Environmental Engineering Reference
In-Depth Information
Hardwoods are a natural early-successional stage
in the forests of Cascadia. In some cases, hardwoods
are much more dominant today than they were his-
torically. Bigleaf maples can form long-lived near-
monocultures in some forests, because they sprout
from stumps after disturbance and quickly form a
canopy that shades out conifer seedlings and inhibits
their regeneration. Forest restoration in maple-
dominated forests therefore typically includes thinning
and herbicide use to prevent additional stump sprouts.
Alder, another important northwestern hardwood, is
short-lived and not shade tolerant. It is also a nitrogen
fi xer that prepares the way for subsequent conifer and
understorey growth. Consequently alder-dominated
stands are often seen as a successional condition that
does not need to be managed if restoration is the goal.
However, in some cases land managers have thinned
alder to make space for planted conifers to speed the
regeneration and development of conifer trees, par-
ticularly in riparian areas where large trees that
eventually fall into streams are important for stream
restoration and the
reinforcement
of salmon
populations.
Oak savannas and woodlands are an important eco-
logical and cultural component of Cascadian forests.
They range from southwestern British Columbia,
into southern Oregon and California, with increasing
species diversity in the south. The native oaks are fi re-
adapted and fi re-dependent species. They need fi re to
keep competing vegetation at bay, and in its absence,
they can be overtopped and out-competed by both
Douglas fi r and grand fi r. Oak woodland and savanna
restoration projects are occurring across Cascadia.
Generally restoration includes cutting or killing in
place competing conifer trees, removing invasive,
mostly non-native brush, reseeding or planting the
understorey with native bunchgrasses and forbs, and
in some cases reintroducing fi re (Apostol & Sinclair
2006 ).
There are no comprehensive data available on the
extent of conifer and oak woodland restoration taking
place within Cascadia, but it is widespread and expand-
ing. The two US federal agencies that control much of
the forest land in the region are actively engaged in
restoration at a scale of tens to hundreds of thousands
of hectares a year (US Department of Agriculture and
US Department of Interior (USDA and USDI) 2011).
Over 1700 km of roads have been removed or stabilized
on National Forests of the Pacifi c Northwest in 2008
alone (USFS 2009). Oak woodland restoration is
being done by local governments, by nongovernmental
organizations such as the Nature Conservancy and by
private landowners.
13.3.2
Interior Western forests
Dry temperate forests of interior western North
America are also the focus of restoration work, but the
dominant issues there are forest health and fi re ecology.
Most interior forests are fi re adapted and fi re depend-
ent. Ponderosa pine is the single most widespread tree
in western North America (Burns & Honkala 1990). It
currently occurs on circa 16 million hectares in the
western United States (Arno 1996), and is extremely
well adapted to fi re. It develops a thick protective bark
even at a very young age. Typically ponderosa pine
forests were on a 7 - 25 - year fi re cycle, with fi res origi-
nating by either Indian burning or lightning. The fi res
kept tree spacing wide and understorey vegetation
(known in North America as brush) at a minimum
(Arno 1996). Elimination of the historic pattern of
frequent low - intensity fi res in ponderosa pine and
pine-mixed conifer forests has resulted in dense thick-
ets of small trees and are experiencing insect and
disease epidemics and severe wildfi res (Arno 1996).
It is estimated that hundreds of millions of hectares
of interior western forests are currently outside their
natural range of variability due to the relative absence
of fi re (Nature Conservancy 2010). In some cases,
such as mixed
fi re regimes
in large wilderness areas,
restoration of these forests can be accomplished by
guiding or managing naturally occurring fi res. How-
ever, in many other areas restoration requires more
active management, particularly thinning, to help
create a more natural forest spacing and structure
before it is safe to bring fi re back into the system. Thin-
ning can be a temporary strategy eventually replaced
by fi re alone, or it can be a continuous tool where
reintroducing fi re is not practical or desired (Arno &
Fiedler 2005 ).
The fi rst recorded efforts to use both cutting and
burning to restore interior pine forests was in 1984 at
the Lubrecht Experimental Forest, managed by the Uni-
versity of Montana (Arno & Fiedler 2005). Since that
time, this approach has become widespread, and federal
agencies in particular have been diligent about reduc-
ing fuel loads. Since 2001 over 14 million hectares
have been treated to reduce fuels. In 2009, the Forest
Service provided a breakdown between restoration
