Pacific Island Ecosystems at Risk (PIER)


Piper auritum


Impact Assessment

Escape and Spread of Piper Auritum Kunth on Pohnpei, FSM

Julie S. Denslow and Duane Nelson

Institute of Pacific Islands Forestry, USDA Forest Service

23 E. Kawili St., Hilo, HI 96720

SUMMARY. Within the last two years, Piper auritum has been introduced to the island of Pohnpei where it has been marketed as a more productive alternative to sakau (P. methysticum). In its native range (Mexico to Colombia), P. auritum occurs in disturbed areas and forest edges where it sprouts prolifically from subsurface rhizomes and can form large thickets in short periods of time. In Hawaii and South Florida it also spreads aggressively and is likely to do so in Pohnpei. P. auritum is likely to become an invasive and noxious weed of sakau plantings and will threaten native forests as well. Potential impacts on the sakau industry include growth reduction from competition and increased exposure to pests and pathogens. Immediate control offers the least expensive and most effective strategy for the control of P. auritum. An economic analysis (Appendix 1) indicates that immediate action and expenditures of an estimated US $93,000 over a three year period would yield US $$3,034,000 benefit and a benefit cost ratio or 32.5. If control is delayed 2-5 years, the area requiring treatment increases dramatically as do costs. We recommend immediate eradication of existing plantings by direct injection or cut stem application of triclopyr amine (Garlon 3A) following label directions.

 INTRODUCTION

Within the last two years, Piper auritum has been introduced to the island of Pohnpei where it has been marketed as a more productive alternative to sakau (P. methysticum). Sakau is used to brew a mildly narcotic drink used in traditional ceremonies. It is an integral part of Pohnpeian traditional culture and a significant economic crop. Rising international demand for P. methysticum for use as a herbal relaxant (kava) has created a potential export market as well. This report examines the ecology and natural history of P. auritum and assesses its potential environmental and economic impacts.

ECOLOGY OF PIPER AURITUM IN ITS NATIVE RANGE.

Piper auritum (Piperaceae) is easily recognized by its large (20-50 cm) leaves unequally lobed at the base and the very characteristic sarsaparilla or anise-like odor of crushed leaves. Plants grow to about 6m in height with a single main stem that often has small prop roots near the base. The large leaves are borne in two alternate ranks and are often held horizontally on horizontal upper branches, thus forming a broad light-intercepting crown with relatively few large leaves (Berger 1983).

Biogeographic and Ecological Range. The natural range of Piper auritum extends from southern Mexico to northern South America (Colombia) where it appears to be genetically uniform with no evidence of subspecific or varietal differentiation (Berger 1983). In Panama,

Croat (1978) reports P. auritum in tropical rain forest, tropical moist forest, tropical dry forest, and tropical premontane forest, which suggests that the species is able to tolerate a dry season of several month’s duration. In Costa Rica the species ranges from near sea level to about 1,500 m (rarely 2,000m) elevation in evergreen and partly deciduous formations or in wet sites in the deciduous formations of Guanacaste. (Berger 1983).

Natural History. In its natural range Piper auritum occurs in disturbed areas and forest edges where it grows in monotypic thickets. It sprouts prolifically from subsurface rhizomes and can form large thickets in short periods of time. It also roots easily from nodes (layering). Like many weedy species, flowering and fruiting occur throughout the year. The very small, unspecialized flowers are arrayed on spikes held vertically above the foliage where they are pollinated by small beetles and flies. As the fruits ripen, the fruiting spike rotates below the foliage. At maturity the fruiting spike is green and fleshy and contains many small fig-sized seeds. Seeds are dispersed by bats which remove the entire spike, by birds which remove portions of the spike, and perhaps by arboreal rodents.

Piper auritum produces safroles, which give its leaves and roots a strong anise aroma. While the effects of these compounds produced by P. auritum are not known, safroles produced by Sassafras album (Lauraceae) are known carcinogens. We find no record of P. auritum containing kava lactones.

Applications in its Native Range. The literature (Joly 1981, R. Marquis comm.) reports that in its native range, people have used Piper auritum for a number of different culinary and medicinal purposes. Medicinal applications include uses as a sudorific, diuretic and stimulant in cases of fever, erysipelas, gout and angina, a local anesthetic, a treatment for gonorrhea and colic, a headache and wound poultice and as both a revulsive and a digestion stimulant. We have no information on the effectiveness of any of these applications. The potential danger of cancer from safrole argues against any consumption of P. auritum, Leaves are much used in for flavoring in Guatemala, especially when cooking meats or the local snail. It is used to season tamales in Mexico.

