Where does the carbon in new spring leaves of a deciduous tree come from?

Where does the carbon in new spring leaves of a deciduous tree come from?

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When a leafless deciduous tree 'comes to life' in the spring and puts forth new leaves, where does the mass for these leaves come from? The tree has no leaves to make use of photosynthesis to get the carbon it needs to grow these leaves, so where does the carbon come from: has it been stored in the root system over winter just for this purpose? And if so, has enough been stored for the tree to produce most if not all of its new leaf growth for this season, or only enough to get a few leaves out that will 'take over' the task of providing carbon fixation (making sugars) via photosynthesis to grow the remaining new leaves?

It has been suggested in the comments that the new leaf buds were grown at the end of the previous season. It would seem to me that this strategy for new growth in the spring would be fraught with all sort of dangers from 'winter kill', so these buds would not remain viable come the next spring. So, are the sugars needed for new spring growth coming from the roots or last seasons leaf buds?

While I can't provide references to actual studies, simple observation suggests that it must be stored in the roots, at least in part. That observation is the existence of maple syrup (and other tree syrups, such as birch: In the spring, before leaves start to grow, sugar-rich sap rises from the roots, and can be collected by tapping the tree.

Where does the carbon in new spring leaves of a deciduous tree come from? - Biology

Trees cool and moisten our air and fill it with oxygen. They calm the winds and shade the land from sunlight. They shelter countless species, anchor the soil, and slow the movement of water. They provide food, fuel, medicines, and building materials for human activity.

They also help balance Earth&rsquos carbon budget.

Can we grow our way out of carbon imbalance by making the landscape greener? Would it help to plant more trees or cut down fewer? And does it matter where they are? (Photograph ©2007 :Duncan.)

Scientists estimate that humans release about nine billion tons of carbon (mostly carbon dioxide) each year by burning fossil fuels and by changing the landscape. About four billion tons end up in the atmosphere and two billion tons dissolve in the ocean. The last three billion go into ecosystems on land, but exactly where these sinks are located remains an open question.

Forests are considered one of the world&rsquos largest banks for all of the carbon emitted into the atmosphere through natural processes and human activities. They cover about 30 percent of Earth&rsquos land surface, while accounting for 50 percent of plant productivity. As much as 45 percent of the carbon stored on land is tied up in forests.

Forests cover 30 percent of the Earth&rsquos land. (Map by Robert Simmon, based on data from the MODIS Land Cover Group, Boston University.)

Did forests hold more or less carbon in the past? Could they store more in the future? Scientists really don&rsquot know exactly how much carbon our forests can hold.

What they do know is that human activities have moved a lot of carbon from long-term, stable storage&mdashsuch as rocks, buried fossil fuels, and old-growth forests&mdashinto forms with short-term, direct impacts on the environment. For instance, when we clear forests, we remove tall trees that can store carbon in their trunks, branches, and leaves for hundreds of years. We often replace them with croplands or pastures that store less carbon for a shorter time. Paved developments store little to no carbon.

Eighty years after it was first cut, this forest in British Columbia still has not regained its former grandeur. (Photograph ©2007 Aviruthia.)

&ldquoThe biggest natural sink of terrestrial carbon lies in our forests and trees,&rdquo says Steve Running, a forest ecologist at the University of Montana. &ldquoAnd the biggest natural source of carbon on land is also the forest. So one of the most important things we can do for understanding the carbon budget is to get a better inventory of the carbon we have in our trees.&rdquo

The key measurement is biomass, or the total mass of organisms living within a given area. A rule of thumb for ecologists is that the amount of carbon stored in a tree equals 50 percent of its dry biomass. So if you can estimate the biomass of all the trees in all the forests, you can estimate how much carbon is being stored on land. Repeating those measurements over years, decades, and centuries would then help us understand how carbon is moving around the planet.

Trees are often held up as a solution to our carbon budget problem. Making something like an economic argument, some people suggest that we can &ldquogrow&rdquo our way out of trouble by making (or keeping) the landscape greener. But would it help to plant more trees? To cut down fewer? And does it matter where those trees are?

The first step toward answering those questions is to figure out just how much carbon our trees store right now.

3D Visions of the Forest

Scientists have used a variety of methods to survey the world&rsquos forests and their biomass. They have systematically measured forests from the ground, venturing into the woods to count trees, measure trunks, and climb to the top of the canopy. Taking to airplanes, they have made photographic, radar, and lidar surveys of different types of forest.

With satellites, they have collected regional and global measurements of the &ldquogreenness&rdquo of the land surface and assessed the presence or absence of vegetation, while looking for signals to distinguish trees from shrubs from ground cover.

Student Kelly McManus measures the circumference of a tree in a coastal Virginia forest. Ground-based studies are crucial to ensure the accuracy of airborne and satellite-based studies of vegetation. (NASA photograph courtesy Lola Fatoyinbo.)

