Corynocarpus laevigatus (karaka)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Habitat List
- Hosts/Species Affected
- Biology and Ecology
- Latitude/Altitude Ranges
- Air Temperature
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Impact Summary
- Economic Impact
- Environmental Impact
- Threatened Species
- Social Impact
- Risk and Impact Factors
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Gaps in Knowledge/Research Needs
- Links to Websites
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Corynocarpus laevigatus J.R. & G. Forst.
Preferred Common Name
Other Scientific Names
- Corynocarpus laevigata Forst.
Local Common Names
- Cook Islands: koopii
- Germany: Karakabaum
- New Zealand: koopii; kopi; Maori peanut; wairarapa
- USA/Hawaii: karaka nut; karakanut; karakaranut; New Zealand laurel
- CCKLA (Corynocarpus laevigatus)
Summary of InvasivenessTop of page
Corynocarpus laevigatus, commonly known as karaka, is a small tree endemic to New Zealand and has so far been noted as weedy in two areas. The first is in southern regions of the North Island of New Zealand, where the evidence strongly suggests it is not native, but instead consists of culturally established populations, with adjacent escapees. The second is in Hawaii where it was originally planted but has since turned aggressive, being given a score of 7/10 in the Pacific Island Ecosystems at Risk (PIER) assessment, and rated as "high risk".
Where karaka has been allowed to spread (it is readily controlled early in the invasion process) its prolific seeding and resultant dense shade excludes native species and alters the composition and ecosystem processes of the host community.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Dicotyledonae
- Order: Celastrales
- Family: Corynocarpaceae
- Genus: Corynocarpus
- Species: Corynocarpus laevigatus
Notes on Taxonomy and NomenclatureTop of page
Corynocarpus laevigatus, J. R. and G. Forst. (Corynocarpaceae) is a small tree (usually to 15m) endemic to New Zealand. "Corynocarpus" means "club fruit", and "laevigatus" means "smooth", in reference either to the skin of the fruit (Molloy, 1990) or the leaf (Poole and Adams, 1990).
C. laevigatus was called karaka by the first (Maori) settlers to the New Zealand mainland, and this is its current local common name for New Zealanders. (It should be noted that 'karaka' is used in some Pacific Island cultures to refer to Planchonella grayana (Klinac et al., 2009)). Originally called wairarapa (Shand, 1896) by Moriori, the original inhabitants of Chatham Islands, currently C. laevigatus is called kopi or koopii (Beever, 1991) by modern Chatham Islanders, all of whom are of mixed Maori and Moriori heritage. (The name 'kopii' is also used in Rarotonga (Cook Islands) but this may refer to a different species (Biggs, 1991)). The name Karakanut is a term widely used in Hawaii for C. laevigatus.
Corynocarpus is in the monogeneric family Corynocarpaceae (Wagstaff and Dawson, 2000). There are five species in the genus: C. similis in the Solomon Islands, New Guinea and Vanuatu; C. cribbianus in New Guinea and north-eastern Queensland, Australia; C. dissimilis in New Caledonia; C. rupestris with two subspecies in eastern coastal Australia; and C. laevigatus in New Zealand. The ancestral taxon had two independent southward radiations, possibly by mid-Tertiary land connections (Herzer et al., 1997), one to New Guinea, Solomon Islands, Vanuatu, and Australia (Queensland and northern New South Wales), and the other to New Caledonia and New Zealand, where C. dissimilis from New Caledonia is most similar to C. laevigatus (Wagstaff and Dawson, 2000).
The single genus of the family, Corynocarpus, is taxonomically isolated by characters such as its petaloid scales and discrete nectaries (Philipson, 1987). Similarly, its pollen is most unusual, with a rounded and a flattened pole, as well as being asymmetric, unlike postulated relatives (Nowicke and Skvarla, 1983). However, its wood is very similar to that of Coriaria in the Coriariaceae, having such unusual features as "scanty vasicentric plus ray-adjacent axial parenchyma" with very wide multiseriate rays (Carlquist and Miller, 2001). Similarly both taxa have trichomoids (half hair and half scale) at their nodes (Kubitzki, 2011).
Unusually, there are no recognised synonyms for this species (The Plant List, 2013).
DescriptionTop of page
The habit of C. laevigatus is a tree growing 15-20 m tall, often with a strong leader. Trunks have a dbh (diameter at breast height) of 60 cm (Dawson and Lucas, 2011), though the largest trunk recorded was 300cm (Stowe, 2003). Bark of mature trees is dark brown, corrugated, with the whitish corrugations fractured into sections about 1x3 cm, by 0.5 cm thick. Bark of younger trees is light brown, and marked, often with short horizontal bands, like sewing stitches. Branches are stout to 3 mm thick, even in young shoots, with raised, roundish leaf scars. Strong sprouts can form on damaged trunks.
Foliage is of alternate, large (up to 30 cm long), simple, entire, elliptic-oblong, glossy leaves to 8 cm wide, and with petioles <2 cm long. Leaves are thick, coriaceous, dark to bright green, shiny on the upper surface, and lighter on the lower surface. Margins are slightly inrolled. The alternate leaves have a yellowish central vein which is slightly raised near the petiole on the adaxial surface, and protruding throughout the leaf on the abaxial surface. Lateral veins emerge at oblique, but regular angles to the main vein, and are very slightly raised on the abaxial surface; they often fork towards their tips. The upper surface is generally covered in small white deposits, like exudates. Additionally small pits occur on the surface in which a small raised gland occurs (The University of Auckland, 2012). A small brown membranous scale (trichomoid) to about 12 mm long and 4 mm wide is found at the base of younger leaves, wrapping around the emerging shoot. These are called intrapetiolar stipules by Kubitzki (2011), but technically the family is considered exstipulate, though the scale is attached to the base of the subtending petiole (The University of Auckland, 2012). Leaves often appear to be in clumps towards the end of the branches, due to the spring burst of growth. Leaf longevity is unknown, but growth patterns indicate they may persist for several years.
