Environmental Engineering Reference
In-Depth Information
13.1
INTRODUCTION
from the northwestern part of this region and head-
ing east and south - east, conifer - dominated rainforests
extend from south-eastern Alaska, south through Bri-
tish Columbia, Washington, Oregon and northern Cali-
fornia. These rainforests generally extend only about
150-300 kilometres inland, to the mountain spine
that includes the Coast and Cascade ranges in the
Northwest, and the Northern Sierra Range in Califor-
nia. Islands of rainforest extend further east, with out-
liers in Glacier National Park in western Montana,
some 800 km east of the Pacifi c coast (Smith et al .
2007). As one travels south and east, the climate
becomes more continental and drier, and rainforests
give way to fi r or oak-pine woodlands in southern
Oregon and northern California, and from there to
pine - fi r forests and woodlands east of the mountain
spine. The Intermountain West of the continent (the
area generally between the Cascade-Sierra and Rocky
mountains) is a series of high, mostly north-south-
oriented mountain ranges separated by deep and wide
valleys. The US Forest Service reports that the inter-
mountain western United States has forest cover on
more than 20% of the total land area. Hardwood
forests in the form of aspen stands ( Populus tremuloides )
and riparian cottonwoods ( Populus spp.) make up about
7% of all the forests in the west (Smith et al . 2007 ).
Annual precipitation varies greatly with elevation,
with effects on plant assemblages all across the region.
The Pacifi c rainforest region is dominated by sitka
spruce ( Picea sitchensis ), Alaska yellow cedar ( Chamae-
cyparis nootkatensis ), western red cedar ( Thuja plicata ),
western hemlock ( Tsuga heterophylla ), Douglas fi r
( Pseudotsuga menziesii ) and, in the south, the famous
coast redwood ( Sequoia sempervirens, ) which is among
the tallest trees on Earth. Deciduous trees play a minor
role, usually limited to early-successional stages follow-
ing disturbance, though bigleaf maple ( Acer macrophyl-
lum ) is fairly long lived, is somewhat shade-tolerant,
and can persist for hundreds of years. Conifers, par-
ticularly Douglas fi r, redwood, spruce and cedar, can
live well over 1000 years (Franklin & Dyrness 1988).
The southern part of the northwest region has a wide
variety of oaks and oak relatives, including Oregon
white oak ( Quercus garryana ), California black oak
( Quercus kelloggii ), canyon live oak ( Quercus chrys-
olepis ), brewers oak ( Quercus brewerii ), tanoak ( Lithocar-
pus densifl orus ) and chinkapin ( Castanopsis chrysophylla ),
a relative of the chestnut. Pine trees also become more
dominant as one moves south, including ponderosa
( Pinus ponderosa ) and sugar pine ( Pinus lambertiana ). In
In this chapter we present an overview of ecological
restoration within temperate forests of western North
America, including Canada and the United States, but
not Mexico. We discuss historic changes to these forests
and conservation and restoration policies that infl u-
ence restoration. A case study is included that provides
a restoration perspective on ponderosa pine forests in
Colorado state, which presents issues typical across the
Intermountain West.
We believe there are four major conclusions about
restoration of western North American forests illus-
trated in this chapter:
• Forest restoration needs vary across western North
America as a function of forest type and related
geography.
• The biggest restoration challenge in forests of the
Pacifi c Northwest, United States, is stitching older,
structurally complex forests together using restoration
silviculture and road removal.
• The biggest restoration challenge in the inter -
mountain area is thinning out forests to improve fi re
resistance and resilience .
• The problem is huge, restoration is only part of the
answer to forest conservation, and managers are learn-
ing as they go.
Western North America - generally lands west of the
continental divide - includes highly varied temperate
forests adapted to a wide range of climate, elevation
and aspect. For the purposes of this chapter, these
forests can be divided into four subregions (see Figure
13.1); they are bounded on the north by boreal forests
of Canada and Alaska, and, to the south, by the tem-
perate and subtropical forests and woodlands of
Mexico. While still largely 'natural' in comparison to
temperate forests elsewhere, these North American
forests have been altered and degraded as a conse-
quence of logging, road building, fragmentation and
changes to fi re frequency and intensity. It is these
changes that necessitate restorative work.
Forests across the region are mostly of natural
origin, with a majority of them in public ownership.
About two thirds of the forests of the United States
within 'Cascadia', also known in the United States as
the Pacifi c Northwest, are in public ownership, and
75% of the forests of the Intermountain West are
public. In western Canada (British Columbia and
Alberta) well over 90% of the forests are owned by the
public, managed by provincial governments. Starting
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