Sri S. Tjitrosoedirdjo

Alpha and beta diversity of plants and animals along a tropical land-use gradient

Assessing the overall biological diversity of tropical rain forests is a seemingly insurmountable task for ecologists. Therefore, researchers frequently sample selected taxa that they believe reflect general biodiversity patterns. Usually, these studies focus on the congruence of alpha diversity (the number of species found per sampling unit) between taxa rather than on beta diversity (turnover of species assemblages between sampling units). Such approaches ignore the potential role of habitat heterogeneity that, depending on the taxonomic group considered, can greatly enhance beta diversity at local and landscape scales. We compared alpha and beta diversity of four plant groups (trees, lianas, terrestrial herbs, epiphytic liverworts) and eight animal groups (birds, butterflies, lower canopy ants, lower canopy beetles, dung beetles, bees, wasps, and the parasitoids of the latter two) at 15 sites in Sulawesi, Indonesia, that represented natural rain forest and three types of cacao agroforests differing in management intensity. In total, we recorded 863 species. Patterns of species richness per study site varied strongly between taxonomic groups. Only 13-17% of the variance in species richness of one taxonomic group could be predicted from the species richness of another, and on average 12-18% of the variance of beta diversity of a given group was predicted by that in other groups, although some taxon pairs had higher values (up to 76% for wasps and their parasitoids). The degree of congruence of patterns of alpha diversity was not influenced by sampling completeness, whereas the indicator value for beta diversity improved when using a similarity index that accounts for incomplete sampling. The indication potential of alpha diversity for beta diversity and vice versa was limited within taxa (7-20%) and virtually nil between them (0-4%). We conclude that different taxa can have largely independent patterns of alpha diversity and that patterns of beta diversity can be more congruent. Thus, conservation plans on a landscape scale need to put more emphasis on the high heterogeneity of agroforests and the overarching role of beta diversity shaping overall diversity patterns.

Can joint carbon and biodiversity management in tropical agroforestry landscapes be optimized

Managing ecosystems for carbon storage may also benefit biodiversity conservation, but such a potential ‘win-win’ scenario has not yet been assessed for tropical agroforestry landscapes. We measured above- and below-ground carbon stocks as well as the species richness of four groups of plants and eight of animals on 14 representative plots in Sulawesi, Indonesia, ranging from natural rainforest to cacao agroforests that have replaced former natural forest. The conversion of natural forests with carbon stocks of 227–362 Mg C ha−1 to agroforests with 82–211 Mg C ha−1 showed no relationships to overall biodiversity but led to a significant loss of forest-related species richness. We conclude that the conservation of the forest-related biodiversity, and to a lesser degree of carbon stocks, mainly depends on the preservation of natural forest habitats. In the three most carbon-rich agroforestry systems, carbon stocks were about 60% of those of natural forest, suggesting that 1.6 ha of optimally managed agroforest can contribute to the conservation of carbon stocks as much as 1 ha of natural forest. However, agroforestry systems had comparatively low biodiversity, and we found no evidence for a tight link between carbon storage and biodiversity. Yet, potential win-win agroforestry management solutions include combining high shade-tree quality which favours biodiversity with cacao-yield adapted shade levels.

Biodiversity patterns and trophic interactions in human-dominated tropical landscapes in Sulawesi (Indonesia): plants, arthropods and vertebrates

The need to capture primary production in order to sustain and improve economic livelihoods has lead to increasing conversion of natural habitat and intensification of agricultural practices in many parts of the world including most tropical regions. Understanding how these processes affect ecosystems and their functioning, in particular in the high-diversity ecosystems of the tropics, has become a key issue in ecological research. In this chapter, our focus is on the agriculture-forest landscapes of Central Sulawesi, Indonesia, an island widely known for its endemic yet still poorly known flora and fauna. The rise of the region to one of the largest cacao producing areas in the world is at the core of recent land-use change and intensification processes. Covering plants (trees, rattan palms, herbs, bryophytes) and several invertebrate (ants, dung beetles, cacao insect herbivores, fruit-feeding butterflies, parasitic Hymenoptera, spiders) and vertebrate groups (amphibians, birds, murids, reptiles), we give an in-depth overview of the determinants of biodiversity in cacao landscapes, including both management and landscape-scale variables into our analyses. Results show that shaded agroforests host a rich community of species. By adopting a large-scale study design we showed that proximity of natural forest is a key predictor for species richness of plants, invertebrates and vertebrates alike. Endemics and forest specialists benefit most from indigenous shade tree cover and proximity to natural forest. Importantly, several functionally important groups such as insectivorous and seed-dispersing birds benefit from tall shade trees, shade tree diversity and proximity to forest edge, while parasitoid diversity is greatest close to natural forests. Available data on the effects of landuse change in cacao landscape of Central Sulawesi is increasing. Change in landscape configuration and management practices are being clearly reflected in the composition of species communities, with likely impacts on ecosystem services such as pest control and pollination. More knowledge is needed especially in terms of species interactions and ecosystem functioning, but also on how existing knowledge can contribute to effective conservation in human-dominated landscapes outside protected areas.

