Effects of Grain Size on Plant Diversity Patterns in a Mediterranean Mountain

Question

Spatial grain size and sampling design are crucial to assess plant diversity patterns, yet their effects on alpha, beta, and gamma diversity along elevational gradients remain poorly understood.

Location

We investigated these effects along an elevational gradient in the Central Apennines (Italy) ranging from 1100 to 2486 m a.s.l.

Methods

Plant presence–absence data were recorded from 83 randomly selected nested plots, each containing seven grain sizes ranging from 0.25 m × 0.25 m to 16 m × 16 m. Alpha, beta, and gamma diversity were calculated at both the nested plot and grain size levels and analyzed along the elevational gradient. Gamma was assessed within 100-m elevational bands by aggregating species occurrences across nested plots and grain sizes within each band. Beta diversity was calculated among all nested plots and grain sizes, as well as within elevational bands, using Sørensen dissimilarity.

Results

Our results revealed a significant effect of grain size on elevational diversity patterns. Alpha diversity exhibited a stronger pattern at larger grain size, with species richness decreasing along the elevational gradient. Gamma diversity mirrored alpha diversity trends, increasing with grain size but decreasing with elevation. Beta diversity did not change with elevation but decreased with grain size.

Conclusion

These results emphasize the strong influence of grain size on plant diversity patterns along elevation gradients, highlighting its importance in biodiversity assessments. The nested sampling approach used appears to be a promising tool for testing diversity patterns along elevational gradients, offering a robust framework for future ecological studies.