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Logjams and Beaver Dams: How Different Landforms Affect the Amount of Carbon in an Ecosystem

Scientists know little about the movement of litter and dead wood from forests to rivers in mountainous temperate ecosystems. Studying this movement is one way

Logjams and Beaver Dams: How Different Landforms Affect the Amount of Carbon in an Ecosystem

Meet the Scientists

What Kinds of Scientists Did This Research?

Geologist: This scientist studies Earth’s processes, such as landslides and volcanoes; Earth’s materials, such as metals and rocks; and the how these processes and materials change over time.

Geomorphologist: This scientist studies the origin, development, and characteristics of Earth’s natural features, called landforms.

Hydrologist: This scientist studies the distribution, movement, and quality of Earth’s waters.

Riparian ecologist: This scientist studies the relationship of living things with their living and nonliving environment in riparian areas. Riparian areas are areas along streams and rivers.

Thinking About Science

Natural resource scientists sometimes face a special challenge. If these scientists want to understand natural processes, they must find ecosystems that have not been changed much by human activities. In the world today, many ecosystems have been changed by human activities.

The scientists in this study wanted to understand a particular process that happens in temperate mountainous forest and river ecosystems. Temperate ecosystems are those that lie between Earth’s tropical and polar regions (figure 1). Temperate ecosystems are not extremely hot or extremely cold, and they have four seasons every year.

A map showing the globe divided into polar, temperate, and tropical regions. — **Figure 1**. Temperate ecosystems are found in Earth’s temperate region.

FIND Outdoors illustration by Stephanie Pfeiffer.

The scientists identified a temperate mountainous forest and river ecosystem that had not been greatly affected by humans. This ecosystem was in Rocky Mountain National Park. National parks are established by the U.S. Congress and are protected by law (figure 2). National parks often include lands and waters kept in their natural condition, making them good places to study natural processes. When an ecosystem is left in its natural condition, scientists can study what happens in an ecosystem that has not had much human impact.

A map of the U.S. showing the location of national parks (marked in yellow). — **Figure 2**. National parks are located throughout the United States. Find the national park that is closest to where you live.

FIND Outdoors map by Carey Burda and Stephanie Pfeiffer.

Thinking About the Environment

A mountain stream running through rocks and vegetation — **Figure 3**. This river rushes through a mountainous environment. Courtesy photo by Babs McDonald.

Rivers, under gravity’s influence, flow from higher land areas towards the oceans. In mountainous land areas, rain and snowmelt flow into rivers (figure 3).

If the area has forests and other vegetation, the rain and snowmelt carry soil, leaves, and dead wood into rivers and downstream. Leaves and other material from the forest floor are called litter. Dead wood includes dead trees, including boles and branches that have fallen to the forest floor.

Sun shining through the trees in a forest — **Figure 4**. Old-growth forests are often found in national parks. iStock photo.

Rivers in mountainous areas also flow through places that are not steep. In these places, the land beside the rivers is flatter, and the rivers flow more slowly. Old-growth forests are found in many of these places, and particularly in national parks (figure 4). When large trees fall, they may become lodged in the river, causing the water to overflow the river’s banks and create multiple channels (figure 5).

Fallen logs block part of a stream in a forest. Water has collected on one side of the logs. — **Figure 5**. Old-growth forests are a source for logs that may fall across stream or river channels. When logs fall across a channel, the water may overflow and additional channels may form.

Colorado State University photo by Ellen Wohl.

A beaver swimming in the water — **Figure 6**. Beavers are mammals that are closely related to rodents, like mice, rats, squirrels, and hamsters. Beavers are **nocturnal**, and they spend most of their time in or near the water. Colorado State University photo by Ellen Wohl.

Recall that streams flowing through flatter places move more slowly than streams flowing down steep hillsides. Beavers build dams in the streams of these flatter areas (figure 6).

Beaver dams back up water in the stream channels, creating beaver ponds (figure 7).

A beaver dam in the foreground and a pond in the background — **Figure 7A**. Beavers build dams to create habitat for themselves.

iStock photo.

A beaver dam and the beaver pond created behind it. — **Figure 7B**. When water backs up behind a dam, beaver ponds are created.

Colorado State University photo by Ellen Wohl.

In national parks and other places with limited human impact, slow-moving streams sometimes flow past old-growth forests. In some of these places, beavers may still be found. The scientists in this study were curious about how old-growth forests and beavers affect river-related carbon movement and storage.

