The restoration of degraded ecosystems can be constrained by uncertainty over former conditions and the relevance of the past given recent changes. It can be difficult to differentiate among contrasting hypotheses about past ecosystem function, and restoration efforts can emphasize species reestablishment without integrating the ecological and cultural processes that once determined their occurrence. As a case study, we analyzed historical descriptions of an endangered oak grassland ecosystem in southwestern British Columbia, Canada, to determine former conditions and assess their validity for defining restoration targets. Twenty-three documents described this ecosystem from 1790 to 1951. Comparison of early survey records with contemporary occurrences suggests habitat loss of >95%. The identity and former range of most native plant species were poorly described, but accounts of ecosystem structure revealed a diversity of floral communities that has been much simplified. Fire, most likely set by indigenous peoples, interacted with edaphic and topographic factors to create this structural diversity. European settlers intensively modified the ecosystem with grazing, cultivation, and introduced flora. These transformations partly explain the current high levels of plant invasion. Restoration must target the ecosystems' former structural diversity and the ecological and cultural processes that maintained it. Given the recent impacts of fire suppression, habitat loss, and plant invasion, however, land managers must balance the reestablishment of historical processes with their potential negative effects in sites with numerous at-risk species. This ecosystem was, and remains, part of a culturally modified landscape, where human activity has maintained unforested areas for millennia but now promotes mostly exotic flora. Although pre-European conditions cannot be fully restored, the historical data provided restoration insights unobtainable from current biological studies emphasizing the end point of long-term ecological change.
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