Sprouting traits of Fagaceae species in a hill dipterocarp forest, Ulu Gadut, West Sumatra

The size distribution of a tree species gives important information about its regeneration strategy. For example, a tree species that regenerates primarily by sprouting will, in theory, have fewer seedlings than species that regenerate from seedlings, which generally form an L-shaped population size structure because of trade-offs in resource allocation between vegetative sprouting and sexual reproduction (Bellingham & Sparrow 2000, Loehle 2000). The results of some field studies suggest that the number of seedlings decreases with increasing dominance of multi-stemmed sprouters (Krugeret al. 1997, Zimmermanet al. 1994). In their study of four co-occurring species ofCastanopsis(Fagaceae), Nanamiet al. (2004) showed that species with a high frequency of sprouting adults had fewer juveniles and vice versa. This suggested that these species were able to co-exist as a result of trade-offs between investment in seedlings and sprouting. In this study, we investigated the sprouting trait of 17 co-occurring Fagaceae species in a Sumatran hill forest. The forest stand at this site shows a varied population structure across species, and hence, should have a varied life history. We tested the correlation between population skewness and proportion of sprouting trees, following the methods of Nanamiet al. (2004). We hypothesized that the species that frequently form multi-stemmed sprouts will show a lower turnover of individuals because multi-stemmed architecture favours persistence (Bellingham & Sparrow 2009).

Spatial patterns and habitat associations of Fagaceae in a hill dipterocarp forest in Ulu Gadut, West Sumatra

Spatial distribution patterns and habitat associations of Fagaceae species in a Fagaceae-codominated hill forest in Sumatra were investigated. Ten Fagaceae species believed to be zoochorous (animal-dispersed seed) and five codominant canopy and emergent anemochorous (wind-dispersed seed) species from Anacardiaceae and Dipterocarpaceae were studied. Five Fagaceae species and all codominant anemochorous species were significantly aggregated while the other five Fagaceae species showed a random distribution pattern. The median distance of small saplings from the nearest reproductively mature tree tended to be shorter for aggregated species than spatially random species. This implied that some Fagaceae species dispersed over longer distances than anemochorous species. Relationships between four habitat variables and distribution of the target species were examined with torus-translation tests. ThreeQuercusand oneLithocarpusspecies showed positive habitat associations. TwoQuercusspecies aggregated at the preferred habitat, but the others were randomly distributed. Thus tree species with specific habitat preference do not only aggregate at the preferred habitat. The three ridge-specialistQuercusspecies showed gradual changes in habitat association, which could reflect avoidance of competition among the species. Most of theLithocarpusspecies showed little correlation with habitat variables. Coexistence of the threeQuercusspecies partly reflected subtle differences in topographical preferences. Distribution of five of the sixLithocarpusspecies was unrelated to topography, so other mechanisms must be sought to account for the maintenance of coexistence in this species-rich genus.

Growth assessment in tropical trees: large daily diameter fluctuations and their concealment by dendrometer bands

Tree stems contract and expand as stem water is depleted and replaced. Band-dendrometer studies suggest that such daily changes are small (<0.2 mm diameter), and they are ignored in most growth measurements. However, several studies using other approaches note larger changes (even >1 cm diameter), suggesting that significant biases are possible. An exploratory study examined the pattern and magnitude of daily stem changes and whether commercial band-dendrometers were able to reveal them. A method involving multiple precision measurements on eight trees in a Bornean hill dipterocarp forest revealed daily shrinkage and expansion of girth of around 1 mm. Fluctuations were greater in bright weather. Band-dendrometers detected these changes but revealed less than a tenth of their magnitude. An analytical model for dendrometer error is presented that predicts how measurement biases can be reduced. Tropical trees can fluctuate appreciably in stem diameter over the day. These reversible changes are of sufficient magnitude to merit concern in growth studies. Influential biases seem especially likely when measurement intervals are short and involve systematic differences in timing and weather. Further study is required to gauge the more general influence of these measurement problems.