Environmental Engineering Reference
In-Depth Information
ing to more lucrative crops, such as rye grass, may also have removed savanna oaks
that cast shade onto their fields on the valley floor. In the foothills, residents viewed
woodlands, open meadows, and savannas primarily as candidate areas for conversion
to other uses, such as residential areas, timber and Christmas tree plantations, and
vineyards, often with assistance from natural resource professionals (Fischer and Bliss
2009).
The Willamette Valley is now home to the cities of Portland, Eugene, Salem, and
Corvallis, and to 70 percent of the state of Oregon's population. On sites with better
soils, dense stands of Douglas fir are managed for timber production on industrial
ownerships, habitat and water on public ownerships, and mixed objectives on family
ownerships. Pure oak stands remain only on marginal sites where other species cannot
thrive and for which people have found no other use or value. One legacy of Euro-
American settlement that has had a dramatic effect on essentially all Willamette Val-
ley oak sites is the introduction of nonnative species, notably Himalayan blackberry
(
Rubus discolor
) and false brome (
Brachypodium sylvaticum
).
The forest and human landscapes of the Willamette Valley coevolved; as human
needs and culture changed, so did landscape structure. Through their use of fire, the
Kalapuyans had, in effect, shaped the ecosystems of the valley to suit their needs; the
needs of people living at low population densities in scattered communities moving
seasonally across a dynamic landscape. Euro-American settlement, elimination of
fire, and shifts in forestry and agriculture further changed the landscape. A century
and a half later, subsequent generations of residents are continuing to transform the
landscape, shaping it to reflect prevailing values, needs, preferences, and constraints.
In the 1990s, a movement emerged to protect remnant oak stands and restore oak
to the valley. Catalyzed by the recognition of oak woodlands and savannas as two of
the most threatened habitats in the state of Oregon (Oregon Biodiversity Project
1998), the Oregon Oak Communities Working Group formed to support the conser-
vation and restoration of oak. Composed of scientists, extension foresters, landowners,
and representatives of conservation organizations, the group focused their initial ef-
forts on the Willamette Valley, where oak savannas historically dominated the land-
scape. The lack of accurate statistics on the historical range of oak woodlands and sa-
vannas in the valley hampered establishment of restoration goals; consequently target
conditions have been the focus of some debate (Fischer and Bliss 2009). Further-
more, invasive species are so ubiquitous, persistent, and resistant to control in the re-
gion that some land managers have accepted “structural” rather than comprehensive
ecological restoration as their goal; that is, failing to successfully replace false brome
with native grasses, they have settled for a target of oaks over grass—any grass (Fischer
2006). Nonetheless, the working group has guided landowners and managers
throughout the Willamette Valley in the restoration of Oregon white oak woodlands
and savannas, removing invasive species, thinning oak stands to favor growth on dom-
inant stems, and, in some cases, reintroducing fire.
What can we learn from the story of these Willamette Valley ecosystems? First,
oak woodlands and savannas are “anthropogenic” ecosystems; that is, human interac-
tion is integral to their establishment and maintenance. While not all ecosystems are
