Aboveground primary productivity in forest ecosystems as a function of species diversity and composition

• Applicant: Professor Dr. Pascal A. Niklaus
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems ; Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: from 2008 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 35758305

The central question of the research group is how tree and shrub diversity in forests affects ecosystem functioning and services. In this subproject, we assess biodiversity effects on primary production. It remains unclear to date if and by which mechanisms tree diversity affects forest productivity. In herbaceous ecosystems, manipulating plant biodiversity generally reveals a positive biomass response to increasing species richness. However, different mechanisms of species interactions may operate in forests due to different sizes and life histories of the component individuals, and responses may therefore differ. Mechanisms may also change with stand development. Density-dependent, herbivore- and pathogen-based mechanisms may dominate early stages while resource-niche based interactions might become important later.We will quantify size and turnover rates of selected C pools, both at the individual and species level, in a way allowing to integrate these to the stand level in established (Comparative Study Plots) and in newly planted (Main Experiment) forest plots. Community-level stand biomass and growth will be quantified (a) using tree height and basal area (and their development over time) as proxies, and (b) these proxies will be scaled to biomass component estimates based on allometric relations. Important baseline data have been collected during the establishment of the field communities and will now help to understand the observed processes in this critical phase of stand development. Extending our activities, we will also include the BEFmod subplot treatments, allowing to directly test and rank density-dependent (fungal pathogens [SP14], insect herbivory [SP8]) and resource-niche based (phosphorus supply [SP5]; herb competition [SP11]) mechanisms.Adopting demographic approaches, we will characterize the turnover of marked leaf cohorts, which can amount for a significant component of net primary production in subtropical forests. Leaf herbivory and foliar fungal pathogen load will be assessed on the same cohorts (cooperation with SP8 and SP14). Leaf area development will be investigated by measuring leaf area index, light quantity and light quality. We will further assess litterfall, a measurement which was not sensible in the earlier phases due to the small size of trees and the dominance of the understory by weeds. In collaboration with SP5, these litter samples will be used to analyze C pools and the (re)cycling of elements including N, P and cations. Also in cooperation with SP5, competition mechanisms will be studied by assessing light climate and nutrient stratification in the canopy.In close collaboration with our Chinese partners, these data will be complemented by an assessment of belowground C cycling including soil respiration, resulting in an integrated understanding of biodiversity effects on ecosystem C dynamics, and the provision of highquality data on tree biomass and primary production to the other subprojects.

• DFG Programme: Research Units
• Subproject of: FOR 891: The Role of Tree and Shrub Diversity for Production, Erosion Control, Element Cycling and Species Conservation in Chinese Subtropical Forest Ecosystems
• International Connection: China, Switzerland
• Participating Persons: Professor Dr. Ma Keping; Professor Dr. Bernhard Schmid; Professor Dr. Zhiyao Tang