Reference ecosystems, characteristic assemblages, and disturbance regimes: Is there a right answer?

Information about reference ecosystems can be obtained by reconstructing past conditions, measuring relatively unperturbed (relict) sites, drawing inferences from ecological relationships, and/or assessing restored sites as a modern model for ecosystem function.  Taking pine-oak forests in North America and Europe as an example, I will compare multiple approaches to reference information to show where distinct lines of evidence reinforce or diverge from each other.  The interpretation of characteristic reference patterns of vegetation and fire disturbance regime takes on a new aspect in light of factors irrevocably changed from the historical ecosystem: non-native species, extinct species, modern land use, and novel climate conditions.  We face three interrelated questions: how well are reference conditions understood? How closely can they be regained?  How closely should management be guided by reference ecosystems given the prospect of changed future environments?  Native pine-oak forests may represent a successful convergence between historical conditions and the traits needed for persistence in the future.  However, the utility of reference ecosystem attributes for guiding management probably does not follow a uniform model, but must be evaluated on a case-by-case basis.