Carbon Flux Sites

Control site

The Control Site is located on one section (267 ha) that has not been thinned nor prescribed burned for many decades. It is typical of unmanaged stands in ponderosa pine forests of the southwestern US. Most old growth trees in the stand were harvested between 1914-16.

The stand currently contains trees from several regeneration cohorts; most overstory trees are about 87 years old. In 2006, tree basal area averaged 30 m2 ha-1, leaf area index (projected) averaged 2.3 (97% in trees), which is close to the maximum for southwestern ponderosa pine forests, and coarse woody debris averaged 13.3 Mg ha-1.

Restoration site

The Restoration Site is located 8 km from the control site on similar basalt-derived soil. The stand was lightly thinned for saw timber and poles several times between 1956 and 1991. The latest thinning occurred in September 2006 (after the far left photo was taken) and removed thickets of small-diameter trees following restoration guidelines commonly used for fuel reduction projects in northern Arizona.

The 2006 thinning occurred on 167 ha in the footprint of the instrument tower that measures fluxes of CO2, water, and energy. Slash produced by the thinning was piled on site and will be prescribed burned in 2007 or 2008. The thinning reduced tree density by 67% (465 to 154 trees ha-1), tree basal area by 39% (20.5 to 12.6 m2 ha-1), and leaf area index by 41% (1.6 to 0.9). Coarse woody debris in 2006 before thinning averaged 8.4 Mg ha-1.

The site is surrounded by the larger Woody Ridge Forest Restoration Project administered by the Coconino National Forest. The sections to the east of the site were thinned to an average basal area of 11 m2 ha-1 in winter 2006 (visible in the photo, left, taken in early 2006), and the sections to the south and north are scheduled for thinning in 2007. Thus, the site is embedded in a larger, managed landscape to ensure similar land use and stand structure in the measurement footprint of the instrument tower.

Wildfire site

The Wildfire Site is located on the Coconino National Forest approximately 32 km from the control and restoration sites and within the perimeter of the Horseshoe-Hochderffer fire complex that burned 10,500 ha of ponderosa pine forest in 1996. Prior to the fire the stand had a tree density of 343 ha-1, tree basal area of 31 m2 ha-1, and leaf area index of 2.4, based on measurements of adjacent unburned stands.

The fire killed all trees within major portions of the burned area. Natural regeneration of trees has not occurred in the tower footprint in the 10 years since the fire. Slow regeneration is common in southwestern ponderosa pine forests after severe fire. Leaf area index averaged 0.6 in 2006 and is comprised entirely of herbaceous plants and a few shrubs. All trees in the tower footprint killed by the fire are present as standing snags or downed logs; salvage logging did not occur after the fire. Coarse woody debris averaged 16.0 Mg ha-1 in 2006.

Site characteristics

Site name

unit

CONTROL  

RESTORATION  

WILDFIRE  

location

 

Centennial Forest, Flagstaff, AZ

Centennial Forest, Flagstaff, AZ

Coconino NF, Flagstaff, AZ

coordinates

degree

35° 5' 23.03" N
111° 45' 44.99" W

35° 8' 35.00" N
111° 43' 39.04" W

35 26' 44.06" N
111° 46' 18.64" W

Elevation

m

2180

2160

2270

Site description

 

unmanaged Forest

stand that is been be treated with restoration thinning and prescribed burning

10,500 ha of ponderosa pine forest burnedin a fire in 1996.

 

 

 

 

 

Soil

 

Complex of Mollic Eutroboralf and Typic Argiboroll

Typic Eutroboralf

Mollic Eutroboralf

 

 

 

 

 

Vegetation type (IGBP)

 

evergreen needleleaf forest

evergreen needleleaf forest

grassland

Dominant species

 

Pinus ponderosa

Pinus ponderosa

grasses, early successional shrubs and forbs

leaf area index*

m2 m-2  

2.3

1.6 to 0.9

0.6 (before fire 2.4)

Understorey leaf area index

m2 m-2  

0.06

0.08

0.6

Above-ground biomass

kg m-2  

12.1

8.9

0.2

tree density

N ha-1  

853

471 to 154

before fire 343

basal area

m2 ha-1  

30

20.5 to 12.6

0 before fire 31

canopy height

m

18

18

<0.5

Tree age

yr

87

87

n.a.

Coarse woody debris:

Mg ha-1  

13.3

8.4

16

 

Soil properties

Treatment

Depth

(cm)

Bulk density

(Mg m-3)

% Sand

% Silt

% Clay

Control

0-5

1.20

36.39

39.35

24.25

Control

5-15

1.21

30.76

34.20

35.04

Restoration

0-7.5

1.41

27.15

60.47

12.39

Restoration

10-16

1.45

13.30

46.37

40.33

Wildfire

0-7

1.12

30.50

56.97

12.53

Wildfire

7-15

1.49

19.66

55.50

24.

LAI and CWD prior to the restoration treatment

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