United States

Department of

Agriculture

Forest Service

Pacific Northwest

Research Station

Research Paper

PNW-RP-569

November 2006

Laminated Root Rot in a Western

Washington Plantation: 8-Year

Mortality and Growth of DouglasFir as Related to Infected Stumps,

Tree Density, and Fertilization

Richard E. Miller, Timothy B. Harrington, Walter G. Thies,

and Jeff Madsen
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Authors

Richard E. Miller is an emeritus soil scientist; Timothy B. Harrington is a

research forester, U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, Forestry Sciences Laboratory, 3625 93rd Avenue SE, Olympia WA 98512; Walter G. Thies is a principal plant pathologist, U.S Department of

Agriculture, Forest Service, Pacific Northwest Research Station, 3200 SW Jefferson

Way, Corvallis, OR 97331; and Jeff Madsen, formerly a silviculturist with The

Campbell Group, LLC, is currently a forestry manager with Port Blakely Tree

Farms, LP, 8133 River Drive SE, Tumwater, WA 98501.

Cover photo

Effects of tree mortality from laminated root rot and other causes are evident in this

landscape view of the 12-year-old Douglas-fir plantation at Voight Creek.

All Photos by Tim Harrington
Abstract

Miller, Richard E.; Harrington, Timothy B.; Thies, Walter G.; Madsen,

Jeff. 2006. Laminated root rot in a western Washington plantation: 8-year

mortality and growth of Douglas-fir as related to infected stumps, tree density,

and fertilization. Res. Pap. PNW-RP-569. Portland, OR: U.S. Department of

Agriculture, Forest Service, Pacific Northwest Research Station. 37 p.

A 4-year-old Douglas-fir plantation in the western Washington Cascades was

monitored for 8 years after fertilization with potassium (K), nitrogen (N), and K+N

to determine fertilizer effects on rates of mortality from laminated root rot (LRR)

and other causes relative to a nonfertilized control. Each element was applied at a

rate of 300 lb/acre on and around 0.2-acre plots replicated seven times in a randomized complete block design. Cumulative mortality from LRR did not differ significantly among fertilizer treatments, and losses were strongly related to density of

infected stumps from the previous stand (r2

 = 0.74). Mortality from disease and

other sources accelerated during the 8 years of monitoring. Average tree growth

and stand volume were greatest in treatment N and were reduced where N was

combined with K. Continued monitoring is needed to identify potential longer

term effects of the fertilizer treatments on susceptibility of Douglas-fir to LRR and

Armillaria spp.

Summary

Laminated root rot (LRR) is the most damaging disease of young-growth Douglasfir (Pseudotsuga menziesii (Mirb.) Franco) in the Pacific Northwest. Laminated root

rot is caused by the fungus, Phellinus weirii (Murr.) Gilb., which survives for 50

years or more in roots after infected Douglas-fir are harvested. Successive stands

can be infected as new roots contact infected wood from the previous stand. Without

removing stumps, changing species, or increasing spacing among potential host

trees, progressively more diseased area can develop in successive rotations. Some

research suggests that application of nitrogen (N) fertilizer may increase incidence

of some tree diseases and pest insects, but that application of potassium (K) fertilizer may reduce disease impacts.

Our study, started in a 4-year-old coast Douglas-fir plantation, is designed to

compare the effects of fertilization with N and K (alone or in combination) on tree

mortality and growth. The study site is located 7 mi east of Orting, Washington.

Soils include one type derived from recessional outwash sand and two types from

nonsorted basal moraine from the last continental glacier. The previous 70-year-old
Douglas-fir stand was harvested in 1993. Density and size of P. weirii-infected

stumps from that stand were evaluated on each of 28, 0.2-acre plots and a surrounding 10-ft-wide buffer, and the plots were then grouped into seven blocks of four

plots each according to their potential for P. weirii infection, estimated as inoculum

index (I.I.). One of the following four treatments was randomly assigned to one

plot per block: 300 lb elemental K/acre (treatment K, applied as potassium chloride), 300 lb elemental N/acre (treatment N, applied as urea), 300 lb K/acre plus

300 lb N/acre (treatment K+N), and a nonfertilized control. Fertilizer treatments

were applied in March 1998. The experimental design is a randomized complete

block with four fertilizer treatments replicated among the seven blocks. Tree mortality from LRR and other sources was monitored annually for 8 years, and tree

size and growth were measured in the first and sixth years after fertilization.

Inoculum index did not differ significantly among soil types, despite their

differences in slope percentage and gravel-cobble content. Among the 18 plots

with infected stumps, cumulative 8-year mortality from LRR had a positive linear

relationship with both I.I. (r2 = 0.53) and density of LRR-infected stumps per acre

(r2 = 0.74). Cumulative tree mortality from LRR or Armillaria spp. did not differ

among fertilizer treatments in the 8 years of monitoring. Cumulative mortality from

other causes, however, averaged 15 trees per acre (TPA) greater in treatment K+N

than in treatment N. We suspect excess of potassium or chloride ions in the soil

solution may be responsible.

Relations among mean 100-needle weight and N and K concentration and

content of foliage collected 6 months after fertilization were examined through

graphical vector analysis. From this we infer that N fertilization offset growthlimiting N-status at this site and that K-fertilization resulted in excess K and toxic

effects. This suspected toxicity may explain why 10-year-old trees in K-fertilized

plots are shorter than those in nonfertilized plots. Conversely, trees in N-fertilized

plots are taller and have greater stand basal areas and volumes than those in

nonfertilized plots. Although an average 62 TPA died by the 12th year after planting,

plantation stocking remained satisfactory at an average density of 390 TPA and did

not differ among the fertilizer treatments. Longer term observations are needed to

assess the future continued effects of fertilization on tree mortality and growth.
Contents

1 Introduction

1 Potential Effects of Fertilization

4 Objectives

4 Methods

4 The Experimental Area

7 Plot Installation

7 The Laminated Root Rot Survey to Determine Inoculum Index

8 Tree Tagging and Density Adjustments

9 Fertilizer Treatments and Treatment Assignment

10 Fertilization

10 Tree Measurement and Laminated Root Rot Status

11 Analysis of Foliage Collected After Year 1

12 Experimental Design and Analysis

14 Results

14 Prethinning Stand Density and Tree Losses From Laminated Root Rot,

by Innoculum Index

14 Inoculum Index by Soil Type

15 Postthinning Stand Density by Soil Type and Subsequent Fertilizer Treatments

15 Initial Mean Height by Soil type

16 Foliar Analysis

16 Tree Losses From Laminated Root Rot After Fertilization

20 Tree and Stand From Armillaria

21 Tree Losses From Other Agents

22 Cumulative Losses and Residual Trees Per Acre

23 Tree and Stand Growth

26 Discussion

26 Laminated Root Rot in Preceding Stand

26 Laminated Root Rot in Current Plantation

27 Foliage Indicators

29 Tree Mortality and Growth Responses to Fertilization

32 Design Considerations

33 Conclusions

34 Acknowledgments

34 Metric Equivalents

34 Literature Cited
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Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

Introduction

The fungus, Phellinus weirii (Murr.) Gilb., causes laminated root rot (LRR), which

is the most damaging disease of young-growth Douglas-fir (Pseudotsuga menziesii

(Mirb.) Franco) in the Pacific Northwest (Childs and Shea 1967). A survey of

nonfederal forest land in northwestern Oregon found LRR to occur on 12 percent

of the land (Gedney 1981). Goheen and Hansen (1993) later estimated that LRR

occurs on 5 percent of the area occupied by Douglas-fir and losses approach 50

percent on the affected areas. Because the fungus survives for 50 or more years in

infected roots and stumps of harvested trees (Childs 1963, Hansen 1976), successive stands of Douglas-fir can be infected as new roots contact infected wood from

the previous stand.

On sandy soils and gentle slopes, push-falling or stump removal is recommended to isolate infected stumps and trees (Thies and Sturrock 1995). Their other

mitigative prescriptions include planting or retaining P. weirii-resistant conifers,

e.g., western redcedar (Thuja plicata Donn. ex D. Don) or ponderosa pine (Pinus

ponderosa Dougl. ex Laws. var. ponderosa) or immune species (hardwoods). To

minimize root contact between infected and healthy Douglas-fir trees, Thies and

Sturrock (1995) recommended spacing Douglas-fir at least 13 ft apart (about 260

trees/acre) when precommercial thinning on deep, well-drained soils. “This strategy

is less likely to be successful where soil conditions encourage a shallow, spreading

root habit” (p. 25). Without mitigative measures (such as removing stumps, changing species, or increasing spacing between highly susceptible Douglas-fir), P. weirii

in residual stumps and roots will infect trees in the replacement stand and result in

progressively more diseased area in successive rotations (Tkacz and Hansen 1982).