Introduction

All living and once-living things contain the element carbon. Much of Earth’s carbon is found in forest plants, trees, and soils. When animals, plants, and trees die, the carbon remains. As these once-living organisms decay, the carbon that they contained goes into the ecosystem. Some scientists are interested in how carbon moves throughout and is stored in ecosystems (figure 8).

An illustration showing how carbon cycles through the environment. — **Figure 8**. Carbon moves across Earth’s surface, underground, and into its atmosphere in a cycle. As a part of the cycle, carbon is often stored for a period of time in various ecosystems. For example, carbon is stored in trees and other vegetation, as well as in the soil and in waterways and oceans. Carbon is also stored in dead wood and litter. Carbon may be stored in ecosystems for many years, even for centuries or over millions of years.

FIND Outdoors illustration by Stephanie Pfeiffer.

Scientists know little about the movement of litter and dead wood from forests to rivers in mountainous temperate ecosystems (figure 9). Studying this movement is one way that scientists can better understand the carbon cycle.

A panoramic view of mountains and a valley covered in trees — **Figure 9**. A mountainous temperate forest and river ecosystem in the Western United States. Colorado State University photo by Ellen Wohl.

The scientists in this study asked three questions about mountainous temperate forest and river ecosystems:

(1) Where is carbon found in these ecosystems?

(2) How do the landforms beside rivers affect how much carbon is stored in or moved out of these ecosystems? and

(3) What natural processes affect the location and amount of carbon in these ecosystems?

Reflection Section

Methods

Many of the valleys in the mountainous Western United States have been forested at some point in history. Before many of the trees were harvested, most of the forests were old-growth forests. The scientists identified six types of areas along rivers in Rocky Mountain National Park (table 1).

Table 1. The scientists studied six different types of valley ecosystems. Each of the boxes with an “X” represents a different kind of valley ecosystem.
Vegetation Type	Landform: Unconfined Valley	Landform: Confined Valley
Old-growth forest with a single stream flow	x
Old-growth forest with multiple stream flows	x
Recently abandoned beaver meadow	x
Long abandoned beaver meadow	x
Old-growth forest		x
Younger forest		x

They wanted to compare old-growth forests with younger forests (figure 10). As discussed in “Thinking About Science,” Rocky Mountain National Park was a good place to study because some of the old-growth forests still remain.

Side by side illustration of a new growth forest (left) with younger, smaller trees and more light and an old-growth forest (right) with larger trees creating a more dense canopy — **Figure 10**. This illustration shows a young forest (A) and an old-growth forest (B). What differences do you notice between the two?

FIND Outdoors illustration by Stephanie Pfeiffer.

A map showing the location of Rocky Mountain National Park. — **Figure 11A**. Rocky Mountain National Park is located in Colorado. FIND Outdoors map by Carey Burda.

The scientists also studied two types of valleys along rivers in Rocky Mountain National Park (figure 11).

A photograph of forests in the foreground and mountains with snow in the background. — **Figure 11B**. Rocky Mountain National Park is a popular national park for hiking, camping, rock climbing, and wildlife viewing. iStock photo.

Confined valleys have steep slopes and often have little vegetation (figure 12). Unconfined valleys, which are flatter places, might have young or old forests. Unconfined valleys might also be areas where beavers built beaver dams (figure 13). After beaver dams are abandoned, the beaver ponds created by the dams slowly fill in with sediment and become beaver meadows (figure 14).

A rocky mountain stream with steep banks on either side. — **Figure 12**. Confined river valleys are steep on both sides of the river. The steep sides are often exposed rock with little vegetation.

Courtesy photo by Babs McDonald.

A stream running through a relatively flat area with vegetation on both sides. — **Figure 13**. Unconfined valleys are relatively flat on both sides of the river.

Colorado State University photo by Ellen Wohl.

A small pond surrounded by vegetation with a mountain in the background. — **Figure 14**. As beaver ponds begin to fill with sediment, they become meadows.

Colorado State University photo by Ellen Wohl.

Why Are Beaver Dams Abandoned?

European colonists in North America hunted beavers for their pelts, or skins. All over North America, beavers were hunted almost to extinction. People did not understand the vital role that beavers play in supporting a diversity of wildlife habitat, promoting water quality, and increasing ecological health. As a result, beaver dams were abandoned over time in the Western United States.

Beavers also abandon dams for other reasons. Beaver dams may fail and be too complicated to fix. Dams may also be abandoned if a beaver pond fills in with sediment or a beaver’s food source is lost.

Today, beavers are now recognized for their ecological contributions and are returning to areas where they once lived. Animals like this moose benefit from the ponds created by beavers. Areas with beaver ponds also work as fire breaks and are safe places for animals during wildfires.

