Joint optimization of cluster number and abundance transformation for obtaining effective vegetation classifications. (16th February 2018)

• Record Type: Journal Article
• Authors: Lengyel, Attila; Landucci, Flavia; Mucina, Ladislav; Tsakalos, James L.; Botta‐Dukát, Zoltán
• Editors: De Cáceres, Miquel
• Is Part Of: Journal of vegetation science. Volume 29:Number 2(2018:Mar.)
• Page Start: 336
• Page End: 347
• Publication Date: 2018-02-16
• Subjects: cluster validation -- clustering -- community similarity -- cover scale -- data type -- multivariate data analysis -- numerical classification -- stability of classification; Plant ecology -- Periodicals; Plant communities -- Periodicals; Plant populations -- Periodicals; 581.7
• DOI: 10.1111/jvs.12604
• Languages: English
• ISSNs: 1100-9233

Abstract

Abstract: Question: Is it possible to determine which combination of cluster number and taxon abundance transformation would produce the most effective classification of vegetation data? What is the effect of changing cluster number and taxon abundance weighting (applied simultaneously) on the stability and biological interpretation of vegetation classifications? Locality: Europe, Western Australia, simulated data. Methods: Real data sets representing Hungarian sub‐montane grasslands, European wetlands, and Western Australian kwongan vegetation, as well as simulated data sets were used. The data sets were classified using the partitioning around medoids method. We generated classification solutions by gradually changing the transformation exponent applied to the species projected covers and the number of clusters. The effectiveness of each classification was assessed with a stability index. This index is based on bootstrap resampling of the original data set with subsequent elimination of duplicates. The vegetation types delimited by the most stable classification were compared with other classifications obtained at local maxima of the stability values. The effect of changing the transformation power exponent on the number of clusters, indexed according to their stability, was evaluated. Results: The optimal number of clusters varied with the power exponent in all cases, both with real and simulated data sets. With the real data sets, optimal cluster numbers obtained with different data transformations recovered interpretable biological patterns. Using the simulated data, the optima of stability values identified the simulated number of clusters correctly in most cases. Conclusions: With changing the settings of data transformation and the number of clusters, classifications of different stability can be produced. Highly stable classifications can be obtained from different settings for cluster number and data transformation. Despite similarly high stability, such classifications may reveal contrasting biological patterns, thus suggesting different interpretations. We suggest testing a wide range of available combinations to find the parameters resulting in the most effective classifications. Abstract : Methodological decisions made during the data analysis influence the outcomes of vegetation classifications. We present a scheme for finding the combination of abundance transformation function and cluster number which results in the most efficient classification. We show how the optimal values of these two variables co‐vary, and how different decisions on any of them can change the patterns revealed.