1. Twenty Years of Forest Development Following Restoration Thinning in Second Growth Douglas-fir Stands
Paul Anderson, Program Manager
USFS PNW Research Station
Stuart Johnston, Silviculturist (Retired)
Siuslaw National Forest
Society for Ecological Restoration, 7 April 2016

2. STUDS: Thinning and Underplanting for Diversity Study
Context for Thinning
Study Design and Implementation
Responses to Thinning
Overstory
Light Regime
Understory Vegetation
Planted Seedlings
Diversity
Conclusions
Society for Ecological Restoration, 7 April 2016

3. Silvicultural Issues in the Northwest Forest Plan Context
What silvicultural practices can land managers use to address the broad suite of ecosystem services desired from moist forests of the Pacific Northwest forests?
To what extent is the production of various ecological and social benefits compatible with production of commodities?
Can young Douglas-fir forests be managed to enhance the diversity of vegetation structure and composition and for the production of wood?
The Siuslaw Thinning and Underplanting for Diversity Study arose in the context of an agency shift to wards Ecosystem Management and the subsequent adoption of the Northwest Forest Plan.
The Northwest Forest Plan represented a compromise intended to balance management for a broadened array of ecological and societal objectives – including economic interests
While the range of threatened Northern Spotted Owl was fundamental in defining the geographic scope of the NWFP ammendments, it was by no means the sole driver.
Past harvesting had substantially depleted existing old-growth over much of the area and therefore there was substantial concern about the loss of old-growth forest habitat and the diversity of organisms associated with old-growth
On the other end of the spectrum was the recognized importance of forest production to local and regional economies
Some key attributes of the Plan are important to recognize in defining the context of forest management responses to the new perspectives outlined in the plan
Among various paradigms that could have been used to frame ecosystem management, the NWFP encoded a conservation biology perspective – every species counts; management to the species for those species deemed of concern
In approaching a landscape perspective in balancing multiple objectives – geographically defined land allocations were assigned
Key Among allocations were the reserves to conserve and develop late-seral forest habitat and to maintain or restore the functionality of aquatic and riparian ecosystems including the important anadramous fisheries
To matrix allocation was defined to accommodate other objectives including sustainable economic timber production
Late-successional reserves actually encompassed hundreds of thousands of acres younger second growth forest previously managed for conventional timber production objectives
Management of these stands was an immediate challenge for some forests like the Siuslaw National Forest in coastal Oregon because a vast proportion of the forest was allocated to Late-successional reserve regardless including an abundance of year-old plantation forests
What silvicultural practices would be useful in meeting emerging priorities?
Society for Ecological Restoration, 7 April 2016

4. Young Douglas-fir Forests of Western Oregon
Douglas-fir dominated
Even-aged
30-70 year-old
High density
Stem exclusion phase
Structurally uniform
Originally managed for timber production
In western Oregon, much of the National Forest landscape is dominated by young, even-aged forests, Originally managed with a timber emphasis but, as in the case of the Siuslaw NF, much of these forests have been designated as Late-successional reserve – to be managed to provide late-successional forest structures and habitats.
Society for Ecological Restoration, 7 April 2016

5. Stem Exclusion Phase Trees dominate site
Relatively narrow diameter range
Little crown differentiation
Competition induced wave mortality
Little species diversity
Little sunlight reaches the forest floor
Little if any understory vegetation
These young forests, typically in a stem exclusion phase of stand development, lack many of the structural and legacy features important to late-successional forest ecosytems.
Society for Ecological Restoration, 7 April 2016

6. Complex Structure Phase
High degree of vertical structure
Crown differentiation
Understory growth
Horizontal crown expansion complete
Tree mortality results in horizontal gaps
Sunlight reaches forest floor in gaps
High degree of species diversity
The target late-successional forest condition emphasizes heterogeneity of structure and incorporation of legacy features that provide a broader array of habitat conditions, including those attributes needed by species uniquely associated with late-successional forest.
Society for Ecological Restoration, 7 April 2016

7. Siuslaw NF as a Component of the Coastal Oregon Landscape
The Siuslaw NF Comprises the major portion of federal forest lands in coastal Oregon
Landscape Legacies of Logging and Plantation Establishment
Increased fragmentation of older forest habitats
Reduced ecological diversity at stand levels
Loss of habitat for some species (e.g. Northern Spotted Owl, Marbled murrelet)
Increased edge effect
More than 90% of the Forest is allocated to reserves – both late-successional reserves and extensive riparian reserves
Society for Ecological Restoration, 7 April 2016

8. STUDS Objective
Characterize the effectiveness of thinning and underplanting to promote the development of structural variability, vegetative diversity and productivity in young, even-age Douglas-fir stands of high site index in the Oregon Coast Range
The Siuslaw Study was undertaken just prior to the designation of much of the Forest as late-successional reserve. To what extent could thinning and underplanting be used to speed the development of structural heterogeneity – to move these forest from the stem exclusion phase to the complex structure phase?
Important to this discussion is the
Society for Ecological Restoration, 7 April 2016