ECONOMY OF PIPER CULTIVATION ON POHNPEI

Several species of Piper are important in the cultural fabric and economy of Pohnpei and FSM. Piper methisticum (sakau, kava, ava) is widely cultivated on Pohnpei (although not in other FSM states); its root is used to make an inebriating drink which is used personally by growers and sold at market and for use in sakau bars. Development of sakau for export is under discussion to supply demand in Hawaii and the US mainland. Piper nigrum is grown in home gardens and commercially for black pepper. Although commercial production of black pepper has declined in recent years, its revival as an export commodity may be attractive in the more diversified economy expected following renegotiation of the Compact. Piper betle is used in the western Pacific in conjunction with the betelnut; P. betle is not an important product in Pohnpei, but may be on other Micronesian islands. Approximately 100 species of Piper occur naturally in the region.

The sakau industry is currently the major income source for much of Pohnpei island’s rural population, generating approximately US$3 million/year. 4000-5000 people (15% of the population) are engaged in sakau-growing and approximately 2500-5000 Ha are planted. Domestic market consists of about 50 licensed sakau bars, a number of retail stores, and numerous unlicensed temporary sakau bars and is estimated at 477,000 kg/yr. (1996). Local demand is mainly for fresh plants, processed (roots pounded and squeezed) fresh and bottled extract, and pounded and frozen roots. There also exists an export market (mainly to expatriate Pohnpeians living in Guam, Saipan, Hawaii, and the US mainland) estimated at 40,000 kg/yr for pounded and frozen roots and liquid extract. Another 660,000 kg. is harvested annually for customary use and personal consumption by farmers and their extended families (W. Raynor from The Nature Conservancy, unpublished data, 1997).

IMPACT OF PIPER AURITUM WHERE INVASIVE

Piper auritum in Hawaii, South Florida and elsewhere. Piper auritum only recently has been introduced to Hawaii, where it has been distributed to kava growers as having medicinal properties. Since the potentially invasive nature of the plant quickly became apparent, the Hawaii Awa Council (hawaiiancouncil@aol.com) has alerted its members to the danger and called for its eradication. In a recent newsletter, Jay Palm (QBI Tropical Division) notes that the species is invasive in Fiji, Samoa and Tonga where monocultures occur in dense close-canopied forest. Piper auritum has also been introduced to South Florida where it spreads aggressively but is not known to set fruit.

Piper auritum on Pohnpei. P. auritum has been introduced within the last 2 years where it is claimed to be a more productive alternative to the traditional P. methysticum. Where planted under shade in tree gardens in the lowlands of U District, P. auritum has attained approximately 50% greater size within a year than adjacent P. methysticum plants established 4 years previously. Suckering has been vigorous and plants have flowered within this short time. Fruit set also may have occurred. Flowers apparently are being pollinated effectively because pendant infructescences were observed. Potential dispersal agents on Pohnpei include fruit bats, Micronesian starling, honeyeater, and whiteyes. At this date, P. auritum has not been harvested so growers do not yet have first-hand information on the quality of the product for traditional uses. As of March, 2000, an estimated 20 growers have established about 50 plants of P. auritum on Pohnpei. Surveys of Kosrae and Chuuk have not detected any planting at this time.

Both P. methysticum and P. auritum also are being planted in clearings in the native forest at higher elevations. These clearings are cultivated for a few years until production falls, at which time they are abandoned and new clearings made in the forest for new plantings (shifting cultivation). Production of sakau is apparently greater on the recently deforested soils than on the long-cultivated lowland soils. However such incursions into montane rain forest presents severe environmental dangers for Pohnpei. These forests are particularly fragile because of the high rainfall, fragile soils, steep slopes, and slow growing trees. They are the main reservoir of freshwater for the island and should receive high priority for protection.

Weed Risk Assessment. Information on P. auritum was submitted to the Weed Risk Assessment program developed by the Australian Quarantine and Inspection Service (Walton, C. et al. 1999) to assess the potential danger of its introduction for agriculture and the environment. This program uses information on the history/biogeography and biology/ecology of the species to evaluate the consequences of its introduction. A score of <1 suggests that the species may be imported without danger, a score of 1-6 suggests that more information is needed to evaluate the plant, and a score > 6 suggests that the species should not be allowed into the country. For Pohnpei, P. auritum attained an overall score of 19 and scores of 13 for its potential effect on agriculture and 15 for its potential effect on the environment. This assessment suggests that P. auritum poses a considerable threat to the ecology and economics of Pohnpei and other high islands in the Pacific.