Inflorescences are of stout, short panicles 15-20 cm long, nearly as wide at the base, and branched. There can be 100-200 flowers per panicle. Flowers open acropetally. Each is subtended by a triangular brown scale (trichomoid) up to 3 mm long, by 4 mm wide, and groups of 2-3 flowers also have their own basal scale.
Flowers are small and white to greenish-yellow, scentless, and have recently been confirmed as gynodioecious by Garnock-Jones et al. (2007). Female flowers (up to 4.0 mm diameter, and with 5 sub-orbicular sepals (up to 2.3 mm long) and 5 spathulate-obovate petals up to 2.4 mm) have staminodes (sterile, with filaments up to 1.6 mm) mounted on the petals, with anthers dorsi-fixed, dehiscing lengthwise, but containing no pollen, and thus appearing dry and shrivelled. A large nectary is present at the base of the staminode (Kubitzki, 2011).The single superior ovary, bearing one ovule, is 1.3 mm long, with a capitate stigma (Garnock-Jones et al., 2007). Male flowers (up to 5.7 mm diameter and with 5 sepals up to 3.1 mm long and 5 petals up to 3.2 mm) have stamens (2.3 mm) containing viable pollen. Male flowers contain a pistil (with ovary up to 2 mm long), but its stigma appears only partially functional (Garnock-Jones et al., 2007), since males set only small quantities of fruit. Neither flower opens widely. Pollen can be described, if meridionally orientated, as weakly heteropolar, bi-colporate, with a mostly psilate (i.e. smooth) exine (Nowicke and Skvarla, 1983).
Fruit are large, orange drupes, ellipsoid to ovate, often slightly asymmetric, and usually around 30-40 mm in length (Essen and Rapson, 2005), and up to 63 mm (Platt, 2003). The fruit is large, with fresh weights up to 13.2 g and dry kernel weights of 2.3 g (Essen and Rapson, 2005). Up to 62 % of the fresh weight of karaka fruit is water (Bannister et al., 1996). Fruit form in clumps of 10-30 per inflorescence. The fruit consists of a thin exocarp (easily removed with fingers; Molloy, 1990), a thin layer <2 mm) of (dry-feeling) fleshy, orange-coloured mesocarp (which was widely eaten by children, including Europeans; Molloy, 1990), and a fibrous endocarp. The flesh is strongly scented (Fountain and Couchman, 1984), commonly associated with attraction to vertebrates (I. Castro, personal communication, 2012). The seed is elliptic, terete with a sub-acute apex. The surface is rough, yellowish, with an open network of fibrous veins, which partially weather away (Webb and Simpson, 2001).
Wood anatomy has been studied in detail (Patel, 1975; Carlquist and Miller, 2001). Growth rings are not evident chiefly because of the abundant, storied, axial parenchyma in discontinuous bands, within which vessels are mostly located. Vessels can be up to 0.2 mm in length, have simple perforation plates, and can vary considerably in frequency. Fibres are very thick. Crystals and starch are present in rays.
DistributionTop of page
C. laevigatus is endemic to New Zealand. It occurs in coastal and lowland forest from Northland, extending south to coastal regions of the lower North Island. It is conspicuously absent from the mountainous core of the North Island, except for some locations around Lake Taupo, which are probably descendants of trees planted by local Maori. Karaka occurs in northern South Island and down the dry east coast to Banks Peninsula (43o45’), but is entirely coastal there, as it is relatively frost-intolerant (Molloy, 1990). However, it can survive as far south as Dunedin when planted (Bannister et al., 1996).
Karaka also occurs in the Kermadec (to the north of New Zealand) and Chatham (to the east of the South Island) Islands groups (Sawyer et al., 2003; Stowe, 2003). Sawyer et al. (2003) give a detailed map of the distribution of karaka throughout New Zealand. Although the New Zealand Virtual Herbarium (2012) includes two locations in inland northern South Island, these are suspect, and if verifiably present and correct, are certainly planted.
However, karaka's natural distribution was probably the north of the North Island (Molloy, 1990; Leach and Stowe, 2005; Costall et al., 2006), especially in districts of low altitude or close to the coast. It is not considered to be naturally occurring in several scattered patches found around inland Lake Rotoiti (approximately 38oS), near Rotorua (Beadel and Shaw, 1991). Note though that Burrows (1996) suggests recruitment could be difficult in dry or open sites due to sensitivity to drought. Karaka is increasingly accepted as having been dispersed from northern New Zealand by Polynesian canoe-voyagers both north to the Kermadec Islands and south through southern North Island and northern coastal South Island, as well as east to the Chatham Islands.
In Hawaii, karaka is now recorded from Kauai (Kokee area), Oahu, Molokai and Hawaii (the Big Island) where it has been spread intentionally by humans (Wagner et al. 1999). In these areas it is now accepted as an aggressive invader.
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|USA||Present||Present based on regional distribution.|
|-California||Present||Little and Skolmen, 1989||Ornamental tree|
|-Hawaii||Localised||Introduced||1891||Invasive||Motooka et al., 2003||Kaua'i (Koke'e region), O'ahu, Hawai'i, Moloka'i|
|Portugal||Present only in captivity/cultivation||Introduced||Not invasive||GL Rapson, Massey University, New Zealand, personal observation, 2012||Garden of Ajuda, Lisboa - plant fruiting|
|New Zealand||Widespread||Native||Invasive||Costall et al., 2006||Natural range - northern North Island Invaded range - southern North Island and northern South Island|
History of Introduction and SpreadTop of page
Though currently widely dispersed through the northern three-quarters of New Zealand, karaka occurs only in coastal areas at the southern portion of its range, and appears to be climatically limited there. In the northern portion of its range, karaka is a regular component of forest, but no aggressive spread has been observed. It is in the middle of its range, where it has only spasmodic occurrences, often in association with kainga (villages) and pa (fortifications), that karaka appears weedy (Costall et al., 2006). In the far south of its range karaka is more restricted (Leach and Stowe, 2005), often found in circles around a central tree (Molloy, 1990), suggesting relatively recent (within the last century or two) dispersal from plantings. Additionally some oral history clearly describes translocations south, e.g., to Kaikoura (Beattie, 1994).
