Identification of Woodland Vernal Pools with Seasonal Change PALSAR Data for Habitat Conservation

Laura Bourgeau-Chavez,Kirk Scarbrough,Sarah Endres,Zachary Laubach,Yu Lee,Michael Battaglia

doi:10.3390/rs8060490

Laura Bourgeau-Chavez, Kirk Scarbrough + Show 4 more

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https://doi.org/10.3390/rs8060490

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Abstract

Woodland vernal pools are important, small, cryptic, ephemeral wetland ecosystems that are vulnerable to a changing climate and anthropogenic influences. To conserve woodland vernal pools for the state of Michigan USA, vernal pool detection and mapping methods were sought that would be efficient, cost-effective, repeatable and accurate. Satellite-based L-band radar data from the high (10 m) resolution Japanese ALOS PALSAR sensor were evaluated for suitability in vernal pool detection beneath forest canopies. In a two phase study, potential vernal pool (PVP) detection was first assessed with unsupervised PALSAR (LHH) two season change detection (spring when flooded—summer when dry) and validated with 268, 1 ha field-sampled test cells. This resulted in low false negatives (14%–22%), overall map accuracy of 48% to 62% and high commission error (66%). These results make this blind two-season PALSAR approach for cryptic PVP detection of use for locating areas of high vernal pool likelihood. In a second phase of the research, PALSAR was integrated with 10 m USGS DEM derivatives in a machine learning classifier, which greatly improved overall PVP map accuracies (91% to 93%). This supervised approach with PALSAR was found to produce better mapping results than using LiDAR intensity or C-band SAR data in a fusion with the USGS DEM-derivatives.

Highlights

Due to increased awareness of the ecological significance of vernal pools, there has been growing interest in identifying, mapping, monitoring, and protecting these valuable forested wetlands
The green polygons (Figure 6) are PALSAR-derived potential vernal pool (PVP) while the blue cells show 2 acre areas that were sampled in the field and were positive for standing water within or touching the cell, and the red cells show areas that were negative for standing water in the field
The phase I study demonstrated the utility of L-band HH polarization 10 m resolution data for detection of cryptic vernal pools in two study areas (NLP and southeastern Lower Peninsula (SLP)) with overall accuracy of 48% and 62%, respectively

Summary

Introduction

Due to increased awareness of the ecological significance of vernal pools, there has been growing interest in identifying, mapping, monitoring, and protecting these valuable forested wetlands. Vernal pools are small (typically less than 1 ha), shallow, isolated, temporary wetlands that are important for maintaining healthy forest ecosystems. Known as temporary or ephemeral ponds, vernal pools occur in various forms throughout the world [1]. Vernal pools are filled with water in the spring, and dry or significantly draw down in summer, exposing all or most (i.e., >50%) of the pool bottom. Woodland vernal pools generally contain water for a minimum of two months in most years and the regular drying prevents fish from establishing populations in these wetlands. Reduced predation pressure from fish and minimum hydroperiods of two months allow the eggs and larvae of many of the Remote Sens. 2016, 8, 490; doi:10.3390/rs8060490 www.mdpi.com/journal/remotesensing

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