Reconstructing Historic Ecotones Using the Public Land Survey: The Lost Prairies of Redwood National Park
Joy A. Fritschle. 2008. Reconstructing Historic Ecotones Using the Public Land Survey: The Lost Prairies of Redwood National Park. Annals of the Association of American Geographers, 98:1, 24-39
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Abstract
Restoration of natural systems depends, in part, on reconstructing historic landscapes to serve as reference ecosystems. The most effective historic landscape reconstruction relies on multiple lines of evidence at different temporal and spatial scales. This study analyzes original Public Land Survey (PLS) records and compares the results with previous work that relied on dendroecology and aerial photograph evidence of vegetation change. Notations in the land survey regarding the location of prairie-woody vegetation ecotones in the Bald Hills of Redwood National Park were transcribed into a geographic information system. Sugihara and Reed (1987) measured the degree of coniferous forest encroachment into prairies and oak woodlands, estimating a 29 percent loss in the spatial extent between 1850 and 1983. The location of 1875–1882 land survey records of ecotones provides evidence that transects across the prairies might have narrowed by as much as 44 percent. Furthermore, this study found evidence of both oak woodland and coniferous forest encroachment into prairies, and that the diminishment of prairies further inland might result primarily from the expansion of oak woodland. A reconstruction of the historic landscape that relies on both field and archival evidence is the best approach to defining reference ecosystems.
Introduction
The restoration of degraded ecosystems can improve the conservation of species, ecosystem productivity, and the welfare of human communities affected by those ecosystems (Dobson et al. 1997; Moore, Covington, and Fule 1999; Primack 2002; Gann and Lamb 2006). The principles and practices of ecological restoration are broadly conceived as “the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed” (Society for Ecological Restoration Science & Policy Working Group [SER] 2002, 2).
Recovery of an ecosystem does not mean the re-creation of an ecosystem to a particular point in history. Rather, it entails a return to the historical or evolutionary trajectory: states in which the ecosystem is structurally and functionally sustainable when subjected to the normal ranges of disturbance and stress (SER 2002). Reaching the desired trajectory requires a thorough knowledge of the current and historical ecology of a site (Moore, Covington, and Fule 1999; SER 2002; Egan and Howell 2005).
Sound restoration planning and evaluation relies on the identification of reference conditions along the trajectory. These reference conditions, or reference ecosystems, involve historical accounts of the ecosystem prior to degradation, and, when available, analyses of contemporary analogous ecosystems that have not been significantly degraded (SER 2002; Egan and Howell 2005). The reconstruction of historic landscapes is critical to the identification and application of reference ecosystems in ecological restoration. …
Study Area
The lower Redwood Creek basin (197 km2) in Redwood National Park (Figure 1) typifies the west-to-east trending vegetation patterns found in the northern redwood region (Olson, Roy, and Walters 1990). On the steep slopes closest to the coast, salt-spray-tolerant Sitka spruce (Picea sitchensis) dominates the forest. Slightly more inland, sheltered from salt spray and constant ocean winds, coast redwoods (Sequoia sempervirens) predominate.
Following the rivers inland to the drier, more fire-prone environments, Douglas fir (Pseudotsuga menziesii) takes over the forest with expanses of prairies and Oregon oak (Quercus garryana) woodlands on the south-facing ridges and upper slopes. Elevations extend from sea level to 1,600 meters; consequently topographically influenced water availability and fire regime appear to be the primary influences for the distribution of plant communities in the basin (Environmental Protection Agency 1998).
Pollen evidence indicates that the vegetation in the region was relatively stable for most of the 5,000 years prior to 1850 (West 1983), although pollen data would not likely identify local changes in the vegetation, such as ecotonal shifts.
Native Americans in Redwood Creek depended on regular, low-intensity ground fires to manage the prairies and oak woodlands for hunting and gathering activities (West 1983; Underwood, Arguello, and Siefkin 2003). The prairies were maintained as fire yards, intentionally burned open areas that increased the abundance and diversity of plant and animal resources (Lewis 1993; Underwood, Arguello, and Siefkin 2003). As white American settlers moved into the region, human land use in the lower Redwood Creek basin shifted from primarily subsistence activities to those focused on commodity resource development of the basin. …
The resulting changes in the landscape reiterate post-white American settlement transformations found throughout the United States. That is, the landscape in Redwood Creek changed substantially in a relatively short period of time, altering energy flows and processes, and propelling nonhuman communities along trajectories of disequilibrium relative to the last 5,000 years (West 1983; Sugihara and Reed 1987). …
Conclusion
The mid- to late-nineteenth-century landscape represents a critical time period in understanding the environmental changes that have occurred in Redwood National Park over the last 150 years. The prairies and oak woodlands in the Bald Hills of Redwood National Park have been significantly encroached by P. menziesii coniferous forest since white American settlement in the basin. This invasion of coniferous forest is likely related to changes in the fire regime as white American settlers ceased regular burning of the prairies and oak woodlands, and expanded road networks (RNSP 2000).
This lack of burning favors the growth of P. menziesii in the Bald Hills. To meet the national park’s restoration andmanagement objectives, park managers have implemented a removal program of encroaching P. menziesii through cutting and prescribed fire (RNSP 2000). They hope to expand the present-day prairies by 25 percent to “better reflect their extent in 1850” (RNSP 2000, 90). While other factors such as cost and probability for success are important considerations, and although a 25 percent expansion in prairies is a commendable goal in the restoration of this landscape, the PLS record suggests that this could represent as little as half of what has been lost due to encroachment of woody vegetation. …
