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)

Snowfall at Mt Rainier, Paradise Ranger Station
1200
inches at paradise
1000
800
snofall (inches)
600
400
200
0
1950 1960 1970 1980 1990 2000 2010
year of winter starting

Atmospheric CO2
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
Soil CO2 evolution
allocation
(b
DO
(a
C
harvest )
removals
) amendments
understory
CO2 from soil,
microbe, root
(a root respiration
(c) exudates
(d (f)
adsorption, )
oxidation
CO3 ) CO3
dissolution
formation
(e
) DOC leaching H2CO3 leaching

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

College of Forest Resources
University of Washington
Box 352100
Seattle Washington 98195-2100
206-543-5355 phone
206-685-3091 fax
SILVICULTURE NUTRITION
WOOD Q UALITY MODELING

Method of biomass cookie 1
determination
For each log section/cookie:
V1 = 1/3 * L * ((A1+A2+(A1*A2)^0.5)
V * % bark * bark density = bark 2 diam. each side
biomass (mm)
4 bark thickness
(0.5mm)
V * % bolewood * density = bolewood
6 cookie thickness (0.1
biomass mm)
% bark present/absent
A1=pi*r1*r2 A2=pi*r1*r2
c1 c2 c3 c4 c5 c6 c7 c8
variable
variable top
stump diameters
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 rota tion
20,900,000 hectares m anage able forest land in W A and OR
785,840,000 Mg C 40 y rotation
0.786 Gigaton C
0.020 Gigaton C/yea r
Currently only about 25,000 ha fertilized/y in PNW
37.6 Mg C /ha increase over 40 y rota tion
1,200,000 hectares m anage able forest land in W A and OR
45,120,000 Mg C 40 y rotation
0.045 Gigaton C
0.001 Gigaton C/yea r

Excess of 3.4 GtC
(8)

grid SD CD
ID
Forest floor
O
A
E
Horizons
25 cm
B
55 cm
85 cm

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 rota tion
20,900,000 hectares m anage able forest land in W A and OR
167,200,000 Mg C 40 y rotation
0.167 Gigaton C
0.004 Gigaton C/yea r
Currently only about 25,000 ha fertilized/y in PNW
8.0 Mg C /ha increase over 40 y rota tion
1,200,000 hectares m anage able forest land in W A and OR
9,600,000 Mg C 40 y rotation
0.010 Gigaton C
0.0002 Gigaton C/yea r

Wilson et al., 2006

Conclusions
1) 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)