Critical Period Threshold Critical Period Threshold Study Study

Effects of up to Five Years of Consecutive Effects of up to Five Years of Consecutive Weed Control Relative to Growth Losses Weed Control Relative to Growth Losses

from Delaying Weed Control for Douglas-from Delaying Weed Control for Douglas-fir and Other PNW Conifer Speciesfir and Other PNW Conifer Species

IntroductionIntroduction What is the relative efficacy of continuous weed control What is the relative efficacy of continuous weed control

through 3, 4 or 5 growing seasons after planting ?through 3, 4 or 5 growing seasons after planting ?

What growth loses, if any, result from delaying What growth loses, if any, result from delaying vegetation control for a year or two after planting? vegetation control for a year or two after planting?

Douglas-fir, western hemlock, western red cedar, and Douglas-fir, western hemlock, western red cedar, and grand fir grand fir

-Multiple years of vegetation control -Multiple years of vegetation control -Delayed vegetation control -Delayed vegetation control -Different sites -Different sites -Different vegetation types and climatic influences-Different vegetation types and climatic influences

Methods- Study designMethods- Study design Randomized block split-plot with 4 blocks of 8 treatments per Randomized block split-plot with 4 blocks of 8 treatments per

conifer species conifer species

OOOOO, TOOOO, TTOOO, TTTOO, TTTTO, TTTTT, OOOOO, TOOOO, TTOOO, TTTOO, TTTTO, TTTTT, OTTTT and OOTTT OTTTT and OOTTT

Plots- 36 seedlings planted in a grid with 10 ft x 10 ft spacing, Plots- 36 seedlings planted in a grid with 10 ft x 10 ft spacing, surrounded by a row of buffer trees. surrounded by a row of buffer trees.

4 sites representing different geoclimatic zones with different 4 sites representing different geoclimatic zones with different vegetation communities and climatic conditions. vegetation communities and climatic conditions.

SitesSites2000 Installation2000 Installation

Central Coast Range LocationCentral Coast Range Location -Starker Forest ground west of Corvallis, OR-Starker Forest ground west of Corvallis, OR -All four species of interest (Douglas-fir, western hemlock, -All four species of interest (Douglas-fir, western hemlock,

western red cedar, and grand fir) western red cedar, and grand fir) 2001 Installations2001 Installations

Spruce Hemlock Coastal Forest Spruce Hemlock Coastal Forest -Weyerhaeuser ground near Seaside, OR -Weyerhaeuser ground near Seaside, OR -(Douglas-fir and western hemlock) -(Douglas-fir and western hemlock)

Low elevation western CascadeLow elevation western Cascade Cascade Timber Consulting ground near Sweet Home, OR Cascade Timber Consulting ground near Sweet Home, OR (Douglas-fir and western red cedar) (Douglas-fir and western red cedar)

Drier Southern Coast RangeDrier Southern Coast Range Roseburg Resources ground near Riddle, ORRoseburg Resources ground near Riddle, OR (Douglas-fir and grand fir)(Douglas-fir and grand fir)

Zone 3-Riddle (Roseburg)

Zone 4-Sweet Home

Zone 1-Starker

Zone 2-Seaside

Planting StockPlanting Stock

•All seedlings were large container stock (Styro 15’s ) with fertilizer in media.

•Grown at Plum Creek Nursery (Cottage Grove)

•Goal was to plant stock as uniform as possible.

Operational ControlOperational Control Target- No more than 25 % coverTarget- No more than 25 % cover

Mechanical Site Prep- all sitesMechanical Site Prep- all sites Excavator piling and removal of obvious shrub clumpsExcavator piling and removal of obvious shrub clumps All remaining hardwood clumps sprayed until dead.All remaining hardwood clumps sprayed until dead.

Chemical Site Prep- T’’’’ Chemical Site Prep- T’’’’ Fall Oust (2oz), Escort (.5oz) and Accord. Other herbicides Fall Oust (2oz), Escort (.5oz) and Accord. Other herbicides

added if needed.added if needed. Follow-up Weed Control-Follow-up Weed Control-

Spring Atrazine and Transline applicationsSpring Atrazine and Transline applications

Weed ControlWeed Control

Weed Control EfficacyWeed Control Efficacy

Results- Starker Site Douglas-firResults- Starker Site Douglas-fir

Volume growth maximized - TTT’’ or TTO’’TTT’’ improved third-year volume by over 150% relative to OOO”Either 2-year treatment improved volume growth relative to the best 1-year treatment by 59%No differences—OTT’’ vs. TTO’’ or TOO’’ vs. OOT

