Life History and Ecology of the Araucariaceae

Araucariaceae: life history and ecology

Araucariaceae is a family of evergreen trees that are usually 60 or more meters. All species of Araucaria genus are in the Southern Hemisphere only, and some specimens of the Agathis genus extend from Malaysia to the equator. Araucariaceae is most prevalent in New Caledonia, the northern part of North Island, New Zealand, but excludes Tonga. In these places, the family is represented by 4 species of Araucaria and 14 species of Agathis. Araucaria heterophylla is restricted to Norfolk Island, Araucaria bidwillii to disjunct locations in south-eastern and north-eastern Queensland, and Araucaria hunsteinii to the eastern half of New Guinea. Araucaria cunninghamii occurs in patches along the Australian northeast coast, and in New Guinea. There are 3 Australian species of Agathis (A. robusta, A. microstachya, A. atropurpurea), that occur principally in vine forests on acidic granites in upland areas receiving 200-300 cm annual rainfall. Agathis Atropurpurea and Agathis microstachya may occur together, but none of the species are found in dense or extensive stands. In southern Queensland, Agathis robusta is also found at Fraser Island on fertile soils in forests dominated by eucalyptuses. Recurrent fire is likely to be important in determining species composition in this case.

In order to look at the life histories and ecology of Araucariaceae, we might want to consider two representatives species, one, Araucaria cunninghamii that grows in New Guinea, and Agathis macrophylla that grows on Vanikoro, in the southern Solomon Islands.

Araucaria cunninghamii lives in fairly moist environments, with average rainfalls from 85 cm to 400 cm and with mean annual temperatures from 11 to 26 degrees Celsius. It is common in lower and mid montane forests at altitudes above 1000 m. As with all Araucaria, it is associated with steep slopes and ridge tops. While the canopy exposes foliage to high radiation and low humidity conditions, cloud interceptions may be an important source of moisture in addition to rainfall. Growth in closed forest is slow and it may take nearly 200 years for individuals to emerge above the angiosperm forest canopy and become reproductively mature. Seedling survival is low and mortality is strongly concentrated on individuals in the first few years. Individual trees may produce in excess of 500 cones in a single year, each containing about 800 seeds. Cones ripen late in the year, and the winged seeds are dispersed early in the wet season. Causes of tree death include storm damage and physiological stress resulting from prolonged shading from other plants. When densities of trees are high, trees are prone to attack from host-specific insects, like the leaf branchlet-mining scolytid, the weevil, and termites.

Agathis macrophylla lives in an area receiving 600 cm annual rainfall. The soils are strongly acidic. Cones hold 110-180 seeds, but only 5-50 percent of these are likely to be fertile. Predation of developing seeds by larvae of moths may further reduce the stock of fertile seeds. Cones ripen and the winged seeds are wind-dispersed in February and March. A maximum seed dispersal distance is 10 km. In the absence of adequate moisture for germination, seeds lose viability within a few months. Growth rates of seedlings in undisturbed forest are slow. It takes 40 years for seedling to reach a height of 0.3 m and 75 years to reach 1.5 m.

Ecology of the Southern Conifers, edited by N.J.Enright and R.S.Hill, Smithsonian Institution Press, Washington,D.C., 1995
de Laufenfels, I.J. "The external Morphology of Coniferous Leaves." Phytomorphology, v.3, n.1,2, March 1953.