Quantifying the effects of competition on the dimensions of Scots pine and Norway spruce crowns

• Published in: International journal of applied earth observation and geoinformation 2022-08, Vol.112, p.102941, Article 102941
• Main Authors: Pitkänen, T.P., Bianchi, S., Kangas, A.
• Format: Article
• Language: English
• Subjects: Competition indices; Terrestrial laser scanning; Tree crown; Tree growth modelling
• ISSN: 1569-8432; 1872-826X
• DOI: 10.1016/j.jag.2022.102941

•We measure dimensions of Scots pines and Norway spruces using point cloud data.•Inter-tree competition affects morphology of tree crowns, particularly their size.•Most applicable strategies to measure competition differ between the species.•Shade tolerance favors the use of distance-independent competition indices.•To optimally measure competition, identifying the actual competitors is essential. Inter-tree competition can be assessed using relatively simple indices derived from tree diameters, heights and locations, but they have often been found to be deficient for predicting tree growth. To better understand these linkages, we measure dimensions of Scots pine and Norway spruce crowns, which are assumed to be affected by competition pressure. We extract these features from terrestrial laser scanning point clouds and model their dependencies on competition. Our results indicate that while competition is a major determinant for crown morphology, the characteristics and most applicable indices of the two species are contrasting. We interpret our results primarily by light competition: pines are seeking for light and invest their resources on widening the crown only in suitable conditions, while spruce may grow large despite of shortage of light. We conclude that shade tolerance affects strongly on the identification of actual competitors, which should be addressed when modelling competition.