Environment of New Zealand
The environment of New Zealand is characterised by an endemic flora and fauna which has evolved in near isolation from the rest of the world. The main islands of New Zealand span two biomes, temperate and subtropical, complicated by large mountainous areas above the tree line. There are also numerous smaller islands which extent into the sub antarctic. The prevailing weather systems bring significantly more rain to the west of the country. New Zealand's territorial waters cover a much larger area than its landmass and extend over the continental shelf and abyssal plateau in the South Pacific Ocean, Tasman Sea and Southern ocean.
Historically having an isolated and endemic ecosystem far into modernity, the arrival of Polynesians about 1300 AD and then later European settlers began to have significant impacts on this system, with the intentional and unintentional introduction of new species and plants which often overwhelmed their natural competitors, leading to a significant loss of native ecology and biodiversity, especially in areas such as bird life.
Today, most parts of New Zealand are heavily modified by the effects of logging, agriculture and general human settlement, though large areas have also been placed under protection, combined in many cases with efforts to protect or regenerate native ecosystems (aided by the fact that especially the South Island of New Zealand has a very low population density).
- 1 Physical environment
- 2 Ecosystems and ecology
- 3 Unsustainable practices
- 4 Environmental politics
- 5 Evaluations of New Zealand's environmental performance
- 6 See also
- 7 References
- 8 The New Zealand environment in film
- 9 Further reading
- 10 External links
For a small country the geography is extremely varied in both landforms and altitude. New Zealand's landscape ranges from the fiord-like sounds of the southwest to the tropical beaches of the far north. The South Island is dominated by the Southern Alps, the highest peak of which is Aoraki / Mount Cook, at 3,724 metres (12,218 ft). The tallest peak in the North Island is Mount Ruapehu (2,797 m), an active, cone-shaped volcano.
Smaller islands include Stewart Island, which lies south of the South Island; Waiheke and Great Barrier islands, near the north end of the North Island; and the Chatham Islands, more than 800 km east of the South Island.
New Zealand has many natural disturbances to its environment which endemic spices have evolved to tolerate. These include local events with short return times like landslides, floods, el nino and fires (rare before the arrival of humans). Long term events like massive eruptions and glacial maximums has also effected the current distribution of species in New Zealand.
New Zealand's soils are affected by bedrock, climate, vegetation and the time it has had to develop, In the central North Island the felsic volcanic rocks is deficient in elements (like cobalt) needed by plants. While the rare ultramafic rocks of the South Island are so rich in required elements it is used as fertilizer. The warmer climate of Northland weathers rock more quickly leading to deeper soils. In Fiordland and similar wet steep environments landslides reduce the time for soil formation.
The climate varies from cool temperate in the south and warm temperate in the north, with the exception of the North Island Volcanic Plateau. Rainfall varies from a low of 325 mm in Central Otago to an average of 5-8,000 mm in Fiordland. Most lowland areas have ample rainfall for farming and habitation. In the South Island, the high Southern Alps, which run north–south, cause a marked difference between the west and east coast climates.
Ecosystems and ecology
New Zealand has a wide variety of ecosystems and classification methods for them. The biota of New Zealand is one of the most unusual on Earth, due to its long isolation from other continental landmasses. Its affinities are derived in part from Gondwana, from which it separated 82 million years ago, some modest affinities with New Caledonia and Lord Howe Island, both of which are part of the same continental plate as New Zealand and in part from Australia.
The only terrestrial mammals that were in New Zealand prior to human habitation were three species of bat. A number of marine mammals are found on the coast and waters of New Zealand. Māori and European settlers introduced a wide range of mammals some of which have become serious invasive species.
New Zealand has a richly varied flora of imported and native species, the indigenous varieties having developed quite significantly due to the geographic isolation of the country before human migration and plant imports became common. However, the combination of external factors such as climate change and invasive species, as well as increasing agricultural and other human land uses have led to widespread damage. New Zealand's forest ecosystems for example are being considered as the second most endangered of the world, with only 7% of the natural habitat remaining.
