Christian Damgaard Computational Ecology and Software ISSN 2220-721X 2011 1(3) 125-137 09/2011 International Academy of Ecology and Environmental Sciences plant-plant interaction plant community dynamics pin-point state-space model latent variables A novel method for measuring plant-plant interactions in undisturbed semi-natural and natural plant communities where it is difficult to distinguish individual plants is discussed. It is assumed that the ecological success of the different plant species in the plant community may be adequately measured by plant cover and vertical density (a measure that is correlated to the 3-dimensional space occupancy and biomass). Both plant cover and vertical density are measured in a standard pin-point analysis in the beginning and at the end of the growing season. In the outlined competition model the vertical density at the end of the growing season is assumed to be a function of the cover of all species at the start of the growing season, and the cover at the start of the growing season is assumed to be a function of the vertical density of all species at the end of the previous growing season. The method allows direct measurements of the competitive effects of neighbouring plants on plant performance and the estimation of parameters that describe the ecological processes of plant-plant interactions during the growing season as well as the process of survival and recruitment between growing seasons. Additionally, the presented method is suited for testing different ecological hypothesis on competitive interactions along environmental gradients, investigating the importance of competition, as well as predicting the likelihood of different ecological scenarios. DOI 10.0000/issn-2220-721x-compuecol-2011-v1-0015 http://www.iaees.org/publications/journals/ces/articles/2011-1(3)/Measuring-competition-in-plant-communities.pdf