Thus, distribution information suggests that karaka originated in the north of the North Island, and was deliberately spread south from there by Maori for whom it was an important food source (Stowe 2003; Leach and Stowe, 2005; Costall et al., 2006). From southern plantings karaka probably dispersed naturally, or was assisted by birds, particularly the native wood pigeon (kereru or Hemiphaga novaeseelandiae), which has a distensible gape (McEwen, 1978; Wotton and Ladley, 2008) and so can ingest the nuts.
The Chatham Islands, 800km to the east of New Zealand, were first settled by the ancestors of the Moriori people about 400-800 years ago (King, 1989). They carried karaka seed in the canoe Rangimata to the north coast of Rekohu, or Wharekauri, local names for Chatham Island (Shand, 1896). Then karaka probably was widely dispersed by the large local woodpigeon or parea, Hemiphaga chathamensis (Powlesland et al., 1997). Dieffenbach (1840) visited the Chathams for about 10 weeks in mid-1840, during the final stages of the killing and enslavement of the resident Moriori by New Zealand mainland tribes of Maori, who had used European ships to invade the Chathams about 1831. Dieffenbach (1840) recorded that karaka, which he referred to as "that strange plant, the karaka tree" formed "the largest part of the forest", often in monospecific stands, with trees growing to 91 cm in diameter and 18 m tall, and dominating the vegetation around Te Wanga Lagoon (which forms about a fifth of the area of the main island), particularly to the east and north. Its alien origins are suggested by its absence from the less disturbed southern plateau vegetation (G.L. Rapson, Massey University, New Zealand, personal observation, 2012), though it does occur in coastal gullies (Powlesland et al., 1997).
The fragmented distribution of karaka in the Chatham Islands suggests it was introduced as a food plant by the first Moriori, but the oral history of this spread has been lost (Shand, 1896). Once on the island, the lack of good-quality woods for building ocean-going canoes meant the inhabitants were trapped there, and their historic links were lost. Dieffenbach (1840) described karaka wood, though "light and spongy", as the only timber available for Moriori to make canoes from, up to 4m long, and suitable only for inshore fishing. Further, preliminary genetic evidence suggests that Chatham and Kermadec karaka lack detectable genetic differences from the mainland material (Wagstaff and Dawson, 2000), supporting a common origin.
Karaka was introduced to Kauai Island of Hawaii before 1891 for horticultural purposes (Smith, 1985). It had naturalised in the Kokee region of Kauai by 1912 (Wagner et al., 1999). It was subsequently deliberately spread into the nearby hinterland (up to 1500m altitude) of Kokee by aircraft in 1929 (Wagner et al., 1999; Motooka et al., 2003) to aid re-afforestation after extensive erosion in the Waimea Canyon (D. Mueller-Dombois, University of Hawaii, personal communication, 2012). Between 1925 and 1937 almost 5000 trees were planted by the Division of Forestry (Little and Skolmen, 1989), possibly for the same reason. Karaka is spreading rapidly and is becoming a problematic weed (Little and Skolmen, 1989); forming dense, monotypic subcanopy stands (Motooka et al., 2003). It is shading out native vegetation in what was probably Acacia koa - Metrosideros polymorpha mesic forest (from 700-1500 m above sea level), endangering rare plants such as the fern Diellia mannii (Aguraiuja and Wood, 2003) and the shrub Exocarpos luteolus (Santalaceae) (Harris, 2002; Sawyer et al., 2003).
Karaka was also taken to the islands of Oahu and Hawaii (the Big Island, where it naturalised) (Wagner et al., 1999). It was introduced to Molokai before 1912 and it is still restricted to one small patch (Little and Skolmen, 1989) at Kamakou Reserve where it is being aggressively controlled (Stone et al., 1992; D. Mueller-Dombois, University of Hawaii, personal communication, 2012).
Maori folklore states that karaka was brought to New Zealand from their ancestral homeland of Hawaiki (Best, 1942), a place which has not been identified with any certainty, and is now considered to be mythical (Stevenson, 1978). At least two "introductions" are recorded in oral histories. One introduction was in the Nukutere canoe, with the karaka being sown at Waioeka, Bay of Plenty (Best, 1925), but its origin is not clear. The other introduction was in the Aotea canoe (Smith, 1913) about 1350 AD, from an island called Rangituhua (which is probably Raoul Island in the Kermadec Islands group; Best, 1942). That karaka was transported to the banks of the Patea River, south Taranaki (Houston, 1965).
Karaka may have originated in the Kermadec Islands, as oral history suggests (Buck, 1949) but there it is limited to patches. However, it is often large and almost monotypic on the main island Raoul, and some adjacent islets (Sykes et al. 2000). It is recorded as forming "lofty trees" with "thick patches" of seedlings by Oliver (1910) but this may be a misidentification (Sykes et al., 2000). Stevenson (1978) suggests Maori could have translocated karaka to Raoul Island from the New Zealand mainland. As it is not buoyant (Oliver, 1910; J Costall, Massey University, New Zealand, personal observation, 2012), it is unlikely to have naturally dispersed across the Pacific Ocean to New Zealand, which implies a more local origin. If Maori did bring karaka seeds across water as "introductions", then the most likely origin of that karaka was Northland, New Zealand, or nearby offshore islands (Molloy, 1990).
