SneakPeek: USGS Public Lecture, Can Our Western Forests Take the Heat?
- Tree death rates have more than doubled over the last few decades in old-growth forests of our western states, possibly reflecting increasing temperatures, with potentially serious consequences for wildlife, fire risks, and the global carbon cycle
- Rising regional temperatures have lengthened the summer drought, likely stressing trees and leading to higher death rates
- Is this alarming trend a harbinger of larger, more abrupt changes in our forests?
Speaker: Phillip van Mantgem, USGS Ecologist
Amelia: Hello, I'm Amelia Barrales and today's guest is USGS Ecologist Phil van Mantgem. Thank you Phil for taking the time and talking to us.
Phil: You bet, well thanks for having me on.
Amelia: So Phil, tree death rates have doubled in the last few decades in our western states...What might have caused the accelerated rates of mortality?
Phil: Well, we have tried to consider a bunch of competing hypothesis so we looked at changes in forest density from fire suppression that didn't really seem to fit the pattern that we were seeing, we looked at changes in fire history that didn't really seem to play out either. What we came back to as probably the most logical explanation for the pattern that we were seeing was an increase in regional temperatures, and that can have a couple of different effects, first it could just increase the amount of drought stress that is out there on the landscape and it can also increase the things the population densities or the activities of things that chew on trees things like bark beetles, fungi, things like that, so there is probably no one single mechanism going on out there but likely warming climate are, is gonna be part of that story.
Amelia: I see. So Phil, could you describe what you and your colleagues found in recent studies?
Phil: Sure, what we found is pervasive increase in forest background mortality rates in old growth stands so that's a surprising result most people in the expectation for old growth forests is that they should be kind of dull demographically they shouldn't show any sort of directional change with an increase or decrease in mortality or birth rate or natality that's not what we found, we found sort of a unchanging birthrate or recruitment of new trees. What we saw was an increase of mortality rate pretty much across the board so if we looked at Pacific Northwest forests, if we looked at forest in California if we looked at forests more in the interior in the rookies we saw this trend of increase in mortality rate and that's not expected.
Amelia: So what do these rising deaths mean for the forests and for the wildlife that depend on them?
Phil: Well if current trends continue if we're seeing an increase of mortality rate but no change in the recruitment rate what we are going to do is change the structure of the forest, we are going have fewer big old trees out there in the landscape so that will change things pretty dramatically for wildlife that depend on old growth forest structure we'll also change how well our forests are able to store or sequester carbon. Big old trees hold a lot more carbon than smaller trees if we have fewer up then likely if not that ecosystem service of carbon sequestration that forests do so nicely won't be as effective in the future.
Amelia:I see ... so I understand that you are giving a lecture at the end of month of March, entitled Can Our Western Forests Take the Heat?! which will cover some of the things that we just talked about correct?
Phil: That's right, we will be covering some of this recent research but will also be talking about some management implications of what we as a society can do about some of these trends.
Amelia: We look forward to hearing a lot more! Again thank you so much for your time Phil.
Phil: Well thank you for your interest.
Amelia: If you are interested in learning more about Phil's upcoming lecture and to view any of our previous lectures, please visit our USGS Evening Public Lecture Series website at http://online.wr.usgs.gov/calendar. His video will be available online at the end of the month of March for viewing.
Amelia: Until next time, I'm Amelia Barrales
This a production of the U.S. Geological Survey, Department of Interior.