More recently a component has been introduced by humans. New Zealand's biodiversity exhibits high levels of endemism, both in its flora and fauna. Until recently the islands had no native terrestrial mammals except for bats (although terrestrial, "archaic" mammals did exist in New Zealand until 19 million years ago, in the form of the Saint Bathans mammal), the main component of the fauna being insects and birds. Its flora is dominated by Gondwanan plants, comprising historically of forests, most famously the giant kauri. New Zealand has developed a national Biodiversity Action Plan to address conservation of considerable numbers of threatened flora and fauna within New Zealand.
Conservationists recognised that threatened bird populations could be saved on offshore islands, where, once predators were exterminated, bird life flourished again. Around 30 species are listed as endangered. The kiwi, a national symbol, is also under threat. A curious bird, it cannot fly, has loose, hair-like feathers and long whiskers, and is largely nocturnal.
Native New Zealand forests are broadly divided into temperate (broadleaf) and beech forests, introduced pine forests also cover a large part of the country. Native deciduous plants are extremely rare, with only 11 species losing all their leaves in winter, none of which are common canopy forming trees. The beech forests are most common in high elevations and cold climates, while temperate forests dominate elsewhere. The temperate forests have a higher biodiversity partially in the canopy and undergrowth flora. It is common for New Zealand's forests to be referred to as rain forest particularly in the western high precipitation zones.
Temperate forests vary across the country, but prefer warmer environments to the beech forests. They are noted for the many canopy layers they have. Near the coast they become stunted  due to salt and exposure to wind.
Beech forests are dived intro four varieties based on the dominant tree species and their geographic distribution is largely related to elevation. Black Beech (or Hard Beech) forests are found in the warmer lowlands of the North Island and northern South Island. Red Beech are found in direr foothills, while Silver Beech occupy a similar elevation but prefer a wetter environment. Mountain Beech are found at high elevation near the tree line, which is New Zealand is below 1000 m.
Beech trees do not flower every year, a year in which they flower is called a mast (or mast year). The effect of the whole canopy flowering at the same time introduces a lot of food into forest at once and leads to a population spike in those species that can quickly respond (typically mice).
New Zealand has extensive natural tussock grasslands in locations where elevation and climate has limited forest growth. This includes the Central Plateau in the North Island and extensive areas of the South Island between the tree line and the alpine environment. There are also smaller areas of tussock grassland on flood plains due to the constantly shifting substrate and greater likelihood of frost. New Zealand’s grassland ecosystems evolved in the absence of grazing mammals. Birds (Moa) and invertebrates were the main browsers until the introduction of sheep, goats and deer in the 1800s. Multiple species of tussock are present and dominate at different elevations and climates, with the maximum size of the species decreasing with increasing altitude. Tussock grasslands also help transfer water from the upper to lower catchment due to comparatively low transpiration.
New Zealand has two main ecosystems where cold and high winds limit biological activity. As the Southern Alps were uplifted relatively recently far from other mountain chains the New Zealand biota has quickly adapted to the new environment. Superficially New Zealand's sub-antarctic islands are similar to the sub alpine zone.
Rivers and wetlands
New Zealand lakes, rivers and wetlands are the most threatened of the countries major ecosystems. Rivers have been dammed ad most of New Zealand's wetlands have been drained. The damming of river can greatly change the sediment content and water flow.
Dune systems are constantly moving and plants have adapted to this environment. Vegetation is stunted due high winds and salt. In the North Island large mangrove forests have formed.
Including the inter-tidal zone, the Marine ecosystem is by far New Zealand's largest and most diverse. It extends from the sub-tropics to sub antarctic waters, more than 30° of latitude. Less than 1% of the area has been surveyed in detail and about 150 new species are discovered every year. The marine environment has been heavily effected by fishing and the introduction of exotic species.
Rare natural ecosystems
Currently there are 72 recognised rare terrestrial ecosystems in New Zealand. They are environments that were always relatively uncommon like caves, serpentine soils or hot springs and those which have become endangered. There are also ecosystems where the physical environment is largely controlled by animal activity, such as areas of significant guano deposition.
Farmland and urban environments are marked by the high number of introduced species, that have not evolved to interact with each other in the same ecosystem. These landscapes can effect the local climate, such as the 2.5 °C temperature rise in Christchurch from the urban heat island effect or the decreased transpiration from farmland. This increase in soil water content and reduction in the stabilising effects of roots leaves deforested areas prone to soil loss and landslides.