IntroductionsTop of page
|Introduced to||Introduced from||Year||Reason||Introduced by||Established in wild through||References||Notes|
|Natural reproduction||Continuous restocking|
|Hawaii||New Zealand||1891||Yes||No||Wagner et al. (1999)||First introduction was to Kauai island.|
Risk of IntroductionTop of page
Karaka is not likely to be introduced accidentally, because it has no vegetative reproduction, does not propagate easily from cuttings, and has large, conspicuous fruit (3.0-6.3 cm long; Platt, 2003; Essen and Rapson, 2005), which cannot be easily mistaken for any other species. However, seeds germinate rapidly and easily (Bannister et al., 1996, Burrows, 1996), so it can be deliberately spread with ease. Furthermore, it can naturalize from garden plants or be dispersed by mammals, especially pigs and possibly deer (Motooka et al., 2003). Although few extant birds have gapes large enough to ingest the fruits, those that do may aid its dispersal (kereru (Hemiphaga novaeseelandiae) and parea (Hemiphaga chathamensis)) (McEwen, 1978; Wotton and Ladley, 2008). Karaka may readily naturalise should dispersers be able to access cultivated specimens.
HabitatTop of page
The general habitat of C. laevigatus is lowland podocarp-broadleaved forest of northern New Zealand (Poole and Adams, 1990), in moderate rainfall regimes and in moderately fertile soil. It forms a frequent, but seldom a major, component of the forest. Coastal populations in frost-free areas can be dense. Karaka is apparently limited by frost, and not found in non-coastal areas in the South Island of New Zealand.
McKelvey and Nicholls (1959) report a "regular stocking" of karaka at a density of 2.5 stems per hectare (1/acre), as typical of much of Northland (north of Auckland) due to regeneration after logging of kauri (Agathis australis) forest, which has created a mosaic of small kauri stands amongst a hardwood matrix, mostly at less than 300m altitude. They also note karaka as rare in podocarp-hardwood forest with taraire (Beilschmiedia tarairi), but locally abundant close to the coast <1 km; related to Maori propagation), often with a dense lower tier. Conning (1998, 1999) note karaka as dominant with taraire in coastal vegetation at Ahipara and Whangaroa, both in Northland. Burns and Leathwick (1996) note that it has a restricted range in good quality kauri forest in Northland and is not very abundant. It occurs in stands amongst pohutukawa- (Metrosideros excelsa) dominated forest on Great Barrier Island, near Auckland (Ogden, 2001). Dense patches are found at Limestone Downs, near Port Waikato, Waikato (Clarkson et al., 2002), and erratically further south, probably representing relicts of planted populations.
On offshore islands of the north of New Zealand, Campbell and Atkinson (1999) describe karaka as "drought-sensitive" in that it cannot survive on drier, rockier islands.
In the south of its current New Zealand range, where karaka is almost certainly introduced, it is associated with cliffs and gullies close to the coast (i.e. largely ungrazed sites), often as small stands of trees <30) up to 8 m tall, and usually with a disturbed or even grazed (i.e., farmed) understorey (G.L. Rapson, Massey University, New Zealand, personal observation, 2012).
Karaka's habitat on the Hawaiian Islands is given by Smith (1985) as Zone C (C1 and C2). Ripperton and Hosaka (1942) define these zones respectively as "mixed open forest and shrubs", often with vigorous grasses (exotic), to less than 800 m, and "mixed open forest" often cleared for farming from 800-1300 m, and note these as desirable zones for non-irrigated agriculture. Zone C has rainfall of 1000-1500 mm/yr, with good soils, due to extensive loss of forest, especially at higher altitudes (Smith, 1985). The Federal Register (2010) gives karaka's habitat as "montane mesic" forest.
Habitat ListTop of page
|Terrestrial – Managed||Managed grasslands (grazing systems)||Secondary/tolerated habitat||Natural|
|Terrestrial ‑ Natural / Semi-natural||Natural forests||Principal habitat||Natural|
|Coastal areas||Principal habitat||Productive/non-natural|
Hosts/Species AffectedTop of page
Karaka affects no known crops. There has been consideration of its potential development as a nut crop (Klinac et al., 2009).
Several reports indicate karaka's potential and actual weediness in native forests of New Zealand. Esler (1974) recorded that karaka increased in lowland forest remnants of the Manawatu, when stock were removed. In the adjacent Horowhenua district, Duguid (1990) noted that karaka had "increased in bush remnants and [was] now shading out other vegetation beneath its heavy canopy". Gabites (1993) noted it spreading into Wellington city bush areas, appearing in native forest areas of the Wellington Botanical Gardens, subsequent to the 1875 survey, where it is now weedy. Sawyer et al. (2003) reported that there were "several places where aggressive regeneration of karaka is leading to replacement of existing plant communities by stands of karaka", including the important conservation reserve of Kapiti Island where karaka formed "dense thickets" after elimination of vertebrate pests. It is also colonizing and establishing populations in several Manawatu forest remnants (P.R. van Essen and M. Greenwood, personal communication, 2012; Greenwood, 2004), though it is now routinely controlled or even weeded out in reserves in the lower North Island (see, for example, Hector, 2011, re Matiu-Soames Island, in Wellington Harbour).
The fern Diellia mannii is the species most critically endangered around karaka in Hawaii, where it is found in sparse understory vegetation with canopy coverage at 75%, mainly of karaka with some Acacia koa. The main threat to D. mannii however, appears to be trampling and perhaps herbivory by goats and deer (Aguraiuja and Wood, 2003), rather than shading.
