Tropical mountain forests: Canopy and understory show sharply different biodiversity patterns across elevation

Date: August 20, 2026

Guangzhou, China: Tropical mountain forests host tremendous biological richness, yet how biodiversity in different forest vertical layers changes along elevation gradients remains poorly understood. To fill this knowledge gap, researchers set up 16 sampling sites spanning a nearly 1500-meter elevational gradient within China’s Yunkai Mountain National Nature Reserve, surveying both canopy tree and understory plant communities, alongside two nationally protected rare fern species: Alsophila spinulosa and Angiopteris fokiensis.

The team found tree-layer α-diversity followed a classic unimodal pattern, peaking at mid-elevation zones. By contrast, understory α-diversity was persistently higher and displayed a striking bimodal trend, with two diversity peaks at 400–600 m and 1000–1200 m.

For β-diversity, community composition clearly differed among low-, mid- and high-elevation zones. Statistical tests including PERMANOVA and PERMDISP confirmed that such community differentiation arose mainly from species turnover across elevational zones rather than within-zone plot heterogeneity. SIMPER analysis further demonstrated that shifts of common dominant species, instead of rare species, drove most compositional dissimilarity. Notably, the dominant contribution of Cunninghamia lanceolata suggested historical human-afforestation legacies shaped present-day community patterns.

The two rare ferns exhibited totally distinct elevational niches: A. spinulosa showed unimodal mid-elevation preference, while A. fokiensis followed a U-shaped distribution. Crucially, their occurrence patterns decoupled from overall community diversity metrics and linked more closely to understory microhabitat conditions.

These findings deliver practical conservation implications. Mountain forest protection should not only focus on tree canopy communities, but explicitly safeguard understory microhabitats and cover complete elevational ranges. Since this work lacked in-situ measured environmental variables, future work shall incorporate soil, light and climate data, functional trait analysis and broader-scale sampling to disentangle natural filtering and anthropogenic disturbance effects.

Original Source

X. Li, Z. Li, K. You, et al., “Differential Elevational Diversity Between Overstory and Understory in Tropical Forests,” Biological Diversity (2026): 1–11, https://doi.org/10.1002/bod2.70034.

Keywords

biological diversity, conservation biology, elevational gradient, tropical mountain forest, vertical stratification

About the Author

Xu Li (First author), PhD, Engineer at the South China Botanical Garden, Chinese Academy of Sciences. He engages in ecosystem ecology research and hydrological monitoring at Guangdong Dinghushan National Observation and Research Station for Forest Ecosystem. His research mainly focuses on forest ecosystem carbon sinks and biodiversity conservation.

Juxiu Liu (Corresponding author), Research Professor and PhD supervisor at the South China Botanical Garden, Chinese Academy of Sciences, and Director of Guangdong Dinghushan National Observation and Research Station for Forest Ecosystem. Her research focuses on ecosystem ecology, with an emphasis on the response and adaptation mechanisms of forest ecosystems to global change, as well as the improvement of ecosystem services in degraded ecosystems.  

Zhiyang Lie (Corresponding author), Associate Professor at the South China Botanical Garden, Chinese Academy of Sciences. Her main research fields are global change ecology, ecosystem ecology and soil science. She focuses on carbon‑nitrogen‑phosphorus biogeochemical cycling in subtropical ecosystems and their response mechanisms to global change such as climate warming.

About the Journal

Biological Diversity (ISSN: 2994-4139) is a peer-reviewed, international, open-access journal sponsored by the South China Botanical Garden, Chinese Academy of Sciences ((SCBG, CAS), and published in partnership with John Wiley & Sons Australia, Ltd. It is dedicated to advancing biodiversity conservation, safeguarding ecosystem functions and services, and promoting the sustainable utilization of biological resources under global environmental change. The journal welcomes original research, reviews, commentaries, and short communications across a broad spectrum of disciplines, including botany, zoology, microbiology, taxonomy, phylogenetics, genomics, cytology, ecology, climatology, economics, sociology, and real-time policy theory. The journal is indexed in Chemical Abstracts Service (CAS) and Directory of Open Access Journals (DOAJ).