High-Intensity Wildfires Are Changing Plant Habitat Structures In Sierra Nevada

Oct 18, 2019

Researchers say forest fires are typically good for rebooting the health of forests, but a new study published in the journal Ecosphere says that high-intensity wildfires are dramatically changing the plant habitat structure of forests in the Sierra Nevada. 

KUNR's Bree Zender spoke with Clark Richter, a PhD candidate at the University of California, Davis and lead author on this study.

ZENDER: Based on what you studied, how would you classify a high-intensity wildfire?

RICHTER: A high-intensity wildfire is a fire where typically the flame heights [are] pretty tall, and they are tall enough to get up into the canopy. In the event that the flame heights aren’t tall, you can find that high-intensity fire results from very dense understories. We’re talking lots of tree seedlings, lots of tree saplings, which serve as ladder fuel--ways for the fire to get up into the canopy.

ZENDER: So, can you tell me what’s been going on in the Sierra to these landscapes post-intense wildfire?

RICHTER: After intense wildfire, often the systems quickly recover as shrub-dominated systems. This is not unusual. Shrubs like ceanothus and arctostaphylos are very good, quick germinators. They very quickly sprout and they very quickly grow in high-severity conditions. Essentially, a high-severity site means that the site is much different than what it was before the fire started. And often, the major characteristics of the high-severity sites is there are lots of light because most of the adult trees were killed off, and so these shrub species respond very well to those conditions. They grow very quickly in high-light conditions, and they quickly dominate the system.

What we are currently seeing is more frequent high-intensity fire and more area burned by high-intensity fire. [It] means that these shrub fields are that much more frequent across the landscape. What’s problematic is the potential for fire to get back into a shrub field, whether it’s from human ignition or a lightning strike or otherwise...and potentially reignite these shrubs and then just continue promoting this high-severity site in these shrub fields--which would have a negative effect on the overall understory plant diversity of the landscape.

ZENDER: This pretty drastic change in the landscape, does that have a negative effect on, say, the wildlife?

RICHTER: So, understory plant diversity is tied to a lot of things. Of course, there’s an aesthetic value to it. Maybe some of your listeners can imagine walking through a mixed-conifer forest...you spot wildflowers on the ground. In high-severity sites, those wildflowers are largely absent. They’re not capable of growing underneath the shrubs.

There are implications for wildlife. Species that for whatever reason depend upon small wildflowers either for sustenance or otherwise could conceivably be impacted; although, there is a lot of research to suggest species of birds and species of bats do especially well in high-severity sites. But the other implications for high-severity sites are changes to the soil structure, increased erosion rates. And again, as these novel conditions that we are experiencing… [or] these new rates of high-intensity wildfire mean that these high-severity sites are more widespread throughout the landscape; therefore, the reductions of understory diversity are more widespread throughout the landscape. The potential for greater erosion and more compromised soil structure is also more widespread across the landscape as a result of more widespread, high-intensity fire.