New Zealand overview

As an isolated archipelago in the South Pacific, New Zealand was one of the last land masses to be colonised by humans. Most of New Zealand’s native plants and animals are found nowhere else. Because New Zealand’s plants evolved in the absence of browsing mammals and the wildlife evolved in the absence of mammalian predators, many of those native species have been severely impacted by non-native or alien species.  As with other isolated islands, such as Hawaii, alien species have had a major impact on New Zealand’s native plants and animals.

Pinus contorta spread into monao shrubland, Rangitekei, New Zealand

Contorta pine spread into native monao shrubland


Already the number of naturalised  plant species exceeds the number of native plant species.  The number of naturalised plant species will continue to grow even if no more species are introduced.  An existing pool of about 20,000 non-native plant species already in New Zealand provides an ongoing source of species that could become naturalised.

Many naturalised non-native species are pest plants or environmental weeds in terrestrial and aquatic environments. The 2008 Department of Conservation consolidated list of environmental weeds contains 328 species of vascular plants .  Two- thirds of environmental weeds were originally introduced as ornamentals.  Examples of terrestrial environmental weeds include a number of species of “wilding conifers”, other trees (e.g. tree privet, woolly nightshade, Taiwan cherry), many vines (including jasmine, banana passionfruit, Japanese honeysuckle, blue morning glory, old man’s beard and climbing asparagus), shrubs (including Darwin’s barberry), grasses including pampas, and ground-cover and other herbaceous plants (e.g. alligator weed, wandering willie, ginger), and ferns (e.g. ladder fern).

Pampas, Cortaderia jubata and C. sellona-C. jubata hybrid- invasive pest plants in New Zealand

Pampas- invasive pest plants in New Zealand

These pest plants can completely replace native vegetation, especially where the natural vegetation is of low stature and /or is regenerating.  The problem is worst close to settlements and in areas where there are abundant sources of pest plant seed or other forms of propagules. Some pest plant species do not reproduce by seed in New Zealand and instead produce new plants from fragments, e.g. wandering willie on land; hornwort in freshwater environments; and alligator weed which is found both on land near water and in shallow aquatic environments.

The vegetation of many freshwater environments is now dominated by, or almost entirely composed of, non-native species.  While there are fewer pest plants in marine environments, they can however, still be locally abundant (e.g. Spartina in estuaries; and Undaria in marine environments (especially harbours)).

In 2016 the Department of Conservation prepared a baker’s dozen list of the worst environmental weeds.

Plant species that are new to New Zealand can be introduced deliberately, either legally or illegally (without the required permits),  or they can arrive accidentally such as on second-hand machinery or in potting mix or contaminated seed mixes.  Illegal and accidental introductions are still causing serious problems.  For example, in 2016 the serious agricultural weed velvetleaf  (Abutilon theophrasti) was found in several regions with its origin being contaminated fodder beet seeds.


Many of New Zealand’s most troublesome animal pest species arrived in the early years of European settlement in New Zealand. This includes predators of our native wildlife including rats, possums, cats, stoats, weasels and ferrets.  Other introductions include mammalian herbivores such as deer, wallabies and goats and a variety of freshwater fish species.  The latter includes perch, rudd and various carp species.  Also introduced are the sports fish- rainbow and brown trout and salmon.

Many native wildlife species are highly vulnerable to predation by alien animal species and now survive entirely or largely on predator free islands or areas of mainland subject to very intensive animal pest control. Animal pest species are also responsible for damaging native forest canopies- especially those containing taraire, puriri, pohutukawa, fuchsia, kamahi and rata.  Rats and possums eat the fruits and seeds of many native species, thereby adversely affecting regeneration.

Some native tree species have what is known as mast fruiting and seeding years. In these years rat numbers rapidly increase providing more food for stoats.  Once the fruit/seed supply is finished, the rats and stoats start eating even more of the native wildlife.  To reduce this risk even more intensive animal pest control is needed.  Unfortunately most of New Zealand ‘s protected and unprotected natural lands receive no animal pest control.  Finance is the primary limiting factor.  Considerable work is being undertaken to find more cost-effective animal pest control methods and approaches.

Many invertebrate species have been introduced into New Zealand. Some of these introductions have been deliberate (e.g. honeybees), and others accidental (e.g. Argentine ants, various wasp species).  Non-native invertebrate pest species can cause significant environmental disruption.  Wasps compete with native bees and birds for honeydew produced in native forests.  In addition to their damaging economic effects, Argentine Ants adversely affect the diversity and functioning of native invertebrate communities, litter decomposition, pollination, seed quality and dispersal.

Non-native fungi, bacteria and various microrganisms can adversely affect valued economic and natural ecosystems and species. The impacts on human health, agricultural and forestry systems are reasonably well known as the same species often cause problems elsewhere.  Impacts on native ecosystems and species from non-native species are often less well known.  The water mould Phytophora Taxon Agathis (PTA) causes kauri dieback disease and is thought to be a non-native.

Pacific Eco-Logic work with examples

Many Pacific Eco-Logic projects have addressed biosecurity matters. These range from ecological survey and monitoring projects requiring the collection of new field data to research projects based on the analysis of existing published and unpublished information including interviews.  We have completed biosecurity projects for terrestrial, freshwater and marine environments.  Examples of projects follow:

Biological control options for environmental weeds in protected areas

Pacific Eco-Logic reviewed potential biological control options for environmental weeds in protected areas  for the Department of Conservation (DOC).  This included evaluating the risks posed by invasive pest plants to protected areas and the potential utility of biological control options for reducing these risks.  The review included an assessment of the use and outcomes of international biological control programmes affecting invasive species in natural areas.  There was an assessment of the potential for biological control to make a difference to the ten worst pest plants identified by DOC staff.

Nelson Lakes

Lake aquatic plant surveillance for pest plants, Lake Rotoroa, Nelson Lakes National Park, New Zealand

Dive survey, Lake Rotoroa, Nelson Lakes National Park

Pacific Eco-Logic has completed two assessments  seven years apart of lake ecological condition for Lakes Rotoiti and Rotoroa in Nelson Lakes National Park.  This was for the Department of Conservation.  These assessments used the Lake Submerged Plant Index  (LakeSPI) methodology which was developed by NIWA with assistance from Pacific Eco-Logic.   The latest report for the two lakes shows the change in lake ecological condition since the very first aquatic plant survey (pre LakeSPI methodology).  As part of this project Pacific Eco-Logic also carried in-lake surveillance looking for new invasive aquatic plants.  Luckily none were found on either visit.

Wilding conifers

Pinus contorta in monao KawekasA major review of the state of knowledge about wilding conifers was prepared for the Ministry of Primary Industries and the multi-stakeholder Wilding Conifer Management Group in 2012.  This report collated information on the locations and impacts of ten problem wilding conifer species, relevant planning provisions and then expenditure of the different public agencies, new research, case studies, future trends, issues and options.  A set of recommendations was prepared for the group.  This led to the next phase – the preparation of a multi-agency strategy.  More recently additional funds have been allocated at the national level for wildling conifer control.


Examples of publications

Please see the “Biosecurity” heading in the Publications page.