Characterization of vegetation change in an arctic mire using remotely sensed imagery

Jessica Del Greco

1

, Kellen McArther

2

, Michael W Palace

3

, Christina Herrick

3

, Anthony John Garnello

4

, Daniel Finnell

5

, Carmody McCalley

3

, Samantha Anderson

3

, Ruth Varner

3 1

University of New Hampshire,

2

University of Minnesota,

3

Institute for the Study of Earth, Oceans, and Space (EOS),

4

University of Arizona,

5

Virginia Commonwealth University

Climate change is impacting sub-arctic permafrost regions through annual warming resulting in the thawing of permafrost peatlands. This thaw induces a change of vegetative species over the landscape, which usually leads to increasing rates of greenhouse gas emissions, such as carbon dioxide (CO 2 ) and methane (CH 4 ). Characterizing these changes in plant communities on a local and landscape level will provide a better estimate of greenhouse gas emissions and aid in more accurate future modeling.

Research Question: How does vegetation type differ in areas

that have been impacted by thawing permafrost?

Figure 1: UAV Imagery of Stordalen Mire 2015

• • • •

Methodology

To estimate the change in vegetation communities, field based measurements combined with remotely sensed image data was used.

At Stordalen Mire , Abisko, Sweden 75 randomized square-meter plots were measured for vegetation composition and individually classified into one of five site-types based on composition and microtopography.

Each of these site types represents a different stage of permafrost degradation Using known rates of methane emissions from each cover type, the percent of methane released over the mire was quantified based on the developed classification map.

Remote Sensing Methods

Drone Imagery GPS Points 2015 Plot Data of Site Types

Georectify image

New Image

Conduct textural analysis of UAV imagery

Image of cover types over mire based on textural analysis

Conduct a neural network (NN) analysis of site types

NN equation created for site types based on pixel information from classified plot types

Apply neural network equation to each pixel

A more accurate image of cover types based on NN and textural analysis

Figure 2: Map of Overall Classification Types

2014 UAV Image

Figure 4: Differentiating Site Types based on Species Composition

Number Misclassified 7 % Misclassified 9.333

Figure 4: A discriminate function analysis was

conducted in order to see if site types could be differentiated based off of the18 species identified across the mire

Results

2015 UAV Image Table 1: Rates of Methane Emission from Each Cover Type Site Types

Tall Shrub Hummock Semi-Wet Wet Tall Gramminoid

Mean Estimate of CH 4 Flux (CH 4 /m 2 /hr)

0 -0.02

2 5 12 Open Water 5 Average flux rates of methane from each site type based on estimates from Christensen et al. (2004) .

20 15 10 5 0 40

Figure 3: Percent of Cover Types Across the Mire

35 30 2014 2015 25

Site Types

Figure 3: The percent coverage of each

site type was calculated across the mire based on the calculated areas. The percent for both 2014 and 2015 is graphed for comparison 700

Figure 5: Comparison of Methane Flux Rates from 2014 to 2015

200 100 0 -100 600 500 400 300 Flux change from 2014-2015 =

+233.523 g CH4/hr

2014 2015

Site Types

Figure 5: Based on methane flux rate

estimates (Table 1) and the overall classification types (Figure 2), a methane budget was created over the mire.

Tall Shrub Site Type Classification Hummock Semi-Wet Wet Tall Gramminoid

ombrotrophic, found in dry areas ombrotrophic, on permafrost ombrotrophic or minerotrophic ombrotrophic wet minerotrophic

     

Summary and Conclusions

Due to high spatial resolution of imagery, accurate GPS ground control points are vital for linking the imagery to the field based measurements Hummock sites have lost 21.5% coverage since 2014, while tall gramminoid sites have increased coverage by 12.1%. o This shows that permafrost thaw has increased from 2014 to 2015 and the vegetation distribution has changed in response A discriminate function analysis showed that site types can be significantly differentiated based on species composition (Figure 4). o Hummock and tall shrub sites were similar in composition as they represent intact permafrost The flux rate of CH4 over the mire for 2014 is 490.02 gCH4/hr while the flux rate in 2015 is 723.54 gCH4/hr. o Therefore, CH4 emissions increased from 2014 to 2015 with a flux change of 233. 52 g CH4/day.

If permafrost thaw progresses more CH4 will be emitted as flux rates increase across the thaw gradient Our estimates of vegetation change may be used to parameterize simulation models and create future scenarios of how the vegetation cover will change in response to climate change.

References/Acknowledgements

Thank you to the ANS research and maintenance staff. Also, thank you to the other NERU mentors: Joel Johnson, Duke Nguyen, Erick and Alison Hobbie, Janet Chen, and Natalie Kashi. This research has been supported by the National Science Foundations REU program: Northern Ecosystems Research for Undergraduates (EAR#1063037).