This document summarizes a study analyzing phosphorus levels in an old-growth Douglas fir forest in the Pacific Northwest. Key findings include: - Phosphorus levels were highest in foliage and lowest in mineral soil below 50cm. - Wood and bark phosphorus levels correlated positively with tree diameter. - Phosphorus levels generally decreased with soil depth and were largely consistent with prior studies. - Clearcutting could remove over 1kg/ha of phosphorus from the ecosystem. Further analysis of nutrient cycling and a larger sample size were recommended.

1. By: Dustin Miller and Jonathon
Tucker
Environmental Analysis 2014-2015
Image source: http://wak.infobaselearning.com/media/10114/OR-tree.j

2. • Keystone Species in
Pacific Northwest
temperate rainforests
• Economically valuable
timber species in the PNW
• Large contiguous stands
exist in TESC forest

3. • The 1994 Northwest Forest Plan
• Shift from focus on timber output to ecosystem
sustainability on public land
• Clear-cut logging still dominant on private land
• Previous studies have shown that continuous
management of forests can cause nutrient depletion and
reduced productivity (Federer et al. 1989, Blanco 2012)

4. • Essential to life
• Major limiting nutrient
• Important role in
driving energy transfer
• Very slow rate of
renewal
• Primary sources
• Weathering
• Dust deposition Image source::
http://www.inorganicventures.com/element/phosphorus
. 2013 Inorganic Ventures, Inc.

5. • 2nd growth temperate forest in the
Pacific Northwest
• Sampling sites based on EEON
plots and PSME overstory
abundance
• Other major overstory species:
• Western red cedar (Thuja
plicata)
• Western hemlock (Tsuga
heterophylla)
• Big-leaf maple (Acer
macrophyllum)
• Major understory species:
• Salal (Gaultheria shallon)
• Sword fern (Polystichum
munitum)
• Oregon grape (Mahonia

6. • Needles
• Litter collected from beneath drip
line
• Stem wood
• 10-15cm core collected with an
increment borer
• Stem bark
• Vertical incision with knife
• Soil o-horizon
• Collected using a 45cm PVC soil
corer 25cm from the base of the tree
• Mineral Soil
• Collected at depths of 5, 15, 25, 50,
and 100cm using a 5cm (r=2.04cm)

7. • Oven-dried at 70°C for >24 hours
• Homogenized using a ball mill
• Wood tissue
• Mortar and pestle
• Knife

8. • Mineral soil samples
• Mehlich-1 extraction
(0.05 M HCL & 0.0125
M H2SO4)
• Organic tissue
samples
• EPA Method 3050b
(Conc. HNO3 & 30%
H2O2)
• Analyzed for total P
using ICP-MS Organic tissue samples mid-digestion

9. • Compton and Cole,
1998
• Tissue (Kjeldahl,
Colorimetric)
• 26ppm Stemwood
• 171ppm Stembark
• 1430ppm Needles
• Soil O-Horizon (Modified
Kjeldahl, Colorimetric)
• 1060ppm Soil
• 240ppm Woody debris
• Mineral Soil Soil (Bray-P)
• 154ppm 0-7cm
• 10ppm 7-15cm
• 6.2ppm 15-30cm
• 2.5ppm 30-45cm
• Ponette et al. 2001
• Tissue (Combustion, ICP)
• 35ppm Stemwood
• 35ppm Stembark
• 984ppm Needles
• Mineral Soil Soil (Dyer-P)
• 200ppm 0-10cm
• 44ppm 40-80cm

10. • Equations provided in Jenkins et al. 2003
• Equation form 2:
• 𝒍𝒏 𝒃𝒊𝒐𝒎𝒂𝒔𝒔 = 𝒂 + 𝒃 × 𝑫𝑩𝑯 + 𝑪 × 𝒍𝒏(𝑫𝑩𝑯 𝒅)
• Equation form 4:
• 𝒃𝒊𝒐𝒎𝒂𝒔𝒔 = 𝒂 + 𝒃 × 𝑫𝑩𝑯 + 𝒄 × 𝑫𝑩𝑯 𝒅
• “a”, “b”, “c”, and “d” are different equation
parameters
• Took the mean output of four different equations for
each tissue type.