Results- Starker siteResults- Starker sitegrand firgrand fir

TTT’’ improved grand fir volume growth by 47% relative to the best 2-year treatment and by 477% relative to OOO’’

(TTO’’) resulted in greater volume than either one-year treatment. No differences – OTT’’ vs. TTO’’ or TOO’’ vs. OOT’’

Results- Starker site- western red cedarResults- Starker site- western red cedar

No differences—OTT’’ vs. TTO’’ or TOO’’ vs. OOT’’

No differences between TTT’’, OTT’’ and TTO’’ OTT’’ improved volume growth compared (TOO’’) by 107%

TTT’’ increased volume relative to OOO’’ by 452%

One-year treatments were not statistically different from OOO’’

Results- Starker Site Western HemlockResults- Starker Site Western Hemlock

Again, no differences –OTT’’ vs. TTO’’ or TOO’’ vs. OOT

Volume maximized by TTT’’, OTT’’ or TTOTTT’’ increased volume by 142% relative to OOO’’

TTO’’ improved volume growth relative OOT’’ by 73%.

Starker Site MortalityStarker Site Mortality

Seaside ResultsSeaside Results

Douglas-firNo differences in volume or height among treatments. (TT’’’) increased diameter relative to plots that were not treated the first year (OT’’’ and OO’’’).

Western hemlockVolume and diameter not significantly affected by weed controlTO’’’ and TT’’’ reduced height growth relative to OO’’’.

Seaside MortalitySeaside Mortality

Sweet Home ResultsSweet Home Results

Douglas-fir

TT’’’ increased volume, diameter and height relative to all other treatment combinations

Western red cedarTT’’’ and TO’’’ increased volume, height and diameter relative to OT’’’ or OO’’’

Both OT’’’ and TO’’’ improved diameter growth relative to OO’’’

No differences in any parameter between one-year treatments (OT’’’ vs. TO’’’)

Sweet Home MortalitySweet Home Mortality

Roseburg ResultsRoseburg Results

Douglas-fir TT’’’ and OT’’’ increased diameter and volume relative to TO’’’ and OO’’’

Grand firTT’’’ and OT’’’ increased both diameter and volume relative to TO’’’ and OO’’’

TO’’’ did not differ from OO’’’ in volume, diameter or height. TO’’’ did not differ from OO’’’ in volume, diameter or height.

Roseburg MortalityRoseburg Mortality

Summary of ResultsSummary of Results• Starker, Sweet Home and Roseburg sites-

-growth increased with increasing years of weed control.

-All other cases- no differences between equivalent-number-of- year treatments.

• Seaside - few differences in volume, height or diameter apparent after 2 years

• Comparison of treatments with equal number of years of weed control- TTO’’ vs. OTT’’ , OOT’’ vs. TOO’’ and OT’’’ vs. TO’’’

-Western red cedar at Sweet Home- only instance in which the earlier application of weed control benefited volume

growth. - Douglas-fir and grand fir at Roseburg- applying weed

control the second year rather than the first year resulted in increases in diameter and volume.

DiscussionDiscussion

Competing vegetation has been slow to fully colonize some sitesCompeting vegetation has been slow to fully colonize some sites

Weed Cover on never-treated plotsWeed Cover on never-treated plots::

-Starker- 31 to 36% year 1, 68 to 81% year 2 and 84 to 90% year 3-Starker- 31 to 36% year 1, 68 to 81% year 2 and 84 to 90% year 3

-Seaside- 20 to 25% year 1 and 53 to 59% year 2 -Seaside- 20 to 25% year 1 and 53 to 59% year 2

-Roseburg- 39 to 41% year 1 and 46 to 53% weed cover year 2. -Roseburg- 39 to 41% year 1 and 46 to 53% weed cover year 2.

-Sweet Home- 63 to 70% year 1 and 82 to 83% year 2. -Sweet Home- 63 to 70% year 1 and 82 to 83% year 2.

2001 vs. 2002 Rainfall2001 vs. 2002 Rainfall

Results- Starker Site Douglas-firResults- Starker Site Douglas-fir

2000 2001

Questions RaisedQuestions Raised

Do we need to apply site-prep and/or first-year herbicide Do we need to apply site-prep and/or first-year herbicide treatments in all cases?treatments in all cases?

If not, can we develop a model to forecast herbicide If not, can we develop a model to forecast herbicide efficacy for a given season?efficacy for a given season?

Is large container stock better suited to compete with first-Is large container stock better suited to compete with first-year weeds than other stock types?year weeds than other stock types?