Transcript Alaback – Opportunities for Restoring Second Growth Ecosystems

Opportunities for Restoring
Second Growth Ecosystems
in Staney Creek:
Scientific Principles
Acknowledgements
Funding provided by:
• U.S. Forest Service, Pacific Northwest
Research Station
• Tongass National Forest, Thorne Bay
Ranger District
• The Nature Conservancy
Fieldwork and analysis: Dee Casey, Kim Hastings,
Mike Ausman
First Some History
Its hard to know where you are going
or where to go if you don’t know
where you have been!
Staney Creek 1976
What Made Staney Creek
so Special in the 1970’s?
• Large concentration of high timber
volume
• Easy accessibility with new road
system
• High value watershed for fisheries
and wildlife (and recreation)
Unique disturbance ecology:
Exposure to very infrequent but
high intensity winds
Implications of Disturbance
• Series of high wind events led to
establishment of many high-volume evenaged forests- with exceptional economic
value
• These same ecological factors led to
challenges in controlling wind damage to
residual stands and ultimately led to large
clearcuts
Staney Creek 2009: extensive
older second growth forests
Forest Resource Issues
Created by Second-Growth
• Secondary forests provide poor habitat
for many wildlife species
• Poor connectivity between high elevation
forest and critical winter range for
wildlife
• Economic costs and ecological implications
of roads
• Economics of wood utilization
• Riparian habitat degradation
Wildlife habitat in forests
Primarily a function of:
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Vegetation structure
Habitat Connectivity
Forage quality
Microclimate and soils/geology
Vaccinium parvifolium
Shaheen Creek
Greatest overall structural diversity and understory
Development usually found in old-growth habitats
Older Secondary Forests provide
poor habitat because:
• Little browse (Vaccinium spp.)
• Poor cover by nutrient-rich
forbs
• Less structural diversity
• Dense canopies provide little
light at understory level
Key challenges for forest
understory plants
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Low or variable sunlight
Less thermal energy during day
Little wind for pollen/seed dispersal
Competition with trees for nutrients
and moisture
• Few “safe sites” for establishment of
new seedlings
Lots of other examples of managed forests
providing poor habitat - but effects transient
Scots pine
plantation
30 years
130 yrs
40 years
400 yrs
Alaback (1982)
If shade and tree density is
the problem then is thinning
the solution?
Problems with fix-spaced
thinning
• Transient response (10-15 years)
• Greatest effect in intermediate spacings
(10-14’)
• Older stands with poor shrub response
Present Condition and
Trends
• Dense older second growth forest
dominates watershed which constrains
wildlife habitat for many key species
• Without management treatments it is
unlikely that wildlife habitats will change
for at least 50 years
• Residual old growth forest patches of key
importance
• Thinning can improve habitat, but effects
are transient
Photo: Mike Ausman
Desired Future Conditions
• Improve wildlife habitat
•Increase overall biodiversity
•Increase landscape connectivity
•Increase economic value of forest
and opportunities for niche markets
How can we best restore
understory biodiversity to
second-growth forests?
1. Provide more resources through fixed-spaced
thinning
2. Create a more heterogenous environment through
variable spaced thinning or canopy gaps
3. Some combination of these approaches?
Resources (light, nutrients)
Evolutionary
Diversification
& history
Biodiversity
Habitat heterogeneity
Landscape
connectivity
Resources (light, nutrients)
Evolutionary
diversification
& history
Biodiversity
Habitat heterogeneity
Landscape
connectivity
Plant species richness closely predicted at regional scales
From energy availability (actual evapotranspiration) (Currie 1999 Am. Nat.)
homogeneity
Natural disturbance
Management
heterogeneity
Why what works
for carrots may
not work as well
for forest
ecosystem
biodiversity
Gap dynamics in tropical
Rainforests -- helps explain
High diversity
Dipterocarp tropical rainforest
Indonesia (S. Siebert)
(Orians 1981)
Small canopy gaps:
Dominant disturbance
Regime: 1-4/trees,
1-4% per year:
Creates stand
heterogeneity
(Ott & Juday 2002)
Extreme landscape heterogeneity
How does thinning affect
habitat heterogeneity in
these forests?
• Compared fixed-spaced thinning and diameterlimit thinning on well and poorly-drained sites
• Evaluated initial effects on canopy & understory
structure
Alaback & Casey, ms.
Effects of
thinning on
spatial
structure
Following thinning:
• Enhanced or suppressed structural
heterogeneity depending on initial stand
condition
• Diameter-limit approach may enhance
heterogeneity, but more replication is needed
to determine generality of this result
Direct enhancement of
heterogeneity: canopy gaps
• Canopy gaps established from 30’ to 150’ in
diameter in critical wildlife habitat areas
• Effects contrasted with thinned and
unthinned forest landscapes
• Summers 2008-9 measured 20 year
response to treatments on 75 sites
CANOPY GAP
THINNED FOREST
Photos: Mike Ausman
CANOPY GAP
UNTHINNED FOREST
Photos: Mike Ausman
20-Year Understory Response to
Gap Treatments
(2008 data only)
• Restoration of understory biodiversity a
difficult and long-term task
• Thinning alone will not restore diversity or
function
• Canopy gaps show more consistent results
than thinning
• The most promising approach is to combine
thinning and gap treatments at the stand and
landscape scale and tailor for management
goals
The Olympic Model of
Second Growth Management
• Goal is to create complex multi-canopy layer
forest that provides habitat for old-growth
dependent wildlife species
• Create control (unthinned) patches as cover
habitats, and for species that grow in shade
• Create matrix of thinned forest
• Establish canopy gaps within the thinned matrix
• Provide greatest habitat patch diversity at stand
scale and greatest species diversity within gap
treatments
(after Harrington et al. 2005)
The “Olympic Model” After Harrington et al. 2005
Thinned matrix
Canopy
gap
Skip
Shaheen Creek
Old growth always will be distinct from managed second growth
Key Points
• Staney Watershed dominated by second growth
with poor wildlife habitat values
• Biological value of forests can be significantly
enhanced through thinning and canopy gaps
• Effects of thinning are transitory, but canopy
gaps have longer-term effect
• Residual old growth forests play key role in
landscape diversity
• Greatest promise lies in combining treatments at
both stand and landscape scales to promote both
wildlife habitat diversity and a diversity of other
resource benefits