Myrica faya L. (Myricaceae)

Macaronesian endemic introduced to Hawai'i in the 19th century. Following extensive reclamation planting, it has spread into a variety of habitats including natural forest, lava flows, roadsides and abandoned pasture.


Species characteristics

Life form, size, lifespan

Evergreen tree to 12 m tall. Often multi-stemmed.

Taxonomy, variation and plasticity

No information is available. However the species is found on isolated islands and under varying climatic conditions and this would suggests that some variation must exist between provenances.

Reproductive biology

M. faya is considered to be a dioecious species, however 'male' plants often produce some fruits and 'female' individuals a few male inflorescences. It appears to be a wind-pollinated species although in Hawai'i it is visited by the introduced Apis mellifera. The edible black drupe (6mm in diameter containing 1-5 seeds) is bird-dispersed in its native range but in Hawai'i it is dispersed by birds (mainly introduced) and feral pigs. About 20,000 seeds per tree are produced every year. In Hawai'i fruits ripen primarily between August and November but may be produced all year round. Seed germination decreases from 80% at 10 weeks to 30% after 78 weeks of dry storage. Passage through birds has no effect whereas its own leaf litter reduced germination. Germination occurs at all light levels but is highest under 55% and 63% of shade.

Resilience and resistance

Nitrogen fixing species which can colonize lava flows. In the Azores it is wind resistant although the bushes are only 2-3 m tall and are much flattened and bent. Allelopathic effect has been suggested. Burnt trees may resprout.

Environmental requirements and successional status

Although adapted to colonize old lava flows, M. faya is a main component of old forests. Regenerates freely under open canopy but not under full canopy.

Products and uses

In Hawaii Portuguese labourers made wine from the fruit.


Status in native range

Range and abundance

Restricted distribution to the Macaronesian islands of the Azores, Madeira and the Canary Islands. The tree is common in most remaining evergreen forests.

Climate

In Canaries the climate is typically mediterranean with wet winters and dry summers. The climate of the Azores is affected by the Gulf Stream with no frost below 500 m and average summer and winter temperatures of respectively 21 C and 14.5 C. Madeira's climate is intermediate. Rainfall on all islands increases with altitude (varying between ca. 750 mm and 2500 mm) and highlands are often covered with cloud and mist.

Site requirements

In the lowland Azores, much altered by man, Myrica faya is the main species to have regenerated on old lava flows. Around an altitude of 600 m, where some natural forest remains, M. faya is codominant in the canopy (5-6 m tall) and sometimes is an emergent. Distribution up to 900 m a.s.l. The species does not appear to regenerate under canopy.

Weediness

No sign of weediness. In fact in the Azores the forests, where M. faya is codominant, are invaded by Pittosporum undulatum, native of eastern Australia.

Pests and diseases

Suffers from a number of diseases resulting in canker, dieback and root rot.


Status in invaded regions

History of introductions and intensity of invasions

Introduced into Hawaii by immigrants from the Azores and Madeira in the late 1800s, probably as an ornamental or medicinal plant. Extensively planted for watershed reclamation in the 1920s and 1930s. Now present on several Hawaiian islands and by 1985 covered 12,200 ha of the Hawaii Volcanoes National Park (HVNP) and considered one of the main noxious species. Common on pasture land.

Patterns of invasion and time-lag

On young, volcanically disturbed soils M. faya rapidly forms dense monotypic stands but does not readily invade closed, late-successional native forest. In HVNP birds disperse the seeds to perch trees, the native Metrosideros polymorpha. Under tree canopy seed densities of 6 to 60 seeds.m-2.yr-1 are found whereas they are absent in the open. Seeds germinate and seedling become established under M. polymorpha canopies.

Natural spread was reported within years of the watershed planting which was then halted. It was first reported in undisturbed areas of the HVNP in 1961 and by 1973 the population was large enough to warrant control.

Site and climate

M. faya is found between 150 to 1310 m a.s.l. in mesic to wet forest. At the altitude of 1250 m, where most of the HVNP invasion is taking place, the mean annual rainfall is ca. 2400 mm without a distinct dry season and the mean January and July temperatures are, respectively, 14C and 17C. Very occasional frosts occur.

Floristic region and vegetation types

The Hawaiian islands are rich in endemic species and are very susceptible to plant invasions particularly in lowland regions. Other woody plants are invading are invading plant communities invaded by M. faya.

Pests and diseases

Some seeds are eaten by rats.

Impact on ecosystem

M. faya changes ecosystem function by altering the nitrogen cycle. Its litter inhibits germination and seedling establishment of the native tree Metrosideros polymorpha. Monospecific stands have virtually no understorey.

Impact on humans and related activities

Not reported.

Control

In the HVNP control was initiated 22 years after M. faya was first recorded. Over four years 92,000 individuals were removed, yet 609 ha of moderate density populations remained and the control programme was abandoned. The use of chemical control in native vegetation, some of which is threatened or endangered, is avoided. Biological control of M. faya is being investigated.


Ecological differences

Existence of ecological equivalent species and competitive interactions in invaded regions

Apparently the actinorrhizal symbiosis, characteristic of M. faya and other species colonizers of low-nitrogen sites, was absent from the native flora of Hawai'i. In competition with the native tree Metrosideros polymorpha, M. faya diameter and height growth is always greater in all size classes.

Differences in status and ecology between invaded and native ranges

M. faya is invasive in Hawaii and is considered a weed whereas in the Azores, where it is native and codominant in evergreen forest, it often fails to regenerate and its habitat is invaded by Pittosporum undulatum. Both the native and invaded ranges are rich in endemic species but have relatively few tree species. The time-lag between the lava flow formation and M. faya colonisation appear to be much shorter on Hawai'i than on the Azores.


Selected references

Gardner, D.E. & Hodges, C.S. (1990) Diseases of Myrica faya (firetree, Myricaceae) in the Azores, Madeira and the Canary Islands. Plant Pathol. 39, 326-330.
Haggar, J.P. (1988) The structure, composition and status of the cloud forests of Pico Island in the Azores. Biol. Conserv. 46, 7-22.
# Little, E.L. & Skolmen R.G. (1989) Common forest trees of Hawaii (native and introduced). Agric. Handbook 679. US Forest Service, Washington.
** Vitousek, P.M. & Walker, L.R. (1989) Biological invasion by Myrica faya in Hawai'i: Plant demography, nitrogen fixation, ecosystems effects. Ecol. Monogr. 59, 247-265.
** Vitousek, P.M., Walker, L.R., Whiteaker, L.D., Mueller-Dombois, D. & Matson, P.A. (1987) Biological invasion by Myrica faya alters ecosystem development in Hawaii. Science 238, 802-804.
** Walker, L.R. & Vitousek, P.M. (1991) An invader alters germination and growth of a native dominant tree in Hawai'i. Ecology 72, 1449-1455.

Pierre Binggeli

May 1997