Palms Svenning: Invasive Palms in Panama Volume 46(2) 2002 Non-Native Ornamental Palms Invade a Secondary Tropical Forest in Panama JENS-CHRISTIAN SVENNING Smithsonian Tropical Research Institute current address:Dept. of Systematic Botany Biological Institute University of Aarhus Nordlandsvej 68 DK-8240 Risskov Denmark svenningC&biology.au.dk Palms are often introduced outside their an example where non-native natural range as beautiful and spectacular ornamental palms massively ornamentals. Some species may however invade a tropical secondary invade natural vegetation and could forest in Panama and seem becomea threat to local native species. likely to become an abundant, if not dominant, Invasive alien organisms are a serious threat long-term part of the to native species and even ecosystems in vegetation. many parts of the world. While invasive Bentikia nicobarica plants cause serious conservation problems Study site in tropical forests on many oceanic islands, Gamboa (09'07'N, 79'41'W) is a town of c. spp., Psychotria pubescens, and P. continental tropical forests seem to have 150 houses located at the Panama Canal and poeppigiana. Palms are among the most been much less affected. However, with surrounded by the 22,104 ha Parque abundant plants throughout the forest, in increasing fragmentation and disturbance of Nacional Soberania. The climate in the area particular in the understory and midstory. tropical forests this situation may well is tropical monsoon climate and the natural change (cf. Phillips 1997; Laurance 2000). A vegetation is semi-deciduous tropical forest. The local palm flora few published accounts of such invasions of The study site is ac. 16 ha secondary The palms comprise 14 species, only six of continental forests already exist (e.g., (probably 40-60 years old) forest that which are native to Panama. Of these, three Laurance 2000). Notably, in an isolated 4-ha divides Gamboa in two parts. The forest are relatively common: the spiny, clonal forest fragment in the Singapore Botanic canopy is generally 15-20 m in height, but understory palm Bactris major Jacq., the Gardens some alien plant species have with taller emergent trees, and is mainly clonal midstory/canopy palm Oenocarpus become common and as many as five non- composed of tree species such as mapora H. Karst. and the climbing native palms species now occurs there Anacardium excelsum, Apeiba tibourbou, Desmoncus orthacanthos Mart. The spiny (Turner et al. 1996). In North America the Bursera simarouba, Cecropia spp., Cordia midstory palm Astrocaryum standleyanum far majority of invasive woody plants are alliodora, Ficus sp., Guazuma ulmifolia, L. H. Bailey, the massive canopy palm escaped ornamental species (Reichard & Gustavia superba, Luehea semannii, Attalea butyracea (Mutis ex L. f.) Wess. White 2001). As palms are among the most Miconia argentea, Ochroma pyramidale, Boer, and the massive understory palm preferred ornamental plants in tropical Schefflera morotoni, Spondias mombin, Elaeis olei fera (Kunth) Cortés have more areas, problems with invasive palms species Triplaris americana, Virola sebi fera, and scattered occurrences. Outnumbering the are to be expected. In fact, palms have Xylopia spp. Lianas such as Gouania native palms, eight species of exotic palms invaded forests from botanical gardens and lupuloides are abundant, and the understory have invaded the forest: urban areas in many parts of the tropics is often dense. Some typical understory (e.g., Lorence & Sussman 1986; Jones 1995; plants are the coarse herbs Aechmea Aiphanes aculeata Willd. - Trinidad to Turner et al. 1996; Horvitz et al. 1998; magdalenae, Carludovica palmata, Costus Colombia, SW Brazil to Peru and Bolivia. Maunder et al. 2001). While little is known spp., Cyclantliùs bipartitus, Heliconia spp, Areca triandra Roxb. ex Buch.-Ham.- India about the effects of invasive nonnative palm and Renealmia cernua, the slender bamboos and Southeast Asia. species on the natural tropical plant Chusquea simplici floraand Rhipidocladum Bentinckia nicobarica (Kurz) Becc. - communities, some appear to be crowding racemiflorum, the grasses Pharus lati folius Nicobar Islands. out native plants (even other palms); e.g., and Olyra latifolia, the ferns Adiantum spp., Dypsis madagascariensis (Becc.) H. Beentje Heterospathe elata on Guam (Jones 1995) Cyclopodium semicordatum, and Tectaria & J. Dransf. - Madagascar. and Livistona chinensis on Mauritius incisa, and various shrubs and treelets, e.g. Livistona saribus (Lour.) Merr. ex A. Chev. - (Maunder et al. 2001). Here I will describe Cupania spp., Lacistema aggregatum, Piper SouthEast Asia adults. The related Dypsis lutescens (H. 1995). A number of other nonnative palm Wendl.) Beentje & J. Dransf. is very species, notably Euterpe oleracea Mart., frequently planted in gardens in Gamboa Livistona saribus, Ptychosperma and produces lots of seedlings there, but macarthurii, Bentinckia nicobarica, and apparently is unable to invade the forest. Areca triandra, also exhibit vigorous While Livistona saribus