Professor Steven Greco – Landscape Ecology: The Sense of Space
Developing sustainable solutions to environmental decline will need a holistic understanding of socioecological connections in time and space. Professor Steven Greco and his team at UC Davis use spatial analysis and visualisation techniques, to improve our understanding of ecosystems, and to inform conservation efforts.
Scale in Conservation
All living organisms exist in a complex web of connections, embedded in the context of the broader ecosystem. As human populations continue to increase, placing natural land under increasing pressure, understanding these connections will make a crucial contribution to preserving and restoring ecosystem function, and to the success of any conservation programme.
Landscape ecology is an approach that focuses on the interacting ecological processes that take place at different spatial scales. These scales range from local mechanisms such as genetic exchange, to regional and inter-continental ones such as disturbance or migration. Professor Steven Greco, a landscape ecologist at UC Davis, describes how his work informs conservation. ‘My research aims to understand how natural systems function in cultural (human-created) landscapes at a variety of spatial and temporal scales and how to inform ecological design to improve those systems,’ he explains.
They found that the choice of a local or regional scale led to dramatic differences in the areas identified for inclusion within a conservation network. Only around a third of the average area at either scale was identified at both scales. Connectivity, considered important to allow the free movement of animal populations between sites, was also notably affected by planning scale. The team also found that just 43.8% of local corridors overlapped with regional ones, while just 53.5% of regional corridors overlapped with local ones. Both planning scales led to the loss of important information for conservation planning: local planning alone resulted in fragmented networks, while regional planning overlooked locally important areas. Achieving the best possible outcomes for conservation will require the use of approaches that integrate information from both local and regional scales.
River Dynamics Aid Natural Succession Processes
Riparian, or river-bank, zones are an example of an ecosystem whose management and restoration requires well-targeted planning. Riparian systems depend on the ability of the river to move and create new habitats through erosion and sediment deposition. These changes allow the river system to support different successional stages of vegetation. In California, riparian zones have the greatest biodiversity of any ecosystem. Human activity can restrict the natural development of riparian ecosystem changes by modifying river flows through dams, or by artificially reducing bank erosion. Planning for the restoration of degraded riparian ecosystems requires an understanding of the ways in which rivers meander, and how this affects vegetation patterns. One way to do this is by producing maps of the age of floodplain surfaces.
Professor Greco and his colleagues used the Sacramento River in California to explore the ways in which riparian ecosystems are affected by land age. The Sacramento River is the largest river in California, and its active meandering constantly produces new land. This allows primary succession by willow and cottonwood trees, providing habitat for threatened wildlife such as the western yellow-billed cuckoo. However, an estimated 95% of the river’s riparian forests have been lost through conversion of the land to agriculture and urban uses, and through flood control measures such as the Shasta Dam. In their study, published in 2007, Professor Greco and his colleagues developed a method of overlaying time slices of floodplain maps to track the patterns of Sacramento River floodplain area over time. They used aerial photographs to map the riparian community vegetation, and link the distribution to the floodplain age class. They found that 71% of riparian vegetation was on land less than 101 years old, and willow and cottonwood had the highest proportional cover on land aged 1–9 and 10–44 years respectively, emphasising the importance of natural river meandering for these habitats. The team’s approach, which used an automated geographic information system (GIS) environment, was designed as a tool that could be used by land managers to assess the reference conditions at sites, in terms of the proportions of different vegetation classes. This would provide a useful baseline to aim for in designing restoration plans, or to minimise the impacts of construction projects.
The role of floodplain age is one of many factors that should be taken into account in the design of landscape projects such as open channels for flood control. Typical channel systems are designed solely for the purpose of flood protection, and are narrow, deep and smooth to maximise water flow and minimise their land footprint. However, these features also reduce their potential as riparian habitats. Professor Greco and his colleagues showed that redesigning flood control channels can enhance their ecological value. In a study published in 2014, the team simulated the effects of expanding the channel footprint area in the Sacramento River region. The river’s antiquated flood control system is currently being redesigned, offering opportunities to improve its role in conservation. The team simulated scenarios with wider channels, and calculated the maximum roughness coefficients – corresponding to higher levels of riparian vegetation – which would achieve the target water flow rates and hence flood protection levels. In all three areas of the river examined, it was possible to increase the roughness coefficient and attain improved flood protection, although this would require a greater land area for the wider channels. In the case of the Sutter Bypass region, it would be possible to design a channel capable of supporting dense woody riparian vegetation.