Sawyer et al. (2003) also reports karaka as a threat in Hawaii to the endangered shrub Exocarpos luteolus.
Biology and EcologyTop of page
Karaka has 46, and sometimes only 44, chromosomes, with median or sub-median centromeres (Dawson, 1997). Chromosomes are very small (0.4-1.3 µm), and hard to count.
Wagstaff and Dawson (2000) detected very little genetic variation for the sequences they tested in karaka; however there is accepted local population-based variation (Essen and Rapson, 2005), probably due to deliberate selection for greater fruit size by Maori.
Phylogenetically, karaka is most closely related to C. dissimilis from New Caledonia, and least closely related to C. similis, the species which is most widespread (New Guinea, Vanuatu and the Solomon Islands) and more northerly in occurrence (Wagstaff and Dawson, 2000). Whilst the Corynocarpaceae family may be placed in the Cucurbitales order this is problematic and the family can still be recognized within the Celastrales order (Philipson, 1987; Wagstaff and Dawson, 2000).
Fossil fruits resembling karaka have been found in a Miocene deposit 5-24 million years old, in Southland, South Island (Campbell, 2002). Palynology suggests karaka arrived in New Zealand as late as the Quaternary (Macphail and McQueen, 1983), though the pollen does not preserve well and is infrequently recorded by palynological studies. However, Wilmshurst et al. (2004) recorded karaka pollen, from deposits during an early period of Maori planting, up to 300 years old.
Karaka plants can flower as early as five years old (Pigott, 1927; Klinac et al., 2009; M. Greenwood personal communication, 2012). Flowers are small, but in massed inflorescences. They are probably insect-pollinated, though they are investigated by honey-eating native birds (Castro and Robertson, 1997). No flowers lacking pollinator access set seed (Klinac et al., 2009). Karaka is gynodioceous; the female trees set "large numbers of fruit on every inflorescence", though many did not ripen, while the male trees are very variable in fruit set, though generally much poorer than the females (Garnock-Jones et al., 2007). Only a few flowers open at any one time, so that flowers and hence fruits can be present over three months (Burrows, 1996).
Production of fruit is prolific (Pigott, 1927), up to 3000 per tree (Garnock-Jones et al. 2007), though this varies greatly from tree to tree (Pigott, 1927; Molloy 1990; G.L. Rapson, Massey University, New Zealand, personal observation, 2012). Garnock-Jones et al. (2007) recorded fruiting in several locations over twelve non-consecutive years, and reported it as ranging from "very poor" to "very heavy", with only slight indications of good and bad years being interspersed. Fruit size can vary within a tree due to the number of fruits developing per inflorescence (Garnock-Jones et al., 2007).
Ripe fruits (at least when detached from the tree) develop a strong, characteristic odour, described as cloying and unpleasant by Fountain and Couchman (1984). The volatile compounds appear to be minimal, being mainly an alcohol and two organic acids (Fountain and Couchman, 1984), with the odour attributed to the ethyl ester of butanoic acid. Ethylene is also produced in small quantities, perhaps causing yellowing and senescence of leaves adjacent to inflorescences.
Karaka seeds do not germinate if they remain in the fruit (Bannister et al., 1996), though the flesh does not persist on the forest floor, presumably due to consumption by birds, insects and introduced mammals. Intact fruits sown in potting mix take over three months to germinate, and have a germination rate of less than 33%. Dehusked seeds germinate after between one and two weeks, at a rate of 80-100%, provided they do not become desiccated (Bannister et al. 1996; Burrows, 1996). Seedlings can emerge from seed buried to 10 cm (Burrows, 1996).
Physiology and Phenology
Flower buds appear in June in the North Island, and flowering occurs in November (end of spring), though some trees are still flowering in mid-December (Garnock-Jones et al. 2007). Variation between years is of orders of magnitude, both for individual trees and for stands (Garnock-Jones et al. 2007). Skey (1871) quotes William Colenso as saying "as the same karaka woods did not bear alike plentifully every year, the years of barrenness were to the tribe seasons of calamity and want, the karaka being one of their staple vegetable articles of food".
Drupes are conspicuous in late summer and autumn (February - April; Salmon, 2001; Sawyer et al., 2003), though ripe drupes usually only remain on the trees for a month at the most before they either fall or are consumed by wood-pigeons (G.L. Rapson, Massey University, New Zealand, personal observation, 2012).
New foliage appears in early spring in New Zealand, beginning mid-September (G.L. Rapson, Massey University, New Zealand, personal observation, 2012).
The wood anatomy makes it impossible to age karaka using the normal method of annual growth rings in the trunk (Patel, 1973). Karaka trees established from seed in a 1962 restoration planting in cool temperate Palmerston North (outside karaka's natural range) attained a height of 14 m in 42 years. The largest total stem diameter was 26.5 cm, a growth rate of 0.68 mm dbh/year, allowing 3 years to reach breast height (M. Greenwood, personal communication, 2012). The largest karaka tree at Westoe, near Palmerston North, was planted in 1950, and had a diameter of 36.5 cm, a growth rate of 0.70 mm/year. By unspecified means Grant (1996, p. 69) dated a northern Hawke's Bay karaka of 55 cm dbh at 160 years, giving a growth rate of 0.34 cm/year, while Burstall and Sale (1984) dated the largest known mainland karaka (dbh 212 cm) at >500 years (growth rate 0.43 cm/year). Stowe (2003) recorded a tree on Lady Alice Island, Hen and Chickens Islands, at 300 cm dbh, which may be older than 600 years.
Seedlings may attain a height of 40 cm within two months (T. Foster, personal communication, 2012), due to large internode lengths and the considerable endospermic reserves of the seed. Seedlings can attain a height of 1.2 m in 3 years in moderate environmental conditions (M. Greenwood, personal communication, 2012). The seedlings rapidly establish large taproots (T. Foster, personal communication, 2012), which probably enhance water uptake.
