Understanding the Long-Term Impacts of Drought: A Ph.D. Student’s Study of the Decline of a Drought-Tolerant Species
By Deborah Chew
California recently experienced its worst drought since 1895, with temperatures hitting an all-time high in 2014 and 2015 and a state of emergency being declared in 2016. Though the state of emergency was lifted the following year, roughly 44 percent of California is still suffering from moderate drought conditions. These conditions are especially severe in the Santa Barbara and Ventura areas, and the local plant communities are suffering as a result. Laura Drake Schultheis, a fifth-year Ph.D. student in the EEMB Department, has been conducting her dissertation research on the impacts of drought on one particular community: chaparral. Chaparral, a shrubland plant community that is classically considered drought-tolerant, appears to have developed a susceptibility to drought due to the growing severity and lengthening duration of droughts and heat waves. Schultheis is analyzing this phenomenon through a study of the big berry manzanita (Arctostaphylos glauca), which has been showing signs of drought-related dieback. (Dieback is a plant condition that leads to progressive death of twigs, branches, shoots, or roots, starting at the tips.)
Schultheis, who has been following the drought status for five years, first observed unusual dieback of this manzanita species in the Santa Ynez mountain range in fall of 2013. Her ensuing research took place on three different levels: a greenhouse experiment, a field survey, and a remote-sensing large-landscape scale. The greenhouse experiment allowed Schultheis to observe and control the factors that influence manzanita mortality on a small scale. The bulk of her research, however, has been conducted through fieldwork and remote sensing.
In Schultheis’ field survey component, which took place over the course of three years, she observed different stands of manzanita from a canopy-level perspective, measured them over time, and determined what factors were influencing them. Specifically, she measured on-the-ground data of plant physiology: photosynthesis, water uptake, and water use. “What I’m able to identify is beyond just what they look like,” Schultheis explained. “In essence I’m getting a window into how the plants are functioning on the inside. For example, I can measure how much water they have flowing through them, couple that with their photosynthetic activity, and therefore get an idea of how stressed they might be internally.” This part of her fieldwork has yielded substantial data, which she is currently in the process of analyzing.
The other component of Schultheis’ fieldwork utilizes remote sensing and reverse ground-truthing. (Ground-truthing involves going to a site to confirm what is seen in photographs while reverse ground-truthing entails the opposite.) Last summer, she went on-site to locate both healthy and sick stands of manzanita and mapped those stands on her computer with a program called ArcGIS. Her next step will be to sync those maps to aerial images of the same location. The aerial images she referred to were taken using AVIRIS (Airborne Visible/Infrared Imaging Spectrometer) technology, a remote-sensing system developed by the Jet Propulsion Lab in Pasadena, California. The lab uses this machine to observe and collect spectral data that are then made available to affiliate groups as a resource that researchers can use and analyze. Since Schultheis is affiliated with UCSB through Dar Roberts, a geography professor who is on her committee, she was able to access the data from the lab. “This is where the ERI fellowship came in,” she acknowledged. “The funding allowed me to take the steps necessary to monitor the manzanita stands on a larger scale.”
Remote technology is essential to Schultheis’ work because her access to the chaparral community is sometimes obstructed by steep inclines, large ravines, or dense foliage. Remote sensing enables her to collect important data that would otherwise be inaccessible and improve her location accuracy when mapping manzanita stands. “One way I collect data from an image is by looking at the visible light spectrum,” Schultheis said. “When I look at images, I’m reading the ‘spectral signatures’—all the regions of the electromagnetic spectrum that are being reflected or remitted by those particular canopies.” Since different canopies emit different light spectra (e.g., a green canopy would emit a different light spectrum than a brown canopy), this technique effectively allows her to separate data on a computer even when she is unable to see a visual difference. The data set she is focusing on is from an AVIRIS flight that was flown in 2014 with 4m resolution imagery. Now that she has mapped the stands with ArcGIS, she plans to integrate those data into the 2014 AVIRIS images and separate out the manzanita species. “The potential here is that I’ve improved the accuracy for species identification in chaparral mapping with these types of data sets,” she said. “I have the data and tools; now I have to analyze the data and see how well I can map sick and healthy manzanita canopies across the landscape.” However, the manzanita species have posed a challenge in this aspect. Schultheis is interested in mapping two different dominant species of manzanita in the area, but the spectral signatures of the two species are virtually indistinguishable from each other in previous aerial image data sets. She will be revisiting the spectral signatures this summer in hopes of identifying some differences that will help her separate the two species when drawing maps.
There are two major implications of Schultheis’ work. The first is that researchers will be able to better predict the consequences of current and future droughts if they can identify at-risk areas and species. “We’re still suffering from a lot of the effects of drought in southern California and we don’t know when it’s going to be over,” Schultheis stated. “Any information we can gain on how plant communities are responding to the drought and where they are most vulnerable is going to provide us with valuable predictive tools.” This knowledge will also help land managers better prevent or work with the changes that are occurring. The second is that the increasing amount of dead vegetation will likely affect the frequency and severity of wildfires. Since dead vegetation burns more easily than live vegetation, there is potential for more ignition sources. “This is something we can all resonate with right now, having just experienced the Thomas Fire back in December,” Schultheis continued. “If we start to see more dead canopies across the landscape, how will that influence our fire regime?”
Schultheis’ fieldwork was significantly affected by the recent Thomas Fire. Before the disaster took place, she was able to easily go out into the field and locate manzanita stands to compare to the images she had on file. However, many of the stands she was mapping in her study area have been destroyed by the fire, thus hindering her ability to ground-truth and confirm what she sees in the AVIRIS images. One field site, which contained several manzanita whose photosynthesis Schultheis had been measuring individually for the last few years, was bulldozed to prevent the fire from spreading. This unexpected impediment will influence her ability to track what changes may have been occurring over time, but Schultheis remains positive. “Thankfully, the aerial images I am working with are all pre-fire, and I have a lot of data from last summer to work with,” she said. “There are also extremely important questions that are being generated as a result of the fire—what sort of plants are going to grow back, how will the landscape change, and what might restoration look like in certain areas?—so you have to keep that in mind as well.”
Once Schultheis finishes mapping the manzanita in her study region, her completed product will be the most comprehensive, highly resolved, and up-to-date map of manzanita species distribution in the Santa Barbara front range. She hopes this, together with her field surveys and greenhouse experiments, will improve her understanding of the mechanisms behind large-scale manzanita dieback and prove to be a valuable tool for predicting future dieback events in the area. This in turn will have significant implications for the region’s fire regime. Additionally, Schultheis has expressed an interest in mapping other chaparral species, as incorporating data from a larger variety of species will allow her to build a more complete picture of how the chaparral community as a whole is responding to the drought. As she continues to research within this ecosystem, her work will be immensely helpful in promoting awareness and understanding of the issues the chaparral community faces today and those it may face in the future. “I love the chaparral,” Schultheis concluded. “It’s a fantastic community—biologically diverse, incredibly resilient, and home to some of the most