The move to carry out genetic engineering in New Zealand is opposed by environmentalists on economic and environmental grounds and the release of genetically modified organisms now has a strict regulatory regime under the Hazardous Substances and New Organisms Act.
Mining in New Zealand often encounters opposition from environmentalists. Coal mining in the West Coast region is of concern and there are plans to start the Cypress Mine, the Escarpment Mine Project, the Mt William North Mining Project, as well as issues at the long established Stockton Mine. Lignite mining in the Southland region is also encountering opposition. Hydraulic fracturing (fracking) is also of concern. A proposed soapstone mine in the Cobb Valley has also raised environmental concerns.
Deforestation in New Zealand is now of negligible concern since logging indigenous forest on public land has ceased and it requires a permit to be carried out on privately owned land. In the past 800 years of human occupation New Zealand has lost 75% of its forests due to deliberately lit fires and land clearance. Pine tree migration from plantations is also an environmental change.
The management of waste in New Zealand has become more regulated to reduce associated environmental issues.
Water pollution in New Zealand is an ongoing issue. A 2009 study tested 300 rivers and streams around the Western world and found the Manawatu River was loaded with the highest gross primary production (GPP). High GPP rates are an indication of poor ecological health and can lead to various environmental issues. Fish and Game, a statutory government body, started a dirty dairying campaign to highlight water pollution due to dairy farming. It led to the creation in 2003 of the Dairying and Clean Streams Accord, a voluntary agreement between Fonterra, Ministry for the Environment, Ministry of Agriculture and Forestry, and regional councils.
in 2011 the Parliamentary Commissioner for the Environment claimed the use of 1080, a pesticide using sodium fluoroacetate, was "effective and safe". The government and Federated Farmers maintain it is an effective tool for controlling possums over large areas. However its use remains contentious, with debate between conservationists and livestock farmers on one side and hunters and animal rights activists on the other. Concerns are also raised about security of potable water supplies in areas where 1080 is applied.
Politics and public opinion
The Values Party, the first ever national level environmental party, was formed in 1973. The Green Party of Aotearoa New Zealand, which was formed in 1991 and included some members from the defunct Values Party, was initially in Parliament as part of the Alliance Party. They currently have nine MPs that put forward green political ideology.
The level of protection of the environment from the different political parties varies according to their position on the left-right political spectrum. The right wing ACT Party scores the lowest and the left wing Green Party scores the highest.
There are a number of different sources for environmental funding in New Zealand.
The Nature Heritage Fund is a New Zealand Government funding body set up in 1990, and administered by the Department of Conservation, for the purchase of land which has significant ecological or landscape features.
To support community efforts, the Community Conservation Fund is available. Funding is for established community groups that have an ecological restoration project on public land that can be sustained after the two year funding period.
Nearly 30 percent of the land mass of New Zealand is in public ownership and has some degree of protection. The level of protection varies according to the land status. New Zealand also has nine wilderness areas where air access is limited, numerous "mainland islands" and marine reserves.
The roots of New Zealand environmental law can be traced to the common law of Britain. The increasing environmental awareness of the 1960s led to a specific body of environmental law that developed in many Western countries including New Zealand. Environmental law became more integrated in the 1980s with the passing of the Environment Act 1986 and the Conservation Act 1987. These Acts set up the Ministry for the Environment, Parliamentary Commissioner for the Environment and the New Zealand Department of Conservation.
Treaties and international agreements
New Zealand is a signatory to a number of treaties and international agreements:
- The Framework Convention on Climate Change, 1992 – ratified on 8 September 1993
- The Convention on Biological Diversity, 1992 – ratified on 16 September 1993
- The Montreal Protocol on Substances that Deplete the Ozone Layer, 1989 – ratified on 21 July 1988
- The Antarctic Treaty, 1959 – ratified on 1 November 1960 – Convention for the Conservation of Antarctic Marine Living Resources, 1980 – ratified on 8 March 1982 – and others
- United Nations Convention on the Law of the Sea, 1982 – ratified on 19 July 1996
- The Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and their Disposal, 1989 – ratified on 20 December 1994
- The Stockholm Convention on Persistent Organic Pollutants 2001 – ratified on 24 September 2004.
- Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter, 1971 (London [Dumping] Convention) – ratified on 30 April 1975 – and the International Convention for the Prevention of Pollution from Ships, 1973 – not yet ratified
- The Convention on International Trade in Endangered Species of Wild Flora and Fauna, 1973 – acceded to on 10 May 1989
- The Convention on Wetlands of International Importance especially as Waterfowl Habitat, 1971 (Ramsar Convention) – signed on 13 August 1976 with effect from 13 December 1976
- Convention for the Prohibition of Fishing with Long Driftnets in the South Pacific, 1989 (Wellington Convention) – ratified on 17 May 1991
- South Pacific Nuclear Free Zone Treaty, 1985 – ratified on 13 November 1986
- Convention for the Protection of the Natural Resources and Environment of the South Pacific Region, 1986 [SPREP] – ratified on 3 May 1990
- The Cartagena Protocol on Biosafety to the Convention on Biological Diversity – ratified on 24 February 2005
New Zealand is a depositary to the following environmental treaties:
- Convention on the Regulation of Antarctic Mineral Resource Activities
- Convention for the Conservation and Management of Highly Migratory Fish Stocks in the Western and Central Pacific Ocean (WCPFC)
- Convention for the Prohibition of Fishing with Long Driftnets in the South Pacific
- Protocol I to the Convention for the Prohibition of Fishing with Long Driftnets in the South Pacific
- Protocol II to the Convention for the Prohibition of Fishing with Long Driftnets in the South Pacific
Evaluations of New Zealand's environmental performance
State of the Environment reporting
Environmental Performance Index
The Environmental Performance Index (EPI) is a method of quantifying and numerically benchmarking the environmental performance of a country's policies. It results in a score out of 100. In 2016 New Zealand scored 88 out of 100, and ranked 11 out of 132 countries. In 2010, in terms of ecosystem effects on water quality New Zealand scored 40.3 points out of 100 for ecosystem vitality for freshwater and was ranked 43rd out of 132 countries.
OECD environmental performance review
In 2007, the Organisation for Economic Co-operation and Development (OECD) conducted an environmental performance review of New Zealand. Some of the main conclusions and recommendations were that:
- energy intensity is about equal to the OECD average
- intensity of water, fertiliser, and pesticide use is low for OECD countries. However, the review period saw 'significant increases, with consequent growth in pressures on the environment'
- New Zealand should strengthen national policy guidance (policy statements, national environmental standards)
- New Zealand should further integrate environmental concerns into economic and sectoral decisions, particularly by using economic instruments to internalise environmental costs of economic activities
- New Zealand should further develop international environmental cooperation.
- Timeline of the New Zealand environment
- Natural history of New Zealand
- Sustainability in New Zealand
- Conservation in New Zealand
- Pollution in New Zealand
- Deforestation in New Zealand
- Climate change in New Zealand
- List of New Zealand animals extinct in the Holocene
- "New Zealand's unique ecology". Science Learning Hub. Retrieved 16 December 2018.
- Walter, H. & Breckle, S-W. (2002). Walter's Vegetation of the Earth: The Ecological Systems of the Geo-Biosphere. New York: Springer-Verlag, p. 86, .
- Bunce, Michael; Beavan, Nancy R.; Oskam, Charlotte L.; Jacomb, Christopher; Allentoft, Morten E.; Holdaway, Richard N. (7 November 2014). "An extremely low-density human population exterminated New Zealand moa". Nature Communications. 5: 5436. Bibcode:2014NatCo...5.5436H. doi:10.1038/ncomms6436. ISSN 2041-1723. PMID 25378020.
- Perry, George L. W.; Wilmshurst, Janet M.; McGlone, Matt S.; Napier, Aaron (2012). "Reconstructing spatial vulnerability to forest loss by fire in pre-historic New Zealand". Global Ecology and Biogeography. 21 (10): 1029–1041. doi:10.1111/j.1466-8238.2011.00745.x. ISSN 1466-8238.
- Taonga, New Zealand Ministry for Culture and Heritage Te Manatu. "7. – Soils – Te Ara Encyclopedia of New Zealand". teara.govt.nz. Retrieved 16 December 2018.
- Robinson, Brett H.; Brooks, Robert R.; Kirkman, John H.; Gregg, Paul E.H.; Gremigni, Patrizia (1996). "Plant‐available elements in soils and their influence on the vegetation over ultramafic ("serpentine") rocks in New Zealand". Journal of the Royal Society of New Zealand. 26 (4): 457–468. doi:10.1080/03014223.1996.9517520. ISSN 0303-6758.
