Muehlenbeckia Astonii Petrie), a Nationally Threatened Plant
Total Page:16
File Type:pdf, Size:1020Kb
Re-establishment of the shrubby tororaro (Muehlenbeckia astonii Petrie), a nationally threatened plant SCIENCE & RESEARCH INTERNAL REPORT 188 David A Norton Published by Department of Conservation PO Box 10-420 Wellington, New Zealand Science & Research Internal Reports are written by DOC staff or contract scientists on matters which are on-going within the Department They include reports on conferences, workshops, and study tours, and also work in progress Internal Reports are not normally subject to peer review This report was prepared for publication by DOC Science Publishing, Science & Research Unit; editing and layout by Ian Mackenzie Publication was approved by the Manager, Science & Research Unit, Science Technology and Information Services, Department of Conservation, Wellington This report was prepared by David A Norton, Conservation Research Group, School of Forestry, University of Canterbury, Private Bag 4800, Christchurch, New Zealand © June 2001, Department of Conservation ISSN 01142798 ISBN 0478220324 Cataloguing-in-Publication data Norton, David A (David Andrew), 1958- Re-establishment of the shrubby tororaro (Muehlenbeckia astonii Petrie), a nationally threatened plant / David A Norton Wellington, NZ : Dept of Conservation, 2001 1 v ; 30 cm (Science & Research internal report, 0114-2798 ; 188) Includes bibliographical references ISBN 0478220324 1 Muehlenbeckia astonii 2 Rare plantsNew Zealand I Title Series: Science and Research internal report ; 188 CONTENTS Abstract 5 1 Introduction 6 2 Study species and area 7 3 Methods 8 31 Seed germination 8 32 Restoration trial field methods 9 33 Statistical analyses 10 4 Results 11 41 Seed germination 11 42 Experiment 1 (Grazing and weeding treatments) 12 43 Experiment 2 (Grazing and companion plant treatments) 13 44 Experiment 3 (Grazing and companion plant growth) 14 5 Discussion 15 51 Limitations of study 15 52 Grazing effects 16 53 Weeding effects 17 54 Habitat restoration 18 55 Status of Muehlenbeckia astonii 18 56 Future management of Muehlenbeckia astonii restoration trial 19 6 Conclusions 19 7 Acknowledgements 20 8 References 21 4 Abstract Most populations of nationally threatened shrubs, including Muehlenbeckia astonii, are dominated by mature plants, with little evidence of recent recruit- ment Restoration of these populations has been seen as a conservation manage- ment priority by the Department of Conservation The research described here sought to quantify the effects of different grazing, weeding and companion planting treatments on such restoration Removal of grazing has clear benefits for Muehlenbeckia astonii and companion plant survival and growth, with a significantly better response when both lagomorphs and stock were excluded Weeding also had clear benefits for Muehlenbeckia astonii survival and growth, with unweeded plants doing significantly less well than weeded plants because of smothering by competing grasses While there was a significant companion plant effect on the survival and growth of Muehlenbeckia astonii, this result is believed to be due to differences between sites rather than to a true companion planting effect The value of the Muehlenbeckia astonii restoration trial will increase with time and it is recommended that the continuation of the trial with regular re-measurement be made a priority in future business planning Re- search on lagomorph impact and control and on competition with invasive plants should be a high priority for the Department of Conservation There would also be considerable value in bringing together the results of the many different restoration trials being undertaken by the Department of Conserva- tion, Universities, and Crown Research Institutes to identify common results and to highlight areas were more research is required Keywords: threatened plants, restoration, grazing, weeds, management, Muehlenbeckia astonii, Wellington Conservancy, New Zealand 5 1 Introduction The New Zealand threatened vascular flora comprises 107 taxa, with a further 307 taxa classified as declining or naturally uncommon (de Lange et al 1999) Of the threatened taxa, 28 (26%) are shrubs, with many of these having a predomi- nantly eastern distribution in the lower rainfall areas of the South and southern North Island Several of these threatened shrub species appear to be facing simi- lar threats including habitat loss, competition with invasive plants, and preda- tion (de Lange & Silbery 1993; Molloy & Clarkson 1996; Rogers 1996; Williams et al 1996; Widyatmoko & Norton 1997; Molloy et al 1999) While the impacts of habitat loss can be addressed through legal protection of remnant sites and resto- ration programmes, the effects of competition and predation are more difficult