Potential Effects of Fertilization

Nitrogen-fertilization in interior forests—

Fertilizer trials east of the Cascade crest suggest that application of nitrogen

(N) may increase incidence of some tree diseases and pest insects, but that

application of potassium (K) may reduce disease.

• In the initial fertilizer trials, weak response of Rocky Mountain Douglas-fir

(Pseudotsuga menziesii var. glauca (Beissn.) Franco) stands to N fertilization was related to low concentration of K in foliage. Specifically, in trials

on soils derived from granitic and metamorphic parent materials, amount

and duration of growth response to N was small, and the 400 lb N/acre

dosage produced much less response than the 200 lb dosage because

Successive stands

of Douglas-fir can

be infected as new

roots contact infected wood from

the previous stand.
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RESEARCH PAPER PNW-RP-569

mortality was greater (Mika and Moore 1990). Of particular concern is

mortality from Armillaria root disease (Armillaria ostoyae (Romagnesi)

Herink) that, like P. weirii, spreads primarily by root contact.

• Rate of Douglas-fir root infection by A. ostoyae is correlated closely with

the ratio of phenolic compounds to sugar compounds in roots. Ratios less

than about 15 favor Armillaria spp. infection in Rocky Mountain Douglasfir (Entry and others 1991). Phenolics are considered plant-defense compounds, but sugar is food for Armillaria (Wargo 1980). Trees fertilized with

N (200 lb N/acre) exhibited a lower ratio as a result of decreasing concentration of phenolics (Entry and others 1991). This is consistent with Shigo

(1973) who claimed that nitrogenous fertilizers reduce production of

phenols in plant tissue, thereby lowering resistance to infection by

pathogenic fungi.

• Large dosage of K (with either small or large dosage of N fertilizer)

increases the phenolic/sugar ratio and also tannin concentrations in roots of

potted seedlings of interior Douglas-fir (Shaw and others 1998). Form of K

in the nutrient solutions was not specified.

Potassium fertilization and agricultural experience—

Research results in east-side forests are consistent with general relationships between

K and agricultural plant health (Perrenoud 1990). Generally K tends to improve

plant health, relative to fungal and bacterial diseases.

Nitrogen fertilization in coast Douglas-fir stands—

Knowing the consequences of N fertilizer for susceptibility of Douglas-fir to

P. weirii is critical because N fertilizer has been conventionally used in recent

decades to improve growth of coast Douglas-fir (Pseudotsuga menziesii (Mirb.)

Franco var. menziesii). The usual prescription of 200 lb N/acre as urea increases

growth in established stands in about 70 percent of field trials in western Oregon,

Washington, and British Columbia (Chappell and others 1992). Doubling this

dosage to 400 lb N/acre provides additional increases in stand growth, in part,

because duration of response is extended (Miller and others 1986). Although rates

of Douglas-fir mortality in established stands often are accelerated by N fertilization, this has been attributed to accelerated growth that intensifies tree-to-tree

competition and suppression.

Increased tree mortality from LRR after N-fertilization of established coast

Douglas-fir stands has not been reported, possibly because potential study areas with

Armillaria root disease, like P. weirii,

spreads primarily

by root contact.
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Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

symptoms of LRR are avoided and trials with high incidence of damage or disease

are usually abandoned as atypical and of random occurrence. Nor has N fertilization

reduced LRR-losses in established stands. The 2-year results after localized fertilization with 400, 1,000, or 2,000 lb N/acre of individual Douglas-fir in a 26-year-old

plantation at Shawnigan Lake, British Columbia, were reported by Wallis and

Reynolds (1974). These large dosages of N as urea failed to cause a visible degradation of P. weirii mycelium growing on the bark in vivo. All cultures from infected

roots were viable. After fertilization, infected trees averaged about half as much

basal area growth as noninfected trees, but a higher percentage of fertilized trees

died. We surmise that the 1,000 and 2,000 lb N/acre-dosages may have created toxic

effects from pH changes (Otchere-Boateng and Ballard 1978) associated with a high

concentration of ions in the soil solution.

A series of investigations in recent decades tested N fertilization of newly

planted trees to reduce mortality of coast Douglas-fir from LRR. Having documented lower incidence of Douglas-fir losses where this species was associated with

red alder (Alnus rubra Bong.), and where total N and nitrate-N concentrations are

characteristically greater, Nelson (1970) reported that survival of LRR was reduced

when P. weirii-infected wood was buried in N-enhanced soil. Subsequently, large

dosages of ammonium nitrate fertilizer were combined with stump removal at five

test locations in Oregon and Washington. Although growth of planted Douglas-fir at

some locations was enhanced by N fertilization (0, 300, 600, 1,200 lb N/acre),

losses from LRR were not affected during the 23 to 27 years after fertilization

(Thies and Westlind 2005). Losses from non-LRR agents were not reported, including possible losses after large doses of a highly soluble N fertilizer.

Additional research information is needed to identify the effects of N and K

fertilization on susceptibility of Douglas-fir trees to P. weirii and other diseases.

Such research should attempt to attribute mortality to specific agents and to adjust

for effects of local inoculum potential and tree density. In designing our study, we

speculated that above-average numbers of (1) Pw-infected stumps or (2) planted and

volunteer Douglas-fir seedlings could increase seedling and sapling losses from

LRR. We assumed that a high density of regenerating seedlings could increase the

likelihood of root contact with infected legacy wood and infected seedling roots. We

further assumed that seedling and sapling density (trees/acre, [TPA]) will also affect

mean tree size and stand yield per acre (basal area or volume). Thus, to isolate the

effects of fertilizer treatment, we needed to recognize, measure, and adjust for these

potentially confounding or masking influences.
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RESEARCH PAPER PNW-RP-569

Objectives

Our study in a young coast Douglas-fir plantation is designed to compare the

effects of fertilization with K and N (alone or in combination) on tree mortality

and tree growth. Based on a literature review, we posed several working

hypotheses:

1. Severity of LRR (i.e., concentration of inoculum) in a mature Douglas-fir stand

is a good predictor of incidence of LRR-caused mortality in the succeeding stand.

2. Addition of 300 lb K/acre as KCl, either alone or combined with 300 lb N/acre,

can reduce incidence of LRR-caused mortality.

3. Addition of 300 lb N/acre as urea can increase incidence of LRR-caused

mortality.

4. Fertilization can increase tree and stand growth.

Methods

Plots were installed in a 4-year-old plantation of coast Douglas-fir. Before fertilizers were applied, each plot was evaluated for its potential to develop LRR, arrayed

in order of that potential, and then separated into seven LRR inoculum concentration groups of four plots each. Different fertilizer treatments were randomly

assigned to three plots in each group; the fourth plot remained nonfertilized.

Tree mortality was monitored annually for 8 years; tree size was measured before

fertilization and in the first and sixth years after fertilization.

The Experimental Area

Location–

Our study area is located 7 mi east of Orting, Washington. Plots were installed in a

4-year-old plantation (1994) managed by the Campbell Group, LLC. Nearly half

of our study plots are located on the former Voight Creek experimental forest; the

remaining plots were located in the same plantation that extends beyond the original

experimental forest boundary. The USDA Forest Service’s Pacific Northwest

(PNW) Forest and Range Experiment Station (currently the PNW Research Station)

conducted silvicultural research on the experimental forest between 1947 and 1981.

Elevations range from 830 to 1,140 ft, and annual precipitation averages about 49

in with about 16 in falling during the growing season (April through September).

Snowfall is infrequent.
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Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

Soils–

Soils supporting the test plantation were derived from either outwash deposits

(stratified sand and gravel) or nonsorted basal moraine, both deposited by the last

continental glacier, the Vashon Stade of the Fraser glaciation (fig. 1). Soils were

originally mapped when the experimental forest was established and remapped in

greater detail as a cooperative project with the Soil Conservation Service (currently

the Natural Resource Conservation Service). Although site index (50-year base)

averaged about 117 ft in the experimental forest, our study area is located on the

lower - quality sands and gravels. Specific soil types are Barneston very gravelly

sandy loam, either on (1) 6- to 30-percent slopes1

 or (2) 30- to 60-percent slopes

and (3) Nargar sandy loam, 6- to 30-percent slopes. Most plots occupied only one

of these soil types (table 1).

Although mean potassium concentration in tree foliage was estimated on some

plots, the K-nutrient status of these soils was not determined before or after fertilization. Weathering of primary feldspar can provide K for cation-exchange sites,

but these immature coarse-textured soils have relatively small content of clay for

Figure 1—The Barneston soil series at Voight Creek, Washington, is formed on

unconsolidated glacial deposits (top several feet of this profile). Note the underlying

stratified outwash sand that is the parent material of soil type 3 (Nargar series).