- Walker, Susan (2008). "New Zealand's remaining indigenous cover: recent changes and biodiversity protection needs" (PDF). doc.govt.nz. Retrieved 16 December 2018.
- "NZ's forests second most endangered in world". The New Zealand Herald. 4 February 2011. Retrieved 4 February 2011.
- "Deciduous plants in New Zealand | New Zealand Plant Conservation Network". www.nzpcn.org.nz. Retrieved 16 December 2018.
- "An Introduction to New Zealand's Temperate Rain Forests". fergusmurraysculpture.com. Retrieved 16 December 2018.
- Taonga, New Zealand Ministry for Culture and Heritage Te Manatu. "2. – Grasslands – Te Ara Encyclopedia of New Zealand". teara.govt.nz. Retrieved 16 December 2018.
- "Beech forest". www.doc.govt.nz. Retrieved 16 December 2018.
- Taonga, New Zealand Ministry for Culture and Heritage Te Manatu. "1. – Grasslands – Te Ara Encyclopedia of New Zealand". teara.govt.nz. Retrieved 16 December 2018.
- Taonga, New Zealand Ministry for Culture and Heritage Te Manatu. "2. – Grasslands – Te Ara Encyclopedia of New Zealand". teara.govt.nz. Retrieved 16 December 2018.
- "Water and Water and tussocks" (PDF). doc.govt.nz. Retrieved 16 December 2018.
- "Alpine ecosystems | New Zealand Plant Conservation Network". www.nzpcn.org.nz. Retrieved 17 December 2018.
- "Wetlands". www.doc.govt.nz. Retrieved 17 December 2018.
- "Sediment". NIWA. 27 May 2009. Retrieved 20 December 2018.
- "Coastal dunes | New Zealand Plant Conservation Network". www.nzpcn.org.nz. Retrieved 17 December 2018.
- "Our marine environment". www.doc.govt.nz. Retrieved 16 December 2018.
- "Naturally Uncommon Ecosystems". Manaaki Whenua - Landcare Research. Retrieved 16 December 2018.
- Williams, Peter A. (2007). "New Zealand's historically rare terrestrial ecosystems set in a physical and physiognomic framework" (PDF). newzealandecology.org. Retrieved 16 December 2018.
- "Ultrabasic sea cliffs". Manaaki Whenua - Landcare Research. Retrieved 8 January 2019.
- "Geothermal". Manaaki Whenua - Landcare Research. Retrieved 8 January 2019.
- "Seabird guano deposits". Manaaki Whenua - Landcare Research. Retrieved 8 January 2019.
- Tapper, N.J. (1 January 1990). "Urban influences on boundary layer temperature and humidity: Results from Christchurch, New Zealand". Atmospheric Environment. Part B. Urban Atmosphere. 24 (1): 19–27. Bibcode:1990AtmEB..24...19T. doi:10.1016/0957-1272(90)90005-F. ISSN 0957-1272.
- Fahey, B., Watson, A., & Payne, J. (2001). "Water loss from plantations of Douglas-fir and radiata pine on the Canterbury Plains, South Island, New Zealand" (PDF). Journal of Hydrology. Retrieved 27 December 2018.CS1 maint: multiple names: authors list (link)
- Derose, R. C.; Trustrum, N. A.; Blaschke, P. M. (1993). "Post-deforestation soil loss from steepland hillslopes in Taranaki, New Zealand". Earth Surface Processes and Landforms. 18 (2): 131–144. Bibcode:1993ESPL...18..131D. doi:10.1002/esp.3290180205. ISSN 1096-9837.
- Fensome, Alex (23 January 2012). "Crowd gathers to protest lignite mining". Stuff.co.nz. Retrieved 13 March 2012.
- Arnold, Niomi (4 February 2013). "Quarry worry". Nelson Mail. Retrieved 24 February 2013.
- Young, Roger. "Ecosystem metabolism in the Manawatu River" (PDF). Cawthron Institute. Archived from the original (PDF) on 11 September 2011. Retrieved 15 May 2011.
