SE Connor Et Al. Forgotten Land-Use Impacts in NW
Total Page：16
File Type：pdf, Size：1020Kb
S.E. Connor et al. Forgotten land-use impacts in NW Australia 1 Manuscript for Journal of Vegetation Science (special issue edited by Thomas Giesecke, Triin Reitalu 2 and Petr Kuneš). 3 4 Title: 5 Forgotten impacts of European land-use on riparian and savanna vegetation in North-Western 6 Australia 7 8 Author names and addresses: 9 Simon E. Connor, Larissa Schneider, Jessica Trezise, Susan Rule, Russell L. Barrett, Atun Zawadzki & 10 Simon G. Haberle 11 12 Connor, S.E. (corresponding author, [email protected]) 1,2 13 Schneider, L. ([email protected]) 3 14 Trezise, J. ([email protected]) 3 15 Rule, S. ([email protected]) 3 16 Barrett, R.L. ([email protected]) 4,5 17 Zawadzki, A. ([email protected]) 6 18 Haberle, S.G. ([email protected]) 3 19 1School of Geography, 221 Bouverie Street, University of Melbourne, 3010 VIC, Australia; 20 2CIMA-FCT, University of the Algarve, Campus de Gambelas, 8005-139 Faro, Portugal; 1 S.E. Connor et al. Forgotten land-use impacts in NW Australia 21 3Centre of Excellence in Australian Biodiversity & Heritage, and Department of Archaeology and 22 Natural History, Australian National University, Fellows Rd, Canberra, 2600 ACT, Australia; 23 4National Herbarium of New South Wales, Royal Botanic Gardens and Domain Trust, Mrs Macquaries 24 Road, Sydney NSW 2000, Australia; 25 5College of Medicine, Biology and Environment, Research School of Biology, Australian National 26 University, Canberra, 2601 ACT, Australia; 27 6Institute for Environmental Research, Australian Nuclear Science and Technology Organisation, PMB 28 1 Menai, 2234 NSW, Australia. 29 30 Printed journal page estimate: 31 8597 words including references (10.7 pages), figures 1.3 pages, total 12 pages. 32 33 Abstract 34 Questions 35 Fire and livestock grazing are regarded as current threats to biodiversity and landscape integrity in 36 Northern Australia, yet it remains unclear what biodiversity losses and habitat changes occurred in 37 the 19–20th centuries as livestock and novel fire regimes were introduced by Europeans. What 38 baseline is appropriate for assessing current and future environmental change? 39 Location 40 Australia's Kimberley region is internationally recognised for its unique biodiversity and cultural 41 heritage. The region is home to some of the world's most extensive and ancient rock art galleries, 42 created by Aboriginal peoples since their arrival on the continent 65,000 years ago. The Kimberley is 2 S.E. Connor et al. Forgotten land-use impacts in NW Australia 43 considered one of Australia's most intact landscapes and its assumed natural vegetation has been 44 mapped in detail. 45 Methods 46 Interpretations are based on a continuous sediment record obtained from a waterhole on the 47 Mitchell River floodplain. Sediments were analysed for geochemical and palynological proxies of 48 environmental change and dated using Lead-210 and Carbon-14 techniques. 49 Results 50 We show that the present-day vegetation in and around the waterhole is very different to its pre- 51 European counterpart. Pre-European riparian vegetation was dominated by Antidesma ghaesembilla 52 and Banksia dentata, both of which declined rapidly at the beginning of the 20th century. Soon after, 53 savanna density around the site declined and grasses became more prevalent. These vegetation 54 shifts were accompanied by geochemical and biological evidence for increased grazing, local 55 burning, erosion and eutrophication. 56 Conclusions 57 We suggest that the Kimberley region's vegetation, while maintaining a 'natural' appearance, has 58 been altered dramatically during the last hundred years through grazing and fire regime changes. 59 Landscape management should consider whether the current (impacted) vegetation is a desirable or 60 realistic baseline target for biodiversity conservation. 61 62 Keywords geochemistry, palaeoecology, human impact, riverine vegetation, savanna, fire regimes, 63 grazing, Australian Monsoon Tropics, Potential Natural Vegetation 64 65 Nomenclature Western Australian Herbarium (2017); Mucina & Daniel (2013). 3 S.E. Connor et al. Forgotten land-use impacts in NW Australia 66 67 Running head Forgotten land-use impacts in NW Australia 68 69 Introduction 70 Human impacts associated with European colonisation beginning in the 15th century 71 profoundly altered ecosystems around the globe. Impacts included the introduction of exotic 72 species, manipulation of fire regimes, deforestation, major land-use changes, displacement of 73 indigenous land management practices and alterations to biogeochemical cycles (Kirkpatrick 1999; 74 Ireland and Booth 2012; Johnson et al. 2017). As these impacts preceded a widespread 75 understanding of ecosystem ecology and research, in many parts of the world it is difficult to 76 understand how ecosystems functioned prior to European colonisation. This raises questions about 77 how to best manage altered ecologies in an era of rapid environmental change (Johnson et al. 2017). 