August 2002. NARI, Papua New Guinea made a comment about wanting to get rid of Samanea saman (Albizia saman); it was seen as a weed of farm and pasture land. This was in contrast to another member who asked for ways to save it from supposed borers and fungal rots. This comment produced a great deal of discussion.
The comment from NARI referred especially to the Markham area, where Samanea has overgrown large areas of pasture rendering them useless. Along river floodplains this tree grows massively and shades out many natives. It may be useful elsewhere, but certainly not in these in parts of Papua New Guinea. Again we are faced with the question of deciding when or if a plant is already a weed or has the potential to become one.
It is listed as being “weedy or invasive elsewhere and are common or weedy in Samoa” in a recent report by Jim Space on the weeds of Samoa: www.hear.org/pier/index.html
The comment made about these species, including Albizia, is:
“A large number of other common or weedy introduced species were noted. Many of these species, which might best be termed aggressive weeds, are mostly prevalent along roadsides or on disturbed sites, although some species, particularly alien trees, can gradually spread into forested ecosystems…. Some of these species could become a problem in the future, since there is often a long lag time between introduction and when a species begins to cause serious impacts. These species (listed in Appendix 2, Table 3) should be monitored for spread and possible control measures, if necessary”
“Some exotic tree species that have been introduced to Samoa include Acacia auriculiformis (earleaf acacia), Acacia mangium (mangium), Bauhinia monandra (orchid tree), Ceiba pentandra (kapok), Delonix regia (flame tree), Gliricidia sepium (mother of cacao, quickstick), Samanea saman (monkeypod) and Thevetia peruviana (yellow oleander). These species often naturalize and are more or less successful depending on local conditions.”
So, whilst not identified as an aggressive invasive species, it is on the “watch these species” list, so care should be taken with its use. It is expected the report will soon be added to the PIER website.
However, a member from Samoa took exception to this, and said: In Samoa, this tree is naturalise and widespread and it was not thought to be a problem. It is useful, being tolerant to swampy areas and recommend for agroforestry. However, it was pointed out that it is most certainly an invasive species in the tropics and this knowledge should temper its use.
Support was given from Fiji. Samanea may be a `weed’ (whatever one of those is), but certainly it is the most widespread exotic tree on the large islands of Fiji (or invasive if you want to be fashionable and prejudiced). Over much of the dry leeward half of the islands, Samanea is the last stand against uninterrupted fire-induced grass and reedlands. By colonising the ephemeral gulleys and watercourses, it forms natural firebreaks and in many places harbours and protects relict communities of native forest species – grimly hanging on in the face of grasslands driven by wildfire. Samanea plays a vitally important ecological role. It should be evaluated on its ecological merit and do not judge it hastily as weed, exotic or invasive.
The general feeling was that the tree was not a weed in Samoa, but it may be elsewhere depending upon what it is doing to whom. In Samoa, it is semi-naturalized since it will reseed, but does not spread since it is not very dispersive. On the other hand, Albizia chinensis (tamaligi) is a terrible invasive weed in Samoa (others did not agree as it is a source of firewood in urban and suburban communities!).
Solomon Islands took a balanced view, seeing how it is viewed being dependent on what part of the country the tree is growing, its use and invasiveness into human space. In Solomons Islands, Samanea is both beneficial as a shade tree in towns and villages, a grass-fire barrier, as well as a weed in some areas. It is, therefore, a good idea to keep in mind what control measures are available to use when and if it becomes a weed. Take, for example, the African tulip (Spathodea campanulata) is not yet regarded as a weed, but an ornamental in some countries in the Pacific, while in others it is now labeled an invasive species. It was also felt by Fiji (the USP herbarium) that Samanea has a place on the drier side of the larger volcanic islands and on the atolls – anything is better than Leucaena leucocephala!