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Christchurch, New Zealand

Syrett P.,Landcare Research | Forrester G.J.,Landcare Research | Harman H.M.,MAF | Meurk C.D.,Landcare Research | And 2 more authors.
BioControl | Year: 2012

To test the theory that successful biocontrol of invasive hawkweeds (Pilosella and Hieracium spp.) would increase bare ground and accelerate erosion, small areas of hawkweed were suppressed with herbicide in a nine-year study. An increase in bare ground resulting from the treatments was maintained throughout. No new invasive species were recorded, and apart from a temporary increase in a perennial grass, no existing exotic species moved into the gaps created. Indigenous plants did not respond either, although at one site where mat plants were prevalent, treatments slowed their decline. As recovery of existing vegetation was minimal, it is likely that invasion of hawkweed is a consequence of degradation rather than the reverse, and if biocontrol is successful, degraded grasslands may suffer further damage, especially in areas that are grazed. The effect may be ameliorated since biocontrol agents are predicted to perform less well under conditions of low fertility and low moisture. Our results emphasize the importance of pre-release ecological studies to clarify the role of invasive plants proposed for biocontrol. © 2011 International Organization for Biological Control (IOBC). Source


Spurr E.B.,Landcare Research | Crossland A.C.,Christchurch City Council
Notornis | Year: 2014

Numbers of bellbird (Anthornis melanura), an endemic honeyeater, counted along transects in forest remnants on the Port Hills near the city of Christchurch, New Zealand, increased since the initiation of intensive mammalian pest control in 2006. Bellbird counts also increased along transects in bush reserves and along a 6.5 km cycle route in the city itself, probably as a result of spill-over from source populations on the Port Hills, because few bellbirds breed in the city. In contrast, counts of bellbirds in domestic gardens in the city did not increase, perhaps because of the continued presence of introduced mammalian predators and/or lack of suitable habitat. We suggest the increased abundance of bellbirds in forest remnants on the Port Hills was likely the result of mammalian pest control but the lack of 'no-treatment' areas means we cannot rule out other causes of the increase such as changing habitat and food availability. © The Ornithological Society of New Zealand Inc. Source


Gillooly M.,Christchurch City Council | Whyte G.,DHI Water - Environment - Health
Proceedings of the 34th Hydrology and Water Resources Symposium, HWRS 2012 | Year: 2012

Understanding the changing flood risks in a coastal city with three major rivers running through urban areas is a significant challenge. Prior to the devastating sequence of earthquakes in Canterbury, New Zealand in September 2010, Light Detection and Ranging (LiDAR) coverage of Christchurch City was based on data acquired in 2003. As a result of ongoing seismic activity, new LiDAR data has been collected following every quake greater than magnitude 6.0. Land damage associated with seismic activity is a combination of uplift, lateral spread and subsidence. Rebuilding the city to achieve prequake levels of service for land drainage within the road and pipe network, as well as understanding the hydraulic capacity of the river systems and waterways, requires a major rethink of the city's existing modelling program. Errors in the 2003 LiDAR dataset meant that important baseline comparisons to determine localised land deformation, and consequent changes to the primary network and secondary flow paths, is difficult to determine. It is not only engineers and stormwater modellers who need to understand the extent of land damage - the Earthquake Commission, the insurance industry, land use planners, and building consent officers all require accurate information on the extent of subsidence and increased flood risk. This paper highlights the importance of having accurate baseline data in order to respond to a catastrophic natural disaster, and demonstrates the modelling techniques and results that were used to respond to Christchurch's changing flood risk. © 2012 Engineers Australia. Source


Kirkcaldie D.,Opus International Consultants Ltd. | Brabhaharan P.,Opus International Consultants Ltd. | Cowan M.,Opus International Consultants Ltd. | Wang C.,Opus International Consultants Ltd. | And 2 more authors.
Bulletin of the New Zealand Society for Earthquake Engineering | Year: 2013

Identified in the Christchurch Lifelines Study as a bridge vulnerable to damage in a major earthquake, the Ferrymead Bridge on the key arterial route connecting the suburbs of Redcliffs and Sumner to the rest of Christchurch has subsequently been under investigation by the Christchurch City Council to increase its traffic capacity and upgrade its earthquake resistance. A contract was let in 2010 to undertake these works. Surviving the September 2010 Darfield earthquake undamaged, the bridge fell victim to the February 2011 Christchurch earthquake with extensive liquefaction and soil lateral spread occurring at the site, displacing the abutments and piers inwards towards the centre of the river. After extensive investigation into options for recovering the bridge, the decision was finally taken to replace the bridge with a new structure. This paper outlines the initial design to widen and seismically upgrade the original bridge, the damage sustained by the bridge from the Christchurch earthquake and measures instituted to stabilise the bridge as a result of that damage, and focuses particulariy on the design now developed for the replacement structure. The significant issues involved in achieving earthquake resistance at a highly liquefiable site and in constructing in an environment of ongoing earthquake activity are discussed. Source


Morgenroth J.,University of Canterbury | Armstrong T.,Christchurch City Council
Urban Forestry and Urban Greening | Year: 2012

The resilience of Christchurch, New Zealand's urban forest has been tested during a year of major earthquakes and aftershocks. Tree loss has resulted from mass soil movement, soil liquefaction, rockfalls, and land slips. At the time of writing, only 384 trees have been documented as removed, however, thousands more are scheduled for removal. Additionally, the changes to the soil environment resulting from liquefaction will require existing trees to adapt quickly to their new soil environment. Their fate will not be known for years. Though the total number of trees removed is unlikely to reduce city-wide canopy cover appreciably, it is important to recognize that spatial patterns of tree loss were highly localized and thus local canopy cover has been drastically reduced in some areas. Short-term management of the urban forest in the aftermath of the earthquake focused on removal of trees deemed unstable or unsafe. In the medium-term, attempts have been made to monitor the health and stability of remaining trees using an asset management system, though some difficulties related to consistency and ubiquity of its use have been identified. Though short and medium-term management have been largely effective, long-term management of Christchurch's urban forests will largely be dictated by government policy, which will be informed by public consultation and land ownership. Many of the benefits provided by urban forests are well understood. However, trees and greenspaces provided additional benefits during earthquakes and in the aftermath. Planted trees in the hills surrounding the city prevented rockfall from damaging infrastructure and human life downslope, while greenspaces were used as a base for search and rescue staff during rescue and recovery operations, and as temporary living spaces for residents who lost their homes. © 2012 Elsevier GmbH. Source

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