Competition among trees is one of the main ecological factors influencing the growth, structure, and productivity of forest ecosystems.
In plantations managed by farmers—often characterized by mixed or semi-natural stands—understanding and quantifying the intensity of competition between individual trees can help improve management strategies.
In this context, competition indices are quantitative tools used to estimate how neighboring trees influence the growth of a specific individual.
However, there is still no clear consensus on which index is most effective in small-scale plantations, where spatial structure and species composition can vary greatly.
A study conducted at the Agricultural Business College in Shaoxing, China, compared several competition indices to evaluate their ability to describe individual tree competition in plantations.
Researchers analyzed data from different tree species grown in forest plots, using diameter at breast height (DBH) as the main growth parameter. This measurement is one of the most widely used indicators in forestry to assess tree development.
The main goal of the study was to identify which indices were most reliable in representing competition and predicting growth differences among trees within a plantation.
The authors tested different types of indices, mainly distinguishing between distance-dependent and distance-independent indices.
Distance-dependent indices explicitly consider the spatial position of trees and the distance between competitors, providing a more detailed representation of local interactions. Distance-independent indices, on the other hand, rely primarily on tree size characteristics such as diameter or height without including spatial information.
This methodological comparison made it possible to evaluate the advantages and limitations of both approaches within the specific context of agricultural plantations.
The results showed that the choice of competition index significantly affects how accurately tree growth dynamics can be described. In many cases, indices that include spatial information proved more effective in capturing interactions between nearby trees. As they better reflect the actual distribution of resources and plant interference.
However, distance-independent indices can still provide useful results when spatial data are unavailable or when plantation structures are relatively uniform. Another important finding concerns the role of microenvironmental conditions.
Spatial analysis revealed a significant spatial dependence of trunk diameter in some areas of the plantation. Suggesting that local factors such as soil properties, water availability, and microclimate may influence tree growth as much as—or even more than—direct competition between individuals.
This environmental heterogeneity can lead to clusters of trees with similar sizes. Indicating that slow-growing trees often occur close to other trees with similarly limited growth. The study also highlighted that overall competition levels in the plantations analyzed were not yet particularly high.
The relatively abundant availability of resources and the young age of plantations suggest that self-thinning processes had not yet begun in a significant way.
As a result, the differences in growth observed among trees were likely more related to local environmental variability than to intense competition.
In conclusion, the research shows that selecting the appropriate competition index is an important aspect of analyzing growth dynamics in farmer-managed plantations.
Integrating spatial metrics with structural parameters allows for a more comprehensive understanding of tree interactions and the influence of local environmental conditions within agroecosystems.
Source: Yang, S., Yu, H., Cong, Y. et al. Comparison of different competition indices in evaluating individual tree competition in farmer-managed plantations: a case study. Sci Rep 16, 1390 (2026). https://doi.org/10.1038/s41598-025-31121-y
Image source: Rotary Alba
Melissa Venturi
University of Bologna (IT)
19 Sep 2023
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