Part 30 Myricaceae - Myrsinaceae
Two members of Myricaceae, the bay berry family, occur on the Hawaiian Islands, Myrica cerifera and M. faya. North American readers may be familiar with Myrica gale, bog myrtle or sweet gale. (Some authorities prefer to place these species in the genus Morella.) Myrica faya, commonly known as the fire tree (see images), was introduced into the Hawaiian Islands by Portuguese laborers in the 19th century as a decorative plant and as a source of fruit for producing wine. Myrica faya is a native of the Azores, the Canary Islands, Madeira, and perhaps southern Portugal.
Fire tree is among the very worst of the invasive aliens on the Hawaiian Islands. Many invasive species owe their success to their wide ecological tolerance–that is, their capacity to utilize a wide variety of habitats–and are particularly good at taking advantage of disturbed sites. This is frequently seen as a fundamental requirement for the definition of a weedy species. Other plants alter a landscape such that their growth is assured while the environment is altered so extensively that local, indigenous species are at a significant disadvantage. Myrica faya falls into the latter category.
Multiple branching from the root base can yield a shrubby growth form, but it is also capable of growing to trees reaching a height of 50' (16 m) under ideal growing conditions, such as along the Hamakua Coast (north of Hilo) where trees of this stature are not uncommon. The Hawaiian Sugar Planters' Association was always on the lookout for fast growing trees to use in reforestation projects. Thus it was that fire tree became one of many alien species planted by that service. Trees were planted on Kaua`i, Maui, and on the Big Island in the 1920s. It was not long, however, before the plant's true nature as a fast growing, invasive plant capable of out-competing indigenous plants was recognized. But the tree was spreading faster than forestry personnel could contain. In 1944 efforts to control growth of fire tree were undertaken by the Territorial Board of Agriculture and Forestry. Efforts to control its spread were, by and large, ineffective. By the mid 1940s fire tree had become established in the vicinity of Volcano (the town) from where it spread into the National Park. As of the report by L. D. Whiteaker and D. E. Gardner, published in 1992, fire tree had been reported on all of the main islands except Moloka`i and Kaho`olawe. The speed of spread of this tree can be appreciated by looking at the area affected as recorded in that paper: 1954: 8,200 acres (3,280 ha); 1962: 21,375 acres (8,550 ha); 1970: 40,000 acres (16,000 ha); 1982 (53,938 acres (21,575 ha). The areas covered and densities by island are as follows: Hawai`i, 50,000 acres (20,000 ha); Maui, 3,000 acres (1,200 ha); O`ahu, 100 acres (40 ha); Kaua`i, 325 acres (130 ha); and Läna`i, 512 acres (205 ha). Estimates at the present time, 17 years after those published data are not immediately available, but the overall area infested by fire tree has not decreased.
What makes this tree so successful? For one thing, it is not fussy with regard to the nature of the landscape in which its seeds happen to fall; steep slopes, level ground, many soil types, and a range of rainfall regimes seem to fit this plant's needs quite nicely. Fire tree is a prolific seed producer–estimates range from 40,000 to 400,000 per year–via fruits that are attractive to birds and pigs, both of which ensure wide dispersal. The most frequent visitor and consumer of fire tree fruits has been shown to be the Japanese White-eye (Woodward et al. 1990). Pigs (Sus scrofa) are also attracted to the fruits and through their disruptive digging make certain that fire tree seeds are well planted. Fire tree meets H. G. Baker's (1965) criteria for an ideal weed: (1) no special requirements for germination; (2) great longevity of seed; (3) continuous production of seeds throughout the plant's growing season; (4) cross pollination by non-specialized visitors; ad (5) capability for both short distance and long distance dispersal.
Other alien species in the islands are similarly equipped for survival, but none are as effective in altering their respective environments as is the fire tree. The feature that sets fire tree apart in this regard is its capacity to fix atmospheric nitrogen through its symbiotic association with Frankia, an actinorrhizal soil bacterium (actinomycetes are soil-dwelling bacteria that resemble fungi in their filamentous growth form). The fixed nitrogen is available not only to fire tree seedlings, but to other opportunistic plant species as well. Native Hawaiian plants, having evolved in a nitrogen-poor environment, do not compete well in the newly 'adjusted' environment and can easily be overrun by weedy species (Vitousek and Walker, 1989).