Population Size and Structure
Density of karaka is very low in the far north of New Zealand (2.5 stems per hectare; McKelvey and Nicholls, 1959) in what is probably its natural vegetation type of kauri (Agathis australis) forest. Further south, where karaka has spread from Maori plantings, populations can be much denser. Costall et al. (2006) recorded karaka canopy coverage as averaging 41% amongst plots in karaka stands, with a maximum cover of 75%. Average density of karaka trees <10 cm dbh (diameter at breast height) in these stands is 547 per hectare, with a maximum of nearly 1000 stems per hectare (Costall et al., 2006). However the relative youth of these invading plants means that basal area in karaka is low at an average of 0.46 m2/ha, with a maximum recorded of 1.44 m2/ha.
Karaka basal area was probably much greater in Maori plantings, some of which were of impressive size. Nineteenth century Europeans recorded substantial groves of karaka in many areas of New Zealand. A once extensive grove near Massey University, Palmerston North, was established by descendants of the Aotea canoe (Massey University. 1988), but is now reduced to about a dozen stems. Beckett (1963) reported a grove of six hectares in extent near Red Rocks, Wellington, about 1890, and McFadgen (1963) a grove 0.8 km long in the Wainuiomata valley near Wellington in 1859.
In invading stands there is a predominance of small stemmed karaka and also seedlings, which follow the standard reverse J shaped curve (Costall et al., 2006). Over the plots sampled in karaka stands by Costall et al. (2006) karaka seedlings <2m high) averaged 11.2 per m2, equaling more than 400 000 per hectare.
As karaka does not disperse far naturally, most seedlings <50 cm high) are found close to parent trees (up to 11 per m2) although some seedlings are found up to 50 m from a parent. Recruitment to the <2m height category however seems to be more evenly dispersed (Costall et al., 2006). Wotton and Kelly (2011) record higher density dependent mortality closer to parents than 20 m away.
As a consequence of these figures for seedling establishment and recruitment, it is not surprising that karaka is spreading aggressively in various areas around middle New Zealand. Demography in karaka's natural range is unknown, but preponderances of seedlings have not been reported from northern New Zealand.
Karaka is generally associated with fertile, well-drained, moist soils, even close to the coast.
As a forest component in the north of the North Island, New Zealand, karaka is commonly associated with Beilschmiedia tarairi and Agathis australis, while in coastal locations it is often found with Metrosideros excelsa. In the southern North Island it is most commonly found in forests with Beilschmiedia tawa and Melicytus ramiflorus, as well as a range of ferns, including tree ferns. Early in the invasion process in the southern North Island it is associated with higher exotic herb cover, suggesting that invaded sites might be already disturbed (Costall et al., 2006). In the South Island, karaka is usually found as isolated groups of trees in pasture, sometimes with flax (Phormium species) nearby.
Karaka requires fertile, moist soils in areas which are not prone to frosts.
ClimateTop of page
|Cf - Warm temperate climate, wet all year||Preferred||Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year|
Latitude/Altitude RangesTop of page
|Latitude North (°N)||Latitude South (°S)||Altitude Lower (m)||Altitude Upper (m)|
Air TemperatureTop of page
|Parameter||Lower limit||Upper limit|
|Absolute minimum temperature (ºC)||-2.3|
|Mean annual temperature (ºC)||11.3||19|
|Mean maximum temperature of hottest month (ºC)||21.3||26.6|
|Mean minimum temperature of coldest month (ºC)||5.3||10|
RainfallTop of page
|Parameter||Lower limit||Upper limit||Description|
|Mean annual rainfall||895||1538||mm; lower/upper limits|
Notes on Natural EnemiesTop of page
Although cattle appear not to cause damage from gnawing large trees, no seedlings are observed in cattle pasture and they are presumably eaten at this stage or at the fruiting stage (Mitcalfe, 1969; Stevenson, 1978; G.L. Rapson, Massey University, New Zealand, personal observation, 2012).
Ashby (1977) reported an infestation of cucumber mosaic virus in karaka, though it was not reported if more than one tree was infected. No other diseases are known in karaka.
Merton (1966) reported a bellbird (Anthornis melanura) feeding extensively on sap from a fissure in the bark of karaka.
Though the foliage and twigs of karaka do not contain the toxin karakin, which is present in the fruit (Skey, 1871), foliage does not appear to be palatable to native herbivorous insects (J Costall, Massey University, New Zealand, personal observation, 2012).
Kiore or Pacific rats (Rattus exulans) often nibble the endocarp of karaka, while the larger Norway rats (Rattus norvegicus) occasionally gnaw open the endocarps, and both species eat karaka flesh (Campbell and Atkinson, 1999). Control of such exotic mammalian predators is routine now on many New Zealand islands and on mainland conservation sites. However there is debate over the impact of this on karaka, with some evidence of its being abundant in the presence of kiore, and other examples where eradication of kiore results in increased numbers of seedlings (Campbell and Atkinson, 1999).
Means of Movement and DispersalTop of page
Karaka appears to be bird-dispersed (McEwen, 1978; Wotton and Ladley, 2008), with its fleshy mesocarp and red-orange exocarp, though it is well-shaped to roll considerable distances, and is even rather bouncy on hard surfaces. While not buoyant, fruits are probably dispersed short distances by white water.
Natural Dispersal (Non-Biotic)
In modern-day New Zealand karaka does not naturally disperse far from the parent tree, most seed germinating within 8 m of a parent. However, the fruit may bounce on the ground allowing some seed to disperse further. Fruit falling into a fast-moving stream can probably disperse along its bed, although tolerance to immersion is unknown.