1 Zulauf, A. S. 1982. Soil survey of Voight Creek Experimental Forest. Unpublished report

On file with: Forestry Sciences Laboratory, 3625 93rd Avenue SW, Olympia, WA 98512.
6

RESEARCH PAPER PNW-RP-569 Table 1—Plot information and treatment by block at Voight Creek, Washington, ordered within blocks by number of initially tagged trees Tagged Tagged Inoc. Douglas- Inoc. Douglas- Block Plota Soilb Index firc Other Cut All Fert.d Block Plota Soilb Index firc Other Cut All Fert.d – – – – – Trees per acre – – – – – – – – – –Trees per acre – – – – – 1 213 3 0 380 5 355 740 K 5 208 3 228 360 5 420 785 0 1 218 3 0 370 0 345 715 0 5 70* 3 475 380 10 320 710 K+N 1 15* 2 0 410 0 130 540 N 5 209 3 214 430 5 855 1,290 K 1 17* 2 0 470 0 290 760 K+N 5 19* 2/3 495 495 0 815 1,310 N

Mean 0 408 1 280 689 Mean 353 416 5 603 1,024

2 217 3 0 460 5 735 1,200 N 6 129* 3 1,168 415 0 425 840 N

2 111* 1 0 465 0 625 1,090 K 6 215 3 926 465 0 680 1,145 02 206 2 0 470 15 865 1,350 K+N 6 27* 2 956 380 0 35 415 K+N2 207 2 0 505 5 1,450 1,960 0 6 204 1/3 310 425 0 1,500 1,925 K

Mean 0 475 6 919 1,400 Mean 840 421 0 660 1,081

3 4* 2 0 520 10 775 1,305 0 7 29* 2 1,951 445 5 630 1,080 03 201 2 0 540 0 695 1,235 N 7 205 1 894 415 0 540 955 K3 202 1 0 570 15 95 680 K 7 221 2 1,389 435 0 810 1,245 N3 8* 3/1 0 590 5 1,545 2,140 K+N 7 40* 2 2,649 450 0 195 645 K+N

Mean 0 555 8 778 1,340 Mean 1,721 436 1 544 981

4 10* 3/1 41 430 0 1,065 1,495 K4 203 3 92 440 5 900 1,345 04 211 2 162 445 5 645 1,095 K+N4 216 3 282 480 0 545 1,025 N

Mean 144 449 3 789 1,240

a Plots with asterisks correspond to those installed in 1947-48 within the former Voight Creek Experimental Forest. The 200-series of plots were newly installed.b Soil numbers correspond to soil types identified in text; a few plots were located predominately on one soil type and a lesser portion on a second soil type: example 3/1.c After the first growing season the initial number of tagged trees changed slightly to reduce within-block differences in trees per acre.d 0 = no fertilizer.
7

Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

cation-exchange. We assume that K is readily leached from these coarse-textured,

clay-poor soils and that relatively small amounts of K are available to plants.

Consequently, we applied a relatively heavy dosage of K and fertilized in spring to

reduce leaching.

Plot Installation

Plot design consists of 0.20-acre (0.08-ha) circular tree-measurement plots centered

within 0.50-acre (0.20-ha) circular treatment plots. Plot centers were spaced at

least 180 ft apart to ensure that measurement trees were not affected by the treatment of adjacent plots. Of the 28 plots, 12 corresponded to original, mechanically

spaced plots in a thinning study at the Voight Creek Experimental Forest. The

remaining 16 plots were also systematically located, but with some adjustment to

ensure that each plot sampled uniform topography and soil.

The Laminated Root Rot Survey to Determine Inoculum Index

The previous 70-year-old Douglas-fir stand on the study site was harvested in 1993.

Stumps located within 62.7 ft of tree measurement plot centers (i.e., 52.7-ft plot

radius plus an additional 10 ft) were examined in summer 1997 for the stain typical

of laminated root rot (Thies and Sturrock 1995) (fig. 2). To facilitate examination

for LRR, stumps were cut near ground level on the uphill side. To assure that

inoculum remained undisturbed, we avoided excavation. Stain on fresh cut stumps

appears in the outer heartwood and is above the point of attachment of major

infected roots (Thies and Sturrock 1995). The stain appears as spots or broad

bands. We assumed that the total root biomass that was infected was proportional

to the total stump circumference showing typical stain.

Stumps with LRR were identified, and their diameter and percentage of

stump circumference infected (CI) were recorded. Locations of infected stumps

were mapped to enable future spatial analysis of the pattern of mortality in the

new plantation. We assumed that the amount of inoculum was proportional to the

infected biomass of the stump and belowground roots. A regression equation was

used to estimate belowground biomass of each stump (Thies and Cunningham

1996):

ln(LRB) = -4.38 + 2.41 ln(DSH)

where ln(LRB) is the natural logarithm of large-root biomass (kg of roots 1.0 cm

[0.4 in] and larger in diameter), and DSH is the diameter at stump height (in cm
8

RESEARCH PAPER PNW-RP-569

measured 15 cm [5.9 in] above mean ground level). Note that the preceding

regression was based on trees found in Oregon; no other data are available.

For each stump, an index of the amount of inoculum present was calculated as:

Inoculum Index (I.I.) = LRB x percent CI/1,000 .

Summing the I.I. of each infected stump on a plot provided the plot I.I. Additionally, assuming that some roots from trees near the measurement plot extended

into the plot, we added 25 percent of the estimated infected biomass of stumps

located within 10 ft of measurement plot boundaries.

Tree Tagging and Density Adjustments

Tree tagging–

Potential crop trees were identified with numbered tags; nearly all were planted

Douglas-fir. Tags were wired to a major branch, then eventually moved and tethered at breast height (4.5 ft above ground). Tree numbering started north of the

plot center and proceeded in clockwise direction within approximate 40° sectors.

Number of Douglas-fir tagged at plot establishment ranged from 360 to 590 TPA

(table 1). Additionally, 0 to 15 TPA of western redcedar or western hemlock Tsuga

Figure 2—Stump of tree from previous 70-year-old Douglas-fir stand showing the stain and

decomposed woody tissue associated with laminated root rot.
9

Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

heterophylla (Raf.) Sarg.) were tagged. Tagged crop trees were considered the

starting stand for inventorying future losses from LRR or other causes.

Density adjustment–

Although originally planted at an average density of about 430 TPA, plots in the

4-year-old plantation differed greatly in numbers of volunteers (table 1); nearly all

were Douglas-fir. Initially (1997), total TPA among the 28 plots ranged from 415

to 2,140 per acre. Of these TPA, 8 percent (plot 27) to 74 percent (plot 207) were

cut to reduce variability in TPA among plots. We assumed that future tree mortality

from LRR would be proportional to stand density, and that large differences in

stand density also would influence tree growth. Consequently, to control Douglas-fir

density within preset limits, we removed excess conifers and all N-fixing red alder

from each plot and the surrounding 20-ft buffer in four stages:

1. At plot establishment (summer 1997), we tallied and then pulled or cut any tree

that was within 5 ft of a larger, presumably planted tree likely to be retained as a

crop tree.

2. After tagging potential crop trees and assigning plots to experimental blocks

(four plots each), we further reduced large differences in TPA among plots in each

block, either by cutting surplus trees on most plots or transplanting seedlings into

gaps in a few plots to attain at least a 15-ft spacing between trees. Transplanted

trees were tagged and tallied as crop trees.

3. After the first growing season (following fertilization in March 1998), we again

adjusted stocking by cutting a few more surplus trees in some plots.

4. After the sixth growing season (Fall 2003) after fertilization, we made a final

adjustment of tree numbers to limit within-block differences to <10 percent of

block means. We also cut some tagged trees on some plots.

Fertilizer Treatments and Treatment Assignment

The four fertilizer treatments are: (1) K—300 lb elemental K/acre; (2) N-300 lb

elemental N/acre; (3) K+N—300 lb K/acre plus 300 lb N/acre; (4) 0–nonfertilized

control. These fertilizer treatments were assigned randomly within each block of

four plots. This was accomplished by arraying the 28 plots in order of increasing

I.I., then separating this array into seven groups (blocks) of four plots each. This

initial sorting ensures that each fertilizer treatment sampled the full range of I.I.

present in these 28 plots (table 1). Because of incorrect assignment of I.I. to two
10

RESEARCH PAPER PNW-RP-569

plots and incorrect application of fertilizer to one plot, final treatment assignment

differed from initial planned assignment. This accidental mix-up changed the order

of I.I.

Fertilization

Agricultural-grade potassium chloride (50 percent K) and granular urea (46 percent N) were applied in March 1998 to designated plots. Each 0.5-acre treatment

plot was divided into 10 equal sectors, and 10 percent of the fertilizer for that plot

was spread evenly on each sector. Weather was overcast, cool, and often drizzling

during and for several days after application; volatilization of urea was unlikely.

