DR LAURA WILLIAMS (Orcid ID : 0000-0002-7468-5159) Article type : Original Article Assessing the efficacy and impact of management of an invasive species in a protected area: Poa annua on sub-Antarctic Macquarie Island L K WILLIAMS 1, B M SINDEL 1, P KRISTIANSEN 1, S C WILSON 1 & J D SHAW 2 1 School of Environmental and Rural Science, University of New England, Armidale, NSW, Australia and 2 Centre for Biodiversity and Conservation Science, School of Biological Sciences, The University of Queensland, St Lucia, Queensland, Australia Received 21 July 2018 Revised version accepted 1 January 2019 Subject Editor: David Clements, Trinity Western University, Canada Running head: Efficacy of invasive plant management Correspondence: Laura Williams, School of Environmental and Rural Science, University of New England, Armidale, NSW, Australia. Tel: (+61) 438 065 206; E-mail: [email protected] Author Manuscript This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1111/WRE.12355 This article is protected by copyright. All rights reserved Summary Plant eradication is difficult, particularly in remote, protected areas. The Southern Ocean Islands are very isolated and highly protected, but the flora contains many alien plants. Small restricted populations have been eradicated, but eradication of established species has proven difficult. A better understanding of the efficacy of control methods at sub-Antarctic temperatures and their off-target impacts may increase eradication success. With interest in controlling non-native Poa annua in the region, we aimed to determine if physical and chemical methods can control P. annua (the sub-Antarctic biotype) in sub-Antarctic conditions and examined their impact on native plants. We quantified the effectiveness of physical control methods on P. annua in situ on sub- Antarctic Macquarie Island through field-based experiments and assessed their selectivity on P. annua compared with native grasses. We also quantified the effectiveness of several herbicides on P. annua at sub- Antarctic temperatures and assessed their selectivity on native grasses. Of the four physical disturbance methods tested, none effectively reduced P. annua cover as one-off treatments. Of the herbicide treatments, glyphosate and trifloxysulfuron sodium were effective and were less damaging to native grass species, indicating potential selectivity. Physical control was of limited effectiveness, but did not affect native species richness. An integrated weed management programme utilising the strategic use of selective herbicides with follow up chemical and physical intervention may balance control and biodiversity outcomes. This research highlights the importance of site-specific testing of control methods and understanding off-target impacts of control when managing alien plant species in protected areas. Keywords: Eradication, alien, weed, off-target impacts, Southern Ocean Islands, annual meadow grass, wintergrass Introduction Author Manuscript Biological invasions negatively impact ecosystems worldwide and protected areas are not immune to invasion. Attempts to eradicate invasive species are becoming increasingly common in protected areas (Foxcroft et al., 2013), however success is difficult to achieve. A review of 173 eradications worldwide found only half to be successful, with success less likely in natural habitats (Pluess et al., 2012). Most successful eradications have This article is protected by copyright. All rights reserved targeted vertebrates. Plants have been more difficult to eradicate, generally because the targeted populations have had persistent seed banks which are difficult to remove and also due to high fecundity of the invasive plants resulting in large populations. Plants are also often cryptic and small in size and the attractive baits and traps that aid animal eradication are not applicable to plants (Panetta & Timmins, 2004; Simberloff, 2013). Small populations of alien plants have been eradicated worldwide, yet successful eradication of established alien species is rare in protected areas with only a few documented cases, mainly from islands (Genovesi, 2011). The Southern Ocean Islands (SOI) consist largely of protected areas (Shaw, 2013), yet over 280 alien plant species have become established (McGeoch et al., 2015). Most of the alien species have limited impact due to their restricted distributions, but some threaten sub-Antarctic ecosystems (Gremmen et al., 1998; Frenot et al., 2005; le Roux et al., 2013). To date, nine successful plant eradications have been recorded from the SOI (Greve et al., 2017; Shaw, 2013, Department of Primary Industries, unpublished data). All of these populations covered just a small area (or were single plants) and all but one were removed physically (McGeoch et al., 2015; Greve et al., 2017). Managers in the region are now considering controlling or eradicating more widespread and established populations (Shaw, 2013; Greve et al., 2017). Some attempts have already been made, but have been unsuccessful due to established seed banks and logistical difficulties associated with managing alien plants in this region (Shaw, 2013). Many factors contribute to the success or failure of an eradication programme, including population size and distribution and invasion characteristics of the target species (Panetta & Timmins, 2004; Simberloff, 2013). Based on short-comings of eradication attempts in protected areas, we have identified two factors that are important to assess when eradicating alien plants from protected areas such as the SOI. First, it is essential to have a thorough understanding of the efficacy of control methods prior to implementation of a management program. In many control programmes management methods are trialled and refined over the course of the project (Hilton & Konlechner, 2010; Cooper et al., 2011; Ryan et al., 2012; Hamilton et al., 2015). This approach can be highly successful for rapid response situations and dealing with small populations. Eradication of established populations is more difficult (Panetta & Timmins, 2004) and a trial-and-error approach may reduce efficiency and increase the timeframe and cost of the programme. Second, it is essential to consider any possible off-target impacts of the control methods used and these are rarely understood (Power et al.). There is a growing body of evidence suggesting that alien plant management can have negative or unexpected outcomes on species other than the target (Caut et al., 2009; Rinella et al., 2009) and this needs to be a fundamental objective of alien species management programmes within protected areas (Buckley & Han, 2014). The importance of understanding the efficacy of control methods used and their potential negative impacts is illustrated by the recent eradication of two invasive Agrostis species on Macquarie Island. A quick response was required, given the high rate of spread of these species in the sub-Antarctic, and so the plants, roots and surrounding soil was removed. The first attempt was unsuccessful, with a second treatment required the following year (DepartmentAuthor Manuscript of Primary Industries, Parks, Water and the Environment, unpublished data) which was destructive, leaving large, deep holes denuded of vegetation which have been slow to recover (Williams, personal observation). If the efficacy and impact of various control methods had been known, eradication of this species could have been more effective and less destructive. This article is protected by copyright. All rights reserved Poa annua (L.) or wintergrass, is considered the worst weed in the SOI based on its widespread distribution and impact (McGeoch et al., 2015). Management of P. annua is being considered on several SOI (de Villiers et al., 2006, Hughes et al., 2015) and an eradication attempt is underway on King George Island in Antarctica. Aspects of the ecology of the species on the SOI are relatively well known, in particular its perenniality, habit of growing in expansive, dense mats and preference of colonising disturbed, nutrient enriched sites (Walton, 1975; Copson, 1984; Frenot et al., 1998; Williams et al., 2018). Extensive research has been undertaken on P. annua in temperate turf grass, where it is difficult to control due to its high plasticity and tolerance of varied environmental conditions (Branham & Calhoun, 2005; Christians, 2006). Physical methods (Beard et al., 1978), herbicides (Finlayson & Dastcheib, 2000, Toler et al., 2007; Cross et al., 2012), biological methods (Gange et al., 1999) and environmental manipulation (Baldwin, 1993) provide some degree of control, but success is highly variable depending on the biotype of P. annua and environmental conditions. This makes it essential to test the efficacy of P. annua control methods under colder SOI conditions using the perennial biotype of P. annua found across most of the SOI. Macquarie Island is a SOI of high conservation status, designated as a Nature Reserve, Biosphere Reserve and World Heritage Area. Over forty native plant species are present on the island, many of which are found across the SOI (Baker & Duretto, 2016). Seven non-native plant species have established. Four species were individual plants/isolated populations and have been removed (Baker & Duretto, 2016), while