Rattans of Vietnam: ecology, demography and harvesting

Abstract

Rattans are spiny climbing palms belonging to the Arecaceae family. Rattans may be single-stemmed or multi-stemmed in which stems (ramet) are clustered in a clump (genet). Rattan is an important non-timber forest product (NTFP) in almost all Southeast Asian countries. As demand for rattan products increases, there is high pressure on the natural populations of rattan. 339 ramets and 215 genets of Calamus platyacanthus, 526 ramets and 93 genets of Calamus rhabdocladus and 533 ramets and 60 genets of Daemonorops mollispina in tropical rain forests of Vietnam were studied in natural populations for basic knowledge on population size and vital rates over three years. The results showed that there was no effect of stem length and clump size on survival of stems and the average survival of stems was from 91% to 98% per year. Rattan stem growth depended on initial stem length, clump size and light availability. Stem growth was fast up to the initial stem length of 10 m. Thereafter, stem growth seemed stable for a while and then gradually became reduced. Clump support to growth rate was gradually reduced for larger stem sizes and there was almost no support for stems longer than 10 m. The three rattan species reproduced clonally and sexually simultaneously in all years of the study. There was more male than female flowering in the three study species. The population growth rates (lambda) were > 1 for the three study species, indicating that populations are growing. Elasticity analysis showed that large stems in big clumps contributed most to lambda value in all study species. Elasticity values of clonal support for shoot growth were higher than those of initial shoot height, indicating that the contribution of clonal supports is important to the population growth. The contribution of sexual and clonal reproduction modes to lambda varied between species with clonal reproduction being more important for two of the three species. We also analysed the impact of stem harvesting in two clustered rattan species, Calamus rhabdocladus and Daemonorops mollispina, at the levels of the individual and the population. We constructed individual matrix and periodic matrix models to evaluate the impact at individual- and population-level of harvesting by harvest simulations of four regimes (harvest cycle every 1, 5, 10 and 15 years). Harvesting had an overall negative impact on survival, growth and reproduction of the study species. But it had a positive impact on vegetative reproduction during the first year after the harvest. Stem harvesting had a strongly negative impact on the population growth of C. rhabdocladus and D. mollispina in comparison with undisturbed populations. The challenge is how to manage rattan extraction in a sustainable way. Without any silvicultural application, it is suggested to harvest wild rattan not more often than once in 15 years for C. rhabdocladus and D. mollispina in order to maintain long-term harvests of these species. Recent extraction rates of C. rhabdocladus and D. mollispina in Vietnam have exceeded their growth rates and resulted in the depletion of these rattans.