Diversity-function relationships changed in a long-term restoration experiment.

Area of Science:

• Ecological restoration
• Plant community ecology
• Ecosystem function studies

Background:

• Biodiversity-ecosystem function (BEF) theory posits that increased species richness enhances ecosystem function.
• BEF theory's applicability to long-term ecological restoration is uncertain due to reliance on short-term, controlled experiments.
• Restoration practitioners often use BEF theory to guide species selection, aiming for higher diversity.

Purpose of the Study:

• To investigate the long-term effects of species richness on ecosystem functions in a restored salt marsh.
• To assess the predictive power of BEF theory in a real-world restoration context over 11 years.
• To evaluate how different metrics of species richness and ecosystem function influence observed relationships.

Main Methods:

• Resampling a 1997 experiment manipulating species richness (1, 3, and 6 species per plot).
• Monitoring plant community composition and multiple ecosystem functions over 11 years.
• Analyzing diversity-function relationships using both planted and measured species richness, and various functional indicators.

Main Results:

• Plant assemblages converged to intermediate richness (mean 3.9 species/0.25 m²), with nonrandom compositional shifts.
• Two dominant species emerged, increasing shoot biomass and negatively impacting species richness.
• Positive diversity-function relationships weakened over time, differing based on richness metric and function indicator.

Conclusions:

• Long-term restoration outcomes may deviate from BEF theory predictions, especially after cessation of intensive management.
• Dominance by a few productive species can reduce overall species richness and alter ecosystem functions.
• Successful restoration may require establishing both dominant functional species and subordinate species for resilience.