Theme 1. Landscape fragmentation effects on biodiversity

In Xishuangbanna, forests have been decimated over the last 30 years by rubber plantation; the remaining forests are highly fragmented and continue to be eroded. We try to understand how fragmentation of forests in Xishuangbanna is affecting diversity and population viability of native species, using a set of 47 permanently marked plots. This forest fragment plot network represents one of few sites in Asia where the effects of fragmentation over time are monitored (the others are the 1000 islands lake fragmentation project in Zhejiang, China, and the oil palm fragmentation project in Malaysia), and is a platform available for external researchers to conduct their research. Our project is unique in that our sites cover 3 major tropical forest types found in Xishuangbanna, namely tropical lowland seasonal forest, tropical limestone forest, and tropical montane forest. This allows us to compare effects of fragmentation on the different forest types, leading to insights at several levels. Additionally, the annual resampling of all plots, allows us to build a detailed account of how climate and fragmentation intersect with plant functional traits to structure community diversity across the forest types.

Key findings

• We have shown consistent declines in all biota tested from forests to adjacent rubber or tea plantations, including mammals (Huang et al. 2020), birds (Sreekar et al. 2016; Dayananda et al. 2017), arthropods (Beng et al. 2016), metazoans (Singh et al. 2019) and fungi (Song et al. 2019).
• We demonstrated that metaDNA Barcoding is an effective means for assessing mesofaunal diversity changes in forest and rubber litter (Beng et al. 2016). We also demonstrated that there was strong turnover in arthropod communities estimated from litter metaDNA sampled every month for a year (Beng et al. 2018).
• We have documented that liana abundance increases and liana wood density decreases towards forest fragment edges, and wood density and survival are negatively related (Roeder et al. 2019) suggesting greater turnover of lianas near fragment edges. This pattern matches world trends. However, fragment effects were small compared to differences between forest types.
• We have shown that liana litter decomposes faster than tree litter in all three forest types but that decomposition rate differs by forest type (Roeder et al. 2022). Decomposition rate by mesofauna was only significantly tied to leaf dry matter content. Soil drivers of decomposition rate also differed between mesofauna and microfauna.
• We have tested whether trees could be used as representatives for all plant life-forms in tropical forests and their responses to fragmentation processes, and concluded that they cannot (Pasion et al. 2018). All life-forms generated community clusters with very similar group membership, suggesting that trees were representative of all vascular plants. However, tree species diversity indices poorly predicted cognate indices of lianas and ferns, and life-form responses to fragmentation.
• We have written a review article assessing what is known about the impacts of climate change on edaphically constrained species (Corlett & Tomlinson 2020). Edaphic specialists account for 10-15% of all plant species. This review will give direction to where future research should be directed to ensure their protection.
  
  

Publications

Beng et al. 2016. The utility of DNA metabarcoding for studying the response of arthropod diversity and composition to land-use change in the tropics. Scientific Reports 6: 24965.

Beng et al. 2018. Seasonal changes in the diversity and composition of the litter fauna in natural forests and rubber plantations. Scientific Reports 8: 10232.

Corlett & Tomlinson 2020. Climate change and edaphic specialists: irresistible force meets immovable object?  Trends in Ecology and Evolution 35: 367-376. 

Huang et al. 2020. Combining camera-trap surveys and interviews to determine the status of mammals in protected rainforests and rubber plantations of Menglun, Xishuangbanna, China. Animal Conservation 23: 689-699.

Dayananda et al. 2017. Topography and soil type are critical to understanding how bird and herpetofaunal communities persist in forest fragments of tropical China. Biological Conservation 215: 107-115.

Pasion et al. 2018. Trees represent community composition of other plant life-forms, but not their diversity, abundance or responses to fragmentation. Scientific Reports 8: 11374.

Roeder et al. 20.19. Growth, mortality and wood density of lianas in fragmented forest in SW China. Journal of Vegetation Science 30: 1143-1152.

Roeder et al. 2022. Liana litter decomposes faster than tree litter in a multispecies and multisite experiment. Journal of Ecology 110: 2433-2447.

Singh et al. 2019. Conversion of Asian tropical forests to monoculture rubber plantation reduces small metazoan α-diversity, and overall diversity. Scientific Reports 9: 5893.

Song et al. 2019. Tropica lforest conversion to rubber plantation in southwest China results in lower fungal beta diversity and reduced network complexity. FEMS Microbiology Ecology 95: fiz092.

Sreekar et al. 2016. Effects of forests, roads and mistletoe on bird diversity in monoculture rubber plantations. Scientific Reports 6: 21822.