The western yellow-billed cuckoo, mentioned above, is an endangered subspecies in California whose riparian habitats are affected by changes in the patterns of river meandering. This cuckoo favours cottonwood habitats around the Sacramento River, dynamic patches of forest whose distribution is constantly in flux, depending on the meandering of the river. Professor Greco has been involved in several studies on yellow-billed cuckoo habitat in the region, one of which explored how the distribution of cottonwood forest on the Sacramento River changed between 1952 and 1987. He used GIS maps of land cover derived from aerial photographs to quantify the amount of woody riparian vegetation in 1952 and 1987. Building on the method used in his 2007 floodplain study, his team further identified subpatches of vegetation on young floodplains as likely cuckoo habitat.
The results, published in 2013, showed that 16% of the river’s riparian vegetation was lost in the 35 years between the two measurements, likely through conversion to agricultural land. Only 15% of the patches in 1952 had the same location in 1987, providing evidence of rapid changes in distribution. One positive finding was that the significant reduction in new floodplain land produced was partially offset by a higher rate of colonisation by cottonwood, probably due to reduced erosion as a result of the effect of Shasta Dam in decreasing water flow. This led to the comparatively small drop of 11% in cottonwood forest production. The new patches were mostly formed through oxbow or floodplain lake processes, highlighting the particular importance of these processes for riparian habitat conservation. Maintaining a stable mosaic of cottonwood patches will require a management approach that allows natural river meandering processes, if populations of the yellow-billed cuckoo, and other threatened riparian species, are to remain viable.
Spatial Modelling to Bring Back the Tule Elk
Another native species in California which could benefit from the broad-scale landscape approach to conservation is the tule elk. This subspecies of elk is endemic to California, but hunting and the large-scale habitat loss to agricultural land development brought it to the edge of extinction in the 1870s, with approximately 2–4 individuals remaining (based on genetic evidence). Captive breeding programmes and reintroduction efforts have increased their numbers to an estimated 3900, although there are no free-ranging animals in the Central Valley portion of their former range. The success of reintroduction has been hampered by unanticipated effects, some of which might be reduced through systematic, spatially explicit habitat analyses to identify optimal release sites.
In 2011, Professor Greco and his colleagues used spatial analysis methods to produce the first systematic evaluation of potential habitat for tule elk reintroduction. Their work evaluated the Merced County Grasslands Ecological Area in the Central Valley, based on the estimated spatial values of land cover and forage, habitat diversity and human impacts. These variables were combined in a geospatial model, with a final suitability value as output, based on the geometric mean of the three input values. The team identified two large areas of high-quality habitat in the San Luis National Wildlife Refuge, which would be suitable candidate sites for release: the San Luis and East Bear Creek Units, and the Kesterton Unit.
In a subsequent study, Professor Greco and his colleagues used a new spatially explicit population model, HexSim, to assess the potential of four different sites in the Central Valley for tule elk release. HexSim offers improved realism through simulation of animal herd movements and barriers to movement. This allows for the incorporation of likely human-elk conflicts. The team used data from other elk herds in California and expert knowledge to add appropriate parameters to the model. Their work, published in 2014, found that the 25-year population forecast was highest at the East Bear Creek site, and this site also had the lowest number of conflicts. This confirmed the team’s previous finding on the suitability of this site, and they hope that modelling approaches of this kind could improve the survival rate of reintroduced species.
Landscape Ecology for a Better Future
Professor Greco is also passionate about the need to equip new generations of ecologists with the tools to apply landscape approaches to conservation. He is the founder of the Landscape Analysis and Systems Research (LASR) Laboratory at UC Davis, currently hosting four graduate students and one Assistant Project Scientist. He also teaches a variety of courses, including site and landscape ecology and GIS for mapping environmental features. One of his recent teaching projects was a case study actively involving students in the design of ecological greenways, using wildlife habitat relationship (WHR) models to produce functional habitat areas for selected focal species. Although WHR models allow landscape architects to incorporate essential information on species life histories, they are not yet taught in most programmes. Professor Greco’s work demonstrates the utility of the concept in producing ecologically effective designs at the undergraduate level.
