Understanding Land Cover Change in a Fragmented Forest Landscape in a Biodiversity Hotspot of Coastal Ecuador

Xavier Haro-Carrión,Jane Southworth

doi:10.3390/rs10121980

Abstract

Understanding forest cover changes is especially important in highly threatened and understudied tropical dry forest landscapes. This research uses Landsat images and a Random Forest classifier (RF) to map old-growth, secondary, and plantation forests and to evaluate changes in their coverage in Ecuador. We used 46 Landsat-derived predictors from the dry and wet seasons to map these forest types and to evaluate the importance of having seasonal variables in classifications. Initial RF models grouped old-growth and secondary forest as a single class because of a lack of secondary forest training data. The model accuracy was improved slightly from 92.8% for the wet season and 94.6% for the dry season to 95% overall by including variables from both seasons. Derived land cover maps indicate that the remaining forest in the landscape occurs mostly along the coastline in a matrix of pastureland, with less than 10% of the landscape covered by plantation forests. To obtain secondary forest training data and evaluate changes in forest cover, we conducted a change analysis between the 1990 and 2015 images. The results indicated that half of the forests present in 1990 were cleared during the 25-year study period and highlighted areas of forest regrowth. We used these areas to extract secondary forest training data and then re-classified the landscape with secondary forest as a class. Classification accuracies decreased with more forest classes, but having data from both seasons resulted in higher accuracy (87.9%) compared to having data from only the wet (85.8%) or dry (82.9%) seasons. The produced cover maps classified the majority of previously identified forest areas as secondary, but these areas likely correspond to forest regrowth and to degraded forests that structurally resemble secondary forests. Among the few areas classified as old-growth forests are known reserves. This research provides evidence of the importance of using bi-seasonal Landsat data to classify forest types and contributes to understanding changes in forest cover of tropical dry forests.

Highlights

While tropical deforestation and degradation, often associated with forest fragmentation and biodiversity loss, continue at high rates, other areas in the tropics are experiencing expansion of secondary forest, which plays a mitigating role in species loss [1,2,3,4,5,6]
Using metrics from the dry season alone achieved a slightly lower accuracy of 94.6% (Kappa = 0.93) while using metrics of just the wet season resulted in an accuracy of 92.8% (Kappa = 0.91; Table 2a)
Regarding the plantation forest class, numbers are very similar across models, but misclassification in the bi-seasonal model occurs almost exclusively with the pasture class while plantation forest data tend to be mistaken more with forest data in the dry and wet season models

Summary

Introduction

While tropical deforestation and degradation, often associated with forest fragmentation and biodiversity loss, continue at high rates, other areas in the tropics are experiencing expansion of secondary forest, which plays a mitigating role in species loss [1,2,3,4,5,6]. These complex dynamics of forest cover change and associated environmental impacts gain even more complexity when changes in cropland, including plantation forests, and other land change processes are incorporated [7]. Detailed analyses of tropical dry forest coverage remain scarce and are considered fundamental to improving knowledge and management of tropical forests [16,17,18]

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