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Unearthing the Secrets Beneath the Forest Floor

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There is a black box hidden beneath the forests of the Pacific Northwest, guarding the secrets to why the trees grow so large! The black box is soil, which harbors immense biological diversity and controls the release of water and nutrients that support the life above ground. Join us as Sue Powell interviews USGS ecologist Steve Perakis and discusses his research about the forests and watersheds in the Pacific Northwest, only in this month's episode of the USGS Oregon Science Podcast.




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[Intro Music begins]

[Steven Sobieszczyk] Hello and welcome! You are listening to episode 12 of the Oregon Science Podcast for Tuesday, November 9, 2010. I'm Steven Sobieszczyk.

There is a black box hidden beneath the forests of the Pacific Northwest, guarding the secrets to why the trees grow so large! The black box is soil, which harbors immense biological diversity and controls the release of water and nutrients that support the life above ground. Join us as Sue Powell interviews USGS ecologist Steve Perakis and discusses his research about the forests and watersheds in the Pacific Northwest, only in this month's episode of the USGS Oregon Science Podcast.

[Intro Music ends]

[Sue Powell] Hello and welcome to the Oregon Science Podcast. I am Sue Powell.
When the Pacific Northwest is mentioned, many people think of forests. They are a dominant feature of large areas from northern California to Alaska. But, few people recognize what's going on beneath the forest. These hidden riches are a key to making each type of forest unique. 
Today, we are talking with Dr. Steve Perakis, who is a research ecologist with the USGS Forest and Rangeland Ecosystem Science Center based in Corvallis. Steve's research focuses on the biogeochemistry of forests and watersheds in the Pacific Northwest.
Steve, welcome
[Steve Perakis] Thanks for having me.
[Sue Powell] The first question is - what is biogeochemistry?
[Steve Perakis] Biogeochemistry is essentially how the building blocks of life, elements like carbon, nitrogen, and phosphorus, influence how ecosystems work. And then how biology shapes how these elements cycle through the biosphere.
[Sue Powell] Excellent. We are talking about the Pacific Northwest - we grow some pretty big trees. Why is that?
[Steve Perakis] Yes, the trees out here are massive. If you had to boil it down to one or two key reasons, those would be climate and the species that we have present in this part of the world. The mild climate that we have, especially in the winter time, allows a lot of trees to photosynthesize and to grow during some of the cooler months when most temperate forests in the world are under a deep freeze. So, we have an extended growing season, and we also have coniferous trees that are able to take advantage of that. These evergreen conifers keep their needles all year long and are able to grow during the winter. In addition, because of their water use, they are able to ‘hold their breath' in the middle of the summer when we have drought conditions here in the Northwest.
The other part of this is that these trees are extremely long lived. Long after many temperate forests stop growing, the trees out here continue to grow and ultimately reach massive size.
[Sue Powell] As we hinted, the western forests are more than just trees. How do you study what's going on beneath the forest floor?
[Steve Perakis] A lot of our work is interested in understanding how trees grow, what allows them to attain such large size, and how they respond to climate across the region. So, a lot of our work focuses on soils. We have to go out there, dig soil pits, collect samples with soil cores, and bring them back to the lab where we analyze them for chemical and biological characteristics.
[Sue Powell] So you're looking at dirt?
[Steve Perakis] We are doctors of dirt!
[Sue Powell] You talked about the key players, the building blocks, like carbon and the nutrients. They are recycled from plant to air and back to plant again. How do these players work in the cycle, and why are they so important?
[Steve Perakis] There are a couple of ways to think about the way that these elements cycle. We can either think about them as a whole ecosystem where we think about what comes in and what goes out. And then, we can break it down to go inside of the ecosystem and then think of the individual players. From a biological perspective, we're most interested in the plants and in the microorganisms that live in the soil. But these biotic parts of the system interact quite a lot with the inanimate parts - things like rocks, dead organic matter in the soil, as well as with the elements up in the atmosphere, things like carbon dioxide and nitrogen, which they're about to bring into the ecosystem and ultimately allow the trees to grow.
[Sue Powell] So it's a big cycle?
[Steve Perakis] It is a big cycle, and there are a lot of feedbacks in these cycles where parts of the system affect other parts of the system, and it happens in a cyclic fashion. 
[Sue Powell] And every forest is different?
[Steve Perakis] Yes and no. We certainly have general principles that we use to describe how many different kinds of forests all over the world work. So, for example, when we have a computer model of how forests might respond to climate change, we might have the model divided out into different parts of the world, but a lot of times the basic processes that drive the model, things like water cycling and nutrient cycling, are shared among different kinds of ecosystems. 
[Sue Powell] So, your research laboratory is very busy, and you mentioned climate change. You are currently working on a climate change study - how might climate change affect the forests in the Pacific Northwest? 
