Lord Howe Island Rodent Eradication Project EPBC Public Environment Report October 2016
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Lord Howe Island Rodent Eradication Project EPBC Public Environment Report October 2016 Appendix H - Biodiversity Benefits Monitoring Package H.1 Biodiversity Benefits Project Report H.2 LHI Land Birds Report 2014 H.3 LHI Land Birds Report 2013 1 Assessing impacts of introduced rats on Lord Howe Island plants including the Little Mountain Palms and its habitat on Mt Gower June 2015 Tony D Auld1, Andrew Denham1, Mark Tozer1 and Ian Hutton2 1, NSW Office of Environment and Heritage, PO Box 1967 Hurstville NSW 2220 2, PO Box 157, Lord Howe Island, NSW 2898 Email: [email protected] Summary We used selective caging and cafeteria trials to determine removal and loss of fruits and seeds to Black Rats (Rattus rattus) on Lord Howe Island. Of the 16 species examined, losses to Black Rats were very high for six species (Howea forsteriana, Olea paniculata, Baloghia inophylla, Jasminium simplicifolium, Smilax australis and Geitonoplesium cymosum); potentially very high but variable for one species (Ochrosia elliptica); moderate for three species (Syzygium fullagarii, Chionanthus quadristamineus, Dietes robinsoniana) (the actual losses may be higher as the trials only ran for a short period) and low-moderate in the remaining 6 species. No species tested was entirely free of seed or fruit losses to Black Rats. This suggests Black Rats are likely to impact on many species across LHI and further testing of species is warranted to examine the number of species likely to be at risk due to impacts on seed production, seed survival and plant recruitment. In addition, further work on what impact the loss of seeds or fruits may have on the affected plant populations is also necessary. The high impact of Black Rats on the Little Mountain Palm (Lepidorrhachis mooreana) on Mt Gower that had been identified by Auld et al. (2010) was confirmed by repeat sampling 8 years after the original sampling was done. While there is some successful recruitment in this species where rodent baiting occurs on Mt Gower, recruitment failure is evident at locations over 100 m or so from bait stations. This suggests that to successfully maintain this critically endangered palm on Mt Gower rat control or eradication will be required across the Mt Gower summit. The habitat of the Little Mountain Palm, the Gnarled Mossy Cloud Forest, was assessed as critically endangered using the IUCN Red List for Ecosystems criteria. Control of Black Rats on the summit of Mt Gower is the most practical means to reduce the threat to this ecological community in the short term. 2 Introduction The flora of Lord Howe Island is recognised as globally significant due to the high level of endemism and unique vegetation communities. Auld and Hutton (2004) detail this as: “The flora of Lord Howe Island has a high level of endemism and many of the floristic assemblages are also unique to the island group (Pickard 1983, Green 1994). There are five plant genera endemic to Lord Howe Island — Negria, Lordhowea and three palms, Howea, Hedyscepe and Lepidorrachis. For the vascular plants, Green (1994) lists 459 species, 241 indigenous (53%), of which 105 are endemic (44%) and 218 naturalised (48%). Of the indigenous vascular plants, 58 species are ferns and 183 are flowering plants. Several more species of both indigenous and naturalised plants have been found since Green’s (1994) work. The high level of endemism is typical of islands and comparable with megadiverse regional areas of continents (Lowry 1998).” It is widely recognised that invasive species may have significant negative impacts on oceanic islands, particularly for many narrow range endemics and ecological communities. While Lord Howe Island was originally free of mammals (except for small insectivorous bats) when first encountered by humans in 1788 and first settled in 1834 (Hutton 1986), Black rats (Rattus rattus) were accidentally introduced when a steamship ran aground in 1918 (Billing and Harden 2000). A number of plant species and vegetation communities have been identified as being at risk from the impacts of Black Rats and house mice on LHI. These impacts include: • Loss of fruits and seeds to rats, e.g. Baloghia inophylla, Chionanthus quadristamineus, Drypetes deplanchei, Elaeodendron curtipendulum, Hedyscape canterburyana, Howea forsteriana, Howea belmoreana, Lepidorrhachis mooreana, Pandanus forsteri, Ochrosia elliptica (Auld & Hutton 2004, Auld et al. 2010); • loss of seedlings and stem damage (the four palm species, Hedyscape canterburyana, Howea forsteriana, Howea belmoreana, Lepidorrhachis mooreana, Dietes robinsoniana (Wedding Lily) and at least two fern species, Asplenium milnei and Adiantum hispidulum) (Auld & Hutton 2004); • impacts on the critically endangered Gnarled Mossy Cloud Forest Ecological Community confined to the summits of the southern mountains (NSW Scientific Committee 2011); As well, the