Conservation Issues. Piper auritum has the capacity to be come established in a number of different ecosystems on Pohnpei. These include natural and secondary montane rain forest, disturbed areas such as agricultural clearings, roadsides, and tree gardens. These ecosystem types comprise the majority of the upland landscape on Pohnpei, thus the potential impact area is considerable. Similar habitats are present on all other high islands in FSM; all are vulnerable to the establishment of this species. It is unlikely that P. auritum would become established in freshwater Terminalia swamps or in mangrove swamps. In natural and secondary forests their dense thickets will prevent the establishment of tree and shrub seedlings, impede the natural regeneration processes of the forest, out-compete native and endemic species, and threaten the natural ecological richness of the islands. Alteration or loss of this forest will threaten the freshwater supply of the island.

Economic Issues. Introduction of a new and invasive species of Piper into the region poses several potential threats to both economically important Piper species and the ecology of Pohnpei. P. auritum may be an alternate host for pests and pathogens of local Piper species. For example, cucumber mosaic virus (CMV), the cause of kava/sakau dieback in Fiji, may occur on a wide range of alternate hosts. If P. auritum also harbors this pathogen, its widespread occurrence in forests and tree gardens of Pohnpei would pose a considerable danger to sakau plants and would make the control of the virus very difficult.

Through thousands of years of selection in cultivation, Piper methysticum has become polyploid (has several sets of chromosomes) and sterile; only female flowers and no seeds are produced. The abundant flower production of P. auritum suggests that the opportunity exists for its hybridization with P. methysticum, potentially diluting its gene pool and masking its desirable qualities.

If sakau roots are mixed or adulterated with roots from P. auritum the resulting reduction in product quality may endanger the development of strong local and export markets.

Introduction and spread of P. auritum will present a significant management problem. Without immediate action, it will spread rapidly in tree gardens where conditions are ideal for its growth. With time, increasing effort and resources will be devoted to its control because its vegetative spread will be difficult to contain. As it becomes more widespread, develops a seed bank, and becomes widely dispersed by birds and bats, control will become highly costly requiring repeated surveys and applications of herbicides. Once well established in native and secondary forests, costs and logistical obstacles to control will become prohibitive. Because of the economic importance of other species of Piper on Pohnpei, use of biological control agents will be limited or unlikely.

CONTROL METHODS

Control of P. auritum is complicated by the growth habit of the plant. Since it readily sprouts from rhizomes and forms dense thickets, hand pulling or grubbing would result in new sprouts unless care is taken to assure that even the smallest piece of rhizome is removed from the soil. Cutting or slashing would encourage basal sprouting. Unless cut tops are removed from the site and destroyed (incineration or drying), new plants could develop from layering of the cut shoots. If mechanical or hand control methods are used, caution should be used to assure that the infestation is not worsened by inadvertently promoting establishment of new plants.

Systemic herbicides such as triclopyr, 2,4-D, or imazapyr likely would be translocated to growing points in the stems and roots and thereby kill the entire plant and greatly reduce re-sprouting. Since most P. auritum is planted in areas of high rainfall and abundant surface water, application methods should minimize the chance of herbicide wash-off and drift to non-target plants or surface water. Direct stem injection would maximize delivery of herbicide to the target stems and minimize non-target effects. Cut stem applications should also be effective, as long as care is taken to remove and dispose of cut stems to prevent sprouting. Foliar application would be effective on small plants, provided there is adequate time for herbicide absorption prior to rainfall. Foliar applications on larger plants (above shoulder height) may be effective, but risk of non-target contamination and exposure to the applicator increase when herbicides are sprayed high into the air.

Regardless of the method used to kill individual plants, treated areas should be monitored annually to assure effective control. Where populations of P. auritum have produced seed, buffer zones should be inspected carefully to locate seedlings originating from bird or bat dispersed seeds. Experience with a small-seeded, bird-dispersed species (Miconia calvescens) has shown that seedlings may appear over 500 meters from the nearest known mother plant. Also P. auritum seeds may be found to persist in a soil seed bank (as is characteristic of many pioneer species). To assure complete eradication, 500 meter buffers (79 ha or 194 acres) should be established and monitored every two years around each mature plant or population for a period exceeding the known seed lifetime. The buffer areas should be inspected carefully by teams sweeping through the area. To reduce control costs, a less certain strategy could be used, establishing buffers of 250 meter radius (20 ha or 48.5 acres per point source) with a more cursory inspection between 250-500 meters (59 ha or 146 acres per point source).

Costs of Eradication. This is currently an incipient infestation that most effectively and cheaply could be controlled by immediate action. Costs of control increase dramatically the longer the population is allowed to spread before being treated. To demonstrate we will consider four control scenarios: 1) Immediate action, 2) Action in one year, 3) Action in 5 years and 4) No action.

Immediate action: All currently known populations would be treated immediately. Seedling surveys would be conducted within a 500 m radius of flowering plants in 2001 and 2003.

