Causes and Consequences of Arctic Greening

Team:K. Fred Huemmrich (University of Maryland Baltimore County)Craig Tweedie (UTEP)Petya Campbell (UMBC)Sergio A. Vargas Z. (UTEP)Betsy Middleton (VCU)Objectives1. Describe tundra temporal change (seasonal and multi-year) through the use of ground, aircraft and

satellite data • examine how these changes are affected by vegetation type, climate, herbivory, etc.

2. Extend results across Alaska North Slope using AVIRIS NG imagery • Utilize hyperspectral information to describe tundra vegetation characteristics (e.g. functional type

cover, GPP, Chl content)• Use historic ground measurements for algorithm development and testing

• Organize and archive ground spectral measurements

Thanks to Robert Hollister, Steve Oberbauer, Mariana Orejel, MayraMelendez, Hector Dominguez, Tabatha Fuson, Stephen Escarzaga, RyanCody, Hana Christoffersen, Jake Harris, and Caitlyn Betway for the fieldmeasurements. This work is supported by NASA grant NNX17AC58A.

Partner

NDVI Time Series - Utqiaġvik (Barrow, BRW) and Atqasuk (ATQ)

Ground measured NDVI for a subset of Circumpolar Active Layer Monitoring (CALM) grid

- Spectral reflectance and vegetation cover ground sampling of 30 plots (5x6 grid, 100 m between plots)

- Allows repeatable scaling to MODIS pixel size- Competed 10 years of data collection

S. Vargas Z.

Partner

Black=BRW, Red=ATQ

Point drop measurements of plant type cover collected mid-summer for CALM grid plots

Significant multiyear increase in green vegetation cover- Greening in BRW due to increase in graminoid

cover only- Greening in ATQ partly due to shrub cover but

mainly due to graminoid increaseTotal green cover (sum of shrub, forb, and graminoid)

strongly related to NDVI

Cover data from R. Hollister

Partner

Blue=BRW, Orange=ATQ

Tundra Multiyear Vegetation Cover Change

Grouping by multiyear NDVI trend classes shows that vegetation cover types determine the potential for multiyear NDVI change

Cover data from R. Hollister

Browning sites tend to have low shrub and high graminoid cover

Strongly greening sites tend to have relatively high shrub and low graminoid cover

Partner

Ground Measured Multi-year NDVI Trends

Fractional coverage averaged by multiyear NDVI slope class

Fractional cover trends averaged by multiyear NDVI slope class

For plant cover change over the 10-year period, graminoid cover has increasing rates of change for no NDVI change to strong NDVI greening, but also a very high increasing rate of change for the browning class (the class with the highest average graminoid cover).

Cover of dead material in the plots shows an increase for the browning class and steadily decreasing trends as the rate of NDVI greening increases.

Tundra Biophysical Variables from AVIRIS NG

PLSR

coe

ffici

ents

Atqasuk

0 4.0gC m-2 d-1

Barrow

Algorithms developed using ground measured reflectance coupled with ground measurements of variables including plant cover types, chlorophyll content, and GPP using Partial Least Squares Regression

Working with Mark Carroll to process AVIRIS NG imagery on ABoVE Cloud

Partner

Yellow rectangles mark locations of CALM grids

High-Latitude Drone Ecology Network (HiLDEN)- Dr. Jeff Kerby and Dr. Isla Myers-Smith

Collected RGB and multispectral airborne imagery (2018-2019) of Barrow, Atqasuk, Toolik and Imnavait CALM subsets using UAS following HiLDENprotocols with the following objectives:• Generate high resolution 3D land surface maps used to characterize tundra

heterogeneity across individual plants or communities at sub-satellite pixel scales• Generate spectrally calibrated multispectral land surface maps used to generate

vegetation indices in order to validate satellite datasets and develop linkages between biomass and ground-based spectra

• Data has been submitted to HiLDEN for synthesis paper- scheduled for late summer 2020• Workflows for data collection and post-processing (including image radiometric

calibration and photogrammetric processing are currently being developed)

Partner

Connections to Ongoing Synthesis Efforts

• Attended the U.S. International Tundra Experiment (ITEX) and Arctic Observing Network (AON) meeting in February – the ground data we are using in this study comes from these groups

• Working with Mark Carroll to use ABoVE Science Cloud for processing AVIRIS NG data

• Data archive efforts• Zesati, S.V., C.E. Tweedie, K.F. Huemmrich, P.K. Campbell, and M. Velez-Reyes. 2019.

ABoVE: Reflectance Spectra of Tundra Plant Communities across Northern Alaska. ORNL DAAC, Oak Ridge, Tennessee, USA. https://doi.org/10.3334/ORNLDAAC/1685

• Spectral data from 2010 through 2018 have been archived in the EcoSIS spectral library. We are currently the top contributors of spectra to EcoSIS

Partner

Engagement with Others

Impacts of the loss of the 2020 field season (if any)• This is the last year of this project, so no effect

Future directions• Processing and analyzing tundra cover from AVIRIS NG flights• Improve rSpectral- R tool for working with hyperspectral data• Papers

• Finalize ASTRAL Web app paper by June/July- Journal RS of the Environ.• Submit “Using canopy reflectance models to examine the significance of NDVI change in

high latitude ecosystems” paper• Finalize spectral data collection protocol paper by June/July- Journal Nature Protocols• Finalize “Hyperspectral mapping of tundra vegetation” paper

Partner

The Future