Publications
Urbanization has been a significant cause of deforestation throughout the latter half of the 20th century, and given global demographic trends, the conversion of forested land to urban uses will likely continue. California has had a long history of converting forests, and urbanization has been one of the principle drivers. While many studies have examined how urbanization alters forest landscape structure at landscape or regional scales, little is known about how urban development influences linear forest edge structure at local scales where individual homeowner decisions dominate. We studied how forest edges at two California coastal oak woodlands (Pacheco Valle (PV) and China Camp (CV)) in the San Francisco Bay Area in California changed in the decades following urbanization. Using remote sensing and object-based image analysis, we isolated 20 urban-forest edges per site and quantified each edge's complexity (measured by sinuosity) for three time points at each site. Edges exhibited low sinuosity immediately following development (PV = 1.584, CC = 1.5625), but grew significantly more complex (in 2003 PV = 1.8705, CC 1.906). Linear forest edge structure at both sites, despite different development dates, showed similar and statistically significant increases in sinuosity by 2003. We attribute the initial, more linear structure to mortality and trunk or canopy damage caused by construction, while ascribing the later, more complex structure to tree recruitment, canopy expansion, and homeowner actions that influence natural processes.
Sudden oak death (SOD) has caused widespread mortality in a number of tree and shrub species throughout coastal California. As a result, canopy changes are directly visible from remotely sensed imagery. To quantify changes in horizontal canopy structure to the oak woodlands in China Camp State Park, California, USA, a heavily hit area, we developed a novel change detection technique that tracks changes to individual objects. Using 4-band, 1 m spatial resolution aerial photography, we classified four annual images (2000 to 2003) with object-based image analysis (OBIA) and employed a GIS for our change detection technique. We identified 352 gaps that contained SOD mortality in 2000 and persisted through 2003. Their median areas and perimeters did not change significantly in that time. However, those gaps that increased in size tended to be smaller than those that decreased, indicating increased mortality in newly infected areas. Our new change detection method allowed us to monitor these gaps one-by-one, revealing ecologically meaningful results that would otherwise be obscured in a landscape-scale analysis.
Dissertation
Where the Woodland Ends: How Edges Affect Landscape Structure and Physiological Responses of Quercus agrifolia
Forests and woodlands are integral parts of ecosystems across the globe, but they are threatened by a variety of factors, including urbanization and introduced forest pathogens. These two forces are fundamentally altering ecosystems, both by removing forest cover and reshaping landscapes. Comprehending how these two processes have changed forest ecosystems is an important step toward understanding how the affected systems will function in the future. I investigated the range of edge effects that result from disturbance brought about by forest pathogens and urbanization in two coastal oak woodlands in Marin County, California.
Oak woodlands are a dynamic part of California's landscape, reacting to changes in their biotic and abiotic environments across a range of spatial and temporal scales. Sudden Oak Death, caused by the introduced forest pathogen Phytophthora ramorum, has led to widespread mortality of many tree species in California's oak woodlands. I investigated how the remaining trees respond to such rapid changes in canopy structure (Chapter 2), and my results revealed a forest canopy quick to respond to the new openings. Urbanization, another disturbance regime, operates on a longer time scale. Immediately following urban development, forest edges are strikingly linear, but both forest processes and homeowner actions likely work in concert to disrupt the straight edge (Chapter 3). Forest edges grew more sinuous within 14 years of the initial disturbance, and continued to do so for the remainder of the study, another 21 years. Individual Quercus agrifolia trees also respond to urban edges decades after disturbance (Chapter 4), and their reaction is reflected in declining stable carbon isotope values (δ13C). This change suggests trees may have increased their stomatal conductance in response to greater water availability, reduced their photosynthetic rate as a result of stress, or some combination of both.
Edges have far reaching and long lasting effects on forest structure and function. Investigations of their impacts on multiple spatial and temporal scales are important in determining the range of effects they have on forest ecosystems. Studies that combine remote sensing, geographic information systems, and field studies may help us understand the ecological consequences of forest edges.
