THE ECOLOGY AND VARIATION OF EUCALYPTUS CAMALDULENSIS DEHNH.

by

J.W. Turnbull
Forest Research Institute, Canberra

INTRODUCTION

The river red gum, Eucalyptus camaldulensis, is the most widely distributed eucalypt in Australia. It has been an outstanding success as a plantation tree in many countries and rivals E. globulus as the most important exotic eucalypt. Its success as an exotic is due to its ability to grow rapidly under a wide range of climatic and soil conditions. Lack of knowledge of the ecology and variation of the species combined with the difficulty in obtaining seed from the more inaccessible regions of its natural range have resulted in the rich gene pool of E. camaldulensis being scarcely utilised.

DISTRIBUTION

E. camaldulensis occurs over more than 5 million km² of mainland Australia in all areas except the southern parts of Western Australia and the coastal fringes of Victoria, New South Wales and eastern Queensland. Between the latitudes 14°S – 38°S its principal distribution is at altitudes 30 m – 225 m but reaching 600 m in the interior (Hall, Johnston, Chippendale, 1970).

It is a species characteristic of water courses, either along rivers, on the adjoining levee banks or on flood plains. In the arid areas and in the tropical regions with a long dry season there is water in the water-courses only for short periods and the river red gum forms a narrow fringe along the margins and frequently also grows in the river-bed.

The species grows in forest formation in two areas:

1. On the plains and hill country in South Australia and Victoria, at approximate latitudes 36°S – 37°S, elevation c. 300 m in limited areas on heavy impermeable soils.

2. On the flood plains along the Murray River in southern Australia where there are large areas of almost pure forest on clayey soils. These sites are inundated for several months each year and the soils crack extensively during the dry season.

The main factors limiting its distribution are temperatures lower than -7°C and its inability to become established unless soil moisture is high for several months following seed germination. Edaphic conditions appear to impose few limits on its occurrence. It occurs on heavy clay in the south, and in the north it is more generally found on sandy alluvial soils. In certain areas, such as near Port Lincoln (South Australia) and Wiluna (Western Australia), it grows on shallow soils over limestone.

Although soil moisture is essential during the early seedling stage, once established E. camaldulensis is one of the most drought tolerant eucalypts and can exist in areas with very low and unreliable rainfall.

CLIMATE

E. camaldulensis grows under a wide range of climatic conditions from tropical to temperate, but the main areas are characterised by 5 to 20 frosts in winter and high summer temperatures. Temperature conditions may vary from a minimum of -6°C to a maximum of 54°C with a diurnal range up to 21°C. The annual rainfall is mainly 250 mm – 650 mm but may reach 1 000 mm in limited areas. In the areas of below 400 mm the species relies on irrigation by seasonal flooding, or a high water table.

Australia has been divided into climatic zones (Anon, 1955). The zones in which E. camaldulensis occurs have the following characteristics:

(1) Tropical Dry West Coast: Rainfall occurs from summer cyclones. The annual rainfall is relatively low, 500 mm – 600 mm, and the winter season is practically rainless. Average annual relative humidity is about 63 per cent. Frosts are rare. The lower reaches of the Ashburton and Fortescue rivers in Western Australia are situated in this zone and the climatic data for Broom (W.A.) are typical (see table on p. 40).

(2) Tropical Inland, Tropical Interior and Tropical Highlands: Rainfall occurs principally in summer. Rainfall and humidity show a fairly uniform decrease from the coast inland, and eventually the accumulated difference becomes marked. In the tropical inland rainfall is appreciable, 650 mm or more and humidity is high, 50 per cent, but the tropical interior has a relatively low rainfall, 250 mm – 450 mm, a low humidity, 34 per cent, and a moderate temperature range. The tropical highlands of northeast Queensland have a relatively high rainfall, 500 mm – 750 mm, a high humidity, 63 per cent, and more rain in winter than the tropical inland and tropical interior. Frosts are rare or absent.