Tree Measurement and Laminated Root Rot Status

At plot establishment, trees recorded as dead from LRR probably died in the

previous 2 years (in the third and fourth growing seasons after planting). Hence,

this initial count of LRR-killed trees (after the fourth growing season) may have

missed some mortality from the first two seasons after planting. After fertilization,

tagged trees were observed annually (1998 through 2005) for mortality, and losses

from Armillaria spp. were noted. We did not attempt to identify which of the

several possible species of Armillaria were involved. We recorded azimuth and

distance from plot center to each tree killed by LRR. Forest pathologists from

PNW Research Station and Washington State Department of Natural Resources

assisted in the identification of the mortality agents for dead trees (fig. 3).

Tree heights were measured after the 1998 and 2003 growing seasons (years 1

and 6 after fertilization). In year 1, height of all tagged trees was measured but in

year 6, only 30 randomly selected trees per plot were measured. Prefertilization

height (1997) was measured concurrently in 1998 by measuring to the whorl of

branches initiated after the 1997 growing season. Tree diameter at breast height

(d.b.h. or 4.5 ft above ground) was measured after the 2003 growing season (year 6

after fertilization). Height was measured to the nearest 0.1 ft with a telescopic pole

or Haglof vertex hypsometer2

 to nearest 0.3 ft, and d.b.h. was measured to nearest

0.05 in with a diameter tape. Heights of nonmeasured trees were estimated by a

height-diameter regression equation developed for each plot and based on measured

d.b.h. Stand volume was calculated for each plot by entering tree height and d.b.h.

data into a general volume equation (Bruce and DeMars 1974). Calculations of

2 The use of trade or firm names in this publication is for reader information and does not

imply endorsement by the U.S. Department of Agriculture of any product or service.
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Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

mean stand characteristics were based on trees surviving through 2003. Trees

identified as missing in 2003 were eliminated from all calculations because the

cause of mortality could not be determined.

Analysis of Foliage Collected After Year 1

Foliage samples were collected in fall after the 1998 growing season (6 months

after fertilization). Three of the seven plots representing each of the fertilization

treatments were selected at random to ensure sampling the entire study area.

Two current-year twigs from the second whorl of branches were clipped from

14 systematically selected trees per plot. On the following day, the 28 twigs from

each plot were composited and dried for about 12 hours in a forced-draft oven at

70 °C (158 °F). Buds were separated from the twigs before drying. The dried

needles were easily stripped from the twigs and were thoroughly mixed before

quartering to reduce sample volume; surplus needles were reserved. The reduced

sample was again quartered and opposite quarters placed in separate plastic bags

labeled subsample A or B for each plot. From each bag, 100 whole needles were

selected, redried at 105 °C (221 °F), and weighed after cooling. This provided

two samples of 100-needle weight for each plot. Remaining needles in the two

subsamples for each plot were sent to Oregon State University (Central Analytical

Laboratory, Department of Crop and Soil Science) for grinding and chemical

analysis without replication. This facility uses standard analytical methods for

agricultural laboratories (Gavlak and others 1994). Air-dried samples are ground

Figure 3—Each dead seedling was partially excavated to identify the cause

of mortality.
12

RESEARCH PAPER PNW-RP-569

or pulverized to pass a 40-mesh screen and subsamples removed for determination

of dry matter content. About 250 mg (0.088 oz) of sample is used to analyze K plus

11 other elements simultaneously by using nitric acid/hydrogen peroxide digestion

(Kingston and Jassie 1986, Sah and Miller 1992) in conjunction with microwave

heating in closed Teflon® vessels. Concentrations of the elements in the digest are

determined by atomic absorption spectrometry or inductively coupled plasma

atomic emissions spectroscopy. Nitrogen is determined with about 150 mg (0.053

oz) of tissue by using a resistance furnace and a thermal conductivity detector as

described by Sweeny (1989). Concentrations of all elements are calculated on a dry

matter basis.

Experimental Design and Analysis

All statistical analyses were conducted in SAS (SAS Institute Inc. 1999) by using a

test criterion of α = 0.10 to judge statistical significance. The experimental design

is a randomized, complete block with four fertilizer treatments replicated seven

times. Experimental units are 0.20-acre circular measurement plots. Four plots

compose each of seven blocks; one of four fertilizer treatments was randomly

assigned to each plot. Our blocking on the basis of I.I. should further ensure that

all treatments had equal chance of sampling comparable intensities of I.I. The 28

plots were located among three soil types but not in equal numbers. Inoculum

index (I.I.) was estimated for each plot after stumps were surveyed in summer

1997 for incidence and severity of LRR (table 1). Our intent was to evaluate I.I. in

the previous, naturally regenerated stand as a predictor of LRR-caused mortality in

the subsequent plantation.

Hypothesis 1 (Incidence of Phellinus in stumps of the original stand and

characteristics of the 4-year-old plantation)–

Conventional correlation analysis was used to evaluate relations between Douglas-fir

mortality from LRR, and TPA in the 4-year-old plantation before fertilization. The

dependent variable was TPA killed by LRR as initially tallied in summer 1997.

In addition, we used analysis of variance (ANOVA) to test for differences in I.I.

among the three soil types in the study area. We assumed that differences in I.I.

among the three soil types would support earlier speculation that risk of LRR was

related to soil characteristics.

Regression analysis was used to test the relation of cumulative 8-year mortality

from LRR after fertilization versus either I.I. or density of P. weiri-infected stumps
13

Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

(stumps/acre). Indicator variables were specified in each model to enable testing of

separate intercepts and slopes for each fertilizer treatment with the extra-sums-ofsquares method (Neter and others 1989). To avoid inflating the coefficient of

determination (r2

), only those plots with LRR-caused mortality, P. weirii-infected

stumps, or both were used in the analysis (18 of 28 plots).

Hypotheses 2 and 3 (tree mortality related to K and N fertilizers)–

First-year (1998) and cumulative 8-year (1998 through 2005) mortality (TPA)

were analyzed by analysis of covariance (ANCOVA) by using 1997 TPA (tagged

trees) as the covariate. With seven blocks of four plots each, sources of variation

in the ANCOVA were:

Source d.f.

Covariate (1997 TPA) 1

Block effects (I.I.) 6

Orthogonal comparisons: (3)

0 and K vs. N and K + N 1

0 vs. K 1

N vs. K + N 1

Error 17

Total (7 X 4) -1 27

To test for treatment effects over time on cumulative yearly mortality from

LRR, Armillaria spp., and other causes, and on current TPA, yearly values for

each variable were subjected to a repeated-measures ANCOVA in SAS procedure

MIXED. The covariate, TPA 1997, was included in each analysis to adjust for

initial postthinning differences in TPA. The analyses were conducted with maximum likelihood estimation assuming an autoregressive covariance structure to

account for time series trends.

Hypothesis 4 (tree growth related to K and N fertilizers)–

Average height of surviving Douglas-fir in years 1 and 6 after fertilization and also

6-year periodic annual height increment (PAI; 1998-2003) of survivors were

analyzed by ANCOVA using average height of tagged trees at fertilization (1997

HT) as the covariate. Average d.b.h. (calculated as quadratic mean diameter =

diameter of the tree of mean basal area), stand basal area, and volume 6 years after

fertilization were analyzed by ANCOVA also using 1997 height as the covariate.

Except for differences in the covariate used, the ANCOVA tables for tree growth

were identical to that for cumulative mortality.
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RESEARCH PAPER PNW-RP-569

Results

Prethinning Stand Density and Tree Losses From Laminated Root

Rot, by Inoculum Index

Douglas-fir density before thinning averaged 1,108 TPA and it was not significantly correlated with I.I. (r = -0.26, table 2). Likewise, early mortality from LRR

was not significantly correlated with initial TPA (r = 0.22).

Only 4 of the 28 plots contained LRR-killed seedlings at plot establishment in

1997 (4 years after planting). Number of LRR-killed trees tallied at plot establishment ranged from 0 to 30 TPA, and averaged 2.1 TPA among the 28 plots (table 2).

This early mortality was related positively to I.I.; the correlation coefficient, r, was

0.33 and statistically significant (table 2).

Inoculum Index by Soil Type

In the preharvest stand, I.I. on soil type 2 (I.I. = 634) averaged about 2.2-fold that

on soil type 3 (I.I. = 286); these means were not significantly different (p = 0.42,

table 3).

Table 2—Correlation matrix and mean values of selected variables before fertilization

at Voight Creek, Washington, per-acre basis

Douglas-fir density Prefertilization

Initial Postthinning mortality (trees

Inoculum density density (1997 per acre) from

Variable index (total) trees per acre) laminated root rot

– – – – – Correlation coefficient (r)a – – – – –

Inoculum index

Initial density -0.264

Postthinning density -.203 0.509

Prefertilization mortality

from laminated root rot .328 .218 -0.046

Index – – – – – – – –Trees per acre – – – – – – – –

Mean 437 1,108 451 2.1

CVb 153 38 13 301

a

 With sample size of 28 (26 d.f.), the sample correlation coefficient, r, must be ≥ 0.317 for statistical significance at α = 0.10, and ≥ 0.375 at α = 0.05. b

 CV = coefficient of variation = (standard deviation/mean) x 100.
15

Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

Postthinning Stand Density by Soil Type and Subsequent

Fertilizer Treatments

Although one plot on each soil before thinning was clearly overstocked (about

2,000 TPA; table 1), stand density of Douglas-fir after initial thinning and before

fertilization did not differ significantly among the three soils (p = 0.13; statistical

test not displayed). Initial stand density of Douglas-fir after thinning averaged 451

TPA (table 2) and also did not differ significantly among the subsequently assigned

fertilizer treatments (p = 0.14; statistical test not displayed). We infer that future

effects of fertilizer treatments were not likely to be confounded or masked by

initially greater numbers of P. weirii-susceptible Douglas-fir among the fertilizer

treatments.

