TRANSECT-BASED PATCH SIZE FREQUENCY-ANALYSIS

A new, transect-based patch size detection met:lod for species pattern is proposed which improves, results obtained with methods described e arlier. The method was rested on an extensive artificial data set toge ther with three of the existing methods considered best: Two and Three Term Local Quadrat Variance (T2LQV and T3LQV) and New Local Variance (NLV). The TLQV methods recovered only some of the existing patterns a nd were heavily dependent on inter-patch distances, whereas NLV almost always produced curves with oscillations. In addition a significance test is proposed, while such a test is seldom found in the earlier met hods. Our method, PASFRAN, determines the frequencies of runs with 1, 2, 3, etc. quadrats containing a certain species and compares those wi th frequencies based on Monte Carlo simulated random configurations. T he comparison is performed for each run length and the significance of the deviation between observed and expected frequencies can be calcul ated on the basis of a large number of simulations. Because this appro ach may be considered a case of multiple testing, a Bonferroni correct ion on the significance level was applied. The method can also be used for the detection of inter-patch distances. In addition, run lengths can be grouped and the test can be applied to the frequencies of combi nations of run lengths. The method can detect dominance patches when q uantitative data on the occurrence of plant species are available. In the same way, it can detect multi-species patterns using sample scores from an ordination analysis such as correspondence analysis. An exten sion towards composite, higher-order patterns is under investigation. The new method appeared to be effective in recovering artificial patte rns, while it is not influenced by the relative values of patch size a nd inter-patch distance. When applied to the distribution of cow dung patches and certain plant species along a transect of 500 quadrats of 10 cm x 10 cm in an alvar limestone grassland, it produced straightfor ward and realistic results as compared with other methods and field im pressions.