Critical Period Threshold Study

1. 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

2. Introduction • 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? • 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

3. Methods- Study design • Randomized block split-plot with 4 blocks of 8 treatments per conifer species • 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. • 4 sites representing different geoclimatic zones with different vegetation communities and climatic conditions.

4. Sites • 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)

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

6. 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.

7. Operational Control • Target- No more than 25 % cover • Mechanical Site Prep- all sites • Excavator piling and removal of obvious shrub clumps • All remaining hardwood clumps sprayed until dead. • Chemical Site Prep- T’’’’ • Fall Oust (2oz), Escort (.5oz) and Accord. Other herbicides added if needed. • Follow-up Weed Control- • Spring Atrazine and Transline applications

8. Weed Control

9. Weed Control Efficacy

10. 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

11. Results- Starker sitegrand 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’’

12. Results- Starker site- western red cedar • 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’’ • No differences—OTT’’ vs. TTO’’ or TOO’’ vs. OOT’’

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

14. Starker Site Mortality

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

16. Seaside Mortality

17. Sweet Home Results • Western red cedar • TT’’’ and TO’’’ increased volume, height and diameter relative to OT’’’ or OO’’’ • Douglas-fir • TT’’’ increased volume, diameter and height relative to all other treatment combinations • No differences in any parameter between one-year treatments (OT’’’ vs. TO’’’) • Both OT’’’ and TO’’’ improved diameter growth relative to OO’’’

18. Sweet Home Mortality

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

20. Roseburg Mortality

21. Summary of Results • Starker, Sweet Home and Roseburg sites- • -growth increased with increasing years of weed control. • 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. • -All other cases- no differences between equivalent-number-of- year treatments.

22. 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 2. 2001 vs. 2002 Rainfall

23. Results- Starker Site Douglas-fir 2000 2001

24. Questions Raised • 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? • Is large container stock better suited to compete with first-year weeds than other stock types?