Initial Mean Height by Soil Type

As anticipated, mean height of Douglas-fir before fertilization averaged greater

(about 30 percent) on soil 3 (Nargar sandy loam) than on soils 1 and 2 (Barneston

very gravelly sandy loam).

Table 3—Unbalanced analysis of variance of inoculum index and mean 1997 Douglas-fir

height among soil types before fertilization at Voight Creek, Washington

Inoculum index 1997 height

Source of variation Degrees of freedom Mean squares p Mean squares p

Soil type 2 406,379 0.420 3.557 <0.001

Error 25 452,474 0.307

Total 27

Means (and standard errors)

Na Inoculum index 1997 height

 Feet

Soil type:

1 4 301 (336) 3.2 (0.3)

2 12 634 (194) 3.3 (0.2)

3 12 286 (194) 4.3 (0.2)

a

 N count equals the number of plots on specified soil type.
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RESEARCH PAPER PNW-RP-569

Foliar Analysis

Needle weight–

Although the mean weight of 100 needles averaged about 12 percent less for

treatment K than for the nonfertilized treatment, the difference was nonsignificant

(p = 0.17, table 4). An increase of about 11 percent in mean needle weight after N

fertilization also was nonsignificant (p = 0.13).

N and K concentration–

The four fertilizer treatments differed in mean N and K concentrations in Douglasfir foliage collected in October after the first growing season after fertilization

(table 4). Nitrogen concentration averaged about 40 percent greater in the presence versus absence of N fertilizer (treatments N and K+N vs. treatments 0

[non-fertilized] and K). Although fertilization with 300 lb K/acre increased foliar

K-concentrations by 12 percent over that of nonfertilized trees, this difference was

not significant (p = 0.30). In contrast, N fertilization reduced foliar K concentration

in first-year needles by about 14 percent (p = 0.10).

N and K content–

Trees fertilized with N had needles that averaged 53 percent greater N content

(p = 0.002). Mean content of K in current foliage ranged from 4.8 to 5.1 mg/100

needles, and did not differ among treatments (p = 0.58).

Tree Losses From Laminated Root Rot After Fertilization

Relation to fertilization—

Douglas-fir losses from LRR continued on the four plots with initial losses from the

disease and commenced on half of the remaining 24 plots, including some where

I.I. = 0. Among the four treatments, mean cumulative 8-year mortality from LRR

ranged from 20 to 41 TPA (table 5). Initial tree density (tagged TPA in 1997) was

significant as a covariate in the ANCOVA for prefertilization mortality from LRR

(p = 0.028). Adjusted treatment means of TPA killed by LRR did not differ among

fertilizer treatments in the year before fertilization (as expected) nor in the first year

or the cumulative 8-year total after fertilization (table 5).

Relation to inoculum index—

Plots with the highest density of LRR-infected stumps in the original stand tended

to be those with the greatest numbers of trees killed by LRR (fig. 4). Cumulative

8-year mortality of Douglas-fir from LRR had positive, statistically significant

Nitrogen concentration averaged about

40 percent greater

in the presence

versus absence of

N fertilizer.

Among the four

treatments, mean

cumulative 8-year

mortality from LRR

ranged from 20 to

41 TPA.

Plots with the highest density of LRRinfected stumps in

the original stand

tended to be those

with the greatest

numbers of trees

killed by LRR.
17

Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

Table 4—Analysis of variance of needle attributes of Douglas-fir one growing season after fertilization at Voight Creek, Washington

Weight of 100

needles N percent K percent N content K content

Mean Mean Mean Mean Mean

Source of variation df squares p squares p squares p squares p squares pTreatmenta (3)

(1) 0 and K vs. N and K+N 1 0.010 0.133 0.816 <0.001 0.046 0.096 46.26 0.002 0.173 0.581

(2) 0 vs. K 1 .008 .173 .001 .802 .016 .296 1.94 .363 .009 .897(3) N vs. K+N 1 <.001 .842 .052 .146 <.001 .917 1.52 .419 <.001 .986

Error 8 .003 — .020 — .013 — 2.09 — .524 —Total 11Means (and standard errors)

Weight of 100

needles N percent K percent N content K content

Fertilizer treatment Weight Relativeb Percent Relative Percent Relative Weight Relative Weight Relative

Grams Milligrams Milligrams

0 0.60 100 1.32 100 0.85 100 7.95 100 5.08 100K .53 88 1.29 98 .95 112 6.81 86 5.00 98N .63 105 1.73 131 .77 91 10.81 136 4.80 94K+N .62 103 1.92 145 .78 92 11.81 149 4.79 94Standard error (pooled from

ANOVA) .03 — 0.08 — .07 — .83 — .42 —

a 0 = no fertilizer.b Relative, where 0 fertilization = 100
18

RESEARCH PAPER PNW-RP-569

Table 5—Analysis of covariance of initial (1997), first-year (1998), and cumulative (1998-2005)

Douglas-fir mortality (trees per acre) from laminated root rot at Voight Creek, Washington

Douglas-fir mortality

Prefertilization First year Cumulative

Mean Mean Mean

Source of variation df squares p squares p squares p

Blocks 6 58.7 0.151 73.3 0.051 6,146.6 0.002

Treatmenta (3)

(1) 0 and K vs. N and K+N 1 68.2 .162 3.4 .727 940.0 .367

(2) 0 vs. K 1 13.6 .522 42.8 .227 288.7 .614

(3) N vs. K+N 1 83.4 .124 4.0 .706 230.9 .652

TPAb 1 184.6 .028 64.3 .143 504.2 .506

Error 17 31.9 27.3 1,094.9

Total 27

Adjusted means and standard errors Douglas-fir mortality

Fertilizer treatmentb Prefertilization First year Cumulative

Trees per acre

0 0.0 2.5 20.4

K 1.5 6.0 29.5

N 6.2 3.0 32.8

K+N 1.3 4.1 40.9

Standard error (pooled

from ANOVA) 2.1 2.0 12.6

a

 0 = no fertilizer.

b Means for prefertilization mortality have been adjusted for prethinning density, and those for first-year and cumulative

mortality have been adjusted for postthinning density.
19

Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

relationships with both I.I. (r2 = 0.53) and density of LRR-infected stumps (r2 =

0.74) (fig. 4). We infer from the linear equation (y = 7.67 + 1.52 x) that in the

absence of visually detectable infected stumps at this location, about eight Douglasfir per acre died from LRR in years 4 to 12 after planting. About 1.5 additional

seedlings died per LRR-infected stump.

Regression intercepts and slopes for both relations did not differ significantly

among fertilizer treatments, indicating there were no significant differences in

cumulative mortality per unit of potential LRR infection. Proximity of a tree to

infected stumps may have increased the likelihood of its death from LRR, but

spatial relationships were not obvious on all plots (fig. 5).

Figure 4—Cumulative (1998-2003) mortality of Douglas-fir from laminated

root rot (LRR) as related to density of LRR-infected stumps of Douglas-fir

at Voight Creek, Washington. Only those plots with LRR-caused mortality,

LRR-infected stumps, or both are shown. 0 = no fertilizer.
20

RESEARCH PAPER PNW-RP-569

Tree Losses From Armillaria

On nonfertilized control plots, seedlings lost to Armillaria spp. in the 8 years after

fertilization averaged 34 TPA (table 6), 70 percent more than trees killed by LRR

(20 TPA, table 5). First-year mortality from Armillaria was significantly greater on

K-fertilized plots (2 TPA) than on control plots (0 TPA) (p = 0.09).

Figure 5—Relative spatial distribution of Douglas-fir killed by

laminated root rot (LRR) and of Douglas-fir stumps infected

with LRR at Voight Creek, Washington. Two plots (29 and 40)

illustrate the relative locations of mortality in plots with low and

high densities of infected stumps, respectively. Treatment 0 =

no fertilizer.

On nonfertilized

control plots,

seedlings lost to

Armillaria spp. in the

8 years after fertilization averaged

34 TPA.
21

Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

Cumulative losses from Armillaria spp. in the 8 years after fertilization were

fewer on N-fertilized plots but not significantly. Treatment means adjusted to a

common initial TPA, averaged 8 TPA on N-fertilized (N, K+N) plots vs. 25 TPA

on 0- and K-fertilized plots (p = 0.17, table 6).