The tropical inland includes the Fitzroy, Lennard, Isdell, Gibb, Drysdale and Ord rivers of the Kimberley area of Western Australia, the Victoria and Katherine rivers of the Northern Territory, and the Leichhardt, Cloncurry, Gilbert, Mitchell and Palmer rivers of northern Queensland. Halls Creek (W.A.), Daly Waters (N.T.), Katherine (N.T.) and Georgetown (Qld.) have climatic data typical for this zone.

The tropical interior includes many inland rivers which do not reach the sea. In this zone are the upper reaches of the Fortescue River, in the Hammersley Range, and Sturt Creek, in Western Australia, Yallagoorie Creek, Napperby Creek, Tennant Creek and the Todd River in the Northern Territory, and the Diamantina River, Queensland. Climatic data for Marble Bar (W.A.), Tennant Creek (N.T.), Alice Springs (N.T.) and Baracaldine (Qld.) are typical for this zone.

The tropical highlands zone is a narrow, north-south orientated strip near the east coast of Queensland. It includes the Isaacs, Burdekin and the upper Walsh rivers. The well known Petford provenance occurs in this zone. Charters Towers has a climate representative of the zone. The nearest station to Petford is Mount Surprise (Qld.).

(3) Subtropical Inland, Subtropical Interior: The subtropical inland and subtropical interior are differentiated mainly by the amount of summer humidity and total rainfall. Rainfall is low, 250 mm, with a slight peak in summer. Humidity is not high even in summer and becomes very low in winter. Mean annual humidity is near 40 per cent in the subtropical inland and closer to 30 per cent in the interior. There is an appreciable range in both diurnal and seasonal temperatures. Light frosts may occur from June to August.

In eastern Australia the rivers of these zones form the upper reaches of the Murray-Darling river system and to a smaller extent, the Lake Eyre system. They include Coopers Creek, the Bulloo, Paroo, Warrego, Balonne, Barwon and Gwydir rivers. In Western Australia the Gascoyne and Wooramee rivers occur in the subtropical interior zones. Representative climatic stations for the subtropical inland are Moree (N.S.W.) and Roma (Qld.); for the subtropical interior Thargomindah (Qld.), Cunnamulla (Qld.), Mundiwindi (W.A.) and Mount Magnet (W.A.) are typical.

(4) Temperate Inland, Temperate Interior: Rainfall is principally in winter in the temperate zone. It ranges from about 250 mm in the temperate interior to 650 mm or more in the temperate inland. The humidity in the temperate inland, 60–70 per cent, is higher than in the temperate interior, 45–55 per cent. Frosts are a feature of the winter and spring months.

These climatic zones occur throughout most of New South Wales, Victoria, and the southern parts of South Australia and Western Australia. The main river system is that of the Murray-Darling with their tributaries such as the Castlereagh, Macquarie, Lachlan and Murrumbidgee rivers. Most of Eyre Peninsula, including Port Lincoln, and the Goldfields area of Western Australia, particularly the Leonora district, are in these zones. The well known Lake Albacutya provenance is in the temperate inland zone. Typical climatic data for the temperate inland zone are from Dubbo (N.S.W.), Wagga Wagga (N.S.W.), Nhill (Vic.) and Peterborough (S.A.). In the temperate interior data from Ivanhoe (N.S.W.), Broken Hill (N.S.W.) and Laverton (W.A.) are representative. Rainbow (Vic.) is the nearest station to Lake Albacutya, and Chapman (W.A.) the nearest to Murchison River.

(5) Dry Continental Interior: The rainfall is very low, 150 mm – 300 mm, unreliable, and may have a slight maximum in summer or be evenly distributed throughout the year. Winters are cool and frosts may occur from May to August. There is a considerable range in the diurnal and seasonal temperatures. Relative humidity is low, 30–35 per cent.

Within this zone E. camaldulensis is scattered along water courses in the Lake Eyre system such as the Finke and Alberga rivers in South Australia. In Western Australia it is found in the Wiluna and Meekatharra areas. Representative climatic stations are Finke (N.T.), Oodnadatta (S.A.) and Wiluna (W.A.).

VARIATION

Although there are no currently recognised varieties of E. camaldulensis the fact that varieties have been erected in the past is evidence of considerable variation within the species. Blakely (1965) lists five varieties and Pryor and Byrne (1969) suggest that many others of equivalent status could be selected. There are taxonomic problems in treating a species in which there is evidence of both clinal variation and formation of ecotypes.

