Main content area

What limits the distribution and abundance of the native conifer Callitris glaucophylla (Cupressaceae) in the West MacDonnell Ranges, central Australia

Prior, Lynda D., Lee, Zoe, Brock, Chris, Williamson, Grant J., Bowman, David M.J.S.
Australian journal of botany 2010 v.58 no.7 pp. 554-564
Callitris glaucophylla, forest trees, indigenous species, geographical distribution, forest fires, seed dispersal, phytogeography, biogeography, population structure, fire regime, history, tree mortality, diameter, plant density, seedlings, recruitment, drought, water stress, Northern Territory
The conifer Callitris glaucophylla J.Thompson & L.A.S.Johnson (Cupressaceae) is a fire-sensitive obligate seeder with a heavily fragmented distribution across the Australian continent. We undertook a broad-scale biophysical survey and analysed the population structure of 21 populations in the West MacDonnell Ranges of central Australia. C. glaucophylla had a patchy distribution associated with steep, rocky metamorphic areas with limited evidence of fire. Variation in population structures was clearly related to recent fire history. Nearly half of 'adult' C. glaucophylla trees (>5-cm stem diameter) from the sampled stands were dead, with the proportion at individual sites related to evidence of fire. Fire scars were evident on 48% of all live trees we measured. The overall density of live adult trees conformed to a negative exponential size-class distribution, consistent with a regionally stable population structure. However, we found higher sapling densities and lower seedlings densities than expected by this distribution. This regional peak in the sapling size class reflects a pulse of recruitment, possibly associated with a wet period in the 1970s. Low seedling densities are probably due to subsequent drought. We conclude that fire controls the distribution of Callitris on the West MacDonnell Ranges, and the timing of recruitment depends on rainfall patterns.