extinctions of two Lord Howe Island plant species, Sicyos australis and Solanum bauerianum, were most likely influenced by consumption of seeds and fruits by introduced animals (Auld & Hutton 2004; NSW Scientific Committee 2010). Solanum bauerianum is now considered to be globally extinct. In this work, we undertook to quantify the impact of introduced rats on 2 aspects of the vegetation of LHI. Firstly, we wanted to understand the breadth of plants species that may be impacted by rats. To do this, in the field we tested the magnitude of fruit and seed loss to rats across a range of species, with the species tested being dictated by fruit and seed availability. For some species we were able to replicate the trials in different locations or at different times of the year. Secondly, we re- examined the size distribution of plants of the little mountain palm (Lepidorrhachis mooreana) on Mt Gower. Previously, Auld et al. (2010) had shown that rats were preventing the establishment of new plants into the parts of the population that were 3 not baited. We re-measured these sites to determine if the impact of rats was ongoing and to try and see if rat baiting was leading to sufficient protection for these palms. Finally, through funding support from an Australian Research Council Grant to TA and others we assessed the extinction risk for the Gnarled Mossy Cloud Forest Ecological Community using the recently developed IUCN Red List for Ecosystems criteria (Keith et al. 2013). Methods Impact of Black Rats on fruits and seeds At one or more sites (See Table 1) we established 5 plots beneath mature plants of several species (Howea forsteriana (Kentia Palm), Ochrosia elliptica (Berrywood), Olea paniculata (Maulwood), Coprosma putida) (Table 1). Each plot contained three treatments: uncaged; caged to exclude only birds (rodents could enter in gaps at each end (see Fig. 1); and caged to exclude both rodents and birds. At each plot, in each treatment we placed 5 mature fruits. The density of fruits so placed was not dissimilar to that found naturally below plants with mature fruits. We recorded the fate of seeds over 3-7 days. We also established an infared camera at one plot for each species to record what animal was responsible for seed removal or loss (these cameras were set up to activate and take 10 photos when a warm blooded animals comes into view of the camera (i.e. a rat , a mouse, a bird, a human). We also established plots for multiple species in a ‘cafeteria’ trial within the habitat where they generally occur. We did this for 12 species at 5 sites (See Table 1). In this trial 5 fruits or seeds of 4-6 species were placed together in small clumps (see Fig. 2). At each plot all seeds were uncaged. Again, like above, the fate of the fruits/seeds was followed over 3-7 days if possible. Impact of Black Rats on the Little Mountain Palm (Lepidorrhachis mooreana) on Mt Gower We repeated the sampling of Auld et al. (2010) (see Appendix 1) and sampled the size structure of stands of Little Mountain Palms in cloud forest on the Mount Gower plateau. We stratified the sampling between areas that have been baited by the Lord Howe Island Board to control rat numbers and those that have never been baited. In each of the baited and unbaited areas we sampled three separate plots for the Little Mountain Palm (Lepidorrhachis mooreana) (6 plots). We also sampled an additional 4 plots in the gradient between baited and unbaited areas. We estimated the distance for each of our 10 sampled plots from an existing bait station to determine if there was any additional benefit of baiting into surrounding unbaited areas. At each plot, we established a 5 m wide transect across the site and sampled all individual palms within the transect. The transects were sampled until we had encountered a minimum of 30-50 Lepidorrhachis individuals with an emergent trunk. We measured the trunk height to the base of the leaves, the number of leaf scars for individuals with a trunk and the height of individuals for individuals without a trunk. Extinction risk for the Gnarled Mossy Cloud Forest Ecological Community To assess the Gnarled Mossy Cloud Forest against the IUCN Red List for Ecosystems criteria (Keith et al. 2013), we searched the available literature for 4 evidence of any threats to the ecosystem that may result in ecosystem decline. We assessed the Gnarled Mossy Cloud Forest against four of the IUCN criteria (see Appendix 2, Auld and Leishman 2015 for more details): • Decline was assessed using historical vegetation reports (Maiden 1898, 1914; Oliver 1916; Pickard 1983; Green 1994; Mueller-Dombois & Fosberg 1998; Harris et al. 2005). For more recent changes, we inspected satellite imagery (Google Earth and 2011 air photo imagery). • For Restricted geographic distribution we used available Geographical Information System data layers for the distribution of Gnarled Mossy Cloud Forest (mapped from Pickard 1983) to estimate both the extent of occurrence and area of occupancy of the ecosystem.