Critical Period Threshold Study Effects of up to Five Years of Consecutive Weed Control Relative to Growth Losses from Delaying Weed Control for Douglas- fir and Other PNW Conifer Species

Introduction What is the relative efficacy of continuous weed control through 3, 4 or 5 growing seasons after planting ? What is the relative efficacy of continuous weed control through 3, 4 or 5 growing seasons after planting ? What growth loses, if any, result from delaying vegetation control for a year or two after planting? What growth loses, if any, result from delaying vegetation control for a year or two after planting? Douglas-fir, western hemlock, western red cedar, and grand fir Douglas-fir, western hemlock, western red cedar, and grand fir -Multiple years of vegetation control -Delayed vegetation control -Different sites -Different vegetation types and climatic influences

Methods- Study design Randomized block split-plot with 4 blocks of 8 treatments per conifer species Randomized block split-plot with 4 blocks of 8 treatments per conifer species OOOOO, TOOOO, TTOOO, TTTOO, TTTTO, TTTTT, OTTTT and OOTTT OOOOO, TOOOO, TTOOO, TTTOO, TTTTO, TTTTT, OTTTT and OOTTT Plots- 36 seedlings planted in a grid with 10 ft x 10 ft spacing, surrounded by a row of buffer trees. Plots- 36 seedlings planted in a grid with 10 ft x 10 ft spacing, surrounded by a row of buffer trees. 4 sites representing different geoclimatic zones with different vegetation communities and climatic conditions. 4 sites representing different geoclimatic zones with different vegetation communities and climatic conditions.

Sites 2000 Installation 2000 Installation  Central Coast Range Location  -Starker Forest ground west of Corvallis, OR  -All four species of interest (Douglas-fir, western hemlock, western red cedar, and grand fir)  2001 Installations  Spruce Hemlock Coastal Forest  -Weyerhaeuser ground near Seaside, OR  -(Douglas-fir and western hemlock)  Low elevation western Cascade  Cascade Timber Consulting ground near Sweet Home, OR  (Douglas-fir and western red cedar)  Drier Southern Coast Range  Roseburg Resources ground near Riddle, OR  (Douglas-fir and grand fir)

Zone 3- Riddle (Roseburg) Zone 4- Sweet Home Zone 1-Starker Zone 2- Seaside

Planting 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 Control Target- No more than 25 % cover Target- No more than 25 % cover Mechanical Site Prep- all sites Mechanical Site Prep- all sites Excavator piling and removal of obvious shrub clumps Excavator 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 added if needed. Fall Oust (2oz), Escort (.5oz) and Accord. Other herbicides added if needed. Follow-up Weed Control- Follow-up Weed Control- Spring Atrazine and Transline applications Spring Atrazine and Transline applications

Weed Control

Weed Control Efficacy

Results- 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 site grand 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 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 Hemlock Again, no differences –OTT’’ vs. TTO’’ or TOO’’ vs. OOT Volume maximized by TTT’’, OTT’’ or TTO TTT’’ increased volume by 142% relative to OOO’’ TTO’’ improved volume growth relative OOT’’ by 73%.

Starker Site Mortality

Seaside Results Douglas-fir No differences in volume or height among treatments. (TT’’’) increased diameter relative to plots that were not treated the first year (OT’’’ and OO’’’). Western hemlock Volume and diameter not significantly affected by weed control TO’’’ and TT’’’ reduced height growth relative to OO’’’.

Seaside Mortality

Sweet Home Results Douglas-fir TT’’’ increased volume, diameter and height relative to all other treatment combinations Western red cedar TT’’’ 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 Mortality

Roseburg Results Douglas-fir TT’’’ and OT’’’ increased diameter and volume relative to TO’’’ and OO’’’ Grand fir TT’’’ and OT’’’ increased both diameter and volume relative to TO’’’ and OO’’’ TO’’’ did not differ from OO’’’ in volume, diameter or height.

Roseburg Mortality

Summary 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.

Discussion Competing vegetation has been slow to fully colonize some sites Weed Cover on never-treated plots: -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 -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 vs Rainfall

Results- Starker Site Douglas-fir

Questions Raised Do we need to apply site-prep and/or first-year herbicide treatments in all cases? Do we need to apply site-prep and/or first-year herbicide treatments in all cases? If not, can we develop a model to forecast herbicide efficacy for a given season? If not, can we develop a model to forecast herbicide efficacy for a given season? Is large container stock better suited to compete with first- year weeds than other stock types? Is large container stock better suited to compete with first- year weeds than other stock types?