Tree Losses From Other Agents

In year 1 and in the 8-year period after fertilization, cumulative mortality from

agents other than LRR and Armillaria was greater after K+N fertilization than after

N fertilization (table 7). “Other” agents included some losses from black-stain root

Table 6—Analysis of covariance of first-year (1998) and cumulative

(1998-2005) Douglas-fir mortality from Armillaria spp. at Voight Creek,

Washington

Douglas-fir mortality

First year Cumulative

Mean Mean

Source of variation df squares p squares p

Blocks 6 17.0 0.023 903.7 0.450

Treatmentsa (3)

(1) 0 and K vs. N and K+N 1 2.5 .493 1,830.0 .170

(2) 0 vs. K 1 16.5 .090 1,140.6 .274

(3) N vs. K+N 1 5.9 .298 96.7 .746

Trees per acreb 1 8.17 .222 484.0 .472

Error 17 5.1 893.6

Total 27

Adjusted means and standard errors Douglas-fir mortality

Fertilizer treatmentb First year Cumulative

Trees per acre

0 0 33.9

K 2.0 15.9

N .9 5.7

K+N 2.2 10.9

Standard error (pooled

from ANOVA) .9 11.4

a

 0 = no fertilizer

b

 Means for first-year and cumulative mortality have been adjusted for postthinning density

(1997 TPA).

Cumulative losses

from Armillaria spp.

in the 8 years after

fertilization were

fewer on N-fertilized

plots but not significantly.
22

RESEARCH PAPER PNW-RP-569

disease, caused by Leptographium wageneri, but most causes were not identifiable.

By year 8, plots treated with K+N averaged 23 TPA killed by “other” agents, compared to 8 TPA for N-only plots; the difference was significant (p = 0.05).

Cumulative Losses and Residual Trees per Acre

The fertilizer treatments did not have a detectable influence on cumulative

Douglas-fir mortality from LRR or Armillaria spp. over time (table 8). However,

cumulative mortality increased over time, especially that resulting from Armillaria

on nonfertilized plots (fig. 6). During each of the 8 years of monitoring, mortality

from other causes was greater after K+N fertilization than after N fertilization

(p = 0.04).

Table 7—Analysis of covariance of first-year (1998) and cumulative (1998-

2005) Douglas-fir mortality from other causes at Voight Creek, Washington

Douglas-fir mortality

First year Cumulative

Mean Mean

Source of variation df squares p squares p

Blocks 6 193.6 0.190 426.2 0.074

Treatmentsa (3)

(1) 0 and K vs. N and K+N 1 159.8 .257 35.1 .663

(2) 0 vs. K 1 217.5 .189 517.3 .107

(3) N vs. K+N 1 562.6 .042 773.7 .053

Trees per acreb 1 9.0 .785 3.1 .896

Error 17 116.3 178.6

Total 27

Adjusted means and standard errors Douglas-fir mortality

Fertilizer treatment First year Cumulative

Trees per acre

0 2.7 7.1

K 10.6 19.2

N 5.2 8.0

K+N 17.9 22.9

Standard error

(pooled from ANOVA) 4.1 5.1

a 0 = no fertilizer.

b

 Means for first-year and cumulative mortality have been adjusted for postthinning density (1997).

The fertilizer treatments did not have

a detectable influence on cumulative Douglas-fir

mortality from LRR

or Armillaria spp.

over time.
23

Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

After thinning and before fertilization, average TPA of Douglas-fir was similar

among the four fertilizer treatments (table 9). Despite subsequent losses from

disease and other agents in the subsequent 8 years, treatment, average tree density

in the 12-year-old plantation in 2005 did not differ significantly as a result of the

fertilizer treatments, ranging from 377 to 405 TPA (table 9). Total mortality of

tagged crop trees from all causes averaged only 62 TPA (-14 percent). By the 12th

year after planting, stocking remained satisfactory at an average density of 390

TPA.

Tree and Stand Growth

Tree size and growth–

As anticipated, tree height in 1997 before fertilization did not differ among the

pending fertilizer treatments (table 9). After covariance adjustment to a common

height before fertilization, both average height growth and total height in 1998

were significantly greater in the presence versus absence of N fertilization (p =

0.01). Growth after N fertilizer was significantly greater for height in 2003, height

PAI from 1998 to 2003, and d.b.h. in 2003. Among these tree-size variables, the

Table 8—Repeated-measures analysis of covariance of cumulative yearly Douglas-fir mortality (trees per

acre) in 1998-2005 from laminated root rot, Armillaria, and other causes, and surviving TPA at Voight

Creek, Washington

Laminated root rot Armillaria Othera Surviving TPA

Source of variation df Fb p F p FpF p

Treatmentsc (3)

(1) 0 and K vs. N and K+N 1 0.37 0.547 0.90 0.352 0.25 0.625 0.06 0.815

(2) 0 vs. K 1 .18 .678 .33 .569 2.47 .130 .35 .558

(3) N vs. K+N 1 .05 .826 .14 .711 4.65 .042 1.06 .313

TPA (1997) 1 .92 .348 .04 .852 2.18 .154 66.43 <.001

Error (treatment effects) 23

Year 7 8.25 <.001 5.93 <.001 6.31 <.001 15.84 <.001

Treatment x year 21 .95 .527 1.11 .346 .74 .790 .73 .803

Error (year effects) 168

Total 223

Note: Adjusted means for each variable are plotted in figures 6. TPA = trees per acre

a Includes some losses from black-stain fungus.

b ANOVA mean squares are not reported by SAS Procedure MIXED; F-statistics are computed via a formula that does not use the

conventional ratios of mean squares.

c

 0 = no fertilizer.

Average tree density in the 12-yearold plantation in

2005 did not differ

significantly as a

result of the fertilizer treatments,

ranging from 377 to

405 TPA.
24

RESEARCH PAPER PNW-RP-569

Figure 6—Cumulative yearly mortality of Douglas-fir from laminated root rot (LRR),

Armillaria, and other causes and resulting density of surviving trees in the 8 years (1998-2005)

after fertilization at Voight Creek, Washington. Means have been adjusted for postthinning

density (1997 TPA). 0 = no fertilizer.
25

Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

effects of N and K fertilizer were often significant but in opposing direction: growth

increased 7 to 12 percent in response to the general effects of N fertilizer, but

decreased 4 to 7 percent in response to K fertilizer.

Stand basal area and volume—

Both live-stand basal area and volume per acre in the 10-year-old plantation (after

the 2003 growing season) differed among treatments. Plots fertilized with N (either

N or K+N) averaged about 28 percent more basal area and about 39 percent more

volume than those not fertilized with N (either 0 or K) (table 9). Moreover, both

basal area and volume per acre in plots fertilized with K+N were 15 to 17 percent

less than in plots fertilized with N only. The results correspond to the effects of

these treatments on tree diameter and height growth. Note that surviving live trees

that had not attained breast height (4.5 ft) were not included in the computation of

stand basal area and volume. They were included in TPA estimates.

Table 9—Tree and stand statistics of Douglas-fir averaged by fertilizer treatment at Voight

Creek, Washington

Fertilizer treatmenta Standard Significant

Variable 0 K N K+N error contrasts (p < 0.10)b

1997 height (ft) 4.0 3.5 3.8 3.6 0.3 NS

1998 height (ft) 5.5 5.5 5.7 5.6 .1 (1)

1998 height growth (ft) 1.7 1.8 2.0 1.9 .1 (1)

2003 height (ft) 18.5 17.4 19.8 18.6 .4 (1), (2), (3)

1998-2003 height PAI (ft) 2.4 2.3 2.7 2.5 .1 (1), (3)

2003 diameter breast

height (in.) 3.0 2.8 3.2 3.0 .1 (1)

1997 trees/acre 443.6 445.0 462.1 455.0 14.2 NS

2005 trees/acre 390.0 386.8 405.0 376.7 18.6 NS

2003 basal area (ft2

/acre) 18.9 17.4 25.0 21.3 1.5 (1), (3)

2003 volume (ft3/acre) 169.9 171.6 259.7 215.8 16.7 (1), (3)

a

 Means for trees/acre have been adjusted for postthinning density; all other means have been adjusted for initial

height.

b

 Orthogonal comparisons tested were (1) 0 and K vs. N and K+N, (2) 0 vs. K, and (3) N vs. K+N; 0 = no fertilizer.

Note: NS = statistically nonsignificant, PAI = periodic annual increment.

Effects of N and K

fertilizer were often

significant but in

opposing direction.