9. Research Questions
Is there development of older-forest structural characteristics?
Increased diameter growth
Development of a second cohort as ingrowth?
Is there vertical connectivity between ingrowth and residual overstory?
Snags and down wood?
Are early-seral opportunities persistent?
What is the rate of canopy closure?
The Siuslaw Study was undertaken just prior to the designation of much of the Forest as late-successional reserve. To what extent could thinning and underplanting be used to speed the development of structural heterogeneity – to move these forest from the stem exclusion phase to the complex structure phase?
Important to this discussion is the
Society for Ecological Restoration, 7 April 2016

10. Overstory Thinning Treatments
Unthinned plots: ~220 trees per acre (~545 trees per hectare)
Light thinning: 100 trees per acre (~250 trees per hectare)
Moderate thinning: 60 trees per acre (~150 trees per hectare)
Heavy thinning: 30 trees per acre (~75 trees per hectare)
Unthinned control plots: A baseline for measurements and demonstrate the pathway of development in unthinned plantations – the “no action alternative”
Light thinning: A typical stocking level which has been widely used in the past to maximize timber fiber production
Moderate thinning: A widely spaced approach designed to accelerate development of stand structural diversity and allow for future thinning
Heavy thinning: A very widely spaced thinning which mimics the densities in late-successional stands.
Society for Ecological Restoration, 7 April 2016

11. Understory Planting Treatments
Operational Planting Trial
Douglas-fir and western hemlock
435 tpa (~1075 tph)
Species Trials
Conifers: Douglas-fir, western hemlock, western redcedar, Sitka spruce, grand fir
Hardwoods: red alder, bigleaf maple
Two separate understory trials were included
Operational underplanting trial comparing performance of Douglas-fir and western Hemlock under different levels of overstory. These were planted at typical operational spacing.
The species trials include a suite of conifers representing various levels of shade tolerance, and a couple hardwoods, species that typically have not been planted but are recognized as providing functional diversity. These were planted in species rows at narrow spacing.
Society for Ecological Restoration, 7 April 2016

12. Initial Post-harvest Condition
Unthinned
Unthinned
75 TPH
75 tph
Some of the earliest responses to emerge from the study were strongly evident by the 8th year post-harvest. Three important features were:
Differential species growth and development of unplanted conifers and hardwoods
Substantial development of understroy vegetation
Rapid canopy closure
I will present some of these findings in the next slides. These results have been reported in the literature – a 2005 paper by Maas-Hebner et al. and a 2006 paper by Chan etal.
150 tph
250 tph
150 TPH
250 TPH
Society for Ecological Restoration, 7 April 2016

13. Early Development through Year 8
Unthinned
75 tph
Some of the earliest responses to emerge from the study were strongly evident by the 8th year post-harvest. Three important features were:
Differential species growth and development of unplanted conifers and hardwoods
Substantial development of understroy vegetation
Rapid canopy closure
I will present some of these findings in the next slides. These results have been reported in the literature – a 2005 paper by Maas-Hebner et al. and a 2006 paper by Chan etal.
150 tph
250 tph
Society for Ecological Restoration, 7 April 2016

14. Overstory Response: Stand Density
Unthinned treatment shows relatively consistent rates of mortality over the 20 year period of monitoring
Thinned treatments have less ongoing mortality and demonstrate ingrowth arising predominantly from planted conifers.
Figure showing decline in TPA over the 0-8 year period is misleading; the reduction actually occurred at time zero with the initial harvest.
Society for Ecological Restoration, 7 April 2016

15. Overstory Response: Mean Tree Diameter
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16. Overstory Response: Stand Basal Area
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17. Overstory Response: Bigger Trees Do Grow Faster
When sorted by diameter – the basal area growth rate per tree was greater in the largest twenty Douglas-fir.
Society for Ecological Restoration, 7 April 2016

18. Understory Light Response:
Unthinned
Light
Moderate
Heavy
46%
13%
25% 6%
One early finding that emerged was the rapidity with which canopies closed following thinning
Canopy cover in thinned units was relatively stable for 2-3 years following harvest, but then began to close between 3 and 8 years post-harvest – at a rate of about 2% per year
In contrast, canopy cover of the unthinned units tended to decrease slightly throughout as canopies receded
Rapid canopy closure suggests that increases in understory light due to thinning may be a very transitory phenomonen
Society for Ecological Restoration, 7 April 2016

19. Understory Vegetation
Averaged over all thinning treatments shrubs and herbs increased in cover following thinning, with shrubs demonstrating the most dramatic increases.
In unthinned stands, herbs tended to increase, possibly with increased filtered light, while shrub cover remained unchanged.
Society for Ecological Restoration, 7 April 2016