Actions and Costs:

Direct control of 20 populations will take 20 working days at $120 per day to be completed in CY2000 = $2400

Seedling surveys of 395 ha. (estimated 5 flowering populations) at $124 per ha. to be completed in CY 2002 and CY 2004 = $48,980 each year

Costs for herbicides, application equipment and other supplies (CY 2000)= $250

Total cost of project (not discounted) = $100,610

Action in one year: This alternative would be similar to "immediate action" however all actions would be delayed by one year. Cost would increase dramatically since more plants will reach maturity, possibly spreading seed over a greater area.

Actions and Costs:

Direct control of 20 populations will take 20 working days at $120 per day to be completed in CY2001 = $2400.

Seedling surveys of 1580 ha. (estimated 20 flowering populations) at $124 per ha. to be completed in CY 2001 and CY2003 = $195,920 each year

Costs for herbicides, application equipment and other supplies (CY2001) = $250

Total cost of project (not discounted) = $ 394,490

Action in 5 years: This alternative is similar to the above but action is delayed for five years. We estimate that 2 generations of plants may have matured and spread seed over a yet larger area, dramatically increasing costs. We assume that increased production costs for sakau due to competition with P. auritum and increased weeding costs would begin to affect the $3 million sakau industry. For this analysis we assume a 5% reduction beginning in year 2 through completion of initial control actions in year 5.

Actions and Costs:

Direct control of 20 populations will take 200 working days at $120 per day to be completed in CY2005 = $24000.

Seedling surveys of.6280 ha. within a 100 meter radius of 20 flowering populations at $124 per ha. to be completed in CY 2005 and CY2007 = 778,720 each year

Costs for herbicides, application equipment and other supplies(CY 2005) = $1000

Total cost of project (not discounted) = $ 394,490

5% market impact in year 2 through 5 = $600,000

No Action: No action would be taken to control P. auritum. The extent of the infestation of Piper auritum will continue to increase. By year two, the $3 million sakau market would be affected by lost production of P. methysticum, increased weed control costs and loss of market value due to concerns over substitution or adulteration of sakau with P. auritum. For the sake of this analysis, a 5% annual reduction is projected for years 2 through 5 increasing to 10% thereafter for the remainder of the analysis period. Potential export market for herbal medicinals may be affected adversely but is not considered separately in this analysis.

A detailed economic analysis listing all assumptions follows in Appendix 1. This economic analysis is based on the benefits of maintaining the productivity and value of the commercial sakau industry on the island of Pohnpei. Future costs and benefits are discounted to present value to facilitate comparison of alternatives. Other benefits not quantified include maintaining the role of sakau in Pohnpeian traditional culture, protection of forest diversity and regeneration processes, protection of forested watersheds and protection of P. methysticum from disease and hybridization.

Alternative

Immediate

1 year

5 years

No Action

Total PNV of sakau industry

$42,308,529

$42,036,713

$40,625,913

$39,273,640

Project Cost

$93,289

$365,105

$1,252,362

$0

Project benefit

$3,034,889

$2,763,073

$1,352,273

N/A

Benefit/Cost

32.53

7.57

1.08

N/A

Project PNV

$2,941,599

$2,397,968

$99,910

N/A

PNV (present net value): the sum of a future stream of benefits and costs discounted to present terms using a specified interest rate.

Project Cost: the sum of a stream of future costs discounted to present terms.

Project benefit: The total value of doing the project. This is simply the difference between the "action" alternative and the "no action" alternative.

BENEFIT/COST RATIO: The ratio of the project benefit divided by the project cost. A B/C ratio > 1 means that benefits exceed costs.

Project PNV: (Project benefit- Project cost)

RECOMMENDATIONS

We recommend immediate eradication of the current populations by direct injection or cut stem application of triclopyr amine (Garlon 3A ) following label direction. Seedling surveys should be done within a 500-meter radius of all populations that have flowered. These surveys should be completed in CY2001, after seedlings have had a chance to develop to a recognizable stage. The same areas should be surveyed again in CY2003, to detect any newly emerging seedlings. A telephone hotline should be established to accept reports from citizens. A quarantine should be established on new importations and a ban should be instituted barring new plantings.

LITERATURE CITED

Berger, W. C. 1983. Piper auritum pp. 304-304 In: Janzen, D. H. (ed.) Natural history of Costa Rica. University of Chicago Press. (describes the natural history of Piper auritum in Costa Rica)

Croat, T. C. 1978. The Flora of Barro Colorado Island. Stanford University Press, Stanford, CA

Janzen, D. 1978. The size of a local peak in a seed shadow, Biotropica 10:78. (describes a dense seed shadow of Piper under a bat roost)

Joly, L.G. 1981. Economic Botany 35:383-390.


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