A computer next to a large machine — **Figure 15**. The scientists used a LECO TruSpec® CN Furnace to measure the amount of organic carbon in the collected samples. Courtesy photo by LECO Corporation.

To conduct their study, the scientists collected samples of the vegetation, sediment, litter, and dead wood found in each of the six types of areas they studied:

(1) old growth forests with a single stream,

(2) old growth forests with multiple streams,

(3) recently abandoned beaver meadows,

(4) long abandoned beaver meadows,

(5) old growth forests, and

(6) newer forests.

Each sample was analyzed for organic carbon using a special machine (figure 15).

Reflection Section

Findings

The scientists found that less carbon is stored in confined valleys than in unconfined valleys.

Confined valleys with steep sides carried carbon into waterways and downstream.

Unconfined valleys with old-growth forest held most of their carbon in large pieces of wood, like logs and tree boles. When trees fell in the stream or river or were otherwise pushed into the channel by the water current, the logs sometimes created logjams. The logjams caused the river to overflow its banks and split into multiple channels (figure 16).

A logjam blocking a river in a forest. The water from the river spills out into surrounding areas. — **Figure 16A**. Logjams in unconfined valleys may cause the stream to overflow and to split into multiple channels.

Colorado State University photo by Ellen Wohl.

An underwater photograph showing a river blocked by logs, debris, and rocks. — **Figure 16B**. The logjams also block areas below the surface of the water.

Colorado State University photo by Ellen Wohl.

Many of the unconfined valleys had abandoned beaver dams. These unconfined valleys held most of their carbon in sediment that was carried into them when rivers overflowed. The scientists found that these unconfined valleys with beaver dams covered less than 25 percent of the river’s total length. However, these valleys held about 75 percent of the total carbon found along the entire river ecosystem (figure 17).

A graph showing megagrams of carbon stored across the different areas. — **Figure 17**. This graph shows the average amount of aboveground and belowground carbon per hectare for each of the six valley types.

FIND Outdoors illustration by Stephanie Pfeiffer.

The scientists identified four places where carbon is stored in temperate mountain and river valleys. Carbon is stored in old-growth single-thread, old-growth multi-thread, old-growth forests, and young-growth forests. Carbon is also stored in logjams or deposited on the floodplain. Carbon is stored in small pieces of matter, such as soil particles, and in living vegetation.

The scientists found that three natural processes supported carbon storage in these floodplain ecosystems:

(1) beaver dams and logjams force water onto the floodplain, where soil particles with carbon content are deposited;

(2) when water is held on floodplains by logjams or beaver dams, the decay of the soil particles is slowed, because the soil is saturated with water; and

(3) logjams decay slowly and therefore hold a lot of carbon in the waterways and on the floodplain.

Reflection Section

Discussion

The scientists found that old-growth forests, logjams, and beaver dams contribute to holding carbon within mountainous temperate forest and river ecosystems. Old-growth forests, logjams, and beaver dams may be found in unconfined valleys, which make up just a small proportion of a mountain river’s length. These landforms and ecological processes play an important role, however, in holding carbon within mountainous Western U.S. ecosystems.

Reflection Section

Adapted from Wohl, E.; Dwire, K.; Sutfin, N.; Polvi, L.; Bazan, R. 2012. Mechanisms of carbon storage in mountainous headwater rivers. Nature Communications. 3:1263.

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3 Natural Inquirer monograph covers.

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A FACTivity, which is an activity to complete after reading the article. The FACTivity helps reinforce major science concepts from the article. These activities are designed to be easy to implement, with few material requirements and options for adapting them for your audience or available resources. Some monograph may have two FACTivities.
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Standards correlations, including Next Generation Science Standards, addressed in both the article and the FACTivity.

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Meet the Scientists
This section introduces the scientists (and others) who worked on the study. In their own words, they each share a memorable science experience, a favorite research project, or something they learned during the course of their education or research.

Use this section to:
- Introduce kids to the variety of people who work in science
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Next Generation Science Standards (NGSS) applications:
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Many of the scientists and engineers featured in this section are also featured on our collector cards. Learn more about their work, how they got interested in their fields, and interesting projects they worked on. Cards can be printed as posters, too.
Thinking About Science
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Use this section to:
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Note that specific standards for this particular monograph are linked on this educator guide tab.

Other resources:

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Use this section to:
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Next Generation Science Standards applications:
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- Understand research questions and hypotheses, including generating their own hypotheses given what they already know
Next Generation Science Standards applications:
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Note that specific standards for this particular monograph are linked on this educator guide tab.

