Recent enhanced tree growth at upper altitude sites in
the western United States: Links to water use efficiency
Louis A. Scuderi and Maria Lohmann,
Department of Earth and Planetary Sciences
University of New Mexico
Basis for the project
• The growth response of high elevation conifers to climate in the
western United States is a fundamental part of the temperature
curve of Mann et al., 1999.
Expected High Altitude Plant Response to
“improving” climate
• “Improving” conditions
–
–
–
–
Warmer temperatures
Increased growing season length
Adequate moisture/water balance
….
• Response spectrum
– Main stem – Increased increment growth
– Whole plant – canopy expansion/densification
– Entire treeline – upward movement of treeline
Recent Results (Salzer et al., 2009)
• Showed that increment growth was increasing for three bristlecone
sites in the western United States
• This increase only was detectable from treeline to 150 meters
below treeline
• The actual elevation of the treeline was not important
Salzer et al., 2009
Some Limitations
• Three bristlecone sites
– Are they truly representative of all bristlecones?
• Bristlecone pine only
– Unknown if the response is species specific or extends to other
treeline species
• Focus on the whole stem response (increment growth only)
– What is happening to the entire plant?
– What is happening for all trees at all sites?
• Responding to what factors?
– Temperature, Precipitation, ??? or some combination?
Purpose/goals of this research
• To evaluate vegetation cover trends for:
– Many sites
– Many species
– Over an elevation range
• To evaluate vegetation growth trends
– INDEPENDENT OF DENDROCLIMATIC ANALYSIS
• To determine whether dendroclimatic analysis suggesting enhanced
growth is supported by other measures of plant growth
Study Area
GIS Based
Processing Steps
Raw and Derived
Data
RAW DATA FROM
AVHRR & MODIS
• Annual NPP (81-00)
• Annual GPP (00-10)
ATTRIBUTE
INFORMTION
• Land cover types
• Tree species
• Species attributes
• Elevation data
• PRISM Climate Data
• Precipitation
• Minimum T
• Maximum T
Extraction of
Analysis Points
CONVERT
• Land cover
• Species maps
Output files
Point Data
• Annual NPP (81-00)
TO
• Delta NPP (81-00)
• Point coverages • Precip, Tmax, Tmin
with 6km spacing • Regression
coefficients (a, b, r)
Stratified By
• Land cover type
• Tree species
• Elevation
Statistical
Analysis
ANOVA and
Regression by:
• Elevation
• Land cover types
• Tree species
• Species attributes
Bristlecone
Pine distribution
- Aristata
- Longeava
Analysis Point Extraction
Grid points placed every 6 km
Alternative placements offset every 2 km N,S,E & W
to test whether placement impacted final results
Repeated for each land cover type and species
Extractions for each grid cell and point location
• NPP Annual (1981, 1982, 1983 …….., 2000)
• Delta NPP (change in NPP from 1981 to 2000)
• Regression equation (a, b, r)
Each of the above then analyzed by:
• Elevation ranges:
• Divided into 500 meter increments from 0 to 4500 meters
• Land Cover type
• 14 Land Cover Types (Mapped from MODIS: USGS)
• Species
• 17 Species (Little, 1991 - USDA species maps)
• Species characteristics (USDA)
• 28 separate attributes
• drought tolerance
• water use
• growth rate
• etc.
Analysis by Land Cover Type
• Between 1981 and 2000 NPP at all elevations increased by an average of
66.9 g C/m2 (~7.0 percent) over the entire study area.
Woodland Shrubland Grassland Forest
All
5.5
Elevations
6.1
11.4
3.1
Above
2000m
6.3
11.2
8.3
3.4
Above
2500m
1.8
5.4
2.4
4.5
Analysis
By
Tree
Species
Species where water availability
is not an issue
Slow growing
Low moisture use
High drought tolerance
Species where water availability
is somewhat of an issue
Range of growth rates
Medium moisture use
Low to medium drought tolerance
Species where water availability
is an issue (medium to high
water use and/or medium to low
drought tolerance)*
Decreasing trends in NPP
or,
Increase in NPP to a certain midforest level elevation and then a
decrease
*includes subpopulations of
bristlecone and foxtail pines in
wetter climates
ANOVA - NPP and moisture use
NPP Change above 2000m
Delta NPP
1981 to 2000
G C/m2
California and Nevada Sites
Elevations Greater Than 2000m
Trends in bristlecone pine NPP
1981-2000
Elevation (m)
P. longaeva
P. aristata
2250
2750
+12.36%
+ 9.67%
------+ 3.95%
3250
+17.34%
+ 4.21%
3750
+36.52%
+ 3.37%
All Elevations
+11.67%
+ 3.82%
Mid-point of 500m range
April
August
Standardized Coefficients
Bristlecone pine NPP
and climate
1981-2000
Annual
Standardized Coefficients
April
August
Bristlecone pine NPP above 2500m
and west of longitude 109
Bristlecone pine NPP above 2500m
and east of longitude 109
Conclusions
•
Increase in NPP for 11 of the 15 species
– Suggests that some, but not all, species are experiencing higher growth over
the past 30 years
– Pronounced increases at the highest elevations
•
Slow growing species with exceptional drought tolerance and low water
usage had the largest increases
– Greater increase for the drier subpopulations of bristlecone and foxtail pine
– Greater increase for Great Basin species
•
Supports the argument for enhanced bristlecone pine growth derived
from tree ring analysis
– For NPP this suggests a change in season length and water availability
associated with higher minimum temperatures
•
The trend at these sites has continued, albeit at a slower rate, from
2000 to 2010 as indicated from analysis of MODIS GPP and NPP data
Questions?