Read my entire dissertation (pdf).
Maggi Kelly was my Ph.D. advisor in the Department of Environmental Science, Policy and Management at UC Berkeley. Check out her lab for more related research.
Undergraduate Research
I have had the good fortune to be involved in four research projects in my undergraduate career. Each of these projects was completed while I was at St. Olaf College.
Northfield Habitat Corridors
Northfield Habitat Corridors sets out to link remnant and restored habitats in and around Northfield, MN, a town of 20,000 just south of Minneapolis. In recent years, Northfield has undergone a significant amount of change with the advent of big box retailers and increased residential development. My project seeks to work with the community to preserve natural areas and limit sprawl in the area.
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Corridors map with land use overlay |
Corridors map with DOT roads overlay |
Using ArcView (a geographic information system) and field observations, I identified what would become habitat nodes in a system of reserves and corridors. I then used ArcView to create a map of optimal connectivity.
The real importance of this project lies in the recommendations I made to the community. Rather than approach the issue as a disinterested expert, I worked with the Northfield Comprehensive Plan to gain community input as to how this project could be implemented. I feel that this project will benefit greatly from citizen input and I value the expertise members of the community bring to the table. This project is available online within this domain and on St. Olaf servers as a community resource.
Age and Size Structure Studies of Relic Balsam Fir Populations
I worked on this project in the summer and fall of 2002 under Dr. Kathleen Shea. Dr. Shea had previously studied the genetic diversity of two isolated, relic populations of balsam fir (Abies balsamea) and was curious about their size and age structures. Using standard increment boring technique, Dr. Shea, Traci Bartz, and I collected core samples and size data from Mountain Maple Hollow, a Nature Conservancy reserve in northeast Iowa, and Big Spring Cliff, an area in Forestville State Park in southeast Minnesota.
The core plots and age data suggest that these two populations are living under stressful conditions. The source of this stress, however, is difficult to pinpoint, as it could arise from a loss of heterozygosity, warm temperatures, or a number of other factors. The results could prove to be important in the development of future conservation plans.
Size Structure Studies of Restored Hardwood Forests
I also worked on this project during the summer of 2002 under Dr. Kathleen Shea with Traci Bartz. Started in 1990, this study continued to gather size data on a number of species of hardwoods restored on the St. Olaf Natural Lands. In addition to collecting the data, my main role in the project was the implementation and use of the global positioning system (GPS) and geographic information systems (GIS).
Using a Trimble TSC1 Asset Surveyor, I created a custom data collection interface that allowed us to associate species, heights, diameters, and ID numbers with the appropriate tree. Once the data was collected in the field, I managed it in ArcView 3.2 (GIS software). This system's benefits are readily apparent: Tree locations are now accurate to within 1 m of their actual location. Also, a tree can be selected within ArcView and all of its associated data are immediately available.
Dr. Shea and I presented a poster on this project at the Ecological Society of America's annual meeting in August, 2003.
GIS Fire Modeling
This, the first of my research projects, was done the spring semester of my sophomore year (2001) under Dr. Charles Umbanhowar, Jr. The goal of this project was to use FARSITE 4.0, a mechanistic fire modeling program, to test the impact of fuels and topography on fire in the historic Minnesota landscape. To do so, I chose Sibley County, a county in southern Minnesota that lies squarely in the presettlement Big Woods region, as my experimental area.
A total of four different types of tests were run. Two simulations involved forest fuels and the other two tested prairie fuels. Within each fuel type, I ran one test with topography accurate to Sibley County and the other without topography. The progress of each simulated fire was plotted and the total area burned was compared among simulations.
In the past, too much evidence may have been placed on rivers and lakes as firebreaks, largely ignoring the effects of fuels and topography. The results of this project indicate that vegetation type may have had a larger influence over fire regime in the Big Woods region when compared to topography.
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©2011 Tim De Chant