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EARTH SURFACE PROCESSES AND LOORMS • Earth Surf.Process.Landforms 37,209-222(2012) Copyright©2011 John Wiley&Sons,Ltd. Published online 21 November 2011 in Wiley Online Library (wileyonlinelibrary.corn)DOI:10.1002/esp.2249 Historic range of variability in geomorphic processes as a context for restoration: Rocky Mountain National Park, Colorado, USA Zan Rubin,*Sara L. Rathburn,Ellen Wohl and Dennis L. Harry Department of Geosciences,Colorado State University, Fort Collins,CO, USA Received 12 May 2011;Revised 4 October 2011;Accepted 10 October 2011 *Correspondence to:Zan Rubin,University of California,Berkeley,Ca,USA.E-mail:ZanRubin@berkeley.edu D Earth Surrace Processes and Landforms ABSTRACT: Evaluation of historic range of variability(HRV) is an effective tool for determining baseline conditions and providing context to researchers and land managers seeking to understand and enhance ecological function.Incorporating HRV into restoration planning acknowledges the dynamic quality of landscapes by allowing variability and disturbance at reasonable levels and permitting riverine landscapes to adapt to the physical processes of their watersheds. HRV analysis therefore represents a practical (though under-utilized) method for quantifying process-based restoration goals. We investigated HRV of aggradational processes in the subalpine Lulu City wetland in Rocky Mountain National Park to understand the impacts of two centuries of altered land use and to guide restoration planning following a human-caused debris flow in 2003 that deposited up to 1 m of sand and gravel in the wetland. Historic aerial photograph interpretation, ground penetrating radar surveys, and trenching, coring, and radiocarbon dating of valley-bottom sediments were used to map sediment deposits, quantify aggradation rates, and identify processes(in-channel and overbank fluvial deposition, direct hillslope input, beaver pond filling, peat accumulation) creating alluvial fill within the wetland. Results indicate(i) the Lulu City wetland has been aggrading for several millennia, (ii) the aggradation rate of the past one to two centuries is approximately six times higher than long-term pre-settlement averages,(iii)during geomorphically active periods,short-term aggradation rates during the pre-settlement period were probably much higher than the long-term average rate,and(iv)the processes of aggradation during the last two centuries are the same as historic processes of aggradation.Understanding the HRVof aggradation rates and processes can constrain management and restoration scenarios by quantifying the range of disturbance from which a landscape can recover without active restoration.Copyright©2011 John Wiley&Sons,Ltd. KEYWORDS: historic range of variability;restoration;aggradation;debris flow;Colorado River Introduction and disturbance within the range of historic levels and thus allows riverine landscapes to create desired habitats through The physical and biological forms and processes of landscapes adaptation to the physical processes of their watersheds.The dis- vary spatially and temporally and are increasingly altered by cussion herein follows the broad definition of disturbance offered human activities. Historic range of variability(HRV) has been by Pickett and White(1985)and Lake(2000),as an event when investigated as a potential tool for envisioning baseline condi- disrupting forces are applied to habitat space occupied by a pop- tions and providing context to researchers and land managers ulation,community,or ecosystem.Our interest is not specifically seeking to understand,enhance,or preserve ecological integrity in how disturbances such as floods or debris flows relate to non- (Landres etal.,1999;Keane etal.,2009).HRV is defined herein as disturbance conditions,but in how the magnitude and frequency the magnitude,frequency,and/or duration of specific processes of a disturbance regime may change with human alteration. such as fire or debris flows prior to intensive human impacts. Disturbances are important processes that drive habitat het- Understanding HRV facilitates'process-based'restoration,a con- erogeneity and encourage species diversity by accommodating ceptual framework supported by a growing number of restoration both colonizing and resident species at the scale of the dis- practitioners and scholars (Wohl et al., 2005; Kondolf et al., turbed site and also at a larger landscape scale that includes 2006), that seeks to re-establish the functions and trajectory of undisturbed patches(Connell,1978;Reice etal.,1990).Com- watershed processes and the habitat structure and variation to monly, post-disturbance colonization is rapid, with most which native species are adapted. Process-based restoration is a riverine studies showing recovery of species richness and abun- pragmatic way of targeting the varied(and commonly unknown) dance within 3 years except in instances of persistent alteration habitat needs of all native species by recovering the physical to physical habitat (Yount and Niemi, 1990; Detenbeck et al., functions that successfully supported these species.Incorporating 1992). Illustrating the regenerative aspects of disturbance, HRV into restoration planning acknowledges the dynamic quality maximum species richness has been found in the first two of landscapes by accommodating and managing for variability decades following a flood (Friedman et al., 1996).