Field-based vegetation monitoring through
spectral technologies: successes and limitations
Heidi Steltzer1 and Geneva Chong1,2
1Colorado State University, Fort Collins, CO
2USGS, Northern Rocky Mountain Science Center, Jackson, WY
Aspen die-off at low
elevations, but
expansion at high
elevations in the San
Juan Mountains
New approaches for field-based
vegetation monitoring are needed
• Observer-based
approaches are:
– Time-consuming
– Costly
– Rely on skilled
observers
Spectral technologies can be used for
field-based vegetation monitoring
• Non-destructive
sampling
• Link to remote
sensing
• Rapid data
collection in field
Spectral technologies
Spectral technologies:
measure reflectance of light
from the earth’s surface
Reflectance varies between green
vegetation and soil surfaces
Spectral technologies:
spectrometers, multi-band sensors,
multi-spectral cameras, and RGB cameras
Using spectral technologies to monitor
vegetation and ecosystem function:
successes and limitations
•
•
•
Arctic tundra
Semi-arid steppe
Restored grasslands
species composition affects
the NDVI-LAI relationship
a)
0.8
LAI (m 2 m -2 )
High Arctic Tundra:
0.6
NDVInpvs = 0.21
D. integrifolia
S. arctica
0.4
∆LAIK
0.2
Steltzer and Welker
Ecology (2006)
2
-2
ΔLAIK (m m )
0.0
0.6
0.4
0.2
0.0
0.2
0.4
NDVI
0.6
0.8
High Arctic tundra: LAI estimates from NDVI
-2
-1
GEP (μmol CO2 m hr )
correlate to ecosystem function
4
b.
3
2
R2 = 0.82
P < 0.001
1
0
0.0
0.2
0.4
2
0.6
0.8
-2
LAI (m m )
Steltzer et al.
JGR-Biogeosciences (2008)
Semi-arid steppe: qualitative vs
quantitative use of imagery
Restored grasslands
Restored grasslands: active soil carbon
decreased where plant cover was low, but
recovered where plant cover was high
High plant cover
24
0.45
9
12
15
18
21
24
27
0.40
0.35
0.30
0.25
Active SOC (g m-2)
NDVI40 (40 cm radius all)
0.50
low cover
high cover
22
20
18
16
0.20
14
4
6
8
10
12
14
Time in CRP (years)
Low plant cover
16
18
2
4
6
8
10
12
14
Time in CRP (yrs)
16
18
20
Advantages of near-surface spectral
measurements
• Spatial
– pure pixels
– sample within an ecosystem
• Temporal
– frequent observations
– particularly important for phenology
• SpecNet – a spectral network
– http://specnet.info
A picture says
3,932,160 words
Acknowledgements
• National Science Foundation
• USGS
• USDA
• Tetracam Inc.
• Joe DeCant
• Jeff Welker
• Rich Conant
• Fred Hummerich and other
Specnetters
• Seth Munson
Limitations and costs of using spectral
technologies
• Species diversity
• Seedling recruitment
• Rare species
Alpine tundra: vegetation types
Walker et al.
Bioscience (1993)