Generally, local topography influences the distribution of palms (Kahn 1987), mainly indirectly through factors like soil conditions, disturbances, heterogeneity of the canopy, and biotic interactions (Svenning 2001). Indeed, the distribution of rattan palms in north Sulawesi seems to depend on topography (Clayton et al. 2002). On the other hand, a

more detailed survey in our study region only detected a relationship between the slope aspect and community composition of rattan palms, but neither directly with topographic position nor inclination (Getto 2009). Rattan palms occur on most types of rock and soil within their natural distribution area (Dransfield and Manokaran 1994). In fact, differences between upper lowland Compound Library and montane edaphic conditions in our study region do not appear to affect the rattan flora (Siebert BGB324 ic50 2005). Elevational ranges of rattan

species On average, rattan species in our study region had elevational range amplitudes of 515 m. This is likely an underestimate because not all elevations could be sampled and because it is likely that some species were not found in the study plots at elevations where they are not frequent. The gaps within the elevational ranges may likewise reflect the sampling methods which did not account for low population densities. In any case, an elevational range amplitude of 500 m is in accordance with previously documented range amplitudes of palms (400–1800 m) in Ecuador (Svenning et al. 2009). We observed a marked shift in species composition at around 1000 m, where many lowland species reached their upper and many montane species their lower distributional limits. Only eight species (23%) were recorded both below and above 1000 m. A similar elevational segregation at around 1000 m has been found among rattan palms in northern Borneo (Watanabe and Suzuki 2008). The shift from lowland dipterocarp forests to montane oak-laurel forests in Southeast Asia also occurs around 1000 m (Dransfield 1979), suggesting that this represents a fundamental vegetation limit in the region. Assemblage composition Overall, there was marked turnover in species composition between the study plots.

Over half of the 34 rattan species were Cepharanthine found in only one or two study sites. We found that elevation was the main factor accounting for shifts in species composition of rattan assemblages. A difference of more than 900 m in elevation led to a complete species turnover of rattan palms. This agrees well with data on bryophytes, ferns, and angiosperms from other tropical mountains, which typically show changes of about 10% per 100 m elevational shift (Kessler 2000a; Bach et al. 2007). In addition, geographical distances between study plots accounted for a considerable proportion in the change of species composition between plots. The similarity of tropical tree assemblages generally tends to decrease with the geographical distance (Condit et al. 2002; Duivenvoorden et al. 2002).