The multispectral separability of Costa Rican rainforest types with support vector machines and Random Forest decision trees

Abstract

Estimating the extent of tropical rainforest types is needed for biodiversity assessment and carbon accounting. In this study, we used statistical comparisons to determine the ability of Landsat Thematic Mapper (TM) bands and spectral vegetation indices to discriminate composition and structural types. A total of 144 old-growth forest plots established in northern Costa Rica were categorized via cluster analysis and ordination. Locations for palm swamps, forest regrowth and tree plantations were also acquired, making 11 forest types for separability analysis. Forest types classified using support vector machines (SVM), a theoretically superior method for solving complex classification problems, were compared with the random forest decision tree classifier (RF). Separability comparisons demonstrate that spectral data are sensitive to differences among forest types when tree species and structural similarity is low. SVM class accuracy was 66.6% for all forest types, minimally higher than the RF classifier (65.3%). TM bands and the Normalized Difference Vegetation Index (NDVI) combined with digital elevation data notably increased accuracies for SVM (84.3%) and RF (86.7%) classifiers. Rainforest types discriminated here are typically limited to one or two categories for remote sensing classifications. Our results indicate that TM bands and ancillary data combined via machine learning algorithms can yield accurate and ecologically meaningful rainforest classifications important to national and international forest monitoring protocols.

Acknowledgements

We are grateful for financial support from NSF-IGERT grant no. 0114304. Field assistants Edwin Peirera, Marvin Zamora and Vicente Herrera were critical to this work. Andres Sanchún, Germán Obando from the Fundacion para el Dessarollo Sostenible de la Cordillera Vocanica Central (FUNDECOR) and Jhonny Mendez and Oscar Quiros from the Comisión de Dessarollo Forestal San Carlos (CODEFORSA) also contributed logistical support for field work. We thank the land owners in the Sarapiquí and San Carlos region who generously allowed us access to their forests. We also thank two anonymous reviewers for their comments helpful to revising this manuscript.