LAI in the quantification of vegetation

disturbance in Irish peatlands

Jerome O Connell, Nick Holden, John Connolly

Biosystems Engineering

University College Dublin

Funded by the EPA, STRIVE under the National Development Plan (2007 – 2013)

LAI ( Leaf Area Index)

Ratio of the total area of all leaves on a plant to the area of ground covered by

the plant.

LAI characterises the canopy/atmosphere interface, therefore is an important

structural measure, often used to derive various biophysical measures.

Direct and indirect approaches.

Gap fraction analysis is a popular indirect approach to LAI

LAI and Peatlands

Peatlands are critical to terrestrial soil carbon stocks.

Over 85% or Irish peatlands are “disturbed”.

Little published work on peatland vegetation disturbance and LAI.

Background

Funded by the EPA, STRIVE under the National Development Plan (2007 – 2013)

Issues in this project

Change detection of peatland vegetation

Need to establish natural growth trends of specific peatland habitats.

Need for ground based vegetation data for verification of satellite based change

detection study.

Objectives

1. Characterise phenology of disturbed and undisturbed peatland habitats using

field based LAI data.

2. Verification of satellite based change detection analysis using undisturbed

(control) LAI vegetation data with know disturbance events.

Change on the ground correlating to change from satellites. High correlation

between ground based LAI and EVI2 (Boegh et al, 2002; Huete et al, 2002; Potithep

et al, 2009)

Undisturbed sites provide baseline conditions; 10% ± this condition = change.

Introduction

Funded by the EPA, STRIVE under the National Development Plan (2007 – 2013)

Materials

Garmin 60CSx GPS

Typically ±2m accuracy

SPOT 4/5 data

Auxiliary data

SunScan Canopy Analysis

System, Delta-T Devices

Measures PAR above (BFS)

and below (probe) the

canopy.

SunScan use’s computable

functions from modelled

illumination data to calculate

instant LAI values ( accurate

to ±0.1 LAI).

Materials

BFS

PDA

Probe

Funded by the EPA, STRIVE under the National Development Plan (2007 – 2013)

Sites 2 raised, 2 blanket, 1 upland

heath.

Sampling Strategy

Unsupervised classification.

Pixels to sample points.

Spatial thresholds applied.

Cross referenced with auxiliary data.

Procedure Track to each point with 1m

proximity alarm.

Sample 3 times in a east, south, west orientation.

Average of 3 readings is LAI for each point.

Take picture of west reading.

Data formatting ArcGIS

ExpertGPS

Excel

Methods

Funded by the EPA, STRIVE under the National Development Plan (2007 – 2013)

Site Co-ordinates Designation Bog type Area (ha) Disturbance

Clara N 53.3211°, W 7.6272° SAC, NHA Lowland raised 4.89 Burning, drainage

Loughdan N 53.1048°, W 6.3292° SAC, NHA Upland blanket 5.00 Drainage, turf cutting

Kerryhead N 52.4082°, W 9.8994° Commonage Upland heath 4.80 Burning

Moanveanagh N 52.4545°, W 9.4075° SAC Lowland raised 5.48 Turf cutting, drainage

Slieve Bloom N 53.0928°, W 7.5793° SAC, NHA Upland blanket 4.19 Drainage, afforestation

Results

Slieve Bloom

Funded by the EPA, STRIVE under the National Development Plan (2007 – 2013)

0.00

1.00

2.00

3.00

4.00

5.00

LAI_28_05 LAI_23_07 LAI_20_08

LA

I

Mean LAI

Plot 1 (Drier) Plot 2 Plot 3 (Clearfell)

0

20

40

60

80

100

LAI_28_05 LAI_23_07 LAI_20_08

% C

V

Coefficient of Variation

Plot 1 (Drier) Plot 2 Plot 3 (Clearfell)

Trends All 3 sites show increasing LAI, with plot1 being the

highest.

Standard deviation of plot 3 increases by over 40% in 10 weeks.

All plots show decrease in Coefficient of Variation (CV), with plot 1and 2 approaching similar levels. May reflect canopy closure.

Plot 3, the disturbed plot, shows the highest CV throughout the sampling periods.

Results

Moanveanagh

Funded by the EPA, STRIVE under the National Development Plan (2007 – 2013)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

LAI_19_03 LAI_24_05 LAI_20_07

LA

I

Mean LAI

Plot 1 Plot 2 Plot 3 Plot 4

0

20

40

60

80

100

LAI_19_03 LAI_24_05 LAI_20_07

% C

V

Coefficient of Variation

Plot 1 Plot 2 Plot 3 Plot 4

Trends

Both cutaway plots show steady increase in mean LAI throughout.

Raised plots show decrease in mean LAI from March to May.

Both cutaway plots show highest CV with plot 3 showing the largest changes.

Both raised plots have slight increases in CV in May.

Results

Kerryhead

Funded by the EPA, STRIVE under the National Development Plan (2007 – 2013)

0

2

4

6

8

10

12

LAI_23_03 LAI_19_05 LAI_07_07

LA

I

Mean LAI

Plot 1 Plot 2 Plot 3 Plot 4 (Wet)

0

20

40

60

80

100

120

140

LAI_23_03 LAI_19_05 LAI_07_07

% C

V

Coefficient of Variation

Plot 1 Plot 2 Plot 3 Plot 4 (Wet)

Trends Plot 1 vs plot 2 significant differences.

Plot 4 (Wet) shows slightly higher LAI than plot 3.

Standard deviation of plot 2 shows considerable increase from May to July.

Plot 4 shows peak CV in May, with plot 3 consistent.

Plot 2 (burnt) shows significant increase in CV from March to May, with gradual stabilisation from May to July.

Continue sampling until Oct-Nov (zenith angle <60°).

Resolve issue with decreasing LAI in spring/summer.

Examine dynamics of the LAI data from disturbed sites with corresponding EVI2 data.

Threshold functions of change.

CV of standard deviation instead of absolute change in LAI and EVI2.

Correlation between LAI and EVI2.

Further Work

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

01/2

010

02/2

010

03/2

010

04/2

010

05/2

010

05/2

010

06/2

010

07/2

010

08/2

010

09/2

010

09/2

010

10/2

010

11/2

010

12/2

010

Mean

LA

I Date

Annual LAI

Mean Cutover Mean Raised Hyp Mean

Funded by the EPA, STRIVE under the National Development Plan (2007 – 2013)

ISIS programme under the French Space agency (CNES)

National Parks and Wildlife Service

Ordinance Survey Ireland

Environmental Protection Agency

ExpertGPS support

Delta-T Devices

Supervisors:

Dr. John Connolly

Prof. Nick Holden

Acknowledgements

Funded by the EPA, STRIVE under the National Development Plan (2007 – 2013)