Other resources:

Use one of the guided reading lesson plans to help kids follow the format of a scientific paper.
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The Methods section also ends with a Reflection Section – two or three questions to help students think through what they just read. These questions are interactive on the distraction-free reading mode.

Use this section to:
- Show students how experiments and studies are designed and carried out
- Explore sampling methods and randomization
- Introduce various data collection tools (e.g. camera traps, surveys, insect collection tools, weather stations, etc.)
- Explain bias and how studies are designed to remove bias
- Help students gain experience with map reading
Next Generation Science Standards applications:
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- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular monograph are linked on this educator guide tab.

Other resources:

Many Methods and Findings sections contain Number Crunches, which are simple math exercises designed to help students interact with the data from the study.
Findings
This section summarizes the data collected during the study. The Findings section usually includes data tables or graphs and highlights the significant data points from the study. This section often mentions statistical analysis or the use of computer programs to model or analyze the data, though these methods are only discussed generally.

The Findings section also ends with a Reflection Section – two or three questions to help students think through what they just read. These questions are interactive on the distraction-free reading mode.

Use this section to:
- Have students practice reading and interpreting graphs and tables
- Compare results between variables and controls
- Explain the concept of statistical significance
- Discuss how no data or negative results still provide valuable information
Next Generation Science Standards applications:
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- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular monograph are linked on this educator guide tab.

Other resources:

Search the website for “map” or “graph” to find activities where students can practice making and reading maps and graphs.
Discussion
This section concludes each monograph article. In it, we summarize the main findings of the scientists’ study. Additionally, we present the scientists’ ideas about the limitations of their study, the big-picture impacts of their research, and the scientists’ plans for future study or action.

The Discussion section ends with a Reflection Section – two or three questions to help students think through what they just read, especially general take-aways from the study. These questions are interactive on the distraction-free reading mode.

Use this section to:
- Discuss what conclusions can and cannot be drawn from the available data
- Explain the difference between correlation and causation
- Explore study limitations and opportunities for further study
- Brainstorm ways the study findings could be applied to real-world situations
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular monograph are linked on this educator guide tab.

Other resources:

Use the “Designing Your Own Study” resource page for videos of scientists discussing their own research studies. The page also includes educator resources to help students plan their own scientific studies.

Additional Resources on the Website

A screenshot of the product tabs for an NI monograph On the website, we pair each monograph with a variety of other resources, as well. Use the tabs on the product page to browse through the following:

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Focus student understanding of the main idea of a paragraph in each section of a Natural Inquirer article through a reading and note-taking process. This lesson plan can be used with any...
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Education Files

Project Learning Tree

If you are a trained Project Learning Tree educator, you may use “A Forest
of Many Uses” and “Loving It Too Much” as additional resources.

Ellen Wohl

Geologist

My favorite science experience was hiking into a remote area of the Nepalese Himalaya to look for flood deposits. Few outsiders had ever visited the area. The local people were...
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Nicholas Sutfin

Geomorphologist

One of my favorite science experiences was taking a whitewater rafting trip with other scientists. We rafted on the Middle Fork of the Salmon River in Idaho’s Frank Church—River of...
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Roberto Bazan

Hydrologist

My favorite science experience was when I was with a crew studying the vegetation in Beaver Creek Meadow in Rocky Mountain National Park. The wildlife we saw and experienced made...
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Kate Dwire

Riparian Ecologist

One of my favorite science experiences has been exploring fens in the Rocky Mountains. Fens are special wetlands that have developed over thousands of years through the accumulation of peat...
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FACTivity – Logjams and Beaver Dams

Standards addressed in this Article:

What Is a Natural Inquirer Monograph?

Reading Modes

What's in a Natural Inquirer Article?

Meet the Scientists

Thinking About Science

Thinking About the Environment

Introduction

Methods

Findings

Discussion

Additional Resources on the Website

Article Selection and Review

Lessons

Lesson Plan – Paragraph by Paragraph

Lesson Plan – S.C.A.N and R.U.N.

Lesson Plan – Double Entry

Education Files

Project Learning Tree

Glossary

bole

dead wood

flood deposit

floodplain

landform

lodge

logjam

majestic

nocturnal

organic carbon

riparian

sediment

snowmelt

topography

Ellen Wohl

Nicholas Sutfin

Roberto Bazan

Kate Dwire

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Caribbean Cruise: Examining the Movement and Quality of Organic Matter Over Time From Two Caribbean Watersheds

Don’t Litter the Stream: An Invasive Tree Species and a Hawaiian Stream Food Web

Additional Resources