Application of ecological field theory in distance-dependent growth modelling

In this study, we compared the performance of an additive competition index and two new index types derived from ecological field theory. One type of competition index at a time was used as a distance-dependent predictor in a diameter growth model, together with a permanent set of distance-independent predictors. One of the new index types was computed multiplicatively from the relative influences of competitors at the location of the subject tree. This may be called the ecological interference potential of competitors. The other new index was a simple spatial integral of the ecological interference potential around the subject tree. Its value depends on the directional distribution of competitors. The results indicated that, for both Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.), the indices based on ecological field theory are better predictors of a growth model than a traditional additive index is. The spatial integral of the interference potential was better than the point value.

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