Unpiloted Aerial System (UAS)-Supported Biogeomorphic Analysis of Restored Sierra Nevada Montane Meadows

Jerry Davis,Michelle Slocombe,Michael Vasey,Philip Lynch,Peter Christian,Suzanne Maher,Leonhard Blesius

doi:10.3390/rs12111828

Abstract

The benefits of meadow restoration can be assessed by understanding the connections among geomorphology, hydrology, and vegetation; and multispectral imagery captured from unpiloted aerial systems (UASs) can provide the best method in terms of cost, resolution, and support for vegetation indices. Our field studies were conducted on northern Sierra montane meadows (with ≤70 km2 watershed area). The meadows exist in various stages of ecological restoration. Field survey methods included GPS + laser-leveling channel survey, cross-sections, LiDAR, vegetation sampling, soil measurements, and UAS imaging. A sensor captured calibrated blue (465–485 nm), green (550–570 nm), red (663–673 nm), near infrared (NIR) (820–860 nm), and red-edge (712–722 nm) bands at 5.5 cm resolution (as well as thermal at 81 cm resolution) and provided multispectral images and derivative vegetation indices such as the normalized difference vegetation index (NDVI) and red-edge chlorophyll index (Clre). This fine-scale imagery extended our morphometric assessment of post-restoration channel bedform patterns and sinuosity related to Carex-influenced soil properties and Salix influence, and also documented groundwater-related effects via Carex patterns evident from spring snowmelt images, as well as NDVI and Clre (derived from spring and summer images) in growing to senescent phenological stages. Carex was significantly associated with low bulk density and high soil moisture, NDVI, and Clre in low-lying areas, and channel sinuosity was significantly associated with willow influence. Our methods can be applied by restoration managers to assess where projects are threatened by renewed incision and to document levels of carbon sequestration significant to addressing climate change.

Highlights

The study of alpine and montane meadows lies at the nexus of an array of environmental sciences including hydrology, ecology, edaphology, geomorphology, and micrometeorology; and understanding the interactions among these systems is key to understanding their response to restoration efforts
Discerning effects of restoration efforts amidst the biologically and geomorphologically dynamic systems of meadow channels can be achieved through the fine resolution afforded by unpiloted aerial systems (UASs) employing multispectral cameras designed for precision agriculture
Low-cost imagery from new constellations of small satellites such as CubeSats from Planet [7] provides four-band 3 m data on mostly a daily basis. These imagery sources provide high temporal resolution and ample spectral data for assessing the signal of meadow restoration coming from changes in vegetation health and hydrologically defined communities, with a transition to more hydrophilic species being a common goal of restoration, and these changes can often be seen even at these relatively coarse resolutions

Summary

Introduction

The study of alpine and montane meadows lies at the nexus of an array of environmental sciences including hydrology, ecology, edaphology, geomorphology, and micrometeorology; and understanding the interactions among these systems is key to understanding their response to restoration efforts. Associations of these sedges with ephemeral flow areas at the lowest elevations in the cross-section of a meadow suggest that channel development could be assessed by detecting vegetation and scouring signals using low-altitude multispectral imagery.

Results

Conclusion