Scientists reveal how regional species pools shape tree diversity and rarity in subtropical and tropical forests

Why do some natural forests hold so many different kinds of rare trees? It's a question that has long puzzled and intrigued ecologists. While early studies focused on local environmental conditions, scientists now know that broader regional forces, like historical climates and species dispersal, also shape local forest diversity.

In new research published in the KeAi journal Plant Diversity, an international research team led by Dr. Jian Zhang from Sun Yat-sen University explored what drives tree diversity and rarity in China's subtropical and tropical forests—some of the most biodiverse forests on Earth at the same latitudes.

Using a large database (VAST-China) of 3,923 forest plots covering 3,307 tree species, the team defined the regional species pool as all the species that could potentially occur in a given area. They then quantified how regional and local factors together determine species richness (how many species live there) and rarity (how uncommon they are).

"We found that the size of the regional species pool is the strongest driver of local tree diversity," shares Zhang. "Forests with larger species pools, supported by favorable climates, varied habitats, and stable historical climates, have far more species locally."

In particular, warmth, complex topography, and steady paleoclimates help species accumulate over time at regional scales, boosting both total diversity and the number of rare trees.

"Large species pools support both high diversity and many rare species," explains lead author Dr. Houjuan Song from Shanxi Agricultural University. "Rare trees thrive where regional species pools are rich and human pressure is low. This tells us we must prioritize rare and endemic species protection in highly damaged and fragmented forests."

"To preserve forest diversity and save rare and endemic species as the accelerating environment changes, we need to protect the areas with large species pools and minimize human disturbance, especially in biodiversity hotspots," Zhang adds.

Contact the author:

Jian Zhang, zhangjian6@mail.sysu.edu.cn

Funder:  

This work was supported by the National Natural Science Foundation of China (32301401 & 32071538), Innovation Program of Shanghai Municipal Education Commission (2023ZKZD36), VILLUM Investigator project "Biodiversity Dynamics in a Changing World" funded by VILLUM FONDEN (grant 16549), Fundamental Research Program of Shanxi Province (202303021222281).

Conflict of interest: 

The author Jian Zhang is an Editor for Plant Diversity and was not involved in the editorial review or the decision to publish this article. The other authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

See the article title: 

The relative role of regional species pools in determining tree species richness and rarity in Chinese subtropical and tropical forests,  Plant Diversity, https://doi.org/10.1016/j.pld.2026.02.002