His team is now applying their experience of landscape ecology techniques to contribute to broad-scale conservation planning efforts in California. In a new research project sponsored by the National Institute for Food and Agriculture through the Hatch Fund, they are carrying out research to enable the design of sustainable habitat conservation systems such as ecological networks at multiple scales. In this project, running from 2016 to 2021, they will continue their work on the development and implementation of spatial analysis and visualisation techniques, to improve our understanding of ecosystem structure, function and change. Their work will also focus on exploring the roles of novel ecosystems in cultural landscapes, and of hydrological systems such as the Sacramento River, to enable ecosystem service provision including flood control while delivering improved outcomes for conservation. Finally, Professor Greco sums up their plans: ‘We intend to study impacted river systems to promote natural values and to provide access for people to experience natural systems through greenway planning and design in urban and agriculturally-dominated landscapes. Ultimately, I’d like to integrate the three modes of landscape conservation: protected reserve areas, ecologically restored areas, and reconciled areas. Protection and restoration of natural resources is greatly needed to improve and maintain environmental quality for both people and wildlife.’
Meet the researcher
Professor Steven Greco
Department of Human Ecology
Landscape Architecture + Environmental Design Program
University of California, Davis
Professor Steven Greco obtained his BSc in Landscape Architecture in 1987 from the University of California, Davis. During his work as a post-graduate researcher, he was awarded his MSc in 1993, and then his PhD in Ecology from UC Davis in 1999. From 2000 to 2007, he worked there as Assistant Professor, and from 2007 he was Associate Professor, before being promoted to full Professor in 2015. From 2015 to 2017 he was Vice Chair of the Department of Human Ecology and Chair of the Landscape Architecture and Environmental Design Program. He is also the founder of the Landscape Analysis and Systems Research Laboratory. Professor Greco teaches courses on a variety of different topics, including Site Ecology, GIS, Landscape Ecology, and Conservation Planning.
T: (+1) 530 754 5983
Eric Larsen, University of California, Davis
Patrick Huber, University of California, Davis
Alexander Fremier, University of Washington
James Thorne, University of California, Davis
Richard Plant, University of California, Davis
Evan Girvetz, International Center for Tropical Agriculture
California Department of Water Resources
US Fish and Wildlife Service
California Department of Fish and Wildlife
Institute of Museum and Library Services
California State Water Quality Control Board
Rocky Mountain Elk Foundation
Sacramento Area Flood Control Agency
SE Greco, Designing functional habitat using wildlife habitat relationships: a missing curricular concept in landscape architecture education, Landscape Research Record, 2016, 5, 101–115.
SE Greco, EW Larsen, Ecological design of multifunctional open channels for flood control and conservation planning, Landscape and Urban Planning, 2014, 131, 14–26.
PR Huber, SE Greco, NH Schumaker, J Hobbs, A priori assessment of reintroduction strategies for a native ungulate: using HexSim to guide release site selection. Landscape Ecology, 2014, 29, 689–701.
AK Fremier, EH Girvetz, SE Greco, EW Larsen, Quantifying process-based mitigation strategies in historical context: separating multiple cumulative effects on river meander migration, PLOS ONE, 2014, DOI: 10.1371/journal.pone.0099736
SE Greco, Patch change and the shifting mosaic of an endangered bird’s habitat on a large meandering river, River Research and Applications, 2013, 29, 707–717.
PR Huber, SE Greco, J Hobbs, Assessment of habitat for the potential reintroduction of tule elk to the San Joaquin Valley, California, California Fish and Game, 2011, 97.
PR Huber, SE Greco, JH Thorne, Spatial scale effects on conservation network design: trade-offs and omissions in regional versus local scale planning. Landscape Ecology, 2010, 25, 683–695.
SE Greco, EH Girvetz, EW Larsen, JP Mann, JL Tuil, C Lowney, Relative elevation topographic surface modeling of a large alluvial river floodplain and applications for the study and management of riparian landscapes. Landscape Research, 2008, 33, 461–486.
SE Greco, AK Fremier, EW Larsen, RE Plant, A tool for tracking floodplain age land surface patterns on a large meandering river with applications for ecological planning and restoration design, Landscape and Urban Planning, 2007, 81, 354–373.