Environmental Engineering Reference
In-Depth Information
settlement in the mid-1800s (Oregon Biodiversity Project 1998; Oregon Department
of Fish and Wildlife 2006). The story of Willamette Valley oak savannas and wood-
lands provides dramatic illustration of the complex interplay between ecological dy-
namics and evolving human values, preferences, needs, and constraints.
The history of oak savanna corresponds to the history of human presence in the Pa-
cific Northwest; both date back more than six thousand years to the end of the most re-
cent dry period in North American climate (Stein 1990). Carbon and pollen studies
reveal no natural baseline for Oregon white oak habitat conditions. Instead, it appears
the habitat assumed a range of ecosystem functions and disturbance patterns through-
out its history (McShea and Healy 2002). For example, tree core data from several
sites in the Pacific Northwest indicate Willamette Valley oaks burned frequently by
low-intensity fires, but only between the mid-1700s and 1900 (Agee 1993). This lack
of consistency suggests that oak may have conformed more to variations in human ac-
tivity than to other ecological processes.
Kalapuya and other local Native American groups were some of the first people to
shape Willamette Valley ecosystems to meet their needs. Prior to European settle-
ment they used fire as a management tool to maintain gardens of camas (
Camassia
quamash
), a native prairie plant whose starchy bulb was a food staple, and to foster the
growth of tarweed, grasshoppers, nut and berry plants, and bracken fern rhizomes
(Agee 1993; Boyd 1999). They also set fires to herd deer for hunting. Oregon white
oak (
Quercus garryana
) is adapted to fire in ways that other species are not. Its thick
bark protects the delicate cambium, and dormant buds are located low on the root
collar below the soil surface so they can sprout even after fire (Tveten and Fonda
1999). The fires the Kalapuya set thinned the understory of the oak woodlands and sa-
vannas, maintaining the stands' open structure, enhancing tree vigor and seedling re-
generation, and increasing mast crops for consumption by both humans and game
(Agee 1993, 1996; Boyd 1999; Peter and Harrington 2002; Van Lear and Brose 2002).
The fires also limited infestations by invasive plants and acorn-boring insects (Ander-
son 2005). The net effect of Kalapuyan management was to create an overstory of
widely spaced, large-crowned Oregon white oak trees with an understory of shrubs
and perennial native grasses (Agee 1990).
Euro-American pioneers in the Willamette Valley also burned the land (Boyd
1999). Yet these settlers who displaced the Native Americans also brought with them
a set of values, preferences, needs, and constraints that stood in stark contrast to those
of their predecessors. Where Kalapuyans saw prime camas grounds, settlers saw po-
tential pastures and crop fields. In open oak woodlands they saw cabin logs, lumber,
and well-drained agricultural fields. And in wildfire they saw a threat to their homes
and settlements. As a result, camas fields were ditched and drained, wooded savannas
were cleared and plowed, and, in the absence of fires, oak stands developed thick un-
derstories and conifers, such as Douglas fir (
Pseudotsuga menziesii
), encroached on
and outcompeted oak in the canopy.
As the region became the nation's timber basket during the twentieth century,
landowners cultivated and encouraged Douglas fir anywhere it would grow, convert-
ing oak-canopied pastures, fields, and woodlands to timber plantations. Farmers shift-