Evaluating links between climate change and recent enhanced tree growth at upper altitude sites in the western United States [Louis Scuderi]

Evaluating links between climate change and recent

enhanced tree growth at upper altitude sites in the

western United States

Louis A. Scuderi and Maria Lohmann,

Department of Earth and Planetary Sciences

University of New Mexico

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

g C/m2/year

0 - 213

214 - 425

426 - 638

639 - 850

851 - 1,063

1,064 - 1,275

1,276 - 1,488

1,489 - 1,700

Global Production Efficiency Model

Global Land Cover Facility, www.landcover.org

1981

Annual NPP (GLOPEM)

0.0

NPPDifference2000-1981

g C/m2/year

High : 2467.93

Low : -2190.16

Pos.

Neg.

Change in NPP 1981 to 2000

Study Area: Western United

States

GIS Based

Processing Steps

Raw and Derived

Data

Extraction of

Analysis Points

Statistical

Analysis

Output files

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

CONVERT

• Land cover

• Species maps

TO

• Point coverages

with 6km spacing

Point Data

• Annual NPP (81-00)

• Delta NPP (81-00)

• Precip, Tmax, Tmin

• Regression

coefficients (a, b, r)

Stratified By

• Land cover type

• Tree species

• Elevation

ANOVA and

Regression by:

• Elevation

• Land cover types

• Tree species

• Species attributes

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

Analysis Point Extraction

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

~67 g C/m2 (~7.0 percent) over the entire study area.

Woodland Shrubland Grassland Forest

All

Elevations

5.5 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)*

Results:

•Decreasing trends in NPP

or,

•Increase in NPP to a mid-forest

elevation and then a decrease at

higher elevation

*includes subpopulations of

bristlecone and foxtail pines found

in wetter regions

ANOVA - NPP and moisture use

NPP Change above 2000m

-174 - -150

-149 - -100

-99 - -50

-49 - -1

0 - 50

51 - 100

101 - 150

151 - 200

201 - 250

251 - 300

301 - 350

351 - 400

401 - 450

451 - 500

501 - 550

Delta NPP

1981 to 2000

G C/m2

California and Nevada Bristlecone Sites

At Elevations Greater Than 2000m

NPP %Change

1981 to 2000

0 - 0

1 - 60

61 - 70

71 - 80

81 - 90

91 - 100

101 - 110

111 - 120

121 - 130

131 - 140

141 - 200

Pearl

Peak

Mt

Washington White

Mountains

Trends in bristlecone pine NPP

1981-2000

Elevation (m) Mid-point of 500m range

P. longaeva P. aristata

2250 +12.36% -------

2750 + 9.67% + 3.95%

3250 +17.34% + 4.21%

3750 +36.52% + 3.37%

All Elevations

+11.67%

+ 3.82%

Bristlecone pine NPP

and climate

1981-2000

Bristlecone pine NPP above 2500m

and west of longitude 109

Bristlecone pine NPP above 2500m

and east of longitude 109

Sta

nd

ard

ize

d C

oeffic

ien

ts

Sta

nd

ard

ize

d C

oeffic

ien

ts

April

April

Au

gu

st

Au

gu

st

Annual

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 arid region Great Basin species

• Supports the argument for enhanced bristlecone pine growth derived from tree ring analysis

– For NPP this suggests a response to 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?