Nitrogen fertilization impacts
on C sequestration and
substitution in Pacific
Northwest Forests
Rob Harrison, APES reader
College of the Environment (July 1)
University of Washington
Seattle, WA
Luna
Julia Butterfly (Hill)
0
200
400
600
800
1000
1200
1950 1960 1970 1980 1990 2000 2010
sn
ofa
ll (in
ch
es
)
year of winter starting
Snowfall at Mt Rainier, Paradise Ranger Station
inches at paradise
Atmospheric CO2
allo
cation
CO3
formation
H2CO3 leaching
understorymicrobe, root
exudates
adsorption,oxidation
DO
C
DOC leaching
CO2 from soil,
root respiration
CO3
dissolution
Soil
CO
2evolu
tion
Mechanisms for Impact on
Deep Soil
(a)∆ in photosynthate allocation, deep vs.
shallow rooting
(b)∆ in quality of litterfall = ∆’s rate of
decomposition and DOC quality
(c)∆ in T or moisture affects microbial
decomposition, production and “quality”
of DOC
(d)∆’s in respiration affect formation of
H2CO3, degassing of CO2, formation of
CO3 and leaching of of H2CO3
(e)DOC production in and moving into
deeper soil profile more likely to adsorb
rather than respire
(f)Removal of OM with harvest reduces
high-quality DOC leaching and “priming”
of soil OM decomposition
(a
)
(c)
(b
)
(d
)
(e
)
(a
) (f)
harvest
removals amendments
Objectives
1) Due to the recent incorporation of atmospheric CO2
into tree wood, substitution of wood for concrete
and/or steel in construction reduces CO2 in the
atmosphere.
2) When PNW forests are fertilized with N, any
increases in wood production can result in
additional CO2 in soil and biomass. The effect of N
fertilization on substitution hasn’t been considered.
3) Our objectives were to quantify this soil, forest and
substitution effects.
N
SILVICULTURE
WOOD Q UALITY
NUTRITION
MODELING
College of Forest Resources University of Washington Box 352100 Seattle Washington 98195-2100 206-543-5355 phone 206-685-3091 fax
c1 c2 c3 c4 c5 c6 c7 c8
For each log section/cookie:
V1 = 1/3 * L * ((A1+A2+(A1*A2)^0.5)
V * % bark * bark density = bark
biomass
V * % bolewood * density = bolewood
biomass
2 diam. each side
(mm)
4 bark thickness
(0.5mm)
6 cookie thickness (0.1
mm)
% bark present/absent
cookie 1
A1=pi*r1*r2 A2=pi*r1*r2
Method of biomass
determination
variable
top
diametersvariable
stump
heights
37.6 Mg C/ha average C increase
Potential tree C sequestration impacts of PNW fertilization
If all commercial forest land in PNW was fertilized
37.6 Mg C/ha increase over 40 y rotation
20,900,000 hectares manageable forest land in WA and OR
785,840,000 Mg C 40 y rotation
0.786 Gigaton C
0.020 Gigaton C/year
Currently only about 25,000 ha fertilized/y in PNW
37.6 Mg C/ha increase over 40 y rotation
1,200,000 hectares manageable forest land in WA and OR
45,120,000 Mg C 40 y rotation
0.045 Gigaton C
0.001 Gigaton C/year
Excess of 3.4 GtC
(8)
Forest floor
O
A
E
B
Horizons
25 cm
55 cm
85 cm
grid CD
ID
SD
As horizons were extracted and sieved with the 25mm
screen, the components were weighed in the field. This
is material from the Bw horizon of Alderwood (glacial)
Samples of <25 mm material were brought back to the lab
for texture, moisture, color & nutrient analyses. Above is
Mud Mt. soil (volcanic). Left to right – A to the lowest Bs
horizon. Once dug and bulk density (Db) measured, the
corer is used to bore holes in the pit sides for lysimeter
insertion. After lab samples are removed, all material from
each horizon is bagged (upper right) and then returned to
the pit at the original depth on filling.
8.0 Mg C/ha average C increase
Potential soil C sequestration impacts of PNW fertilization
If all commercial forest land in PNW was fertilized
8.0 Mg C/ha increase over 40 y rotation
20,900,000 hectares manageable forest land in WA and OR
167,200,000 Mg C 40 y rotation
0.167 Gigaton C
0.004 Gigaton C/year
Currently only about 25,000 ha fertilized/y in PNW
8.0 Mg C/ha increase over 40 y rotation
1,200,000 hectares manageable forest land in WA and OR
9,600,000 Mg C 40 y rotation
0.010 Gigaton C
0.0002 Gigaton C/year
Wilson et al., 2006
Conclusions1) Forest fertilization in the PNW yields increases in forest
productivity though though still a relatively small (0.56%)
impact on the Global C cycle.
2) Most PNW forest C is in soil, but soil increment response to
N is relatively small and long-term impacts unknown.
3) Over long periods of time, substitution of wood for concrete,
steel and other products will have the largest impact on
global CO2 for both unfertilized and fertilized forests. At age
150 y, production forests exceed unharvested forests in net
C impact. Old-growth forests do not sequester additional C.
4) In the long-term, it is absolutely essential that some forest
products be removed and used to displace other materials
that result in higher net CO2 to the atmosphere.
LEACHATE COLLECTIONS FROM 4
TENSION LYSIMETERS AT ONE PLOT
• O horizon darkest
• A horizon least
reliable
• B horizon color
varies
• C or deep B horizon
most predictable
(good yield and
colorless)