to address, especially at a large scale Furthermore, while restoration can be used to increase extant populations and establish new populations, restored populations still face threats associated with competition and predation The original justification for this research programme focused on the need to better understand the threats that shrub species face in the wild and especially the factors that are likely to limit the success of restoration programmes using these species The intention was that the results would have wider implications for the restoration of threatened shrub species and that a manual on the restoration of woody plants would be produced For the reasons discussed later in this report, it was felt that the production of such a manual would be inappropriate at this stage but an alternative approach to addressing the more general restoration issue is highlighted at the end of this report The research was initiated as part of an integrated plant conservation pro- gramme in Wellington Conservancy (Empson & Sawyer 1996), although the re- sults will be of use to all people implementing national species recovery pro- grammes The research originally aimed to work with Muehlenbeckia astonii (Endangered) and Pittosporum obcordatum (Conservation Dependent) How- ever, it was decided early on to switch from P obcordatum to Olearia gardneri (Critically Endangered) because there was already an active restoration research programme with P obcordatum (by Northland Conservancy) and because of the higher risk of extinction with O gardneri Unfortunately, problems with obtaining sufficient nursery grown plants of Olearia gardneri (due to the fail- ure of the contracted nursery to deliver plants) delayed the establishment of the Olearia gardneri restoration trial with plants not due to be planted until 2002 However, the restoration site has been fenced (protecting remnant O gardneri and Coprosma wallii (Declining) from cattle damage) and plants of O gardneri and C wallii, and of a number of associated species are being propagated ready for planting in spring 2001 and 2002 These plants have been purchased as part of this research project and the restoration trial will be co-ordinated by the Masterton Area Office with scientific input from the author This report there- fore focuses only on the Muehlenbeckia astonii restoration trial The objectives of this research were to quantify the effects of grazing, weed control and companion planting on the establishment of Muehlenbeckia astonii plants in a field restoration as a basis for improving future conservation plantings of this species This report presents the results of this work and 6 highlights issues for the future management of the Muehlenbeckia astonii restoration trial 2 Study species and area The following information on Muehlenbeckia astonii has been summarised from Lovell et al (1991), de Lange & Silbery (1993), and de Lange & Jones (2000) Muehlenbeckia astonii (Polygonaceae) is a rounded, bushy, deciduous, divaricating shrub up to 3 m height that can live for at least 100 years It is endemic to the south-eastern North Island and eastern South Island as far south as Kaitorete Spit in Canterbury and was a distinctive member of the grey scrub ecosystems (Wardle 1991) in this area, but is now considerably reduced in extent Although it is known from 37 sites scattered throughout its historic range, it is only common at one (Kaitorete Spit), with the remaining sites containing less than three plants per site on average It produces insect pollinated flowers with individual plants either female or inconstant males While inconstant male plants occasionally produce seed through selfing, this usually has low viability The fruit are animal dispersed, with birds and geckos thought to be important Ecologically, Muehlenbeckia astonii appears to be most common in grey scrub communities on free-draining fertile sites such as coastal sands, loess covered hill slopes and uplifted coastal terraces It has also been recorded from ephemeral wetlands in the North Island The sites in which it occurs typically experience summer drought (at Orongorongo station, close to the research site used here, December through February are the driest months) Several factors appear to have lead to the decline in Muehlenbeckia astonii including habitat loss, preda- tion and trampling, disease, recruitment failure, introgression and competition Because of these factors, Muehlenbeckia astonii has been listed as Endangered in the most recent listing of New Zealands threatened plants (de Lange et al 1999) This research was undertaken at Turakirae Head, between Wellington and Palliser Bay at the southern extremity of the Tararua Ecological District (Fig 1) The area comprises a series of uplifted beach ridges, the most recent dating from the 1855 Wellington