title: Functional composition drives ecosystem function through multiple mechanisms in a broadleaved subtropical forest.
abstract: Understanding the role of biodiversity (B) in maintaining ecosystem function (EF) is a foundational scientific goal with applications for resource management and conservation. Two main hypotheses have emerged that address B-EF relationships: niche complementarity (NC) and the mass-ratio (MR) effect. We tested the relative importance of these hypotheses in a subtropical old-growth forest on the island nation of Taiwan for two EFs: aboveground biomass (ABG) and coarse woody productivity (CWP). Functional dispersion (FDis) of eight plant functional traits was used to evaluate complementarity of resource use. Under the NC hypothesis, EF will be positively correlated with FDis. Under the MR hypothesis, EF will be negatively correlated with FDis and will be significantly influenced by community-weighted mean (CWM) trait values. We used path analysis to assess how these two processes (NC and MR) directly influence EF and may contribute indirectly to EF via their influence on canopy packing (stem density). Our results indicate that decreasing functional diversity and a significant influence of CWM traits were linked to increasing AGB for all eight traits in this forest supporting the MR hypothesis. Interestingly, CWP was primarily influenced by NC and MR indirectly via their influence on canopy packing. Maximum height explained more of the variation in both AGB and CWP than any of the other plant functional traits. Together, our results suggest that multiple mechanisms operate simultaneously to influence EF, and understanding their relative importance will help to elucidate the role of biodiversity in maintaining ecosystem function.
authors.affiliation: Department of Life Science, Tunghai University, Taichung, 40704, Taiwan. jyhmin@thu.edu.tw.
authors.forename: Jyh-Min
authors.identifier: 0000-0002-6293-1551
authors.initials: JM
authors.lastname: Chiang
authors.affiliation: Department of Biology, University of California Riverside, Riverside, CA, 92521, USA.
authors.forename: Marko J
authors.initials: MJ
authors.lastname: Spasojevic
authors.affiliation: Smithsonian Tropical Research Institute, Apartado Postal 0843-03092, Panamá, República de Panamá
authors.forename: Helene C
authors.initials: HC
authors.lastname: Muller-Landau
authors.affiliation: Department of Natural Resources and Environmental Studies, National Dong Hwa University, Hualien, 97401, Taiwan.
authors.forename: I-Fang
authors.initials: IF
authors.lastname: Sun
authors.affiliation: Department of Life Science, Tunghai University, Taichung, 40704, Taiwan.
authors.forename: Yiching
authors.initials: Y
authors.lastname: Lin
authors.affiliation: Taiwan Forestry Research Institute, Taipei, 10066, Taiwan.
authors.forename: Sheng-Hsin
authors.initials: SH
authors.lastname: Su
authors.affiliation: Department of Agricultural Chemistry, National Taiwan University, Taipei, 10617, Taiwan.
authors.forename: Zueng-Sang
authors.initials: ZS
authors.lastname: Chen
authors.affiliation: Department of Agronomy, National Chung Hsin University, Taichung, 402, Taiwan.
authors.forename: Chien-Teh
authors.initials: CT
authors.lastname: Chen
authors.affiliation: Department of Biology, University of Maryland, College Park, MD, 20742, USA.
authors.forename: Nathan G
authors.initials: NG
authors.lastname: Swenson
authors.affiliation: Department of Biology, University of Dayton, Dayton, OH, 45469, USA.
authors.forename: Ryan W
authors.initials: RW
authors.lastname: McEwan
mesh_terms: D044822:Biodiversity; D018533:Biomass; D017753:Ecosystem; D065928:Forests; D010944:Plants
keywords: Complementarity hypothesis; Forest carbon dynamics; Functional diversity; Functional trait; Mass-ratio effect