Demography of the long-lived conifer Agathis ovata in maquis and rainforest, New Caledonia

The endemic New Caledonian conifer Agathis ovata occurs as an emergent tree in fire-prone shrublands (maquis), and fire-sensitive rainforest. Growth, survivorship and recruitment over 5 yr were compared for populations from forest and maquis on ultramafic substrates in New Caledonia to investigate whether demographic behaviour varied in response to the strongly contrasting forest and shrubland environments. Growth of seedlings and of small (30-100 cm height) and large (100 cm height; 5 cm DBH) saplings was slow, but varied significantly among stages, site types and years. The greatest difference in growth rates was among stages, seedlings growing 0.34 cm.yr–1, small saplings 1.06 cm.yr–1 and large saplings 2.13 cm.yr–1. Tree DBH increased by only 0.05 cm.yr–1 and, based on these rates, individuals with DBH of 30 cm are estimated to be more than 700 yr old. Few trees (3.5%) produced cones in any year and seedling recruitment was low, but some recruitment was recorded each year in both maquis and forest. Rates of recruitment per parent were highest in forest (1.28.yr–1, cf 0.78.yr–1), but the higher density of trees in maquis meant that overall recruitment was greater there (92 ha–1.yr–1, cf 56 ha–1.yr–1). Seedling mortality ranged from 0.9 to 2.9% among years with no significant difference between maquis and forest. No sapling mortality was recorded, but annual tree mortality ranged from 0 to 1.4%. Evidence from a recently burned site indicated that while trees may survive fire, seedlings and saplings do not. Post-fire seedling recruitment per ha from surviving trees was four times lower than in unburned sites, but growth rates were four times higher. Similar demographic attributes, including high survivorship, low growth rate and low rates of recruitment over a long reproductive life, characterize Agathis ovata populations in both maquis and rainforest in New Caledonia and are indicative of a broad tolerance of light environments that is unusual among tree species. These demographic attributes help to explain the long-term persistence of the species in these strongly contrasting habitats.