From a study of what is known of the variation pattern it is clear that the northern populations are significantly different from southern populations. Pryor and Byrne (1969) report differences in the operculum shape, the shape and glaucousness of juvenile leaves, bark colour, presence or absence of lignotubers and branching habit. Karschon (1972) suggests a possible division into two sub-species north and south of a line running from Rockhampton, Queensland (23°S), to Broome, Western Australia (18°S). This is also the approximate dividing line between areas of summer and winter rainfall.

The concept of two sub-species is deceptively simple as a closer examination of a large number of provenances shows. A study of the polyphenols of the leaves and seeds of E. camaldulensis from 62 localities throughout Australia was made by Banks and Hillis (1969). Their data showed that there was a north-south division but that within the two regions divergence has taken place between the major drainage systems. This pattern has arisen because the species is chiefly confined to watercourses and there has been no opportunity for gene flow between populations in adjacent drainage systems. Four geographical regions, Kimberley (W.A.), Southwest (W.A.), Pacific (eastern Qld.) and Southeast (Murray-Darling Rivers), were clearly delineated on the basis of phytochemical differences. Poor correlations were obtained for a large area extending from inland Queensland through Central Australia. This may have been due to the uncoordinated drainage pattern over the region, which has resulted in isolated populations. A more intensive sampling could have revealed a pattern.

The phytochemical provenances of Banks and Hillis correspond largely to morphological observations on seedlings and adult material (Larsen, unpublished). Within each region there is still considerable variation including variation in physiological characteristics, e.g. tolerance of extremes of temperature, and adaptation to high alkalinity or salinity (Karschon 1971a, 1971b; Lacaze, 1970).

The selection of seed from different drainage systems within a broad climatic classification offers the best overall guide for the choice of material for initial provenance trials. Within the interior a more intensive representation may be necessary to sample the variation pattern. The following provenance groups will assist in the sampling.

1. Murray-Darling System

1. Approximate location: Southeast Australia, 25°S–37°S, 140°E–150°E.

2. Climatic zones: Temperate inland, temperate interior, subtropical inland. The typical southern form of E. camaldulensis is in this region.

2. Wimmera Basin

1. Victoria, 35°S–37°S, 142°E–144°E.

2. Temperate inland. This is a small internal drainage system which includes several salt lakes, e.g. Lake Albacutya.

3. Northeast Slopes

1. Eastern Queensland, 16°S–26°S, 145°E–150°E.

2. Subtropical highlands, tropical highlands.

There is a well defined form, intermediate between E. camaldulensis and E. tereticornis, occupying this region. It follows the western slopes of the Great Dividing Range but extends across it in the Charters Towers area and on Cape York Peninsula. It is a zone of gradual change from E. camaldulensis in the west to E. tereticornis in the east but the cline may be disturbed by introgression of E. alba. The well known Petford provenance is in this region.

4. Gulf of Carpenteria

1. Northwest Queensland, eastern Northern Territory. 17°S–22°S, 136°E–145°E.

2. Tropical inland.

The E. camaldulensis in this region has the typical appearance of the northern form.

5. Timor Sea Drainage

1. Kimberley area of northern Western Australia, northwest Northern Territory, 14°S–18°S, 124°E–133°E.

2. Tropical inland.

The typical northern form of E. camaldulensis, usually with a well defined axis, occurs in this region. In the Kimberley area there is evidence of some hybridisation with E. alba. The Katherine provenance has been the main representative of this region in provenance trials.

6. Indian Ocean Drainage

1. Coastal Western Australia, 20°S–29°S, 114°E–120°E.

2. Tropical dry west coast, tropical interior, subtropical interior.

In the southern part of this region there is introgression with E. rudis.

7. Western Interior

1. Central Australia, 17°S–35°S, 119°E–136°E.

2. Tropical interior, subtropical interior, temperate interior, temperate inland, dry continental interior.

This is an area of uncoordinated drainage with isolated populations. Some of the more drought resistant provenances probably occur in this region.