But to assess biomass, you have to know the area, density and, most importantly, the height of the trees. Researchers have achieved this on small scales, but to use the traditional methods on a global scale is prohibitively expensive and time-consuming.

&ldquoWe need to see Earth&rsquos vegetation in three dimensions,&rdquo says Jon Ranson, a forest ecologist based at NASA&rsquos Goddard Space Flight Center. &ldquoBy measuring the height of forests, we can then estimate above-ground biomass and estimate the carbon stored in that forest. The more accurate the measurements, the more certain our estimates of the carbon.&rdquo

The first map to estimate forest heights on a global scale came in 2010. Michael Lefsky of Colorado State University combined broad views of the horizontal land surface from the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA&rsquos Terra and Aqua satellites with vertical height from NASA&rsquos Ice, Cloud, and land Elevation Satellite (ICESat).

The height of the world&rsquos forests range from over 40 meters in the U.S. Pacific Northwest, to just under 20 meters for the boreal forests that ring the Arctic. In this map, darker green relates to taller forests. [NASA Earth Observatory map by Jesse Allen & Robert Simmon, using data from Michael Lefsky, Colorado State University].

The result was a map showing the world&rsquos tallest forests clustered in the Pacific Northwest of North America and in portions of Southeast Asia, with shorter forests covering broad swaths across Canada and Eurasia. The tallest tree canopies are the temperate conifer forests&mdashfull of Douglas fir, western hemlock, redwood, and sequoia&mdashthat often grow taller than 40 meters (131 feet). Boreal forests of spruce, fir, pine, and larch usually reach less than 20 meters (66 feet) into the sky. In the middle are the temperate, broadleaf forests of Europe and the United States and the undisturbed tropical rain forests, which both average 25 meters (82 feet) tall.

The backbone of the mapping effort was data from the Geoscience Laser Altimeter System (GLAS) on ICESat, which pulsed laser light at the planet&rsquos surface more than 250 million times in its seven years of flight (2003-2009). Those pulses made direct measurements of 2.4 percent of Earth&rsquos forest surfaces and measurements for 24 percent of the forest patches on surface. That left it to Lefsky to extrapolate and to work out mathematical model estimates for the forests surrounding the ICESat samples.

Michael Lefsky combined wide-scale observations of vegetation with precise laser measurements from ICESat, which were taken along narrow tracks (black lines), to construct a map of forest heights. (NASA map by Jesse Allen and Robert Simmon.)

The global map was the first of its kind, but Lefsky and colleagues knew there was still a lot of uncertainty to be cleared up with better instrumentation and coverage. &ldquoThis is really a first draft,&rdquo said Lefsky, &ldquoand it will certainly be refined in the future.&rdquo

Mapping the Tropics

Sassan Saatchi, a remote sensing scientist at NASA&rsquos Jet Propulsion Laboratory, is one of several collaborators and friendly competitors working on that next draft of forest maps. He is working with satellites to see the forests for the trees and the carbon. His focus has been the thick stands of trees around the mid-section of Earth.

Tropical forests, such as those in Gabon, Africa, are an important reservoir of carbon. (Photography courtesy Sassan Saatchi, NASA/JPL-Caltech.)

&ldquoI first visited a tropical forest in 1994 for a project on the Bahian Coast of Brazil, and I was mesmerized by the complexity and beauty,&rdquo Saatchi says. &ldquoI fell in love with the landscape, with the biodiversity of plants and animals, and with the people. Every time you see a tropical forest, you find something new. For a person with a background in physics and mathematics, it is one of the most complex and challenging systems to understand and model.&rdquo

Because they grow year-round, tropical forests are believed to be the most productive on Earth. They store vast amounts of carbon in the wood and roots of their trees, though scientists have only been able to make broad, speculative estimates about just how much.

&ldquoIn the northern forests of the United States, Canada, and Europe, there are usually sophisticated forestry systems to measure structure and biomass by state or region,&rdquo Saatchi says. &ldquoIn the tropics, we often have no clue how forest carbon is distributed on a local level.&rdquo

What researchers do know is that tropical deforestation and forest degradation account for between 10 and 20 percent of all manmade emissions of carbon dioxide, a significant greenhouse gas. Images from satellites, the space shuttle, and the International Space Station have been showing the smoke plumes for decades. Deforestation is big business, as large-scale producers of palm oil, soybeans, beef, and leather add to the pressure on tropical forests from small farmers working to raise themselves out of poverty. Rising global demands for these commodities mean that these fires may not stop anytime soon.

Fire is commonly used to clear forested land in the tropics. An astronaut aboard the International Space Station captured this photograph of burning in Brazil on August 14, 2010. (NASA astronaut photograph ISS024-E-11941, courtesy the NASA-JSC Earth Observations Lab.)

