Decline of Callitris intratropica R. T. Baker & H. G. Smith in the Northern Territory: Implications for Pre- and Post-European Colonization Fire Regimes

Abstract

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 for 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 heaqvy stocking of juveniles. A TWINSPAN classification divided this continuum into four groups. There were no significant differences between the cover of rocks, grass or shrubs between the four groups of stands, nor was there a significant association with substrate type. 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 uninhabited Arnhem Land Plateau revealed a significantly greater count of dead stems than counts of living C. 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 C. intratropica stags died since the 1940s. It is argued that the widespreadt crash of C. intratropica populations is a response to a change in fire regime associated with the coming of Europeans.