Historic Anthropogenically Maintained Bear Grass Savannas of the Southeastern Olympic Peninsula
David Peter and Daniela Shebitz. 2006. Historic Anthropogenically Maintained Bear Grass Savannas of the Southeastern Olympic Peninsula. Restoration Ecology Vol. 14, No. 4, pp. 605–615
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Abstract:
This paper documents the existence and character of a little known fire-maintained anthropogenic ecosystem in the southeastern Olympic Peninsula of Washington State, U.S.A. Due to cessation of anthropogenic burning, there is no longer an intact example of this ecosystem. We present evidence from Skokomish oral tradition, historical documents, floral composition, tree-ring analysis, stand structure, and site potential to describe former savanna structure and function. We believe this system was a mosaic of prairies, savannas, and woodlands in a forest matrix maintained through repeated burning to provide culturally important plants and animals. The overstory was dominated by Douglas-fir (Pseudotsuga menziesii). Bear grass (Xerophyllum tenax) likely was a dominant understory component of the savannas, woodlands, and prairie edges. These lands grew forests in the absence of anthropogenic burning. Wide spacing of older trees or stumps in former stands and rapid invasion by younger trees in the late 1800s and early 1900s suggest a sudden change in stand structure. Shade-intolerant prairie species are still present where openings have been maintained but not in surrounding forests. Bark charcoal, fire scars, tree establishment patterns, and oral traditions point to use of fire to maintain this system. A common successional trajectory for all these lands leads to forested vegetation. These findings suggest that frequent application of prescribed burning would be necessary to restore this ecosystem.
Introduction
Some anthropogenically maintained ecosystems owe their character to cultural burning and are inherently unstable when management practices change. Fire-dependent habitats that were maintained through burning by Native Americans include the prairies and savannas of western Washington State, U.S.A. Although these habitats were common in the region prior to European settlement (Jones 1936; Norton 1979; Leopold and Boyd 1999), their former extent in the southeastern Olympic Peninsula is not well known. …
Prior to European settlement, anthropogenic burning in many areas was regular, constant, and long term, causing cumulative effects reflected in current plant communities and species distributions (Pyne 1982; Anderson 1996, 2005; Boyd 1999). Prairie and savanna flora and fauna were integral components of diets, medicines, baskets, and rituals of local tribes (Norton 1979). The most significant sources of complex carbohydrates in the diets of Olympic Peninsula tribes came from bulbs and rhizomes found in prairies and savannas. Bracken fern (Pteridium aquilinum (L.) Kuhn) and Common camas (Cammasia quamash (Pursh) Greene) were commonly used by the Skokomish and other native peoples in wetter Washington coastal environments (Gunther 1974; Norton 1979; Deur 2000). Berries growing in prairie forest ecotones were important sources of sugars and vitamins. Bear grass, used in Skokomish basketry and burial ceremonies (Gunther 1974; Shebitz 2005), also grew historically on the periphery of prairies (B. Miller, Skokomish Tribe, 2004, personal communication). According to Skokomish oral tradition, fire intervals were determined, in part, to maximize production of Trailing blackberry (Rubus ursinus Cham. and Schlecht) (B. Miller, Skokomish Tribe, 1996, personal communication). Prairies and savannas provided important Blacktail deer (Odocoileus hemionus) and Elk (Cervus canadensis) winter range, and were convenient places to hunt (Kruckeberg 1991; B. Miller, Skokomish Tribe, 2004, personal communication). …
Our objective is to provide evidence for the historic existence and character of an anthropogenically managed savanna ecosystem on the southeastern Olympic Peninsula of Washington as mixed prairie forest areas supporting extensive patches of bear grass. We compare data from two vegetation types identified on 1929 aerial photographs as savanna and matrix forests and describe forest invasion of savannas in the late 1800s. We interpret current vegetation in light of tree-ring analysis, fire history, and native oral traditions to reconstruct former savanna vegetation. We discuss our results in terms of site potential, cultural influence, and fire history. This information is assisting current efforts of the Olympic National Forest (ONF) in restoring savannas to the area. …
Discussion
The modern moist maritime climate of western Washington developed about 4,500 years ago (Barnosky 1983) and does not support the frequency of natural fire required to maintain savannas. Rapid forest succession on former savannas after 1877 demonstrates forest potential in the absence of anthropogenic fire. In most of western Washington, fire-return intervals ranged from 90 to 300 years, with forests, not savannas, developing between fires (Henderson et al. 1989; Agee 1990).
The past existence of bear grass savanna is supported by open areas in the 1929 aerial photographs with few snags or logs; remnant prairie species; large, old, widely spaced Douglas-firs with low limbs; bark charcoal and fire scars; and lack of mound-pit topography. Skokomish oral traditions, court testimony, and high fire frequency required for open conditions suggest anthropogenic management. …
People have likely inhabited western Washington for the past 10,000 years (Ames and Maschner 1999). Although we have little knowledge of their cultures, it has been suggested that anthropogenic burning to maintain open areas on the Olympic Peninsula began over 3,500 years ago (Wray and Anderson 2003). Olympic Peninsula tribes used controlled burns to favor specific plants even after the establishment of reservations in the mid-1800s (James and Chubby 2002). …
Jones (1936) described bear grass in “open park-like forests” transitioning to closed forest. The successional trajectory of abandoned bear grass savanna under current climate is toward forest of the Western hemlock/salal/bear grass or similar plant associations (Henderson et al. 1989). …
In our study area, low-intensity savanna fires might not have scarred many trees, so tree-ring records are not adequate to determine the fire-return interval. Kertis (1986) found an apparent anthropogenic fire frequency of 11–34 years from the mid-1700s to 1900 in oak woodlands about 30 km northeast of our study area, but this conservative estimate was based on few trees and only on fires hot enough to cause scars. Miller (B. Miller, Skokomish Tribe, 2004, personal communication) stated that the Skokomish Tribe burned about every 2–3 years. Because stand structure varied from parklands to open prairies, we suspect that more open core areas were burned at short intervals (2–3 years), whereas peripheral areas burned less frequently and possibly incidentally, depending on weather conditions during burning. …
Conclusion
We conclude that an anthropogenic bear grass savanna ecosystem was an important part of the southeast Olympic Peninsula vegetation for at least the last several hundred years. Flora, fire history, 1929 aerial photographs, historical documents, and oral traditions all support its existence. Its anthropogenic nature is supported by Skokomish oral traditions, historical accounts, and a historical fire regime in surrounding forests that is too infrequent to account for savanna structure. …
There is no single model for restoration, so understanding ecosystem function is essential. Although the processes that created the community may not operate the same today, if modern cultures see value in former ecosystems, an understanding of those processes may enable sufficient restoration of the structural and floral components to provide those values. By working with indigenous cultures, there is great potential to understand the pivotal role that traditional land management practices played in shaping the landscape. But beyond the mechanistic understanding of how things came to be, is the revitalization of the culture that gave purpose to this landscape in the beginning. In the end, it will be the success of this cultural revitalization and the degree to which it finds sustenance in the extended societal matrix that will determine the success and longevity of the landscape restoration. …
