surface soils have been modified by various natural (weathering) and human influences (burning and cultivation) (CSIRO, 1971).
The soils at Lake Murray are loams and sandy loams of varying depths (mostly shallow) overlying yellow and grey clays. Further away from the lake up the slopes, the soils are red sandy clays. Drainage varies from poor at some sections of the lake shore, to good further up slope. The soils appear to be better drained and more fertile than at other A. mangium sites.
Climate
The main difference between Lake Murray and other areas of the Western Province where A. mangium has been collected is the rainfall. The mean annual rainfall is about 3100 mm, which is about 1000 mm greater than Balimo and 1400 mm greater than Morehead. The dry season is also less severe and shorter than either of the other two areas.
Figures for temperature and other climatic variables are not available but it is believed that the temperature would be cooler (in general) than the coast with a greater difference between minimum and maximum temperatures and between seasons. Overall humidity levels would most likely be higher. This is an important factor in selecting provenances for trials in a number of tropical countries. Fungal problems associated with high humidity levels have been encountered with A. mangium in nurseries and trials. There is potential for areas such as L. Murray to provide more fungi-resistant material as well as being more suitable for plantings in high rainfall areas.
The Acacias of Lake Murray
Two Acacia species, A. mangium and A. aulacocarpa are known from the Lake Murray area. Both species are predominant along the foreshores of the lake system with A. aulacocarpa more common than A. mangium. The oldest trees of A. mangium were found on old garden sites where their age could be roughly gauged by talking to the villagers about when they last worked the site. Ages of 15–25 years were mentioned for the older material. Populations remote from the lake shore were restricted to disturbed areas like the Kungun Lake track - a road that was accessible for about 4 km. A. mangium and A. aulacocarpa were occasional to common here while a rival pioneer species Alphitonia sp. was abundant.
Both acacias were of relatively moderate stature compared to populations further east and south, i.e. A. mangium trees were up to 15 m while A. aulacocarpa attained 20 m in height. This is probably a function of the habitat and the way in which this particular disturbed niche is formed through the rise and fall of the water level. Form also was relatively poor as aged individuals, particularly A. mangium, were somewhat sprawling in appearance. A notable characteristic of A. mangium was its relatively large phyllodes.
The lake margin habitat of the acacias at Lake Murray is noteworthy: the fluctuating levels of the lake appear to produce a relatively narrow “disturbed” niche along the lake shore which is colonized by Acacia species. The predominance of an Indo-Malayan rainforest assemblage on the free-draining elevated terrain of the area suggests an aseasonality of climate and a high soil fertility that typically precludes the acacias from vast areas of this type throughout New Guinea. The Lake Murray acacias may be thus viewed as “fringe-dwellers”. They occupy the edges of the lake where periodic inundations control their occurrence and life cycle. This may also explain why the stands are mostly young and the size of the trees generally smaller than trees further south. As opportunists they occupy one of the few open habitats in the area.
Elsewhere along the lake foreshore Melaleuca leucadendra and Lophostemon suaveolens are locally common where lengthy inundation influences plant growth. Tall closed forests, dominated by Indo-Malayan rainforest species (including Calophyllum sp. and Mangifera sp.) attaining 35 m in height, were present at higher elevations. Occasional Gymnostoma papuana were also sighted but all were sterile (in one of the northern villages the people dig up wildlings in the bush and replant them around the village for timber and shelter).
Seed collections
Seed was collected from the Lake Murray area as well as other parts of the Western Province (south of the Fly River on the Oriomo plateau) and is available as bulked samples (from up to 100+ parents) or, in some cases, as individual tree lots from up to 30 parents.
Seed of species referred to in this paper may be obtained by contacting the Australian Tree Seed Centre (see address above), Telex: AA62751, Fax: 61-6-2818312.
ACKNOWLEDGEMENTS
ATSC acknowledges the assistance by staff of the Department of Kahutanan, Merauke, staff of the Department of Primary Industry, Lake Murray and numerous village people from throughout the collection areas.
REFERENCES
Boland, D.J., Brooker, M.I.H., Chippendale, G.M, Hall, N., Hyland, B.P.M., Johnston, R.D., Kleinig, D.A. and Turner, J.D. 1984 Forest Trees of Australia. Nelson-CSIRO.
CSIRO 1971 Land resources of the Morehead-Kiunga Area, Papua New Guinea. Land research series No. 29. CSIRO.
Gunn, B.V.G. and McDonald, M.W. 1991 Seed collections of E. urophylla, E. pellita and acacia species from Indonesia. ATSC internal report.
House, A., Larmour, J., McDonald, M., Morse, G. and Vercoe, T. 1991 Seed Collections from Cape York Peninsular and Papua New Guinea, 1990. ATSC internal report.
Pryor, L.D. and Johnson, L.A.S. 1981 Eucalyptus, the universal Australian. In Ecological Biogeography of Australia. Vol. 1, pp. 501–36 (ed. A. Keast) (Junk, The Hague).
Thomson, L.A.J. and Cole, E.G. 1986 Seed collections in Papua New Guinea. ATSC internal report.
Turnbull, J.W., Skelton, D.J., Subagyono, M. and Eko Bhakti Hardiyanto. 1982 Seed collections of tropical acacias in Indonesia, Papua New Guinea and Australia. Forest Genetic Resources Information 12:2–15. FAO, Rome.
van Royen, P. 1963 Sertulum Papuanum 7. Notes on the vegetation of south New Guinea, Botany 13: 195– 241.
| Figure 1. The seed collection area in Papua New Guinea. |  |
1 In this paper, New Guinea will refer to the land mass irrespective of political boundaries.
2 Manuscript received September 1991
