Different Taxonomic and Functional Indices Complement the Understanding of Herb-Layer Community Assembly Patterns in a Southern-Limit Temperate Forest

The efficient conservation of vulnerable ecosystems in the face of global change requires a complete understanding of how plant communities respond to various environmental factors. We aim to demonstrate that a combined use of different approaches, traits, and indices representing each of the taxonomic and functional characteristics of plant communities will give complementary information on the factors driving vegetation assembly patterns. We analyzed variation across an environmental gradient in taxonomic and functional composition, richness, and diversity of the herb-layer of a temperate beech-oak forest that was located in northern Spain. We measured species cover and four functional traits: leaf dry matter content (LDMC), specific leaf area (SLA), leaf size, and plant height. We found that light is the most limiting resource influencing herb-layer vegetation. Taxonomic changes in richness are followed by equivalent functional changes in the diversity of leaf size but by opposite responses in the richness of SLA. Each functional index is related to different environmental factors even within a single trait (particularly for LDMC and leaf size). To conclude, each characteristic of a plant community is influenced by different and even contrasting factors or processes. Combining different approaches, traits, and indices simultaneously will help us understand how plant communities work.This research was funded by FUNDACIÓN CAJA NAVARRA, grant number 10833 (Program “Tú Eliges, Tú Decides”) and UNIVERSIDAD DE NAVARRA (projects “Biodiversity Data Analytics and Environmental Quality” and “Red de Observatorios de la Biodiversidad de Navarra (ROBIN)”). M.V. was supported by DEPARTAMENTO DE EDUCACIÓN, GOBIERNO DE NAVARRA (Ayudas predoctorales para la realización de programas de doctorado de interés para Navarra; Plan de Formación y de I + D 2018). A.G. was supported by the Spanish Ministry of Science and Innovation, grant number RyC2020-030647-I, and by CSIC, grant number PIE-20223AT003. J.P. was supported by the Spanish Ministry of Science and Innovation and EU “NextGenerationEU/PRTR”, grant number FJC2020-042954-I.Peer reviewe