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