20. Understory Vegetation
Averaged over all thinning treatments shrubs and herbs increased in cover following thinning, with shrubs demonstrating the most dramatic increases.
In unthinned stands, herbs tended to increase, possibly with increased filtered light, while shrub cover remained unchanged.
Society for Ecological Restoration, 7 April 2016

21. Understory Vegetation Diversity
Measures of species diversity clearly indicate differences in community diversity between unthinned and thinned stands. However – different indices indicate different tendencies related to abundance weighted measures. Effective number of abundant species is increasing while the effective number of very abundant species is decreasing.
Society for Ecological Restoration, 7 April 2016

22. Understory Vegetation Diversity
Measures of species diversity clearly indicate differences in community diversity between unthinned and thinned stands. However – different indices indicate different tendencies.
Society for Ecological Restoration, 7 April 2016

23. Operational Planting – 15 Year Survival
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24. Operational Planting – Year 15 Seedling Height
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25. Operational Planting – Year 15 Height Distribution
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26. Operational Planting – Year 15 Height Distribution
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27. Operational Planting – Seedling/Sapling Slenderness
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28. Stand Structure – Diameter Distributions
Thinning and underplanting produces more large trees and provides opportunity for second planted cohort to develop. Natural regeneration is playing a very limited role in development of a secodntree cohort.
Society for Ecological Restoration, 7 April 2016

29. Thinning Impacts on Snag and Down Wood Recruitment: Observed Mortality
Society for Ecological Restoration, 7 April 2016

30. Conclusions: Overstory
Regardless of mortality, all stands grew following thinning
Mean tree diameter growth rate was greater for thinned stands than for unthinned stands
Individual tree diameter growth was greater for heavily thinned stands than for lightly or moderately thinned stands
The greatest rates of basal area accretion were in the larger diameter trees
Rates of canopy closure were high in thinned stands, particularly in the first 8-10 years
Society for Ecological Restoration, 7 April 2016

31. Conclusions: Understory
Abundance and diversity of herbaceous and shrub vegetation increased with increasing thinning intensity
Increased light was positively correlated to abundance of shrub and herbaceous understory vegetation
Natural regeneration was absent in unthinned stands and highly variable in abundance and composition among thinning treatments
Planted seedlings of more shade tolerant western hemlock have outgrown planted seedlings of Douglas-fir in thinned stands, but vigor of Douglas-fir may be improving
Planted understory pines are attaining heights that extend into the lower reaches of the overstory canopy
Douglas-fir - 11,400 to 26,100 tph; western hemlock to 8900 tph; red alder - 1,500 to 23,300 tph
Society for Ecological Restoration, 7 April 2016

32. Phase II: From Treatments to Regimes
Without further silvicultural intervention can the understory development initiated in a single thinning and underplanting be sustained?
How do we operationally harvest in a second thinning entry?
Impacts on advanced regeneration and understory vegetation?
Effects on legacy down wood and snags?
Potential damage to residual overstory trees
What are the economic considerations in a second thinning
Operational constraints on production rate?
Economic value of harvest?
Influence of initial thinning on wood quality?
Society for Ecological Restoration, 7 April 2016

33. Thank you! Dan Mikowski, USFS PNW Bill Emmingham, Oregon State Univ.
Sam Chan, USFS PNW
David Larson, USFS PNW
Kathleen Maas-Hebner, Oregon State Univ.
Dennis Dykstra, USFS PNW
Doug Maquire, Oregon State Univ.
Loren Kellogg, Oregon State Univ.
Steve Pilkerton, Oregon State Univ.
Society for Ecological Restoration, 7 April 2016

34. Understory Vegetation Diversity
Measures of species diversity clearly indicate differences in community diversity between unthinned and thinned stands. However – different indices indicate different tendencies.
Society for Ecological Restoration, 7 April 2016

35. Large–Scale Silviculture Studies of the Pacific Northwest10 20 30 40 50 60 70 90 80
100
Treatment-Wide Percent Residual Basal Area (%)
Matrix as Percent of Total Treatment Area (%)
CFS (4a)
DEMO (2a)
DEMO (3a)
DEMO (4a)
DEMO (3b)
STUDS (2a)
STUDS (4a)
STUDS (3a)
YSTDS (2a)
YSTDS (2b)
YSTDS (4a)
UAMP (4a)
CFS (2a)
UAMP (2b)
OHDS (3a-d)
LTEP (5a-d)
FES (3a-b)
DMS_RT (3a)
DMS_IT (3b)
DMS_IT (3a)
DMS_IT (2a)
gap (overstory removed)
patch (unthinned)
10 ac
Controls (1a)
CWS (3a)
CWS (4a)
CFS (5a)
DEMO (4b)
CFS (3a)
CFS (3b)
(unthinned)
CWS (4b-c)
LTEP (3a-b)
UAMP (2a)
Poage and Anderson (2007)
Society for Ecological Restoration, 7 April 2016