Using Unmanned Aerial Vehicles (UAVS) and Automatic Camera Traps to Assay Mangrove Estuaries and Tropical Dry Forest on the Pacific Coast of Costa Rica

Adam M Yaney-Keller, Purdue University

Abstract

The northwestern coast of Costa Rica is a landscape defined by a complex mixture of biodiverse habitats, agriculture, urban development, and popular tourist destinations. This rugged coast contains two of the world’s most endangered forest types, mangrove estuaries and tropical dry forests. However, many of these important habitats have been degraded or destroyed, and what is left resides largely in national parks or remote places. Due to their small size and ambiguous conservation value, habitats in remote regions often fall to the wayside in conservation planning and management effort, and many basic attributes of these fragmented forests remain unknown. One such region lies to the south of Santa Rosa National Park and north of the Papagayo peninsula,an area of the Gulf of Papagayo best known by its popular local beach, Playa Cabuyal. Sparsely inhabited, this area contains a mixture of pasture land, fragmented tropical dry forest, and two small sized (≤1 km2) mangrove estuaries. As one of the last sections of north Pacific coast outside of a national park without significant development, gaining basic inventory knowledge of this area is critical for determining base lines about the flora and fauna that persists in this increasingly fragmented region. Rapid biological assessment technologies have become increasingly popular and available to biologists and managers who wish to study biodiversity in remote regions, none more so than unmanned aerial vehicles (UAVs) and automatic camera traps. These two technologies have been adapted for biological assays in the past decade at a rapid pace, and have pushed the boundaries of our understanding of difficult to access habitats and their inhabitants. They present a promising solution to this problem, and so were chosen to determine the mangrove forest structure and terrestrial vertebrate biodiversity of this remote and wild region. A UAV equipped with a commercially available normalized difference vegetation index (NDVI) sensor was used to assess two mangrove estuaries using aerial photography at both 10 cm and 100 cm resolution during both dry and wet seasons. Structural parameters such as mean and maximum canopy height, percent canopy coverage, and species were then compared to field-based 2 measurements on canopy mangrove trees (≥ 5 cm DBH) from 22 fourteen meter diameter circular plots spread throughout the forests. UAV-derived measurements at both resolutions of plot maximum canopy height and canopy coverage showed no statistical difference from plot measurements. NDVI measurements revealed distinctions between red (Rhizophora racemosa) and black (Avicennia germinans ) mangroves during dry season measurements. Additionally, I used 13 automatic camera traps to assess the terrestrial vertebrate species assemblage over a period of 1,498 trap days. Seventy species from 42 families in 27 orders were detected, including several vulnerable and near threatened species such as great curassow (Crax rubra), American crocodile ( Crocodylus acutus) and jaguar (Panthera onca ). Tropical dry and mangrove forests had the highest avian diversity, while edge habitat had the highest mammalian diversity. Herpetofaunal diversity was greatest in the mangrove habitat. The findings of this study suggest a surprising complexity and wealth of biodiversity within this remote and fragmented region of the Gulf of Papagayo. Overall, these results indicate a need for further study and protection of both the animals and habitats that make up the region.

Degree

M.S.

Advisors

Paladino, Purdue University.

Subject Area

Ecology|Conservation biology|Remote sensing

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