A monograph of Cyrtostachys (Arecaceae)

SummaryCyrtostachys Blume (Areceae: Arecaceae) is treated in this study as a genus of tree palms with a disjunct distribution pattern across Malesia and consisting of seven species. Three species are newly recognised (C. bakeri Heatubun, C. barbata Heatubun and C. excelsa Heatubun). Five previously accepted species (C. brassii Burret, C. kisu Becc., C. microcarpa Burret, C. peekeliana Becc. and C. phanerolepis Burret) are reduced to synonymy with C. loriae Becc. and one species (C. compsoclada Burret) is removed to Heterospathe as Heterospathe compsoclada (Burret) Heatubun, while C. ledermanniana Becc. is considered as a doubtful taxon. A determination key is presented and detailed descriptions provided for all taxa. A phylogenetic analysis of all species in the genus was performed based on morphological data. Despite the poorly resolved tree topologies, Cyrtostachys is resolved as monophyletic, with C. glauca H. E. Moore as sister to all other species, and the west Malesian species C. renda Blume probably representing a dispersal from within a Papuasian clade into the Sunda shelf. Natural history observations, including uses and conservation status are also presented in this monograph.

Terrestrial herb communities of tropical submontane and tropical montane forests in Central Sulawesi, Indonesia

Although the diversity of terrestrial herbs is high tropical forests and although herbs may play important roles, e.g., as competitors of tree seedlings, most tropical botanical research to date has focused on trees. We studied the diversity, taxonomic composition, and biogeographical relationships of terrestrial forest herbs at two sites of tropical mountain forest at different elevations (Pono: 1000 m, Bariri: 1400 m) in Central Sulawesi. The study was conducted in 400 plots of 5 × 5 m2 (200 for each site). At Pono, we recorded 91 angiosperm herb species in 28 families, and 112 ferns and lycophytes in 15 families whereas at Bariri we found 77 angiosperms in 25 families and 94 ferns and lycophytes in 20 families. At both sites, the most species-rich angiosperm families were Araceae, Orchidaceae, and Zingiberaceae. The species numbers recorded by us are much higher than those reported in any previous tropical forest herb inventories and point to a previously underappreciated richness of plant assemblages on Sulawesi. Biogeographically, significantly more fern species reached their western than eastern distributional limits on Sulawesi, showing that the zoogeographical Wallaces line separating continental Asia and its shelf islands from the Moluccan region also holds for spore-dispersed plants.

Tropical rainforest conversion and land use intensification reduce understorey plant phylogenetic diversity

Conversion of rainforest into agricultural land affects multiple facets of tropical plant diversity. While the effects of tropical land use change and intensification on species diversity are comparatively well studied, the effects on phylogenetic diversity (PD) and structure of plant communities are largely unknown. Furthermore, it is not clear how the loss of native species and addition of alien species collectively affect PD and structure. We investigated the PD and structure of understorey plants; a diverse and ecologically important, yet poorly studied group. We studied four prominent land use systems (tropical lowland rainforest, jungle rubber agroforest, rubber plantations, and oil palm plantations) in the lowlands of Sumatra (Indonesia), a region experiencing dramatic land use changes. Across the four systems, we investigated differences in four metrics of phylogenetic community structure (PD, mean pairwise distance, mean nearest taxon distance, and their abundance‐weighted variants). Our analyses were based on a comprehensive vegetation survey consisting of 32 plots, 1,197 species of vascular plants, and 146,599 plant individuals. Our results showed that forest conversion into agricultural systems leads to a pronounced loss of PD. Furthermore, the standardized effect size of mean pairwise distance indicated a gradual change from clustered to overdispersed phylogenetic community structure with increasing land use intensity from forest over jungle rubber to the monoculture plantations. In most land use systems, the presence or absence of alien plant species did not affect phylogenetic structure. Only in oil palm plantations, removing alien species from the data led to a more overdispersed structure. In conclusion, conserving the PD and structure requires efficient protection of the last remaining rainforests. Synthesis and applications. Forest conversion into agricultural areas negatively affects phylogenetic understorey plant diversity and leads to a shift from clustered to overdispersed phylogenetic community structure. These trends are partly driven by alien species particularly in oil palm plantations. Protecting the remaining rainforests and considering multispecies agroforestry systems in favour of intensive monoculture plantations are thus imperative to conserve phylogenetic plant diversity and community structure.