Long-Term Drought Effects in Southern California

July 8, 2015

Professor of Biology Cheryl SwiftSouthern California's ongoing drought is an issue that Professor of Biology Cheryl Swift is very familiar with. Two of her research projects—carried out in the Puente Hills and along the Tujunga River—focus on the effects of weather phenomena on native trees, and more specifically how these native plants adapt in areas designated as restoration projects that serve as mitigation for habitat destruction.

What sparked your interest in this field?

I first became interested in plants during my first upper division botany class And, in my ecophysiology class I got excited about Mediterranean ecosystems because I grew up in Southern California. Here, our spring starts in January and goes through June. The beauty and diversity that can be found in this Mediterranean ecosystem is kind of inspiring; the flowers found here are drop to your knees beautiful. As an ecophysiologist you are looking at how plants respond to stressors. In particular I became interested in riparian (streamside) ecosystems because no one was looking at them.

Can you describe your current research?

I'm involved with a project that has to do with riparian habitats in the Tujunga River in the Angeles National Forest. This is something I've been working on for the last 20 years. These streamside communities have water because they're next to a stream, but if you step back and you think about it, the attributes that are going to enable plants—specifically trees—to grow rapidly and to outcompete other individuals for light are the same attributes that place them in great risk during drought. We already have this extended summer drought so we've been working on what happens to these species and how they respond but we're also interested in looking at mortality as a result of the ongoing drought in California.

Another project I'm working on is located in the Puente Hills and it studies the effects of restoration practices on a handful of species, in particular the way they use water. Our preliminary results, which have been presented at a couple of meetings, suggest that restoration that involves irrigation actually places plants under stress. Water stress occurs when plants have to use more energy to remove water from the soil. For all the species that we examined, those that were exposed to irrigation when they were establishing, were under more water stress during the dry season in the summers, than the control individuals that occurred naturally.

Then, we did some measurements on individual plants that were not watered and those individuals behaved more like the control group.

What are the implications of your research?

These restoration projects involving irrigation are mitigation for other projects that are destroying coastal sage scrub in other parts of Los Angeles County. One of the pieces of an approved mitigation project is achieving a certain amount of native tree cover within a certain number of years. These are mostly mitigation projects for the destruction of gnatcatcher habitat. These areas are watered to get the cover to a point where gnatcatchers will use them. But, the long term effect of watering may reduce the resilience of this community to drought. And, it's very possible that we're not just in a one year or two year drought, we're probably in a decadal drought cycle.

If the restored areas that are currently hosting gnatcatchers aren't resilient, the long term outlook of restoration projects for gnatcatcher habitat may be problematic.

How do students in your environmental studies courses participate in your research?

Students in many of my courses have the opportunity to conduct hands-on research related to my work in ecology. During one trip to the Tujunga River, students in my integrated research methods class were introduced to different ways of analyzing a community, including basic surveying. Students camped out overnight allowing them to conduct two days of research, surveying, data gathering, and sampling along the stream. I want my students to understand that we are in a global diversity hotspot in Southern California. I want them to be able to appreciate how humans impact this system and know that we can change how we impact this environment.