[Steve Perakis] At a pretty large scale, some of the major effects that are going to happen with climate change are probably going to be related to wildfire. One of the big predictions of climate change is warming of course, and one of the major effects of warming is that we're going to have intensified summer droughts, and we're going to have more intense summer wildfires because of that. But, there are also a lot of subtle effects that are going to be happening, even in the absence of wildfire. These are basically the direct climatic influences on plant growth. Those can happen in two broad ways. There are direct effects of climate on plant growth - how well do they grow? How much photosynthesis can they carry out? And, there are indirect effects, where climate affects soils and nutrient supply in soils, which then affect how plants grow. 
[Sue Powell] How do you study these effects?
[Steve Perakis] One of the studies that we have right now is occurring on the Olympic peninsula in Olympic National Park and Olympic National Forest. We have research sites that are set up across a wide, natural gradient in rainfall from the very, very wet coastal temperate rainforests on the Pacific side, around the Olympic Mountains to more dry forests. We essentially compare these forests and also exchange materials across sites to understand how they might behave in new climates. 
[Sue Powell] You also talked about nitrogen. Early studies suggested that nitrogen was the limiting factor in Pacific Northwest forests. What has your research shown?
[Steve Perakis] Our research has, to some degree, confirmed that. Many forests are nitrogen limited, but what we've also been learning is that many forests in this part of the world aren't nitrogen limited. Worldwide, we've all heard of nitrogen fertilizers. Most farmers apply nitrogen fertilizers to their fields to help plants grow, and forests are no different. But, one of the unique features of forests in the Pacific Northwest is that some of the soils here are extremely nitrogen rich because of natural processes, because of nitrogen fixation. And because of that, there is plenty of nitrogen for many of the forests to grow, and other nutrients like calcium and phosphorus might be more important in shaping the productivity of these systems. 
[Sue Powell] You mentioned fire, another hot topic in the Pacific Northwest. You found some surprising long-term effects of fire on carbon and nutrients. 
[Steve Perakis] That's right. Most of the studies of fire that are done generally tend to run in soon after a fire and try to understand what happens immediately. Our approach was to come at it from a completely different perspective. What we did was look for sites that had burned at various times in the past, including forests for which we have no recorded fire history, scaling back 800 years. We tried to see what kind of long-term legacy did fires leave on these soils. 
[Sue Powell] What did you find?
[Steve Perakis] What we learned was that carbon and other nutrients can accumulate in the forests of the Pacific Northwest for at least 500 years after a wildfire. What that means is the decisions we make now about how to manage wildfire are going to have implications for many centuries into the future. 
[Sue Powell] Another research topic that you work on is riparian zones. They occur along the boundary where forests meet streams. What tree species are commonly found growing along Pacific Northwest streamsides? 
[Steve Perakis] The simplest way to think about what species are out there in riparian forests is to classify them largely into two groups - the conifers and the broadleaf trees. Some of the coniferous trees are things like Sitka spruce near the coast, or western red cedar, or Douglas-fir. Most of the broadleaf riparian forests are dominated by red alder, which is a nitrogen-fixing plant.
[Sue Powell] When managers restore riparian vegetation, are conifers the best candidate for planting?
[Steve Perakis] That's a great question. The answer to the best candidate depends on what your goals are because the conifers perform a different role than the broadleaf trees. The conifers grow very, very tall, they provide a lot of shade, and ultimately when they fall in the streams, they provide very, very large wood, which is good for creating habitat for fish. The broadleaf trees, on the other hand, grow much more quickly, but the litter that they produce, the dead organic material, the leaves and the branches, are much more biologically available. They function as better food for the organisms. So really, you need a mix of both conifers and broadleaves to have a healthy ecosystem. 
[Sue Powell] Well great, to wrap it up, understanding how carbon and nutrients cycle in forests is crucial for evaluating forest productivity, the composition of the forest, the diversity, and change. Steve's research examines forest soils to unearth clues about how the entire ecosystem functions, and to provide the best science available for resource managers to make informed policy and management decisions. 
Thanks a lot, Steve. 
[Steve Perakis] It's been fun. 
[Sue Powell] More information about the research Steve talked about is available on a fact sheet at http:/ Check out our transcripts for links to more information on Steve's and other research at USGS FRESC. 
For those who subscribe through iTunes, you can access the transcripts at our website: If you have any questions or comments about the USGS Oregon Science Podcast, please email us at
Thanks for listening!

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This podcast is a product of the U.S. Geological Survey, Department of the Interior.

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