Description: Elaeocarpus joga was described by Elmer Drew Merrill in 1914. It is still a readily visible canopy tree in northern Guam and some areas of Palau. It is easily recognized by its spreading branches within its relatively tall, tiered, pagoda-form architecture. E. joga trees can reach heights of up to 20 m (~60 ft) or more, but often they get trimmed by frequent typhoons that keep the heights of these woody plants on Guam and other Mariana Islands where they occur down to about 15-18 m (45-50 ft). E. joga is evergreen tree with simple, oblanceolate, entire and petiolate leaves that are alternately arranged along the stems; the leaves have an attractive green color, but turn red before falling. Its flowers are feathery white, cup-shaped and produced in racemes which develop in clusters (Stone 1970). The fruits are ornamentally attractive blue drupes, thus the common name for many species of Elaeocarpus as “Blue Marble Tree.” There is actually no blue pigment in the fruit; the blue color results from an optical phenomenon resulting from the refraction of light through the outer surface which appears to be blue (e.g., see Lee 1991). Young fruits of Elaeocarpus are green and appear to turn blue as they mature. Fruits contain one to five seeds. Many fruits are produced each year, but germination rates are low because the seed coverings of E. joga fruit are very hard and must be weathered or broken apart to allow the seeds to start absorbing water.

Distribution: Elaeocarpus joga is a relatively large, rugged tree that is endemic to the Mariana Islands and Palau. Today E. joga is still a distinctive component of the limestone forests of the Mariana Islands, and also provides a striking canopy in the urban forest; however, its continued existence is endangered by a series of anthropogenic threats. Indeed, this unique tree is one of the forest species that have become rare in recent decades due to habitat loss, increasing fragmentation, loss of avian seed dispersers, and impacts of alien ungulates (e.g., see Raulerson and Rinehart 1991). Naturally ocurring in open areas and forests on limestone deposits, E. joga has been an important fruit source for native birds and fruit bats that did or do occur in the Mariana Islands and Palau. According to a forestry study in the mid-20th century, E. joga was still common in the forested limestone soil regions of Guam; and since it was one of only two native species with suitable form and stem/trunk diameter, it was being considered for their possible “economic conversion into lumber” (Skolmen 1967). However, the abundance of this native tree in some areas of the Mariana and Palau Islands may be deceptive because nowadays it does not appear to be germinating well. Fruits contain one to five seeds and many fruits are still produced each year, but germination rates are low apparently because the seed coverings of the E. joga “fruit are very hard and must be weathered or broken apart to allow the seeds to start absorbing water” (McConnell et al. 2014). It has been suggested that because the seeds of the E. joga do not sprout easily, they may “need acid treatments similar to the digestive systems of birds to increase germination” (Kitalong et al. 2008). The loss of native birds in the pre-contact or post-contact periods (before and after European contact) may help explain the declining germination rates and resulting reduced population size of E. joga.

Uses by Island or Island Group:

Uses in Palau: Elaeocarpus joga is known as Dekemerir in Palau where it is an important food for forest birds and probably for fruit bats; this large native tree “makes a handsome tree for reforestation or beautification” (Kitalong et al 2008). According to Tuyama (1941), the wood of this native tree is “yellowish-white, light and soft,” and was used for canoe building material in Palau. It is worth noting that although the Palau population of E. joga occurs abundantly on the volcanic island of Babeldaob, the Marianas populations are only known from limestone based soils and have been shown to be in decline (Ritter & Naugle 1999). In addition to its use for potential forest replanting and aesthetic enhancement, Kitalong et al. (2011:71) referred to the traditional use of certain plant species, including E. joga, as fertilizer for farming taro in Palau:

“Leaves from many species of trees can be used as green manure for the taro patches, including Osmoxylon oliveri (kesiamel), Musa spp. (banana, tuu), Cocos nucifera, Areca catechu and the large leaves of the giant taro, Cyrtosperma merkusii (prak). In Ngatpang, the women also use Elaeocarpus joga (dekemerir) and Cerbera manghas (chemeridech) as fertiliser (G. Emesiochel [informant]). Fertili[z]er, most commonly green manure, is both placed in the planting hole and spread on the top of the prepared beds as mulch to promote soil fertility [bold added for emphasis].”

Uses in Guam: Recent trends in promoting the use of native plants for landscaping and reforestation have triggered the study of E. joga by horticulturists and foresters in Guam (Muniappan et al. 2000; also see Skolman 1967; Raulerson and Rinehart 1991). However, as noted above, the seeds of the E. joga trees (known in Chamarro as Yoga) in its native range of the Mariana Islands and Palau are not germinating well (perhaps due to the loss of native birds as noted above), and as a result the majority of the E. joga “trees on Guam are mature, and the species is no longer recruiting well” (Ritter and Naugle 1999; also see Marler and Lawrence 2015 for more information about this species, its distribution on Guam and the effects of human-related impact).