An assessment of the environmental impacts of Cyclone Larry on the forest landscapes of northeast Queensland, with reference to responses to natural resource management issues in the aftermath

Turton, Stephen M., and Dale, Allan (2007) An assessment of the environmental impacts of Cyclone Larry on the forest landscapes of northeast Queensland, with reference to responses to natural resource management issues in the aftermath. Report. James Cook University & CSIRO, Cairns, QLD, Australia.

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[Extract] Introduction Disturbances, both natural and anthropogenic, shape forest ecosystems by controlling their species composition, structure and functional processes. The tropical forests of the Wet Tropics of northeast Australia have been moulded by their natural disturbance and land-use history and over many millennia but particularly over the past 100 years1. Forests of the region are subjected to a range of natural disturbances, including bush fires, droughts, floods, occasional landslides and tropical cyclones. All these natural disturbances interact in complex ways with anthropogenic disturbances across the landscape, such as land-use change resulting from forest conversion to agricultural systems, indigenous fire management regimes, earlier logging practices, urban and peri-urban development and infrastructure projects, such as major roads, powerline corridors and dams.

Tropical cyclones are significant natural disturbance phenomena for forest ecosystems in the Wet Tropics of northeast Australia, especially for forests near the coast2. For this reason, even continuous forests in the region have been described as hyper-disturbed ecosystems with patches of damaged forest constantly recovering from previous cyclonic events, often in concert with floods, droughts and fires. Cyclones are part of the ecosystem dynamics of these forested landscapes and recovery of canopy cover following such events is often remarkably rapid, although forest structure and composition may take many decades to recover. The same cannot be said for fragmented forests in the Wet Tropics, located within either an agricultural, urban, linear infrastructure or grassland matrix. These forest fragments are particularly vulnerable to impacts of tropical cyclones and their associated strong winds, largely due to their high forest edge to area ratios.

Severe cyclones cause widespread defoliation of rainforest canopy trees, removal of vines and epiphytes, along with the breakage of crown stems and associated tree falls. These catastrophic impacts typically result in significant changes in forest microclimates in the understorey and canopy, and complex vegetation and faunal responses to newly created light, temperature and humidity regimes. Cyclonic disturbance has also been shown to accelerate invasion by exotic tree, vine and grass species leading to a decline in biodiversity of native plant species in some forest regions.

Given the relatively high frequency of tropical cyclones, there is a general consensus that they contribute to the structure and function of tropical rainforests in cyclone-prone areas, with ecosystem impacts and recovery processes occurring at several spatial and temporal scales. Impacts of tropical cyclones on forests at the landscape-scale (>10km) are the result of the complex interaction of anthropogenic, meteorological, topographical and biotic factors. Three main factors control forest damage at this scale: 1) wind velocity gradients resulting from cyclone size, speed of forward movement, cyclone intensity and proximity to the storm track, complicated by local convective-scale effects; 2) variations in site exposure and other effects of local topography (e.g. severe lee waves or leeward acceleration, windward exposure, topographic shading); and 3) differential response of individual ecosystems to wind disturbance as a function of species composition and forest structure.

Severe Tropical Cyclone Larry, with maximum wind gusts were near 240 km h1, crossed the coast near Innisfail (Fig. 1) as a Category 4 storm on 20 March 2006 causing extensive damage to human communities, primary industries, infrastructure and ecosystems across a 100 km strip of coastal lowlands and adjacent uplands. The system was moving at 25 km h-1when it crossed the coast and was still Category 4 status when it crossed over the Atherton Tablelands some 60 km from the coast (Fig. 1). Cyclone Larry produced numerous tornado-type features within the system’s eyewall and feeder bands that have been linked to patches of catastrophic forest damage. Larry was a very 'compact' system with its radius of maximum winds extending only 20-30 km from the centre (BOM, this report).

We examine the landscape-scale impacts of Cyclone "Larry" on the ecosystems of far north Queensland and provide a comparison with previous cyclones that have impacted along the wet tropical coast of Queensland over the period 1858-2006. We also discuss responses to the natural resource management issues facing the affected region in the aftermath.

Item ID: 29946
Item Type: Report (Report)
Funders: Australian Government Marine and Tropical Sciences Research Facility (MTSRF)
Projects and Grants: Project 4.9.3 Impacts of urbanisation on North Queensland environments: management and remediation
Date Deposited: 28 Nov 2016 22:43
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050209 Natural Resource Management @ 100%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960307 Effects of Climate Change and Variability on Australia (excl. Social Impacts) @ 40%
96 ENVIRONMENT > 9610 Natural Hazards > 961003 Natural Hazards in Farmland, Arable Cropland and Permanent Cropland Environments @ 60%
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