Erin E. Beller

Historical landscape ecology of an urbanized California valley: wetlands and woodlands in the Santa Clara Valley

Historical records provide information to land managers and landscape ecologists attempting to understand current trajectories in altered landscapes. In this study, we synthesized a heterogeneous array of historical sources to reconstruct historical land cover in California’s Santa Clara Valley (a.k.a. “Silicon Valley”). To increase and assess accuracy, we used the triangulation of overlapping, independent data sources and the application of certainty level standards. The region has been subject to extensive urbanization, so we also evaluated the applicability of historical landscape reconstructions to the altered landscape. We found evidence for five major land cover types prior to significant Euro–American modification. Valley freshwater marsh, wet meadow, alkali meadow, willow grove, and valley oak savanna have all experienced extreme decline (85–100%) since Euro–American settlement. However, comparison of historical land cover patterns to contemporary land use suggested several new strategies for environmental recovery, despite the limitations of surrounding urbanization. We also observed a temporal shift in riparian habitat along the mainstem of Coyote Creek, from a relatively open mixture of riparian scrub, sycamore woodland, and unvegetated gravel bars to dense riparian forest, likely resulting from stream flow regulation. By identifying former land cover patterns we provide a basis for evaluating local landscape change and setting restoration targets, including the identification of residual features and under-recognized land cover types. These findings suggest that reliable historical landscape reconstructions can be developed in the absence of standardized historical data sources and can be of value even in highly modified regions.

Toward principles of historical ecology

Rising temperatures and sea levels, biological homogenization and biodiversity loss, habitat fragmentation, and other environmental changes are dramatically reshaping landscapes across the globe. In this context, understanding the patterns, drivers, and consequences of these changes has become one of the central challenges facing environmental scientists and managers today. Yet to do so requires a long-term perspective on environmental systems that predates many of the accelerated anthropogenic impacts of the recent past. How, then, can we understand these changes in the context of decadeand century-scale ecosystem trajectories and human history? What was the structure, function, and dynamics of ecosystems like before these changes? And how have people shaped these systems over time? Th ese questions are the domain of historical ecology. Historical ecology is the study of nature over time, oft en (though not necessarily) with a focus on human–environment interactions and the causes and consequences of changes caused by human actions in the recent past ( Crumley, 2003 ; Rhemtulla and Mladenoff , 2007 ). Th e fi eld includes both researchers who wish to document ecological patterns and dynamics in the recent past using historical methods, as well as those interested in historicizing ecology— that is, understanding the relationships between nature and human culture over time (cf. Szabo [2014] for a detailed treatment). It draws on a broad range of qualitative and quantitative sources that vary in temporal and spatial coverage, require creative and thoughtful methods to synthesize and interpret, and are oft en integrated in ways that cross traditional disciplinary boundaries ( Fig. 1 ). Data include traditional archival sources such as written documents, maps, oral histories, land surveys, landscape views and photography, along with biological and physical data such as sediment and pollen records, tree rings, species lists, and habitat relationships ( Swetnam et al., 1999 ; Egan and Howell, 2001 ; Vellend et al., 2013 ). While relying on data from the past, historical ecology is an inherently future-oriented discipline given its emphasis on temporal dynamics and change trajectories ( Higgs et al., 2014 ). It provides vivid narratives of past landscapes and change that are of interest to specialists and nonspecialists alike (e.g., Sanderson, 2009 ; Grossinger, 2012 ). Historical ecology is part of a long tradition of understanding relationships between humans and environmental change and shares strong topical and methodological affinities with paleoecology, environmental history, and historical geography. It is similar to “temporal ecology” (sensu Wolkovich et al., 2014 ), though temporal ecology relies more on time series data, rather than integrating a broad array of data types within their historical context. Historical ecology has much in common with landscape and restoration ecology, ecological subfi elds that emphasize spatial patterns and processes, human–environment interactions, and temporal dynamism. As a fi eld, historical ecology largely operates at the intersection of ecology, history, anthropology, and geography, using tools and techniques from all four disciplines to help people conceive of what populations, communities, ecosystems, and landscapes existed in the past and how they have changed over time ( Szabó, 2014 ). It also relies heavily on the history of science, since interpretation of oft en fragmentary, qualitative, and idiosyncratic historical data requires an understanding of the historical, scientifi c, and cultural contexts in which past records and scientifi c data were produced ( Raby, 2015 ). Studies cast a broad net of topics of interest, from traditional ecological questions such as documenting population abundance and community composition, habitat distribution, and ecological processes and functions, to geographic questions such as changes in geophysical patterns and processes 1 Manuscript received 18 February 2017; revision accepted 7 April 2017. 2 Resilient Landscapes Program, San Francisco Estuary Institute, 4911 Central Avenue, Richmond, California 94804 USA; 3 Department of Geography, University of California Berkeley, 565 McCone Hall, Berkeley, California 94720 USA; 4 Environmental Studies, Colby College, 5351 Mayflower Hill, Waterville, Maine 04901 USA; 5 School of Environment, Resources and Sustainability, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G; 6 Wildlife Conservation Society Global Conservation Programs, 2300 Southern Blvd, Bronx, New York 10460 USA; 7 Forest and Conservation Sciences, University of British Columbia, 3609-2424 Main Mall, Vancouver, British Columbia, Canada V6T 1Z4; 8 School of History, Philosophy, and Religion, Oregon State University, 322 Milam Hall, Corvallis, Oregon 97331 USA; and 9 School of Environmental Studies, University of Victoria, Room 205, House 4, Victoria, British Columbia, Canada V8P 5C2 10 Author for correspondence (e-mail: erin@sfei.org) doi:10.3732/ajb.1700070 O N T H E N AT U R E O F T H I N G S : E S S AY S New Ideas and Directions in Botany

Ecological dynamics and ecological restoration

In ecological restoration we are faced with the challenge of making decisions about ecosystem management with imperfect information about system dynamics and trajectories. For example, a restoration ecologist evaluating a denuded floodplain might be asked to determine if the area can support a cottonwood forest. Can cottonwood seedlings naturally recruit and persist here, or do they need to be seeded? How will the upstream presence of tamarisk populations (or other invasive species) affect the establishment of the cottonwood forest? How do we prevent the conversion to a tamarisk-invaded state? Is it possible to establish a cottonwood forest on this site that would be resilient to invasion? Taking a perspective that considers how theory and practice can be integrated, we consider how questions such as these can guide our approach to the restoration of native systems.

Futures Past Exploring California landscapes with the San Francisco Estuary Institute

These maps, based on research by the San Francisco Estuary Institute’s Center for Resilient Landscapes, reconstruct California ecosystems as they were in the late 18 th and early 19 th centuries, and compare them to present-day landscapes. They are designed to provide an understanding of the complexity and diversity of California ecosystems, to help explain how landscapes worked, to track persistence and change, and to identify potential future scenarios. The changes made evident when the maps are compared remind us of the enormous power we have to shape the landscapes we inhabit, and of the wide range of potential options available—options to create diverse, functional, and beautiful landscapes, inspired by the past and grounded in local potential—as we imagine and then create the future.