Securing Landscape Resilience to Tropical Cyclones ...

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Figure 1 The Wet Tropics bioregion and World Heritage Area, north-east Australia (courtesy of Peter Bannink, Australian ..... limitation (Shilton et al., 2008).
Securing Landscape Resilience to Tropical Cyclones in Australia’s Wet Tropics under a Changing Climate: Lessons from Cyclones Larry (and Yasi) geor_724

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STEPHEN M. TURTON Centre for Tropical Environmental and Sustainability Sciences, School of Earth and Environmental Sciences, James Cook University, Cairns, Qld 4870, Australia. Email: [email protected] Received 6 June 2011; Revised 28 August 2011; Accepted 8 September 2011

Abstract Tropical cyclones are part of the ecosystem dynamics of rainforests in the Wet Tropics of Australia, and intact forest areas show remarkable ability to recover from cyclonic disturbance. However, forest remnants, littoral rainforests, and riparian vegetation have been shown to be particularly susceptible to cyclonic winds and post-disturbance weed invasion with consequences for their long-term conservation values. I evaluate the frequency and intensity of tropical cyclones impacting the Wet Tropics region since records began in 1858. The recent Category 4 cyclones featured in this study, Larry and Yasi, had return intervals of about one in 70 years. I then discuss the natural resource management (NRM) lessons from Cyclone Larry and put forward practical recommendations on how authorities should deal with natural resources in the clean-up and recovery phases. I argue that natural resources must be treated as valuable commodities by including their protection and rehabilitation in the same way that human livelihoods, infrastructure and industry are covered in disaster management planning. This requires NRM issues to be included in disaster response policy and legislation, together with ensuring that structures are in place to mitigate the effects of cyclones on natural resources. There is a general consensus that tropical cyclone intensity will increase under climate change while frequency will decrease slightly. This has profound implications for the long-term sustainability of ecosystems in the Wet Tropics. There is a real risk of a phase shift to vegetation types dominated by disturbance species, including weeds, at the expense of cyclone intolerant species. It is therefore important that we begin to build more cyclone resilient landscapes to reduce the vulnerability of our remaining rainforest habitats and primary production systems. Securing landscape resilience requires greater NRM investment in key areas, including landscape connectivity, river repair, protecting coastal assets and cyclone resilient farms. While climate change poses a long-term threat to the rainforests of the region, we need to focus on more immediate pressures affecting our remaining biodiversity, notably clearing of native habitat, habitat fragmentation and degradation, and biosecurity issues. KEYWORDS tropical cyclones; ecological effects; resilience; natural resources; biodiversity conservation; contested landscapes; climate change; rainforest

I dedicate this paper to Dr Len Webb AO (1920–2008) for inspiring me to study the myriad interactions between tropical cyclones and the contested rainforest landscapes in the Wet Tropics region of Australia.

Geographical Research • February 2012 • 50(1):15–30 doi: 10.1111/j.1745-5871.2011.00724.x

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Geographical Research • February 2012 • 50(1):15–30

Introduction Natural and anthropogenic disturbances shape forest ecosystems by controlling their structure, species composition, and functional processes (Dale et al., 2001). The rainforests of the Wet Tropics of north-east Australia (Figure 1) have been shaped by their natural disturbance and human land use history over many millennia, but particularly over the past 150 years (Pannell, 2008; Stork et al., 2008; Turton, 2008a). Rainforests of the region are affected by a range of natural disturbances, including infrequent but damaging bush fires, droughts, floods, occasional landslides, severe thunderstorms, and tropical cyclones. All these natural disturbances interact in complex ways with anthropogenic disturbances across the landscape, such as forest clearing and habitat fragmentation (see Stork and Turton, 2008). Tropical cyclones (also known as hurricanes and typhoons) range in intensity from comparatively weak systems, where maximum wind speeds do not generally exceed 160 km h-1, to extremely destructive, where maximum wind gusts have been recorded in excess of 350 km h-1 (Turton, 2008b). Severe cyclones cause widespread defoliation of canopy trees, removal of vines and epiphytes, along with breakage of crown stems and significant tree falls (Lugo, 2008; Turton and Stork, 2008). Significant changes in canopy cover result in profound changes in under- and mid-storey microclimates (Turton, 1992; Bellingham et al., 1996; Lugo and Scatena, 1996; Turton and Siegenthaler, 2004), and complex vegetation and faunal responses to newly created light, temperature, and moisture regimes (Bellingham et al., 1994; Harrington et al., 1997; Lugo, 2008). Cyclonic disturbance also accelerates the invasion of exotic tree and understorey weed species leading to a decline in biodiversity of native species (Bellingham et al., 2005; Murphy et al., 2008). In a recent review, it has been shown that there has been an increase in the numbers of weed species in the Wet Tropics region over recent decades, with many of these species favouring disturbed habitats (Stork et al., 2011). Tropical cyclones impact on rainforests at both the landscape and local scales (Boose et al., 1994; Grove et al., 2000; Turton and Stork, 2008). Impacts at the landscape scale (>10 km) are the result of complex interactions of anthropogenic, meteorological, topographical and biotic factors. Damage patterns at this scale are driven by three main factors (Boose et al., 1994): (1) wind veloc-

ity 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. Impacts at the more local scale (279

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