Ellen Cieraad's Research

Quantative plant ecology & physiology

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Double whammy caused by climate change

Invasive species can have detrimental effects on ecosystem services, including food security and indigenous biodiversity. Similarly, climate change has been predicted to affect global food provision and the stability of ecosystems. Many studies assess the direct effect of either of these issues facing today’s world; however, of course they operate in tandem and this can create complex effects. While it is well established that climate change may facilitate the abundance and/or range expansion of invasive species, it is less known that it may also impact the ability to control and manage this invasion. If, for example, climate change results in the increase in abundance of an invertebrate crop pest, and at the same time in a decrease of a natural pest control agent (for example, insectivorous birds), then climate change can accelerate the impacts of invasions, and create a ‘double whammy’ for the receiving ecosystem. Similarly climate change may alter the effectiveness of ways to control invasive species.

(c) wikipedia

(c) wikipedia

In a recent article, we show that increasing air temperatures over >60 years in New Zealand has reduced the window of opportunity to effectively control an invasive mammalian pest (European rabbit Oryctolagus cuniculus – using Central Otago, South Island, as an example).

Latham ADM, Latham MC, Cieraad E, Tompkins DM, Warburton B 2015. Climate change turns up the heat on vertebrate pest control. Biological Invasions 17(10): 2821-2829. doi: 10.1007/s10530-015-0931-2

Anthropogenic control of invasive vertebrate species is most effective in times when natural food is limiting. In the case of rabbits in temperate southern New Zealand, the most effective period of control is during the coldest period in winter, when temperatures are sustained below approximately 5°C and the above-ground palatable vegetation available to rabbits reaches an annual low. Our study found that the milder winters in recent years resulted in the window of control starting later and ending earlier in the year, and that those windows are increasingly punctuated by warm temperatures. Overall this has resulted in suboptimal conditions for poisoning because of the higher availability of natural foods.

While longitudinal records detailing the effectiveness of control operations are not available, this study suggests that the trend towards warmer winters over the past >60 years has significantly reduced the window of time for effective control of rabbits in temperate New Zealand. As winters are likely to continue to warm, alternative methods of management warrant investigation.

Climate change may thus exacerbate the unwanted impacts of invasive species by reducing our ability to manage them effectively.


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Threatened Environment Classification

A goal of the New Zealand Biodiversity Strategy is to ‘halt the decline in New Zealand’s indigenous biodiversity, and to maintain and restore a full range of remaining natural habitats and ecosystems to a healthy functioning state’. Meeting this goal requires knowledge of how much of the full range of natural ecosystems remains, and how well they and their biodiversity components are protected. However, reliable information is surprisingly difficult to bring together at a national level.


One way to assess broad patterns of loss and protection of indigenous species habitats is to combine maps of land cover, legal protection status and the abiotic environment. The first such combination analysis was produced nearly 10 years ago, and was used to create a simple, six-category ‘Threatened Environment Classification’ that has been adopted by many agencies, decision-makers and private biodiversity practitioners across the country.

Recently, my colleagues and I revised and published an updated Classification with updated land cover (LCDB4.0; based on 2012 satellite imagery) and information on protected areas for natural heritage purposes (2012), which they combined with LENZ (Land Environments New Zealand). You can find our paper here. The new analysis shows that New Zealand’s lowest, flattest, warmest and driest environments have lost high proportions of their indigenous cover and what remains is poorly protected ‒ even less so than previously estimated. In contrast, the highest, steepest, coolest, and wettest environments have been less reduced by human land use and are much better protected ‒ more so than previously estimated.

Cieraad E, Walker S, Price R, Barringer J 2015. An updated assessment of indigenous cover remaining and legal protection in New Zealand’s land environments. New Zealand Journal of Ecology 39(2): 309-315.

The Threatened Environment Classification provides a high-level, standardised national framework for assessing biodiversity representativeness and protection that and can assist both planning and reporting. Land in the first two categories of the classification (less than 20% indigenous cover remaining) is recognised as a priority in biodiversity protection policy, especially on private land. In combination with site survey, the Classification can help resource managers to identify places that are priorities for formal protection against clearance and/or incompatible land uses, and for ecological restoration to restore linkages, buffers and lost species.

The Threatened Environment Classification is freely available, and can be accessed in several ways. The easiest way to view it and create maps is in Landcare Researches GIS portal Our Environment  (under “About Ecosystems and habitats” tick “Which areas of indigenous vegetation are under threat?”).

More information and resources are available on http://www.landcareresearch.co.nz/resources/maps-satellites/threatened-environment-classification