Plots fertilized with

N (either N or K+N)

averaged about 28

percent more basal

area and about 39

percent more volume than those not

fertilized with N.
26

RESEARCH PAPER PNW-RP-569

Discussion

Laminated Root Rot in the Preceding Stand

Based on number and size of infected stumps in the preceding stand, the estimated

amount of P. weirrii innoculum (I.I.) was unrelated to soil type, despite large differences in slope percentage and gravel-cobble content among the three soils. These

results do not support earlier speculations: Reynolds and Bloomberg (1982) suggested that gravel content and shallow soils decrease soil volume available to roots

and thus increase frequency of root contacts and spread of LRR. Based on literature

reviews, Littke3 stated that factors that increase frequency of root contacts or

shorten the interval to root occupancy will increase mortality from LRR.

Laminated Root Rot in Current Plantation

Cumulative 8-year tree mortality from LRR was clearly related to I.I. of the previous stand. This supports our working hypothesis 1 that I.I. is a useful predictor

of future LRR. However, the relation with density of LRR-infected stumps (r2 = 0.

74) was considerably stronger than that with I.I. (r2

 = 0.53). This result suggests

that, when predicting plantation susceptibility to LRR, there may be no benefit

from taking the additional measurements required to calculate I.I.

Thies and others (2005) also compared the utility of I.I. and a simple count of

infected stumps in the parent stand to predict losses from LRR in the replacement

stand of Douglas-fir. Their sample consisted of a total of 119 plots at five locations.

Note that each 0.10-acre plot was centered on a P. weirii-infected stump. Therefore

in contrast to our fewer but larger plots at a single location, their range of I.I. or

number of infected stumps did not include zero. This smaller range of values for the

predictor variables could help explain their low r2 value (0.31 and 0.39 for I.I. and

number of infected stumps per acre, respectively) and their conclusion that there

was too much unexplained variation in their models for either variable to be useful

in predicting future losses from LRR.

The trend of accelerating rates of mortality from LRR for all treatments is

probably a result of accelerating rates of the tree growth and their ability to occupy

progressively larger soil volumes, which would increase their probability of contact

3 Littke, W. [N.d.]. Detection and evaluation of laminated root rot disease in Douglas-fir

stands. [Centralia, WA]: [Weyerhaeuser Western Forestry Forest Pest Management Team]

38 p. Unpublished study plan. On file with: Forestry Sciences Laboratory, 3625 93rd

Avenue SW, Olympia, WA 98512.

Based on number

and size of infected

stumps in the preceding stand, the

estimated amount of

P. weirrii innoculum

(I.I.) was unrelated

to soil type.

When predicting

plantation susceptibility to LRR, there

may be no benefit

from taking the

additional measurements required to

calculate I.I.
27

Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

with LRR inoculum. Based on our recent surveys, LRR-caused mortality is increasing faster in treatment K+N than in the other treatments; however, we cannot

predict if this trend will continue.

Foliage Indicators

Current-year foliage collected in year 5 after planting on nonfertilized plots averaged 1.32 percent N (moderately deficient) and 0.85 percent K (more than adequate for normal growth of coast Douglas-fir saplings) (Carter 1992). Mean

weight of 100 needles the first growing season after fertilization did not differ

significantly among fertilized and nonfertilized trees. Needles of K-only-fertilized

trees averaged about 12 percent lighter than nonfertilized, but N-only fertilized

averaged about 5 percent heavier. When the foliage was collected, current twigs

were visibly longest on N-fertilized trees and shortest on K-only fertilized trees.

Fertilization with 300 lb N/acre, both as a single treatment or combined with K,

increased both N concentration and content in needles by at least 30 percent, and

decreased K percentage by 8 to 9 percent. Reduction of K concentration in Douglas-fir foliage after N fertilization is frequently reported (Heilman and Gessel

1963, Peterson and others 1986, Thies and others 2006).

Fertilization with K-only may have slightly increased K concentration but not

content over that in control needles, in part because needles were lighter (table 4).

Thies and others (2006) applied both smaller (200 lb K/acre) and larger (400 lb K/

acre) amounts of potassium chloride (KCI) in spring to newly planted Douglas-fir.

Needles collected that fall averaged slightly greater K-concentration than needles

from nonfertilized seedlings, although differences were statistically nonsignificant

(p > 0.05). Although average concentration of K in needles from nonfertilized

seedlings at that site (0.85 percent) was similar to that at our Voight Creek study

area, further comparisons are not possible because 100-needle weights were not

determined.

Moore and others (2004) provided useful information about foliar nutrient concentrations and variation in four species, including Rocky Mountain Douglas-fir

(var. glauca). Their recommended K-concentration for optimal growth of that

variety is 0.60 percent, which is considerably lower than the 0.85 percent that

both we and Thies and others (2006) measured in foliage on nonfertilized coast

Douglas-fir.
28

RESEARCH PAPER PNW-RP-569

These relations among foliar weight, nutrient concentration, and content can be

presented graphically (fig. 7) and used to assess effects of fertilization on nutrient

status (Timmer and Ray 1988). Their table for interpreting relations after fertilization follows.

Response in Change in

Direction of Needle Nutrient Nutrient Possible

shift weight Conc. Content status diagnosis

A + - + Dilution Nonlimiting

B + O + Unchanged Nonlimiting

C + - - Deficiency Limiting

D O - - Luxury consumption Nontoxic

E - ++ ± Excess Toxic

F - - - Excess Antagonistic

Addition of 300 lb K/acre at Voight Creek resulted in a type F shift in needle

weight and N relations, which suggests excess K status and antagonistic interactions

between K and N status. This treatment also resulted in a type E shift in needle

weight and K relations, which suggests excess K in the needles and possible toxic

effects. Our mortality and growth data (table 9) generally support these indications

of unfavorable nutrient status after K-fertilization.

The combined K+N treatment did not result in major shifts in foliar relations

that would have indicated unfavorable nutrient status or a growth-limiting diagnosis

(fig. 7). We infer from mortality and growth data (table 9), however, that this

combination resulted in increased mortality from “other” causes (table 7) and

reduced 6-year height growth and stand basal area and volume in 2003 (table 9).

Our K source, KCl, is a highly soluble fertilizer. We used KCl instead of

potassium sulfate (K2SO4) because it is a more concentrated source of K and to

avoid adding another nutrient, sulphur. Our experimental dosage was deliberately

large to ensure adequate treatment strength to induce an effect. We infer from the

visually poorer vigor of K-only fertilized trees relative to the nonfertilized control,

however, that excessive K+ or Cl- ions may have had a temporary toxic effect on

these trees. Because K-fertilization did not reduce foliar concentration of magnesium (Mg), we infer that a Mg deficiency was not induced by our K fertilization (as

a potential explanation for reduced growth of K-fertilized trees).

Our mortality and

growth data generally support these

indications of unfavorable nutrient

status after K-fertilization.

Excessive K+ or Clions may have had

a temporary toxic

effect on these

trees.
29

Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

Tree Mortality and Growth Responses to Fertilization

Seedlings died from LRR, Armillaria, and other agents (table 10). Despite seedling

losses from various agents in the 8-year period after fertilization, the 12-year-old

plantation averaged 390 TPA and was adequately stocked. Because initial number

of tagged trees (crop trees) varied among the 28 plots, we used initial TPA after

thinning as a covariate to adjust observed treatment means of mortality to the common or average TPA for all plots (451 TPA). Observed means for the nonfertilized

and K-only treatments were increased slightly through this adjustment because their

Figure 7—Graphical analysis of nutrient

concentration, nutrient content, and dry

weight of Douglas-fir needles for (a)

nitrogen (N) and (b) potassium (K) 1

year following fertilizer treatments at

Voight Creek, Washington. Each variable

is expressed as a percentage of the

nonfertilized control.
30

RESEARCH PAPER PNW-RP-569

mean TPA in 1997 was less than the overall average TPA. Conversely, raw means

for the N and K+N treatments were adjusted slightly downward. This adjustment

changed treatment means, but seldom changed treatment rankings.

Contrary to our hypothesis 2, fertilization with K fertilizer at 300 lb K/acre did

not reduce tree mortality from LRR. Instead, we observed increased cumulative

mortality from “other” causes in K-fertilized plots (12 more TPA died after K-only

fertilization than in the nonfertilized control and 15 more TPA died after K+N than

after N-only fertilization (table 7). We hypothesize that additional losses after KCI

fertilizer may be caused by a toxic effect of excess potassium or chloride ions in the

soil solution. Moreover, this suspected toxic effect apparently decreased tree growth

response to N.

