Fire regimes and interval-sensitive vegetation in semiarid Gregory National Park, northern Australia

Jeremy Russell-Smith, C YATES, Chris Brock, V Westcott

    Research output: Contribution to journalArticle

    Abstract

    Few data are available concerning contemporary fire regimes and the responses of fire interval-sensitive vegetation types in semiarid woodland savanna landscapes of northern Australia. For a 10300km2 semiarid portion of Gregory National Park, in the present paper we describe (1) components of the contemporary fire regime for 1998-2008, on the basis of assessments derived from Landsat and MODIS imagery, (2) for the same period, the population dynamics, and characteristic fine-fuel loads associated with Acacia shirleyi Maiden (lancewood), an obligate seeder tree species occurring in dense monodominant stands, and (3) the fire responses of woody species, and fine-fuel dynamics, sampled in 41 plots comprising shrubby open-woodland over spinifex hummock grassland. While rain-year (July-June) rainfall was consistently reliable over the study period, annual fire extent fluctuated markedly, with an average of 29% being fire affected, mostly in the latter part of the year under relatively harsh fire-climate conditions. Collectively, such conditions facilitated short fire-return intervals, with 30% of the study area experiencing a repeat fire within 1 year, and 80% experiencing a repeat fire within 3 years. Fine fuels associated with the interior of lancewood thickets were haracteristically small (<1tha-1). Fine fuels dominated by spinifex (Triodia spp.) were found to accumulate at rates quivalent to those observed under higher-rainfall conditions. Stand boundaries of A. shirleyi faired poorly under prevailing fire regimes over the study period; in 16 plots, juvenile density declined 62%, and adult stem density and basal area declined by 53% and 40%, respectively. Although the maturation (primary juvenile) period of A. shirleyi is incompletely known, assembled growth rate and phenology data indicated that it is typically >10 years. Of 133 woody species sampled, all trees (n=26), with the exception of A. shirleyi, were resprouters, and 58% of all shrub species (n=105) were obligate eeders, with observed primary juvenile periods < 5 years. Assembled data generally supported observations made from other northern Australian studies concerning the responses of fire-sensitive woody taxa in rugged, sandstone-derived landscapes, and illustrated the enormous challenges facing ecologically sustainable fire management in such settings. Contemporary fire regimes of Gregory National Park are not ecologically sustainable. 
    Original languageEnglish
    Pages (from-to)300-317
    Number of pages18
    JournalAustralian Journal of Botany
    Volume58
    Issue number4
    DOIs
    Publication statusPublished - 22 Jun 2010

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