Vector Transmission (Biotic)
The only extant native avian vectors able to disperse karaka in New Zealand are the kereru (Hemiphaga novaeseelandiae) of the mainland (McEwen, 1978), and the parea (H. chathamensis) on the Chatham Islands (Powlesland et al., 1997). No exotic birds have the gape to disperse karaka. While not a favoured part of a kereru's diet (McEwen, 1978; Powlesland et al., 1997), birds will sometimes fill their crops with karaka fruit (when they often appear to be "drunk" due to in situ fermentation; G.L. Rapson, Massey University, New Zealand, personal observation, 2012), digest the flesh, and defecate viable kernels (Wilkinson and Wilkinson, 1952). There is some evidence of dispersal of karaka between islands in the Hauraki Gulf, Auckland, New Zealand, which may be due to increasing populations of kereru (Campbell and Atkinson, 1999, 2002; Atkinson, 2004).
Mammals which ingest karaka are cattle, pigs, and deer (Motooka et al., 2003; Mitcalfe, 2004; Klinac, 2007). These appear to cause no adverse effects, so dispersal by these agents is possible, although karaka kernels probably do not survive passage through a mammalian digestive tract. Possum (Trichosurus vulpecula), an introduced forest pest, eat ripe fruit, but do not ingest kernels (Cowan, 1990).
Impact SummaryTop of page
|Cultural/amenity||Positive and negative|
|Economic/livelihood||Positive and negative|
|Human health||Positive and negative|
Economic ImpactTop of page
Karaka has no known economic impact in New Zealand except the cost of its control, which can involve manual pulling, cutting or herbicide application.
Those selling honey may be negatively affected as honey bees (probably Apis mellifera) are very susceptible to toxins in the nectar of karaka (Palmer-Jones and Line, 1962). The toxins cause mortality to workers but queens remained unaffected.
Environmental ImpactTop of page
Bell (1974) tested extracts of karakin on pigeons (presumably Columba livia), for which 3-5 fresh fruits were lethal, rats (Rattus species), cats (Felis domestica) and sparrows (Passer domesticus), all of which are exotic to New Zealand. Symptoms were generally vomiting and convulsions, although results were variable, due to the age of the organism, and perhaps also the age of the fruit, as well as the quantity eaten. No antidote was found.
Kiwi (Apteryx mantelli), an endangered native flightless bird, sometimes ingest karaka (at least in captivity), and this appears to induce anorexia, lethargy and difficulty in walking (Shaw and Billing, 2006).
Impact on Habitats
Common to dominant in coastal areas, karaka is not a significant component of forests in its natural range, the northern part of New Zealand. However in the southern half of the North Island, where it is aggressively invasive, it has a significant impact on native vegetation, largely a consequence of the dense shade it forms, and its prolific seed production.
In Hawaii, reports suggest that even when karaka is removed from a site, native Hawaiian species still find it difficult to establish (Spjut, 2004). This is thought to be connected to the continued presence of karaka's root toxins. However there is no supporting evidence of this and it is certainly not a case of autoallelopathy, since karaka seedlings are common underneath parent trees.
Impact on Biodiversity
Post-invasion, karaka has the effect of progressively homogenizing the native vegetation through reduction in cover of herbaceous species (Duguid, 1985; Costall et al., 2006), which is of particular concern for rare species. Invaded areas may also have a higher cover of exotic shrubs (Costall et al., 2006). Furthermore, native tree seedling species appear to recruit only with difficulty under karaka canopies (Costall et al., 2006). This is likely to have long-term effects on the composition of native forests.
The growth rate of karaka seedlings allows them to emerge through dense, robust, ground cover of exotic weeds, such as Tradescantia fluminensis and Hedychium gardnerianum, when native seedlings cannot (Williams et al., 2003). It remains to be seen if karaka can then shade out these noxious herbs.
Threatened SpeciesTop of page
|Threatened Species||Conservation Status||Where Threatened||Mechanism||References||Notes|
|Diellia mannii||National list(s) National list(s)||Hawaii||Competition - shading||Aguraiuja and Wood, 2003|
|Exocarpus luteolus||National list(s) National list(s)||Hawaii||Harris, 2002; Sawyer et al., 2003|
|Platydesma rostrata||CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered); USA ESA listing as endangered species USA ESA listing as endangered species||Hawaii||Competition - monopolizing resources; Competition - shading||US Fish and Wildlife Service, 2010a|
|Pritchardia hardyi (Makaleha pritchardia)||CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered); USA ESA listing as endangered species USA ESA listing as endangered species||Hawaii||Competition - smothering||US Fish and Wildlife Service, 2010b|
|Stenogyne purpurea (purplefruit stenogyne)||CR (IUCN red list: Critically endangered) CR (IUCN red list: Critically endangered); USA ESA listing as endangered species USA ESA listing as endangered species||Hawaii||Competition - monopolizing resources||US Fish and Wildlife Service, 2010b|
Social ImpactTop of page
Skey (1871) reports Colenso's description of violent spasms and other adverse effects caused by poisoning from the karaka kernel, and identified a glucoside (karakin) as the 'bitter principle'. Mild cases of toxicity resolve themselves through time (Shaw and Billing, 2006). Platt (2003) suggested that the cause of human poisoning was a seed-borne fungus (like an ergot), rather than the kernel itself, which is supported by the number of animals which do safely ingest the fruit and seed (Mitcalfe, 1969; Stevenson, 1978; Mitcalfe, 2004; Connor, 1977).