Thies and others (2006) tested the efficacy of the same KCI fertilizer at smaller

and larger dosages (200 and 400 lb K/acre) and also in combination with urea (200

lb K and 200 lb N/acre). The fertilizers were broadcast shortly before 2-1 Douglasfir seedlings were planted in and around a total of 44, 0.05-acre plots. The soil at

their study area was mapped as Cispus cindery sandy loam, a very deep, somewhat

Table 10—Summary of initial trees per acre after thinning (TPA97),

cumulative (1998-2005) mortality after fertilization by source, and final

trees per acre (TPA05) for Douglas-fir at Voight Creek, Washington

Cumulative mortality by source

Fertilizer

treatmentb TPA97 LRR Armillaria Other Total TPA05

Trees per acre

Adjusted means from tables 5, 6, 7, and 9a

0 443.6 20.4 33.9 7.1 61.4 390.0

K 445.0 29.5 15.9 19.2 64.6 386.8

N 462.1 32.8 5.7 8.0 46.4 405.0

K+N 455.0 40.9 10.9 22.9 74.8 376.7

Unadjusted meansc

0 443.6 19.3 32.9 7.1 59.3 384.3

K 445.0 28.6 15.0 19.3 62.9 382.1

N 462.1 34.3 7.1 7.9 49.3 412.9

K+N 455.0 41.4 11.4 22.9 75.7 379.3

Note: LRR = laminated root rot.

a

 Adjusted means from analyses of covariance adjusted for initial trees per acre.

b

 0 = no fertilizer.

c

 Unadjusted means from analysis of variance.

Fertilizer at 300 lb

K/acre did not reduce tree mortality

from LRR.
31

Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

excessively drained soil on slopes of zero to 8 percent (USDA SCS 1987). Based

on modal characteristics of this soil (coarse texture, low clay content), we infer that

reactions and fate of K (KCI) and N fertilizers at this location would be similar to

those at our Voight Creek study area. Losses from LRR in the 7 years after fertilization were similar for all fertilizer treatments and the no-fertilizer treatment. They

concluded that a single application of K or K+N to Douglas-fir seedlings at the rates

tested was not an effective management strategy for LRR. Losses from other causes

averaged 51 percent of total losses in the 4 years before the plots were thinned to

500 TPA. Of the total losses in the next 3 years, 17 percent were not from LRR.

For the entire 7-year period after planting and fertilization, non-LRR losses were

not related significantly to fertilizer treatment (Thies, unpublished data).

Results of this research do not support our hypothesis 3 that application of

N fertilizer could increase tree mortality from LRR. Nitrogen-fertilized plots did

not have a greater number of LRR-killed trees (table 5) or mortality per unit of I.I.

or density of LRR-infected stumps (fig. 4). Nitrogen-fertilized plots, however, did

have reduced losses from Armillaria, although these reductions were not statistically

significant (table 6).

Six years after fertilization, N-only fertilization resulted in the largest trees

and the greatest stand basal area and volume, presumably in response to improved

fertility. Thies and Westlind (2005) also reported no effect of N fertilization (300,

600, 1,200 lb N/acre as ammonium nitrate) on losses of Douglas-fir from LRR at

five locations, and reported a decade-long growth response to N at one of these

locations.

To confirm observations from our study at Voight Creek, we plan to assess the

continued effects of fertilization on tree mortality. We acknowledge that detecting

treatment effects on rates of tree mortality is often difficult. Statistical tests of shortterm changes in LRR-caused mortality are often statistically nonsignificant despite

large differences in mortality among treatment means, because statistical comparisons are based on a large experimental error (Thies, unpublished data).

We surmise that detecting effects of N fertilizer on Douglas-fir growth at

N-deficient sites (like our Voight Creek site) is inherently easier than detecting

changes in rates of mortality from LRR. One simple explanation is limited sample

size: all trees contribute to growth (for some period of time), but relatively few

trees die, especially from LRR.
32

RESEARCH PAPER PNW-RP-569

Design Considerations

Our study design differs from the other study involving N- and K-fertilization to

reduce losses of Douglas-fir seedling to LRR (Thies and others 2006). Our circular

(0.2 acre) plots were systematically located in a 4-year-old plantation, whereas

those near Morton, Washington, were smaller (0.05 acre) and each was centered on

a P. weirii-infected stump. Our Voight Creek plots are four times larger and should,

therefore, provide a larger sampling of P. weirii -infected area. At plot establishment and after an initial thinning to reduce stem density by cutting mostly volunteers, our plots averaged 451 TPA at fertilization. In contrast, the deliberately close

planting spacing near Morton provided a greater TPA sample when fertilized

(4,720 TPA). Fertilizers in our study were applied before the fifth growing season

after planting rather than before planting. Consequently, in our study, older seedlings and greater vegetative cover probably captured more of the fertilizer. Our

dosage (300 lb N/acre) exceeded the dosage near Morton (200 lb N/acre).

We suggest the following techniques could improve effectiveness of future field

trials testing fertilization and root disease:

1. Conduct trials at locations where treatment is likely to eliminate a growthlimiting factor; e.g., where there is a large amount of disease inoculum or where N

or K is deficient.

2. Confine trials to uniform conditions or increase plot size. Create experimental

blocks on recognizable strata, e.g., similar inoculum index, stand density, soil type,

or slope class. This can reduce the error term by partitioning out variation associated with those strata.

3. Install an adequate number of replications; more replications are desirable where

plots are small or site or stand conditions are variable.

4. Use a covariate that expresses differences in pretreatment or starting conditions

among plots, e.g., number of Phellinus-infected stumps, I.I., or stem density.

As documented in the “Methods” section, we used several of these techniques

when designing this field trial. Fortuitously, our blocking on I.I. resulted in the four

treatments also being nearly balanced among the two contrasting soil series in

experimental area (table 1). Because the gravelly Barneston series (soils 1 and 2) is

much less productive than the Nargar sandy loam (our soil 3) This balance avoided

a potential confounding with the fertilizer treatments and simplified our interpretations of growth response related to fertilizer (table 11).
33

Laminated Root Rot in a Western Washington Plantation: Eight-Year Mortality and Growth of Douglas-Fir...

Conclusions

1. Numbers of and disease severity in P. weirii-infected stumps from the preceding

70-year-old stand differed greatly among our 28, 0.20-acre plots and their immediate buffer areas. Twelve plots had no infected stumps. Inoculum index estimated

from infected stumps of the preceding stand was not related to soil type, which

included both gravelly and nongravelly soils.

2. The I.I. was a useful blocking factor to ensure uniform sampling of the potential

for LRR-infection among the fertilizer treatments.

3. Mortality of Douglas-fir trees caused by LRR averaged only about 2 TPA in

years 3 and 4 after planting, but the subsequent annual rate of mortality increased

through year 12.

4. Subsequent cumulative 8-year mortality from LRR was significantly related to

both I.I. and density of infected stumps per acre. Seedlings also died from LRR in

plots in which no infected stumps were detected.

5. Cumulative mortality per unit of potential LRR inoculum did not differ significantly among treatments, indicating that neither K nor N fertilization changed

Douglas-fir susceptibility to LRR.

6. Cumulative tree mortality from other causes in the first year and 8 years after

fertilization was greater on K-fertilized plots. We infer that trees died soon after

fertilization from possible toxic effect of excess potassium salts, especially when

combined with urea fertilizer.

7. The N fertilization increased tree growth and size by year 10 after planting; K

fertilization may have decreased tree growth.

Table 11—Growth characteristics for the seven nonfertilization plots

Item Barneston (N=3) Nargar (N=4) Difference

Absolute Percent

Mean height (SE) (ft):

1997 3.5 (0.3) 4.4 (0.5) 0.9 26

2003 17.8 (0.8) 20.7 (1.7) 2.9 16

Mean d.b.h. (SE) (in)

2003 2.7 (0.1) 3.5 (0.3) .8 30

Mean stand (SE) in 2003:

Basal area (ft2/acre) 17.1 (0.7) 25.9 (5.3) 8.8 51

Volume (ft3/acre) 128 (35) 276 (66) 148 116
34

RESEARCH PAPER PNW-RP-569

Acknowledgments

We thank the former forest owner, Champion Pacific Timberlands, Inc. and the

PNW Research Station for initially funding this study, and the Campbell Group,

LLC for permitting our continued use of the study area. Michael Anne French, Dan

Lovato, Brian Burke, Harry Anderson, and Douglas Westlind assisted us greatly.

Thanks to Pam Phillips, Robert Nichelson, Dan Omdal, Amy Ramsey, and Melanie

Kallas for their assistance with the field measurements. Thanks also to technical

reviewers of our draft manuscript: Tim Max, Terry Shaw, Pat Cunningham,

Gregory Filip, and Darlene Zabowski.

Metric Equivalents

When you know: Multiply by: To find:

Inches (in) 2.54 Centimeters

Feet (ft) .305 Meters

Miles (mi) 1.609 Kilometers

Acres 0.405 Hectares

Ounces (oz) 2840 Milligrams (mg)

Pounds (lb) 0.454 Kilogram

Pounds per acre (lbs/acre) 1.1208 Kilograms per hectare

Degrees Fahrenheit (oF) 0.556 and

subtract 17.8 Degrees Celsius

Square feet per acre (ft2/per acre) 0.230 Square meters per hectare

Cubic feet per acre (ft3/acre) 0.070 Cubic meters per hectare

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