Langkap (Arenga obtusifolia) invation and its impact to biodiversity in Ujung Kulon National Park, West Java (Indonesia)

The Langkap forests are far from common in the Malayan Region. They are not mentioned in any of the enumerations of vegetation type compiled by van Steenis (1935, 1957 and 1965). According to the experienced forester and botanist Endert, who visited Ujung Kulon in 1931, the Langkap forests are not known from any other locality in the region (cited from Hommel, 1987). However, some authors stated that Langkap also found in Siberut (Whitten, et al., 1989; Baruna, 1989), in Panaitan (van Borssum Walkers, 1951 in Hommel, 1987) and in Nusa Kambangan Island (Gunawan, 1988). In Siberut and Nusa Kambangan Islands, Langkap is not a dominant species (Baruna, 1989; Gunawan, 1988). Comparative analysis of Hommel's study in 1981-1983 and vegetation analysis in this study indicate that Langkap invasion has become a common phenomenon in many parts of Ujung Kulon area. Relative density of Langkap in all stages from 8 transects provide other quantitative evidence that in areas where Langkap is more dominant in pole stage, it have higher dominance in sampling and seedling stages. The present of Langkap in all plant stages also indicate the stability of Langkap regeneration and means that Langkap will maintain their dominance in its community over long period. In areas where Langkap is dominant, there will be a considerable decrease of relative density of under growth species, including seedling and sapling of many plant species. This phenomenon is closely related with poor light under the forest crown. Consequently, the Langkap dominance has serious implications for the forest dynamics. For regeneration, the three species of the upper canopy are almost completely depend on incidental gaps in the Langkap layer. Over long-term period, these condition will has serious impacts to plant and animal diversity in the park. The stability of Langkap regeneration ability is supported by advantageous biological properties, especially: (1) Langkap has the capacity of rapid recuperation after destruction of the supra-terraneous parts, by means subterraneous shoots; (2) Langkap has ability to produce many seeds. Our calculation on 9 Langkap trees on May-June 1992 resulted that 1 tree can produce many seeds. Our calculation on 9 Langkap trees on May-June 1992 resulted that 1 tree can produce 945-5400 seeds per fruiting spadices; (3) Langkap has ability to defend against herbivory. In this way, Langkap also take advantage in term of their seed dispersal