Risk and Impact FactorsTop of page Invasiveness
- Proved invasive outside its native range
- Has a broad native range
- Abundant in its native range
- Is a habitat generalist
- Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
- Pioneering in disturbed areas
- Tolerant of shade
- Benefits from human association (i.e. it is a human commensal)
- Long lived
- Fast growing
- Has high reproductive potential
- Damaged ecosystem services
- Ecosystem change/ habitat alteration
- Increases vulnerability to invasions
- Modification of successional patterns
- Monoculture formation
- Reduced native biodiversity
- Threat to/ loss of endangered species
- Threat to/ loss of native species
- Competition - monopolizing resources
- Competition - shading
- Competition - smothering
- Rapid growth
UsesTop of page
Karaka was an important food crop for Maori in New Zealand and is apparently still consumed in some regions. Although used for canoe-building on the Chatham Islands, the canoes were small and not ocean-going (Dieffenbach, 1840). Karaka does make an important contribution to food of the native wood pigeons (Hemiphaga spp.).
Klinac et al. (2009) reported on the potential of karaka to be a new nut crop in New Zealand. They concluded that the "nuts are easily stored and handled, have a long shelf and storage life, and are potentially suitable for a wide range of added-value processing applications (e.g. roast nuts, crumb, flour, puree, even beer) with a gluten-free, 'high-health' nutritional profile", and that commercial development had much potential. This potential has yet to be developed.
Karaka, perhaps because it has a soft wood, and a rather smooth trunk, was the species used to carve dendroglyphs on the Chatham Islands. Some of these carvings are still extant, although many have been lost in the past century (Jopson and McKibbin, 2000). The purpose of these carvings is unknown, although the comments of Jefferson (1956) suggest they were memorial markers for deceased islanders, perhaps because bodies were buried in a sitting position on the nearby beaches, with heads above the sand, until the flesh had disappeared.
Drupes have been strongly selected for by the Maori and were widely used as a food source. Trees around settlements have 20% larger fruit than those in the surrounding areas, though this is possibly because kereru (H. novaeseelandiae) preferentially disperse only the smaller fruit (Essen and Rapson, 2005), with several being stored at once in the crop. Karaka groves were culturally very important to Maori and battles were sometimes fought for possession of groves (Klinac et al., 2009). Poor flowering and fruiting years could be times of famine for local tribes (Skey, 1871).
The dry flesh was often taken for immediate consumption, particularly by children, who report it as quite edible. On the Chatham Islands, the flesh was considered sweet, either raw or dried into flour and made into oily cakes (Skinner and Baucke, 1928). The flesh of the fruit decomposes quickly once dropped from the tree, and so is not storable. However the kernels, called kopia by Maori, koopii by Moriori, or Maori peanut or karakaranut by Europeans (Massey University. 1988; Sawyer et al., 2003), could be stored. Lengthy preparation of kernels was routinely applied.
Many existing groves of karaka have considerable cultural significance to local Maori. As a tree that provided food for Maori it is taonga (treasure).
In the south of the North Island karaka is valued as a food plant for kereru, a threatened native pigeon (H. novaeseelandiae).
Detection and InspectionTop of page
Karaka is easily detectable and identifiable by size, colour and shape of fruit.
Similarities to Other Species/ConditionsTop of page
The endemic Corynocarpaceous species of New Caledonia, Corynocarpus dissimilis, is closely related to C. laevigatus (Molloy, 1990; Wagstaff and Dawson 2000; c.f. Stevenson, 1978, who considered the merits of combining the two species). The two species are very similar with comparable foliage (Stevenson, 1978; Mike Wilcox, personal communication, 2012). However the fruit of C. dissimilis is generally larger, to around 5 cm long, while the other species in the genus have either rounder or larger fruit than karaka (Molloy, 1990). Wood-wise, C. dissimilis has crystals only in the peripheries of rays, and striations on the vessel walls, distinguishing it from C. laevigatus and C. cribbianus (Carlquist and Miller, 2001). In terms of chromosomes, C. rupestris appears to be tetraploid, while other Corynocarpus have 44-46 chromosomes (Dawson, 1997). Garnock-Jones et al. (2007) consider it likely that species of Corynocarpus other than karaka are also gender dimorphic.
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Areas which largely lack karaka, but are adjacent to seed sources, should be routinely monitored for developing infestations. These are best dealt with, once identified, by manual removal of karaka seedlings whilst they are clearly visible and easily accessible. Seedlings <50 cm are easily pulled out, having only a strong central root, and very little lateral root growth. There is usually no seed bank. Control of seedlings should be followed by logging of any parent trees or cutting of plants providing an infestation source. Karaka seldom sprouts from a rootstock, but large stumps could be painted with herbicide to ensure their deaths. The soft, parenchymatous wood means stumps rot readily.
Motooka et al. (2003) report karaka as sensitive to glyphosate applied via bark notchings. They note that Triclopyr, dicamba and 2,4-D are less effective. Imazapyr applied to the bark kills trees. Triclopyr (as Pathfinder (TM) II) in vertical streaks is effective on cut trees.
Public education is probably the best method for preventing the movement of the species and the public should be discouraged from planting it in gardens, as it can spread from there. Eradication of karaka outside of desired zones or natural ranges is strongly recommended.
Many existing groves of karaka have considerable cultural significance to local Maori. As a tree that provided food for Maori it is taonga (treasure), and so such groves should be conserved, and internal genetic diversity preserved as much as possible, since the plants are likely to have been deliberately selected by Maori (Jones and Simpson, 1995; Platt, 2003; Essen and Rapson 2005).
Gaps in Knowledge/Research NeedsTop of page
There are major gaps in knowledge regarding karaka's behaviour in forests in its natural range, its susceptibility to herbicides, the nature of the toxic responses noted in Maori children by European explorers, and the details of recipes for the safe preparation of products from karaka kernels.
ReferencesTop of page
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24/11/2012 Original text by:
Gillian L Rapson, Institute of Natural Resource, Massey University, Private Bag 11222, Palmerston North, New Zealand
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