Western Springs Pines Ecological Alternatives
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Western Springs Pines: Consideration of Alternative Management Options – Ecological Perspective The Tree Consultancy Company October 2020 Western Springs Pines: Consideration of Alternative Management Options – Ecological Perspective The Tree Consultancy Company PREPARED BY: ANNABELLE COATES BIORESEARCHES (BABBAGE CONSULTANTS) 128 MONTREAL STREET, CHRISTCHURCH REVIEWED BY: CHRIS WEDDING FOR: THE TREE CONSULTANCY COMPANY DATE: 21 OCTOBER 2020 REFERENCE: BIORESEARCHES (2020). WESTERN SPRINGS PINES: CONSIDERATION OF ALTERNATIVE MANAGEMENT OPTIONS – ECOLOGICAL PERSPECTIVE. PREPARED FOR THE TREE CONSULTANCY COMPANY. COVER ILLUSTRATION: PINE TREES AND INDIGENOUS UNDERSTORY VEGETATION WITHIN WESTERN SPRINGS, 1 OCTOBER 2020 Level 4, 68 Beach Road, Auckland 1010; PO Box 2727, Shortland Street, Auckland 1140. 128 Montreal Street, Christchurch 8140; PO Box 2373 Christchurch, 8140 T: (09) 379-9417; www.bioresearches.co.nz CONTENTS Page 1 INTRODUCTION ................................................................................................................ 1 1.1 Purpose of the Report ......................................................................................... 1 1.2 Report Scope ....................................................................................................... 1 1.3 Independence ...................................................................................................... 2 1.4 Site description .................................................................................................... 2 2 The three management options ....................................................................................... 4 2.1 Option 1 - Full stand removal in line with the consented works ......................... 4 2.2 Option 2 - Staged removals (e.g. meet WLB’s objective in a stepwise fashion over time) ......................................................................................................................... 4 2.3 Option 3 - Select removals (e.g. removing trees based solely on risk management) ................................................................................................................... 4 2.4 Option 4 – Status Quo (no management) ........................................................... 5 3 Effects on ecology ............................................................................................................. 6 4 Summary ......................................................................................................................... 10 5 Recommendation ........................................................................................................... 12 Appendix – Reference Information ............................................................................................. 13 i 1 INTRODUCTION Western Springs Reserve, Grey Lynn, has been closed to the public since 2018 due to an elevated risk of the existing exotic Monterey pine trees (Pinus radiata) falling during adverse weather events. There is various evidence and expert opinion from specialists, including arborists, ecologists, geotechnical engineers and landscape architects, with regard to the risk of failure of the pines and impacts on other values, including ecological values, of clearance of the pines. However, there remains some disagreement as to the best way to manage the reserve, particularly the pine trees, some of which are at imminent risk of failure. Auckland Council have been granted a resource consent to remove the stand of Monterey pines (Pinus radiata) at Western Springs. The stand of pines is approximately 100 years old and is exhibiting a decline in stand health, and increased risk of failure as a result of various factors such as wind throw, insect damage and other age-related factors. The resource consent was appealed by the Society for the Protection of Western Springs Forest Incorporated to the Environment Court in 2019. Subsequently a new set of conditions was issued following mediation between parties and the appeal dismissed. 1.1 PURPOSE OF THE REPORT The purpose of this report is to provide a review of four options for the Western Springs pine tree stand, including three clearance methods and a ‘do nothing’ approach. The review includes consideration of supplied information, including arboricultural and ecological, and determines likely outcomes for the ecological values at Western Springs Reserve. 1.2 REPORT SCOPE There is disagreement between stakeholders regarding the most appropriate way to manage the vegetation, particularly the pine trees. Bioresearches has been commissioned to provide an independent assessment of the proposed approaches and associated methods (including ‘do nothing’). The four methods are: a. Full stand removal in line with the consented works b. Staged removals (e.g. meet Waitemata Local Board’s objective in a stepwise fashion over time) c. Select removals (e.g. removing trees based solely on risk management) d. Maintain the status quo (‘do nothing’). The contents of this assessment is based solely on ecological values. It does not consider pine tree health, risk of failure, land stability, landscape and visual effects, or the pros and cons of each tree removal method from an arboriculture perspective. However, information relating to these aspects may be referred to in this report where ecological outcomes may be affected. 1 Existing documents were provided and reviewed (Appendix 1). A site visit was undertaken on Thursday 1 October 2020. This report does not constitute a full assessment of effects, rather it is intended to inform potential effects based on assessments already undertaken (e.g. Wildlands 2016) and revised management options. If a decision is reached to manage the site in a way other than the currently consented clear felling option, a new assessment of ecological effects may be required to inform any resource consent applications. 1.3 INDEPENDENCE Bioresearches are fully independent of this process to date. We have no conflicts of interest with regard to the project and have no intention of tendering for, or providing ongoing services in relation to this project in the future. The author of this assessment is Canterbury based. 1.4 SITE DESCRIPTION Full detailed site descriptions have been provided in various reports including the ecological assessment (Wildlands 2018) and the evidence of Nicholas Goldwater (2018). A summary description of the site is as follows. The site comprises an approximately 3.2 ha block of mixed forest vegetation. The block is dominated by old, senescing radiata pines, with a mixed indigenous dominated sub- canopy and understory though exotic species are also present. Indigenous species in these vegetation tiers are common both in the immediate area, and in the wider ecological district. A list of vegetation species encountered within the site can be found in the Wildlands report; however, this should not be considered an exhaustive list and it is possible other species are also present within the site. The block of vegetation is contiguous with mixed vegetation contained within the boundaries of Auckland Zoo, located on the northern and western boundaries of the site. A number of invasive pest plants are present within the site including tradescantia (Tradescantia fluminensis), wild ginger (Hedychium gardnerianum) and mile-a-minute (Dipogon lignosus). It is understood that pest management has resulted in reductions in weed biomass; however, recent closure of the block to contractors for health and safety purposes will prevent ongoing management and likely result in the reinvasion of pest plants to areas where they have been previously under control. Motions Creek flows along the south western boundary of the site, and there are a number of overland flow paths throughout the site, following the topography of the slope. At least one overland flow path, in the northern portion of the site, is likely to contain water on a permanent to semi-permanent basis and therefore, may provide habitat for indigenous fish species such as eels (Anguilla sp.) and banded kōkopu (Galaxias fasciatus). These species are known from Motions Creek. The site supports a range of common native and exotic birds. It is directly adjacent to Western Springs Lake which provides dabbling bird habitat and wading bird roosts. It is likely that copper skink 2 (Oligosoma aeneum), a common, ‘Not Threatened’ (Hitchmough et al., 20161) indigenous skink is present throughout the site. It is considered unlikely that geckos are present in the site although it should be noted that forest gecko (Mokopirirakau granulatus) and elegant gecko (Naultinus elegans elegans) have been recorded within the adjacent Auckland Zoo grounds. Long-tailed bats (Chalinolobus tuberculatus) are known to use mature P. radiata pines as solitary, communal, and maternity (breeding) roosting habitat. No bats were detected during a survey undertaken by Wildlands (2018). Wildlands considered it unlikely that bats would be present as the pines within the site reportedly did not contain the cracks and holes that bats tend to favour. However, Wildlands did not completely discount their presence. Bioresearches’ site visit revealed that the pines did support an abundance of cracks and holes that bats could potentially use (we observed many being used by rosellas and kingfishers throughout our brief visit) but we also consider it highly unlikely bats would utilise the habitat for the following reason. The distribution pattern of long-tailed bats in the Auckland