In addition to the capacity to change its environment favorably for its own growth and to produce a huge seed crop, fire tree has been shown to out compete the major native tree species significantly under certain circumstances. In a study published in 2006, G. P. Asner of the Carnegie Institution of Washington and colleagues compared the growth of fire tree and `ohi`a (Metrosideros, Myrtaceae) in Hawai`i Volcano National Park using remote sensing techniques coupled with ground level measurements. Detected differences in structure, biochemistry, and physiology of the two species revealed that under hotter and drier conditions–when water stress is at its highest–growth rates of fire tree were 16-44% higher than `ohi`a. Combining these techniques has the capacity to provide important insights into how vegetation-climate interactions affect the growth of an invasive species.
A few years ago I had the pleasure of introducing a colleague from the University of British Columbia to Hawai`i Volcanoes National Park (he's the tee-shirt model in the section on breadfruit). Nearing the Kilauea Iki observation platform on the Devastation Trail Boardwalk, I noticed a familiar plant not far off the trail, went over to it, and yanked it out of the ground. The immediate reaction of my colleague, a well-behaved field biologist, was to chastise me for disturbing the vegetation in a National Park, of all places. Thus, was he introduced to the fire tree. Later in the day, along trails in other parts of the park, we came across other uprooted fire trees waiting to be taken to the trash heap, which, incidentally, needs to be monitored to prevent resprouting.
While simple physical removal is a tried and true means of dealing with seedlings, or even young saplings, it obviously can't be applied to mature trees. Physical removal, regardless of the size of the trees, requires finding them in the first place, and with the mobility of birds and pigs, trees can be found virtually anywhere. Application of herbicides has also been tried, with limited success, but accessibility to the trees remains the problem. And, of course, the larger the tree, the larger the equipment needed to remove it. This leaves finding a reliable biological control agent as the last option. My most recent enquiry along these lines (early May 2012) revealed no startling breakthroughs.
In pre-DNA sequence days, Myrsinaceae were considered to consist of some 30 genera and about 1,000 species widely distributed in tropical and subtropical regions. Reflecting the changes brought about by the new technology, members of the family are now considered as part of Primulaceae, the primula family (Mabberley, p. 568). This change, although undoubtedly significant in the grand theme of things, does not affect Myrsine, the genus of interest to us here. Myrsine, known in Hawaiian as kölea, consists of about 200 species many of which are important sources of timber and other wood products. The Hawaiian Islands are home to 20 species, one of which is thought to be extinct; three are considered rare and or endangered. The first example here is a very young Myrsine lessertiana, known as kölea lau nui (see image). The photograph illustrates one of the characteristic features of this species, namely the pink to red young leaves, which are in marked contrast to the dark green, shiny older leaves. Wood from this species was used to make anvils on which kapa cloth was pounded. The sap of the tree provided an important red dye for the cloth, while kölea charcoal was used as a black dye. The Hawaiian name for this species, kölea lau nui, means the large-leaf kölea.
In contrast, Myrsine sandwicensis (see image) is called kölea lau li`i, the small-leaf kölea. A particularly attractive member of this genus is Myrsine linearifolia (see image) which was photographed beside the Pihea Trail, Kaua`i.
Two other genera of Myrsinaceae are represented on the Hawaiian Islands, Ardisia with two naturalized species (no images), and Embelia with the single endemic species E. pacifica (see image). The Hawaiian name for Embelia is kilioe.
Baker, H. G. 1965. Characteristics and modes of origin of weeds. In H. G. Baker and G. L. Stebbins (eds.) The genetics of colonizing species: proceedings of the first international union of biological sciences symposia on general biology. Pp. 147-168. Academic Press, New York.
Asner, G. P., R. E. Martin, K. M. Carlson, U. Rascher, and P. M. Vitousek. 2006. Vegetation-Climate interactions among native and invasive species in Hawaiian rainforest. Ecosystems 9: 1106-1117.
Vitousek, P. M. and L. R. Walker. 1989. Biological invasion by Myrica faya in Hawai`i: plant demography, nitrogen fixation, ecosystem effects. Ecological Monographs 59: 247-265.
Whiteaker, L. D. and D. E. Gardner. 1992. Firetree (Myrica faya) distribution in Hawai`i, pp. 225-240. In C. P. Stone, C. W. Smith and J. T. Tunison (eds.). Alien plant invasions in native ecosystems of Hawai`i: management and research. University of Hawai`i Press, Honolulu.
May 10, 2012