Rainfall, land use and woody vegetation cover change in semi-arid Australian savanna

• Published in: The Journal of ecology Vol. 93; no. 3; pp. 596 - 606
• Main Authors: Fensham, R.J, Fairfax, R.J, Archer, S.R
• Format: Journal Article
• Language: English
• Published: Oxford, UK British Ecological Society 01.06.2005; Blackwell Science Ltd; Blackwell Science; Blackwell Publishing Ltd
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Applied ecology; Biological and medical sciences; botanical composition; Climate change; climatic factors; density dependence; Drought; eucalypt savanna; fire; fires; Forest ecology; Fundamental and applied biological sciences. Psychology; General aspects; Grasslands; grazing; history; Human ecology; land use; Moisture content; Overstory; plant communities; Plant ecology; population dynamics; Rain; rainfall variability; Savannas; structural change; Understory; Vegetation; vegetation cover; water stress; woody dynamics; Woody plants; Queensland; Australia; Oceania; Australia, Queensland; Savannah; Environmental factor; Grazing; Climatic zone; Land use; rainfall variability; Semi arid zone; eucalypt savanna; Fire; woody dynamics; Plant cover; Density dependence; structural change; Drought
• ISSN: 0022-0477; 1365-2745
• DOI: 10.1111/j.1365-2745.2005.00998.x

1 The relative roles of climate and management for driving changes in woody cover in savannas over the past century are the subject of active debate. Perspectives arising from short-term, small-scale, local experiments are rarely tested over larger scales and longer time frames. 2 Regression analysis and aerial photography were used to assess the relative importance of land-use history (fire and grazing), rainfall and initial woody cover (woody cover at the beginning of a sample period relative to the range of woody cover expressed within a land type) in accounting for rates of change in overstorey and understorey cover between the 1940s and 1990s in central Queensland, Australia. Analyses included 279 site-period combinations representing five semi-arid eucalypt savanna land-types within a 125 755 km2 region. 3 Fire and grazing variables provided no explanatory power. In general, relative rainfall (rainfall for a given period standardized against mean annual rainfall) was positively related and initial woody cover negatively related to rates of change in both the overstorey and the understorey. The interaction between rainfall and initial woody cover was significant, reflecting the fact that increases in cover coincided with low initial cover when rainfall is higher than average, whereas decreases in cover typically occurred with high initial cover, regardless of rainfall. 4 On average, overstorey and understorey cover increased over the second half of the 20th century. This pattern is consistent with the first half of the 20th century having more intense droughts and being drier overall than the relatively wet second half. 5 The findings highlight the primary importance of interactions between rainfall fluctuations and density dependence as determinants of large-scale, long-term woody plant cover dynamics in savannas subject to large rainfall excess and deficit over multi-year time-scales.