Bunya, also called Bunya Pine, Bunya-bunya.

Araucaria bidwillii

Origin:

The tropical and sub-tropical genus Araucaria (19 species) originated in rain forests. Most species are endemic to Australia, New Zealand, New Caledonia and Papua New Guinea, with another two in South America. In earlier times the genus was more widely distributed globally, and it's thought extinction and habitat loss has primarily been due to gradually increasing aridity over the millennia. Bunya is a very ancient species with fossil records dating back 185 million years.

Climate:

Native populations of bunya are found in Queensland in two widely separated regions, northern and southern. Annual precipitation for the southern group is 1100-1400mm in summer with a dry season from April to September. The geographically constrained northern population has a more even rainfall distribution of 1500-2000mm but is considered a relict population vulnerable to extinction. Elevation restraints in both regions are 150-1000m. Mature bunyas are reasonably cold-tolerant to about -5°C

Plant Description:

A large gymnosperm tree – long-lived, slow-growing, single-trunked, evergreen, coniferous and resinous, monoecious, and can grow to more than 50m. Branches are approximately horizontal outwards from the trunk and can curve upwards terminally, up to 7m long, and are arranged in a whorl around the trunk with tufts of spiky imbricate and long-lived leaves clustered towards branch ends. Leaves spiral round branchlets and are narrowly triangular, imbricate, coriaceous, 10-50 X 3-15mm, with fine, numerous, parallel non-conspicuous veins. The thick bark is grey-black and exfoliates in horizontal strips. Trees develop a distinctive open base, dome-shaped canopy as they mature and drop individual leaves and lower branchlets and branches.

Relatives:

The three genera in the Araucariaceae family are primarily native to the southern hemisphere. Bunya relatives include Norfolk Island Pine, Monkey Puzzle tree and the Wollemi Pine, first discovered in 1994. The closest relative to bunya is A. hunsteinii which is native to PNG and can grow to a 50-90m giant with a trunk diameter of 3m. Although these trees are all conifers and produce cones, they are not members of the Pinaceae, illustrating how common names can be misleading.

Soils:

Rich, moist, well-drained volcanic soils are best, but it can grow in most types. The pH can be acid, neutral or basic, and bunya shows some tolerance to salt spray.

Propagation:

Mainly by using seeds which are recalcitrant with no dormancy period, germinating rapidly in moist soil when fresh. After imbibition, seeds undergo an unusual process called cryptogeal germination. They rapidly produce a fleshy below-ground tuber (an enlarged hypocotyl): almost all the starch reserves of the seed are efficiently transferred to the tuber, and then the seed detaches from the tuber. Several months or sometimes years later the tuber sends a shoot up through the overlying soil, and then begins photosynthesis and subsequently develops into the tree. Cuttings have also been successful but must be taken from upright-growing shoots; cuttings from side shoots will not grow erect.

Cultivars:

None known. The species exhibits significant genetic diversity, and the northern group could become increasingly important for breeding studies that may help save the species from extinction. The extremely long life cycle of bunya makes any breeding work to improve qualities, eg juvenility period, tree size and regular cropping, very challenging.

Flowering and Pollination:

Male axillary cones in small clusters of 2-6 are cylindrical, 6-15 X 8-15cm, initially erect then pendulous at anthesis. Solitary erect female cones on a short peduncle are ovoid-sub-globose, 20-30 X 20-25cm, and can weigh 4-5kg or more. The female seed cones (the heaviest in the conifers) often form higher in the tree than male, are dark green in colour and often fall whole, ie without dehiscing. Pollen cones usually appear in April and mature in September or October and seed cones are produced in December to March about 17 months after pollination. Whorled cuneate woody bract/scales that make up most of the seed cone contain one brown seed each and terminate with a curved caducous tip. Pollination is by wind and fertilisation may take many months.

Cultivation:

Bunya is a flexible species and can be grown in many climates and regions outside its endemic areas. Only minimal fertilisation is necessary as it's not particularly nutrient hungry. Ectomycorrhizal associations are not formed, and there is a preference for uptake of nitrogen in the nitrate form rather than ammonium. Allowance should be made for aggressive surface roots that may occur. It can be grown in a container for a few years before having to be planted out.

Wind Tolerance:

Good. They can be made into windbreaks, and grown in windy coastal areas despite their height.

Pruning:

Branches below head height are pruned for safety reasons. Central stem pruning when young can encourage some branching to reduce height.

The Fruit:

Fallen seed cones turn from green to creamy-brown as they dry out. The edible parts are the wingless seeds - there could be 30-100 of these per cone, cuneate 4-5 X 2.5-3cm, with each one surrounded by a woody (29% of seed dry weight) non-edible tan-coloured seedcoat. Tubers are also edible. The dried kernel contains about 65% starch, 8% of protein and 8% fibre.

Fruit Production and Harvesting:

Bunya seedlings may take some decades before cropping. The fruiting cycle in mature trees (pollen release through to mature cones) extends beyond a single year, resulting in irregular yearly cropping resembling alternate bearing in other species. The norm is for a large crop one year, followed by a number of intervening years of low yield. 2018 was a bountiful year, so the next big crop may be 2-3 years away.

Fruit Uses:

Nuts that will be stored for some time should be frozen to prevent the nutmeat turning rancid. Energy reserves are stored almost exclusively as starch, unlike most other nuts where oils predominate. It's claimed they can be eaten raw from a fresh cone, but for most people the flavour becomes much more enjoyable when roasted. If roasting, pierce the seedcoat beforehand (as with chestnuts) to avoid explosions. They can also be prepared by boiling, which softens the tough seedcoat; then the two ends of the seed are gripped and bent backwards to allow the kernel to slide out. Kernels are also sometimes dried, frozen, or ground into a flour. Bunya nut flour can be used in soups, desserts, breads and many other dishes. The tuber is often described as having a coconut-like flavour.

Pests and Diseases:

Bunya plants are pest-tolerant.

Comments:

Bunyas are iconic Australian trees. In the past they were extremely important for indigenous Australians as they provided a major food source in the main cropping year. At those times they had great social events when messages were sent to other tribes to come together and share the bounty. This is not a tree for suburban gardens given it will become so overwhelmingly dominant. In parks and other suitable large areas where they can be grown, for safety reasons a large area around the base of the tree should be fenced off until all the cones have fallen. With suitable cherry pickers and cranes, mature cones can be harvested from the canopy.