Current

Professor, Ecological Evolution Group,
Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Yunnan, China.

My research is focussed on tree species diversity and distribution patterns in relation to environmental variables in lowland rain forests of Borneo and Southeast Asia. This includes investigating the amount of forest structural damage caused by drought, fire and logging and their effects on tree species diversity and composition, but also species-habitat associations in old growth forests. I have build up a large database of plant morphological traits, which in combination with a GIS environmental and tree species inventory database can be used to study floristic, diversity and plant functional traits in relation to the environment. I am also interested in theoretical and statistical problems with current diversity and ordination methods. These treat species as independent sample units and ignore that these species are connected via their evolutionary histories thus potentially overlooking many interesting additional diversity and floristic patterns. Last, but not least, I am also very interested in new species identification techniques, such as DNA-barcoding and next-gen sequencing, because after hundreds of years of traditional morphological systematic work it is still frustratingly difficult to identify tropical trees. At Xishuangbanna Tropical Botanical Gardens I hope to expand my studies to include the whole of Southeast Asia, up to the most northern limits of naturally occurring Dipterocarp forests.

Past projects

Trees of Sungai Wain

Nationaal Herbarium Nederland, Leiden University, The Netherlands

During several years of ecological field work in the Sungai Wain area, I have collected a huge amount of tree specimens from this region. Since there are hardly any general tree guides available for Borneo, it occurred to me that it would be nice to put my checklist of tree species of Sungai Wain on the internet with brief descriptions and pictures of all species. I hope that this checklist will increase the interest of the general public for the spectacular trees of this region and thus contribute to the sustained protection of this unique forest  reserve near the city of Balikpapan.

The influence of chance processes on tropical tree species diversity, dominance and distribution in the rain forests of Borneo

Nationaal Herbarium Nederland, Leiden University, The Netherlands

Financed by the Dutch Science Foundation (NWO-WOTRO), May 2004 to June 2006

Currently there are two competing theories that explain tree species dominance, distribution and diversity patterns in tropical forests: the niche-assembly and the neutral theory. The niche-assembly theory states that tree species can co-exist because each species has its own specific niche and thus avoids competition with other tree species. The neutral theory, on the other hand, discards these species specific habitat associations, and states that chance processes, in the form of dispersal limitation, determine tropical tree species co-existence.

Studies carried out so far, provide evidence in favour of both theories. They show that tree species can have specific habitat preferences (supporting the niche-assembly theory), but they also show that the presence of a tree species at a site is often determined by chance (supporting the neutral theory). Apparently there exists a balance between dispersal-assembly and niche-assembly processes. Our aim with this study is to disentangle these effects of environment and chance on tree species dominance, distribution and diversity patterns at different spatial scales, so that we get insight into the relative importance of both processes on local, landscape, regional and Borneo wide spatial scales.

The results of this study will be used to develop scientifically sound conservation strategies for tropical rain forests. Knowledge of the relative importance of dispersal- and niche-assembly theories on tropical tree species dominance, distribution and diversity patterns is important in this respect since both give rather contrasting recommendations on how to conserve tropical forest trees in the most efficient manner.

Macaranga and Mallotus species of Borneo (Jenis-jenis Macaranga dan Mallotus di Borneo)

Nationaal Herbarium Nederland, Leiden University, The Netherlands

Financed by the European Union (ENBI WP13), February 2004-April 2004

During this project I developed an interactive website in English and Bahasa Indonesia for the identification of all Macaranga and Mallotus species occurring in Borneo. This website provides keys to the species, a spot character list, descriptions of all species accompanied by detailed photographs from field and herbarium specimens, and above all an interactive method to determine forest disturbance level based on Macaranga and Mallotus field inventories. This website is visited regularly by people from all over the world and especially from Asia.

Rapid assessment of flora and fauna integrity of lowland dipterocarp forest based on the results of the different flora and fauna studies carried out in Kalimantan within the NWO programme ‘Biodiversity of Disturbed Ecosystems’.

Nationaal Herbarium Nederland, Leiden University, The Netherlands

Financed by the Dutch Science Foundation (NWO-WOTRO), July 2001 - June 2003

Objective: Develop a rapid assessment method for fauna and flora integrity of lowland dipterocarp forest based on newly and previously collected data of the different flora and fauna studies carried out in Kalimantan within the NWO programme ‘Biodiversity of Disturbed Ecosystems’.

The NWO priority programme ‘Ecology of Disturbed Ecosystems’ had yielded a large amount of information on flora and fauna forest disturbance indicators. The results of these studies provided valuable tools for assessing the effects of forest disturbance on species diversity. The value of these results were expected to further increase if integrated into a single survey method that describes forest structure, species diversity and its recovery in a way that is useful for forest management and land-use planning. The project involved 1) sampling of vegetation structure, plant diversity and fauna diversity in overlapping plots and 2) sampling in areas with similar disturbance histories at different localities to make the results found so far more generally applicable and avoid pseudo-replication.

Macaranga and Mallotus (Euphorbiaceae) as indicators for forest disturbance in East Kalimantan, Indonesia

Nationaal Herbarium Nederland, Leiden University, The Netherlands

Financed by the Dutch Science Foundation (NWO - WOTRO), June 1996 - May 2000

During this study I revised several sections of the genus Mallotus (discovering three new species along the way) and produced the first phylogeny for this genus (which showed that in fact the genus was polyphyletic). I also did extensive fieldwork in East Kalimantan, Indonesia to study the natural habitat of species in the genera Mallotus and Macaranga. These data were used to describe forest regeneration after logging and forest fire, and produce an indicator method for assessing forest disturbance in the lowland forests of Borneo.