8. Lake Eyre Basin

1. Northern South Australia, south eastern Queensland, 20°S–32°S, 133°E–145°E.

2. Tropical interior, subtropical interior, dry continental interior.

This region covers a large area with a small and unreliable rainfall, provenances adapted to drought conditions probably occur in the area. It is a region of internal drainage.

SEED AVAILABILITY

E. camaldulensis has been planted extensively throughout the world. Practically all the seed for these plantations was from the forests along the Murray River, or from inland areas in New South Wales. Even now almost all bulk seed of this species collected in Australia comes from the Murray-Darling System.

Since 1964 the Forest Research Institute in Australia with assistance from F.A.O. has made seed collections of E. camaldulensis from throughout its natural range. These collections have primarily been intended to make available a wide range of provenances for research. Small research samples from most river systems are available at a nominal cost or on an exchange basis. More recently it has been possible to make larger collections of seed from localities which have shown early promise of being superior in provenance trials, e.g. Lake Albacutya, Silverton, Port Lincoln, etc.

REFERENCES

ANON. (1955). Atlas of Australian Resources, Climatic Regions, Drainage Systems. Dept. National Development, Canberra.

BANKS, J.C.G. and HILLIS, W.E. (1969). The characterisation of populations of Eucalyptus camaldulensis by chemical features. Aust. J. Bot. 17: 133–146.

BLAKELY, W.F. (1965). A Key to the Eucalypts. 3rd Ed. Forestry and Timber Bureau, Canberra. pp. 359.

HALL, N. (1972). Summary of Meteorological data in Australia. Leaflet No. 114, Forestry and Timber Bureau. Canberra, pp. 72.

HALL, N., JOHNSTON, R.D. and CHIPPENDALE, G.M. (1970). Forest Trees of Australia. 3rd Ed. Aust. Govt. Pub. Serv., Canberra. pp. 333.

KARSCHON, R. (1971a). Low Temperature Effects on Ecotypes of Eucalyptus camaldulensis Dehn. Leafl. Div. For. Volcani. Inst. Agric. Res., Ilanot, No. 40.

KARSCHON, R. and PINCHAS, LYDIA (1971b). Variations in heat resistance of ecotypes of Eucalyptus camaldulensis Dehn. and their significance. Aust. J. Bot. 19:261–272.

KARSCHON, R. (1972). A summary of ecotypic variation in Eucalyptus camaldulensis Dehn. Oxford Univ. For. Soc. J. 7th Series. No.2:9–13.

LACAZE, J.F. (1970). Project No.6: Etude de l'Adaptation Ecologique des Eucalyptus. Compte rendu operationnel (1970). Docum. 4th Sess. For. Res. Comm., F.A.O. Jt. Subcomm. Medit. For. Probl., Ankara. 21 pp.

PRYOR, L.D. and BYRNE, O.R. (1969). Variation and taxonomy in Eucalyptus camaldulensis. Silvae Genet. 18:64–71.

TURNBULL, J.W. (1973). Report on Northern Territory - Kimberley seed collection expedition, May–July, 1972. For. Genet. Res. Info. FAO For. Occ. Paper 1973/1:26–28.

APPENDIX     CLIMATIC DATA FOR SOME METEOROLOGICAL STATIONS IN AUSTRALIA

Note:

a) Sources: 1) Average Climatic Water Balance Data of the Continents,
Part IV, Australia, N.Z., and Oceania.
C.W. Thornwaite Associates, Laboratory of Climatology
Publications in Climatology Vol. XVI No. 3
Centerton, New Jersey 1963

2) Climatic Averages: Australia. Meteorological Summary.
Commonwealth of Australia, Bureau of Meteorology
Iss. by the Director of Meteorology
Melbourne 1969

3) Summary of Meteorological Data in Australia.
Forestry and Timber Bureau Leaflet No. 114.
Compiled by N. Hall.Canberra 1972

4) Forestry and Timber Bureau, Canberra.
(In: The Rhodesia Bulletin of Forestry Research No.2 (Part 1)
Rhodesia Forestry Commission 1970).

b) Observations: P = mean monthly precipitation, mm
Max = mean monthly maximum temperature °C (approximate)
Min = mean monthly minimum temperature °C (approximate)