SP 1: Primary production

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

Principal investigator(s):

Co-Principal investigator(s):

Phd candidate(s):

Contact address:

Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich

Summary

A central question in biodiversity research is how experimental manipulations of plant diversity affect primary productivity. Grassland experiments have shown a positive relationship between the two variables, but it is not clear if the same holds for forests. In addition, the mechanisms by which diversity may affect productivity are hotly debated, in part because of limited information contained in previous experimental designs. We believe that the planned experiment in combination with the comparative studies in subtropical China will offer an ideal opportunity to address these questions. Together with the subproject of the Chinese partner, Keping Ma, this subproject will obtain estimates of different components of primary productivity at ecosystem level and relate them to observed or experimentally manipulated species richness, functional richness and single or joint occurrences of particular tree and shrub species. Whereas the subproject on the Chinese side will focus on belowground biomass production, the present subproject will focus on aboveground biomass production, estimated via cover, basal stem area and plant height data. During the first three years of the project phase, diversity–productivity relationships will be analyzed in three parallel studies: A, in comparative study plots, B, in harvested plots and C, in the main experiment.

Objectives

This subproject will investigate the relationship between plant biodiversity (species richness / functional richness / species composition / species identity) and the net primary productivity at the community and ecosystem level. In contrast to grassland experiments, productivity will not directly be measured via harvests but rather indirectly via measures of cover, basal stem area and plant height, using estimation functions between these variables and biomass data obtained at the individual and population level. We hypothesize that the species and functional richness of shrubs and trees will lead to increased productivity, which may in turn lead to increases in other ecosystem variables.

For the first three years of the project phase, the work will be split into three main objectives

• Diversity–biomass relationship in comparative study plots
• Diversity­–biomass relationship in harvested plots
• Diversity­–biomass relationship in the main experiment

In the longer term, the aims of this main study are:

• (1) To document changes in realized species richness and biomass abundance distributions over time as a function of initial species richness and composition.
• (2) To quantify the effect of species richness and composition on stand-level aboveground biomass production.
• (3) To analyze the mechanisms underlying the relationship found in 2.