Figure 8
Conceptual model of the stand and spatial dynamics of Callitris intratropica on sand sheets on the Arnhem Plateau, based on a synthesis of results from this and previous publications (see main text for details). (a) Small C. intratropica groves (stands) fluctuate in size and structure in response to fire damage which affects the ability of groves to exclude flammable grasses. The incursion of grasses into the stands allows fires to repeatedly burn into the groves. Once degraded, groves often die or are reduced to single isolated trees within a relatively short period of time. Singleton trees eventually die or, if fire frequency is reduced, can lead to the development of a new fire-excluding grove. Seed dispersal can also lead to new groves if seedling cohorts are able to establish in areas free from fire for several decades. In the diagram, the width of each arrow reflects our approximation of likely probability of the transition between the various states. (b) Under traditional Aboriginal fire regimes, the stand dynamics result in an ever-shifting mosaic of groves and singleton trees on fire exposed Eucalyptus sand sheet savannas. Under the modern fire regime of Kakadu National Park, the frequency and intensity of fires has increased such that the groves have been destroyed and most singleton trees on sand sheets have died. This is a gradual process that commenced in the twentieth century following the breakdown of traditional Aboriginal fire management. We suspect that complete elimination of C. intratropica on fire-exposed sand sheets is likely in the next few decades under current fire regime.