- Evaluating the use of 1080: Predators, poisons and silent forests (Parliamentary Commissioner for the Environment, June 2011): http://www.pce.parliament.nz/assets/Uploads/PCE-1080.pdf
- 1080 an effective tool to protect native wildlife (Office of the Minister of Conservation, 2008): http://www.doc.govt.nz/about-doc/news/media-releases/2008/1080-an-effective-tool-to-protect-native-wildlife/
- Call for reason in 1080 debate (Federated Farmers, 14 August 2008): http://www.fedfarm.org.nz/n628,10.html Archived 28 September 2011 at the Wayback Machine
- Example include:
- "Poison bait dropped in Fiordland National Park despite opposition". One News. Television New Zealand. 4 October 2010. Retrieved 19 May 2011.
- "Consent granted for 1080 drop". Timaru Herald. 29 March 2011. Retrieved 19 May 2011.
- Williams, David (19 May 2011). "Alarm as 'hunters end' DOC's poison drop". The Press.
- Beasley, Michael (August 2002). "Guidelines for the safe use of sodium fluoroacetate (1080)" (PDF). New Zealand Occupational Safety & Health Service. Archived from the original (PDF) on 9 February 2013. Retrieved 17 December 2007.
- "Current state of New Zealand's biodiversity". Retrieved 24 June 2013.
- Vote for the Environment Archived 5 June 2010 at the Wayback Machine. Environmentvote.org.nz. Retrieved on 19 August 2011.
- "Wilderness Areas". tramper.nz. Retrieved 19 December 2018.
- "Mainland islands". www.doc.govt.nz. Retrieved 19 December 2018.
- "Marine reserves A-Z". www.doc.govt.nz. Retrieved 19 December 2018.
- Multilateral Environmental Agreements | Ministry for the Environment. Mfe.govt.nz (5 November 2010). Retrieved on 19 August 2011.
- Treaties and International Law – Treaties for which New Zealand is the depositary – NZ Ministry of Foreign Affairs and Trade Archived 5 November 2015 at the Wayback Machine (13 May 2011). Retrieved on 19 August 2011.
- "The State of New Zealand's Environment 1997". Ministry for the Environment. 1997. Retrieved 3 September 2008.
- "Environment New Zealand 2007". Ministry for the Environment. December 2007. Retrieved 3 September 2008.
- The state of New Zealand’s environment: Commentary by the Parliamentary Commissioner for the Environment on Environment Aotearoa 2015
- "Archived copy". Archived from the original on 8 February 2010. Retrieved 10 February 2010.CS1 maint: archived copy as title (link)
- "Data | Environmental Performance Index - New Zealand". Yale. 2019.
- Sage, Eugenie (30 May 2012). "NZ drops to 43 in Government's favoured water report Green Party of Aotearoa New Zealand". Green Party. Archived from the original on 5 June 2012. Retrieved 7 June 2012.
- "Country Profiles; New Zealand". Yale Environmental Performance Index. 2012. Archived from the original on 15 December 2012. Retrieved 7 June 2012.
- OECD (2007). Conclusions and Recommendations: OECD Environmental Performance Reviews: New Zealand. OECD, Paris
The New Zealand environment in film
- Wild South series
- He Ao Wera – a documentary by Mike Smith and Hinekaa Mako about the effects of climate change on communities in Aotearoa.
- Earth Whisperers/Papatuanuku – this Kathleen Gallagher film was shot around New Zealand by cameramen Alun Bollinger and Mike Single. It focuses on 10 visionary New Zealanders out to prove that a shift in consciousness can heal our environment.
- OECD Environmental Performance Reviews New Zealand. OECD Publishing. 2007. ISBN 978-92-64-03057-2.
- Cessford, Gordon (2001). The state of wilderness in New Zealand (PDF). Wellington, N.Z: Department of Conservation. ISBN 978-0-478-21971-5.
- The academic journal "ENNZ: Environment and Nature in New Zealand". Environment and Nature in New Zealand : Ennz. ISSN 1175-4222.
- Ministry for the Environment
- Department of Conservation
- Parliamentary Commissioner for the Environment
- Ecological Economics Research centre New Zealand (formerly known as the New Zealand Centre for Ecological Economics)
- Environlink – a regional council driven funding scheme for research
- ourfuture.net.nz – a project for mapping environmental initiatives in New Zealand
- www.greenpages.org.nz - a directory of environmental organisations in Aotearoa