Preliminary assessment of gidgee (Acacia cambagei) woodland thickening in the Longreach district, Queensland

Abstract

Abstract. Gidgee (Acacia cambagei) forms woodlands and forests on moderately fertile clay soils throughout semi-arid areas of north-eastern Australia. Analysis of soil data from Queensland indicates that gidgee's environmental domain has a broad overlap with treeless Mitchell grassland although a preference for slightly coarser soils with higher phosphorus and lower potassium content. Mapping of woody cover change for an area of central Queensland suggests that gidgee thickening and spread has occurred between 1951 and 1994. However, this increase has been more than offset by loss of gidgee cover by clearing in other areas. Gidgee thickening and encroachment onto grassland is a problem for graziers because the trees suppress grass and are unpalatable except when very young. Landholder surveys and other information indicate that gidgee has recruited sporadically and that thickening occurred with a massive seedling recruitment in the 1950s with a smaller recruitment wave in the 1970s. These waves coincide with relatively wet times and the extreme rainfall abundance in the 1950s has a multi-century expected recurrence. There are historical records describing gidgee death during the extreme droughts in the first part of the 20th century. Young gidgee plants are fire sensitive but well-established gidgee stands are fire retardant, and the importance of fire for control of gidgee thickening is unknown. One scenario explaining gidgee dynamics emphasises the role of environment (mostly climate and soil), while another emphasises management (mostly fire). Research priorities are presented and may contribute to appropriate management of gidgee woodlands.

A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests

“…(2008) Footnotes as in Table A1. Fensham and Fairfax (2005) Footnotes are as given in Table A1 1973-1976, 1987-1993, 1996-2000, 2000-2004 Temperate mixed conifer and broadleaf (500-600)…”

“…In the sub-humid environments of northeast Australia ( Fig. 5; Table A3), multi-year droughts have repeatedly triggered widespread Eucalyptus and Corymbia mortality (Fensham and Holman, 1999;Rice et al, 2004;Fensham and Fairfax, 2007), and have also caused tree death in Acacia woodlands (Fensham and Fairfax, 2005). There is also documentation of drought-induced mortality in temperate Nothofagus forests in New Zealand (Hosking and Hutcheson, 1988).…”

Climate‐related trends in Australian vegetation cover as inferred from satellite observations, 1981–2006

“…Russell‐Smith et al (2004) and Brook & Bowman (2006) report the expansion of rainforest into open Eucalypt forest in northern and north‐eastern Australia, and Butler et al (2006) report the invasion of Eucalypt trees into montane grasslands in south‐east Queensland. Increases in the cover of woody species have been observed in semiarid woodlands and shrublands in the west (Watson et al , 2007), north (Fensham & Fairfax, 2003) and north‐east of Australia (Fensham & Fairfax, 2005; Krull et al , 2007). Most of these studies attribute observed vegetation changes to altered management regimes – notably fire regimes – over the past 50–100 years.…”

A continent under stress: interactions, feedbacks and risks associated with impact of modified land cover on Australia's climate

“…This was attributable to a reduction in pasture burning in grazing lands. Fensham & Holman (1999) and Fensham & Fairfax (2005) recorded evidence of locally occurring tree death in eucalypt and acacia woodlands in the same region attributed to the increased competition for soil moisture during drought. In south‐west Queensland, the extreme drought experienced from 2001 to 2006 resulted in substantial death of long‐lived perennial grasses, trees along watercourses and extensive areas of understorey native shrubs (Hassett et al , 2006).…”