Relevance of the Cell Neighborhood Size in Landscape Metrics Evaluation and Free or Open Source Software Implementations

Paolo Zatelli,Duccio Rocchini,Nicola La Porta,Maria Giulia Cantiani,Clara Tattoni,Stefano Gobbi,Marco Ciolli,Nicola Zorzi

doi:10.3390/ijgi8120586

Abstract

Landscape metrics constitute one of the main tools for the study of the changes of the landscape and of the ecological structure of a region. The most popular software for landscape metrics evaluation is FRAGSTATS, which is free to use but does not have free or open source software (FOSS). Therefore, FOSS implementations, such as QGIS’s LecoS plugin and GRASS’ r.li modules suite, were developed. While metrics are defined in the same way, the “cell neighborhood” parameter, specifying the configuration of the moving window used for the analysis, is managed differently: FRAGSTATS can use values of 4 or 8 (8 is default), LecoS uses 8 and r.li 4. Tests were performed to evaluate the landscape metrics variability depending on the “cell neighborhood” values: some metrics, such as “edge density” and “landscape shape index”, do not change, other, for example “patch number”, “patch density”, and “mean patch area”, vary up to 100% for real maps and 500% for maps built to highlight this variation. A review of the scientific literature was carried out to check how often the value of the “cell neighborhood” parameter is explicitly declared. A method based on the “aggregation index” is proposed to estimate the effect of the uncertainty on the “cell neighborhood” parameter on landscape metrics for different maps.

Highlights

In recent decades, landscape metrics were one of the main tools for the study, quantification, and possibly the parametrization of the changes of the landscape and of the ecological structure of a territory [1,2]
In order to answer to these questions the aims of our work are: (i) to investigate how the cell neighborhood size affects the results of landscape metrics calculation using both tests map and real maps; (ii) to examine the transparency of the settings of the cell neighborhood size in different software; (iii) to understand if the cell neighborhood size settings are usually reported in the scientific papers and, how reliable are the comparisons of different works developed with the same or different software
For the first artificial test map (Figure 3), configured as a chessboard, Table 2 shows how a 4-cells cell neighborhood (CN) (GRASS, FRAGSTATS using 4 cells) is able to recognize the 5000 patches corresponding to single pixels and to correctly evaluate the corresponding metrics, while using 8-cells CN (QGIS, FRAGSTATS using 8 cells) one single patch is detected

Summary

Introduction

Landscape metrics were one of the main tools for the study, quantification, and possibly the parametrization of the changes of the landscape and of the ecological structure of a territory [1,2]. Landscape metrics became standard and gained the status of an indispensable instrument for those who investigate landscape change dynamics in ecology [6,7] and in many other disciplines such as soil protection and water management [8,9,10]. We realized that the cell neighborhood size is one of the most sensible parameters but a literature analysis highlighted that not many works have investigated its influence. Each software provides information about the setting of cell neighborhood size with different emphasis

Objectives

Methods

Results

Conclusion