has no adults in the spontaneous regeneration in or just outside forest, it is abundant as well established, Summit Botanical Garden (also see small to massive (leaves reaching 3-5 m in Hubbuch & Craft 1995). Euterpe oleracea height) juveniles in much of the forest and Ptychosperma macarthurii are also well (despite only a limited number of adults in naturalized in the adjacent forest, the first Gamboa) (Fig. 4). It seems likely that at dominating large tracts of swamp forest. Juvenile Livistonia least some of these juveniles will be able to reach maturity and thus it may simply be a Birds and ants may facilitate invasion Ptychosperma macarthurii (H. Wendl. ex question of time before Livistona saribus Birds seem to be an important seed H.J. Veitch) H. Wendl. ex Hook. f. - becomes naturalized, too. Bentinckia dispersal vector for non-native palm species Australia and New Guinea. nicobarica likewise has no adults in the into the Gamboa forest and may be a key Roystonea oleracea (Jacq.) O. F. Cook - forest, but has several well-established large factor in the invasion of PALMS natural Lesser Antilles to Colombia juveniles in one sector of the forest (Fig. 5). vegetation by these species (as they Roystonea regia (Kunth) O. F. Cook - As this species exhibits profuse probably are elsewhere, see Horvitz et al. Northern Caribbean. spontaneous regeneration in unkempt parts 1998). The fruits of all of the non-native of the Summit Botanical Garden, some 8 species seem to be quite popular with many Status of the non-native species km away, I suspect its scarcity at the study local bird species. Of particular importance Of these eight species, at least four appear site simply reflects is rarity in the gardens of might be Gray-headed Trushes (Turdus completely naturalized, all having many Gamboa. grayi) which are abundant both in the urban reproductive adults in the forest and lots of parts of Gamboa and in the forest (Fig. 6). regeneration: Roystonea regia occurs in high Invasions outside Gamboa? Close to a direct observation of bird- abundance as both seedlings (Fig. 1) and The distribution of most of the exotic palms mediated dispersal from Gamboa into the juveniles throughout and appears to be suggests that they are currently dispersal forest, I once observed a Blue-crowned more or less taking over a wet, central part limited within the Gamboa forest: With Motmot (Momotus momota) flying out of the forest. It is also quite frequent as exception of Roystonea regia and Aiphanes from the forest and sitting for several large subadults and adults all over the forest, aculeata, the other species are all highly minutes eating (swallowing, and not and is by far the most abundant palm concentrated in parts closest to the main regurgitating) Ptychosperma macarthurii reaching the upper canopy. Ptychosperma garden source areas. Thus, given time at fruits and then flying back into the forest. macarthurii (Fig. 2) and Areca triandra (Fig. least the well-naturalized Areca triandra and Forest birds like Keel-billed Toucans 3) are abundant as seedlings, juveniles, and Ptychosperma macarthurii must be expected (Ramphastos sul furatus) and Gray-headed adults in the western half of the forest and to spread and become abundant in all of the Chacalacas (Ortalis cinereiceps) are also sometimes completely dominate the forest. This raises the concern that with frequently observed eating palm fruits in understory. While Aiphanes aculeata is less time the exotics may also spread to the Gamboa gardens. While birds may provide abundant, it is nevertheless common both neighbouring national park. Indeed, this has the colonization opportunities for the exotic as immature and adult individuals in most of already occurred. I have observed both palm species, it is less clear why non-native the forest. adults and juveniles of Areca triandra and palms are able to be successful once inside Roystonea regia as well as a number of the relatively diverse Gamboa forest. One Roystonea oleracea has a much more more or less massive, well-established factor might be the abundance of leaf cutter restricted occurrence in the forest, being juveniles of Livistona saribus in the edge of ants (mainly Atta colombica) in this and concentrated in one creek, but here appears the forest of the national park bordering other secondary forests. At leaf cutter ant well naturalized with many adults and much Gamboa. While I have not surveyed other nest sites in the Gamboa forest, exotic as regeneration (as I was unable to distinguish Canal Area forests systematically, at least well as native palms seem to be among the seedlings and juveniles of the two Roystonea regia occurs frequently in forest few plants able to regenerate successfully Roystonea spp., I am assuming that they and scrub close to houses in the whole (Fig. 5). Perhaps the high fiber content of belong to the species whose adults occur Canal Area. It seems particularly well the palm leaves causes the ants to generally most close by). Dypsis madagascariensis naturalized in swamp or lakeside forests, i.e.