Neighbourhood Diversity Effects on Tree Growth Shift Over Time in a Long-Term Forest Biodiversity Experiment

Area of Science:

• Ecology
• Forestry
• Biodiversity Science

Background:

• Species richness-productivity relationships (SPRs) are typically positive at the community level but can decrease at the individual level due to competition.
• Understanding how competition and niche differentiation interact in diverse forests is crucial for predicting forest productivity.

Purpose of the Study:

• To examine the long-term effects of neighborhood tree species richness, basal area, and niche differences on focal tree growth.
• To investigate how these factors influence forest productivity over time in a changing environment.

Main Methods:

• Utilized 12 years of growth data from a large forest biodiversity experiment.
• Analyzed the impact of neighborhood species richness, basal area, and niche differentiation on focal tree growth.
• Assessed the influence of tree traits and environmental conditions (e.g., rainfall) on growth responses.

Main Results:

• The positive effect of neighborhood basal area on focal tree growth in species-rich stands became negative as stands aged, but this was counteracted by niche differentiation.
• Focal trees with acquisitive traits exhibited stronger responses to neighborhood competition and niche differences.
• Responses to neighborhood richness were more pronounced in dry years compared to wet years.

Conclusions:

• Greater niche differences can effectively balance increased competition in species-rich forest stands.
• These mechanisms allow diverse forest stands to achieve higher total biomass than less diverse stands.
• Niche differentiation is a key factor in maintaining forest productivity and biomass in diverse ecosystems.