Decline of Callitris intratropica R.T. Baker & H.G. Smith in the Northern Territory: implications for pre- and post-European colonization fire regimes

Callitris intratropica R.T. Baker & H.G. Smith occurs in a range of environments throughout the lower latitudes of the Northern Territory. A geographic survey of the demographic structure of stands revealed a continuum ranging from populations which have a majority of dead individuals, a lack of regeneration and fire-scarred living adults, to stands with few dead or damaged individuals and a heavy stocking of juveniles. Damaged stands were most common and occurred throughout the species' range, while the healthier stands were more typical on coastal sites with > 30% tree canopy cover. Stands with dense regeneration were significantly associated with an area actively protected from fire by a forestry operation. A helicopter survey on parts of the remote and currently unihabited Arnhem Land Plateau revealed a significantly greater count of dead stems than counts of living Callitris intratropica trees. Detailed studies at one site on the Arnhem Land Plateau showed that there is currently a high mortality of tagged stems, and that the abundant Callitris intratropica stags died since the 1940s. It is argued that the widespread crash of Callitris intratropica populations is a response to a change in fire regime associated with the coming of Europeans.