11. Total P
(ppm)
Standard
Deviation
Mean
Estimated
Biomass
(kg/ha)
Mean Total P
(kg P/ha)
Stem wood 18.86 ±7.52 97055 1.83
Stem bark 71.14 ±18.18 27046 1.92
Foliage 1342.30 ±337.62 3204 6.93
Soil O-horizon 710.84 ±297.74 2518 17.90

12. Mean
Bioavailable
P (ppm)
Standard
Deviation
Estimated g
P/.02m3
5 cm 415.35 ±256.67 6.08
15 cm 322.47 ±448.04 4.12
25 cm 167.15 ±238.93 3.23
50 cm 63.99 ±69.71 2.11
100 cm 43.79 ±39.86 0.29

13. Results show significant positive correlations between wood P and DBH (p=.0113) and bark P and DBH (p=.0200)
y = 0.8986x + 16.07
R² = 0.562
0
10
20
30
40
50
60
70
80
90
100
0 50 100
Bark P vs DBH
Bark P vs DBH
Linear (Bark P
vs DBH)
y = 0.3874x - 4.4693
R² = 0.5729
0
5
10
15
20
25
30
35
0 50 100
Wood P vs DBH
Wood P vs DBH
Linear (Wood P
vs DBH)

14. y = 154.58x - 97.668
R² = 0.937
-20
0
20
40
60
80
100
120
0 0.5 1 1.5
Depth(cm)
Mean Soil Density (g/cm3)
Mean Soil Density vs Depth
Mean Soil Density
(g/cm^3) vs Depth
(cm)
Linear (Mean Soil
Density (g/cm^3)
vs Depth (cm))
y = -35.92ln(x) + 217.62
R² = 0.8653
y = -0.1977x + 79.052
R² = 0.7137
-20
0
20
40
60
80
100
120
0 200 400 600
MeanPlantAvailableP(ppm)
Depth (cm)
Mean P vs Depth
Mean P vs
Depth
Log. (Mean P
vs Depth)
0
20
40
60
80
100
120
0 100 200 300 400 500 600
Depth(cm)
Estimated Soil Plant AvailableP (ppm)
0
20
40
60
80
100
120
-100 0 100 200 300 400
Depth(cm)
Estimated Soil Plant AvailableP (ppm)
Estimated Total = 1157kg/ha Estimated Total = 1343kg/ha

15. • Literature comparison
• Bark and needle concentrations very consistent with prior measurements
• O-horizon concentrations lower than expected, possibly due to
methodological differences
• Wood concentrations lower than expected
• Old-growth Douglas-fir forests and P sequestration
• 3.7kg/ha, or 0.32% of estimated measured P pool, removed in a
stem-only clear-cut harvest.
• These results are consistent with predictions made using computer modeling
in Blanco 2012.
• Loss of P through slash decomposition and runoff
• Further Studies
• Kjeldahl instead of EPA 3050b
• K, Ca, Mg
• Greater Sample Size
• Use of an O2 DRC

16. • We would like to thank Carri, Abir, and Clyde for their
guidance, feedback, and patience throughout the year.
• Special thanks to Jenna and Sina for all the help with
methods, instrumentation, and equipment
• Kaile and the rest of the SSC staff

17. • J. Jenkins, D. Chojnacky, L. Heath, R. Birdsey. 2003. Comprehensive Database of Diameter-
based Biomass Regression for North American Tree Species. USDA Forest Service,
Northeastern Research Station. GTR-NE-319
• C. Federer, J. Hornbeck, L. Tritton, C. Martin, R. Pierce. 1989. Long-term depletion of
calcium other nutrients in eastern US forests. Environmental Management 13(5), pp. 593-601
• J. Blanco. 2012. Forests may need centuries to recover their original productivity after
continuous intensive management: An example from Douglas-fir stands. Science of the
Total Environment 437, pp. 91-103
• Q. Ponette, J. Ranger, J. Ottorini, E. Ulrich. 2001. Aboveground biomass and nutrient
content of five Douglas-fir stands in France. Forest Ecology and Management 142, pp. 109-
127
• J. Compton, D. Cole. 1998. Phosphorus Cycling and Soil P Fractions in Douglas-Fir and Red
Alder Stands. Forest Ecology and Management 110, pp. 101-112.