Plot size matters: Toward comparable species richness estimates across plot-based inventories.

Area of Science:

• Ecology
• Biodiversity Science
• Forestry

Background:

• Biodiversity indicators must be comparable across inventories for effective monitoring.
• Species richness (SR) is a key indicator, but its measurement is affected by plot size.
• Current National Forest Inventory (NFI) data are difficult to compare due to differing plot sizes.

Purpose of the Study:

• To develop a methodological framework for comparing species richness (SR) across plot-based inventories with varying plot sizes.
• To enable harmonized pan-European biodiversity monitoring.
• To provide reliable and comparable SR estimates for diverse ecosystems.

Main Methods:

• Utilized NFI data from Norway, Slovakia, Spain, and Switzerland.
• Constructed sample-based rarefaction curves by aggregating plots to represent SR-area relationships.
• Estimated and corrected for environmental heterogeneity (EH) introduced during plot aggregation.
• Employed Conway-Maxwell-Poisson distribution models for underdispersed SR data.

Main Results:

• The developed method successfully corrected for environmental heterogeneity (EH) across all studied countries.
• The approach demonstrated better performance in Norway and Switzerland.
• Direct SR comparisons using country-specific NFI plot sizes were found to be misleading.
• Adjusted rarefaction curves enabled reliable SR comparisons, reducing plot size effects.

Conclusions:

• The proposed framework provides a robust solution for comparing species richness across inventories with different plot sizes.
• This methodology can harmonize pan-European biodiversity monitoring efforts.
• The approach is applicable to various plot-based inventories and count data beyond SR, enhancing biodiversity assessments.