Environmental Engineering Reference
In-Depth Information
under the infl uence of natural disturbances including
insect outbreaks, wildfi re and windstorms (Wimberly
et al
. 2000). Only about 10% of the temperate rain-
forest within western Oregon and Washington is pres-
ently in old-growth conditions (Forest Ecosystem
Management Assessment Team (FEMAT) 1993). An
estimated 80% of the original old growth in large
valleys along the mainland coast of British Columbia
has been logged (Ministry of Forests 2003). Generally,
there is more unlogged rainforest in the north, and
progressively less in the southern and eastern parts of
the region.
Relatively large patches of never-logged rainforests
persist and do not require ecological restoration. These
forests have infrequent fi res despite naturally high
levels of fuel accumulation. They lack roads, and do
not have invasive species. The main risks to these
remaining old-growth forests are from activities on
nearby or adjacent lands, particularly fi res that origi-
nate elsewhere, or from windstorms that blow unim-
peded across adjacent clearcuts.
Previously logged forests of Cascadia today are char-
acterized by dense conifer plantations, or young mixed
hardwood and conifer stands where replanting did
not occur. Managed forests often have dense road net-
works and can be highly impacted by invasive species.
Unplanted clear-cuts sometimes have dense shrub
growth that inhibits tree regeneration for decades.
Older clear-cuts that were not replanted (replanting
was uncommon until the 1950s) tend to be dominated
by hardwoods, particularly alder and maple. Maple is
long-lived and shade-tolerant, and can also inhibit
regeneration of conifer trees if left untreated. A big
concern in the Pacifi c Northwest is forest fragmenta-
tion - the reduction of the size of forest patches - par-
ticularly in old, late-successional forest (Altman &
Hagar 2007 ).
The main restoration issues for previously logged
forests of the Northwest are:
• Low complexity of forest structure in young, even -
aged, hardwood or shrub-dominated forest stands.
• Excessive
was created to protect and recover old-growth forest
dependent species, most notably the Northern spotted
owl (FEMAT 1993). A typical restoration approach
entails thinning dense young stands in a variable
manner so as to create openings, reduce competition
and encourage more rapid tree growth. A goal is to
establish more vertical and horizontal diversity as well
as patchiness of spatial
heterogeneity
at both the
stand and landscape scales (Tappeiner
et al
. 1997 ;
Carey
et al
. 1999 ; Franklin & Norris 1999 ; Franklin
et
al
. 2002 ; Muir
et al
. 2002 ; Apostol & Sinclair 2006 ).
Existing roads are used for thinning operations, and
may be removed or decommissioned after one or more
thinning operations are completed.
Road removal and decommissioning are important
aspects of forest restoration in Cascadia. Many logging
roads were built on steep mountain midslopes, with
soil material cut from the high side and deposited on
the low side. Frequent culverts cross these roads. The
culverts are often undersized and are not well main-
tained. Fill slopes are subject to failure due to weight
and lack of compaction, resulting in numerous wash-
outs and debris fl ows that have badly damaged for-
merly productive salmon streams (Apostol & Sinclair
2006). Full restoration involves removing drainage
structures and pulling the fi ll material back up onto
the road bed to match the pre-existing contours as
much as possible. This is a very expensive operation,
often costing US$6700 or more per linear kilometre
(Napper 2006 ).
More commonly, roads are 'stabilized' by pulling out
the undersized culverts and replacing them with
surface drain dips. This prevents debris build up and
catastrophic failures. Roadbeds are ripped and reseeded
or planted (Bagley 1998). Where continued access is
needed, culverts are replaced with larger, 'salmon-
friendly' stream crossings. New roads are kept narrow,
and are regraded to allow water to run directly across
them rather than alongside them. This eliminates the
need for ditches and culverts, and reduces mainten-
ance costs.
Variable thinning is designed to create a more het-
erogeneous forest structure and composition, reduce
susceptibility to insect, disease and fi re - induced
mortality and accelerate the rate at which remaining
trees grow by removing competition. Conventional
forest thinning attempts to maximize wood fi bre
development, while restoration thinning maximizes
structural complexity and, presumably, biological
diversity.
numbers
of
roads,
some
of
which
are
poorly built.
• Invasive species, particularly in or near urban areas.
• High tree density in older multilayer forests impacted
by fi re exclusion.
• Fragmentation of remnant forest patches.
Active restoration is increasingly common on public
forest lands where old growth conifer conditions are
desired. The Pacifi c Northwest Forest Plan of 1993