78 A common baseline for large-scale ecosystem management is the concept of Potential 79 Natural Vegetation (PNV). PNV takes information from areas of assumed natural vegetation (late- 80 successional) and extrapolates to other (impacted) areas with similar environmental conditions 81 (Loidi & Fernández-González 2012). The PNV approach has been criticised because its predictions 82 sometimes conflict with the fossil record (Carrión & Fernández 2009; Rull 2015; Abraham et al. 83 2015). PNV also fails to account for ecosystem dynamics (Chiarucci et al. 2010) and is unable to 84 simulate ecological structure in cultural landscapes (Strona et al. 2016). Despite these constraints, 85 PNV remains an accessible baseline for conservation and management decisions. 86 Northern Australia is regarded as one of the largest areas of intact tropical savanna 87 worldwide (Woinarski et al. 2007; Bowman et al. 2010; Ziembicki et al. 2015). If this is true, PNV 88 maps for the region should constitute a valuable baseline (Beard et al. 2013; Mucina & Daniel 2013). 89 Yet the ecosystems of Northern Australia have been extensively modified since European 4 S.E. Connor et al. Forgotten land-use impacts in NW Australia 90 colonisation through livestock grazing, disruption of Indigenous land curation and the introduction of 91 invasive species, among other impacts (Hnatiuk & Kenneally 1981; Lonsdale 1994; Vigilante & 92 Bowman 2004; Douglas et al. 2015; Radford et al. 2015). Impacts are linked to extinctions, declining 93 native mammal populations, altered stream ecology, eutrophication, erosion and catchment 94 instability (Payne et al. 2004; Woinarski et al. 2007; Ziembicki et al. 2015). 95 Taking a different view, recent research links the recent decline of fire-sensitive species 96 across Northern Australia to interactions between fire and flammable grasses (Trauernicht et al. 97 2013; Bowman et al. 2014). Uncertainties surrounding the causes of recent species losses remain 98 obscure in the absence of reliable historical evidence for 19th and early-20th century environmental 99 change in this sparsely populated region. Such evidence could provide a critical test of ecosystem 100 integrity and reveal long-term drivers of species decline. 101 Northern Australia is home to high levels of biodiversity, much of which remains 102 undocumented (Barrett & Barrett 2011, 2015; Barrett 2013, 2015; Maslin et al. 2013; Moritz et al. 103 2013). Phylogenetic research reveals extraordinary levels of genetic diversity and endemism, 104 perhaps equal to the recognised biodiversity hotspots of Eastern Australia (Moritz et al. 2013). The 105 Kimberley region in NW Australia is internationally recognised for its extensive rock art galleries, 106 which are some of the most ancient examples of human artistic expression globally (Aubert 2012) 107 and are situated in an ancient cultural landscape created by Indigenous Australians (Rangan et al. 108 2015; Hiscock et al. 2016). There is a pressing need to understand and document the region’s 109 biological and cultural heritage as economic development pressures on the Northern Australian 110 environment intensify. 111 In this paper, we confront the assumed natural vegetation of the Kimberley region with 112 fossil evidence, aiming to assess the ecological integrity of the region’s tropical savanna and riparian 113 vegetation types. Our data pertain to the savanna woodlands and riparian thickets (Mucina & Daniel 114 2013) of the Mitchell Plateau, one of the last areas of the Australian continent to experience 5 S.E. Connor et al. Forgotten land-use impacts in NW Australia 115 European colonisation (McGonigal 1990). We compare pollen data with independent geochemical 116 data to understand the timing, direction and drivers of two centuries of environmental change. 117 118 Methods 119 Study area 120 The Kimberley Region is situated in NW Australia and constitutes a biogeographically and 121 geologically distinct entity within the Australian Monsoonal Tropics (Pepper & Keogh 2014). The 122 region is characterised by complex and ancient geology, which has combined with long periods of 123 subaerial exposure and weathering to create unique landforms and topography (Pillans 2007; Tyler 124 2016). The Kimberley region is broadly divided into three geological basins: the extensive Kimberley 125 Basin in the north, the Ord Basin to the south and east, and the Canning Basin to the south and west. 126 These basins are separated by two orogenic belts of metamorphosed