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An intense debate is underway on the different approaches to measuring the importance of neighbour interaction. Both the ecological meaning and the statistical suitability of one of the most popular indices have been seriously questioned, but no simpler and practical alternative tools have been proposed up to now. This paper proposes a novel approach based on the use of new normalized indices which scale the effects of neighbours and environment to the maximum target-plant potential. Two indices related to environmental suitability and size-asymmetry are suggested as tools to stratify data in homogeneous subsets before analysis, and an index of normalized neighbour effect (Nn) is proposed to integrate the measuring of neighbour importance and intensity. When tested on literature data, Nn index proves to be very highly correlated to the most currently used importance index. At the same time, it is moderately but significantly correlated to the intensity index. Yet, an accurate reanalysis of three published datasets proves that several detected trends are predictable on the basis of the inherent properties of the used indices. This is inextricably linked to the use of the same phytometers at different productivity levels. Thus, a glimpse is proposed towards the opportunity to use groups of equivalent competitors, each one working at a different point of the gradient, but all in a comparable range of environmental suitability and potential size-asymmetry relative to neighbours. Once defined these equivalence conditions, the normalized Nn metric is suited to measure how the relative weight of neighbour impact changes along the productivity gradient.

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