&ldquoTropical forests have a high diversity of plants, and are extremely variable over the landscape and in their interaction with the climate, yet they are poorly measured and monitored,&rdquo Saatchi notes. &ldquoI have worked every measurement and mathematical tool I could muster to try to understand and map this complexity.&rdquo

Working with 14 colleagues from 10 institutions around the world (including Michael Lefsky), Saatchi set about compiling and analyzing measurements from four space-based instruments&mdashthe GLAS lidar on ICESat, MODIS, the QuikSCAT scatterometer, and the Shuttle Radar Topography Mission&mdashand from 4,079 ground-based forest plots. The team mapped more than three million measurements of tree heights and correlated them to measurements of trees from the ground. They calculated the amount of carbon stored above ground and in the roots. And they extrapolated their results over forest areas where there is less ground sampling but some known characteristics.

The result, released in May 2011, was a benchmark map of biomass carbon stocks covering 2.5 billion hectares (9.65 million square miles) of forest in 75 countries on three continents. Though previous efforts have mapped tropical forests on regional or local scales, the new map is &ldquothe first effort to quantify the distribution of forest carbon systematically over the entire tropical region,&rdquo Saatchi says.

This map shows total carbon stored in biomass in New Guinea, a heavily forested island just north of Australia. (NASA map by Robert Simmon, using data from Saatchi et al., 2011.)

The researchers found that nearly 247 gigatons (billion tons) of carbon was sequestered in tropical forests, with 193 gigatons stored above ground in trunks, branches, and leaves, and 54 gigatons stored below ground in the roots. Forests in Central and South America accounted for 49 percent of the total, with Southeast Asia sheltering 26 percent and sub-Saharan Africa with 25 percent of the carbon storage.

Almost as important as knowledge of the amount of biomass in an area is information about the uncertainty of the data. Areas of New Guinea where the carbon biomass is relatively well known are shown in green, while more uncertain measurements are orange and red. (NASA map by Robert Simmon, using data from Saatchi et al., 2011.)

Saatchi is most proud that his map not only assesses the carbon stock, but also gives a clear picture of the quality and certainty of the assessment. &ldquoOur map tells us the carbon at any location in the tropical forests and how certain we are about our estimation,&rdquo Saatchi says. The research team created mathematical models to show the margin of error in their carbon assessments. On the national and regional level, Saatchi says, the uncertainty is between 1 and 5 percent. &ldquoGiven that biomass estimation from ground measurements has about a 10 to 20 percent error over large plots, our uncertainty in global mapping is very reasonable.&rdquo

Knowing something about the error bars is important for building confidence with resource managers and economists who are trying to assess the needs and values of forests. It is also important for pointing researchers to the areas where more work is needed.

&ldquoWe can advance science by studying uncertainty, and the land part of the global carbon cycle is very uncertain,&rdquo Saatchi asserts. &ldquoData collection on the ground is extremely limited because of the difficulty of access and the lack of infrastructure in most tropical regions&mdashthough that is something we do not necessarily want to change. Still, we really need more systematic and transparent measurements of tropical forest.&rdquo

Close-Up on the United States

&ldquoResource managers need to see forests down to the disturbance resolution&mdashthe scale at which parking lots or developments or farms are carved out by deforestation,&rdquo says Josef Kellndorfer of the Woods Hole Research Center (WHRC). His research team recently took it down to that level when they released the National Biomass and Carbon Dataset (NBCD) for the United States in April 2011.

The National Biomass and Carbon Dataset (NBCD) is the largest high-resolution map of forest biomass yet assembled. Scientists at the Woods Hole Research Center created the map by combining satellite data with precise ground-based measurements. (Map by Robert Simmon, based on data from Woods Hole Research Center.)

&ldquoWe are providing information on a management scale,&rdquo Kellndorfer notes. Forests in the U.S., as well as their carbon content, are mapped down to 30 meters, or roughly 10 computer display pixels for every hectare of land (4 pixels per acre). &ldquoThis data set is a comprehensive view of forest structure and carbon storage, and it provides an important baseline for assessing changes in the future.&rdquo

Over six years, Kellndorfer, Wayne Walker, and their Woods Hole team collaborated with the U.S. Forest Service and the U.S. Geological Survey (USGS) to assemble a national forest map from space-based radar and optical sensors, computer modeling, and a massive amount of ground-based data. They divided the country into 66 mapping zones and ended up mapping 265 million segments of the American land surface. Kellndorfer estimates that the mapping database includes measurements of about five million trees.

The researchers started with data from the Shuttle Radar Topography Mission, which was flown on the space shuttle Endeavour in 2000. With that space radar, the USGS and NASA&rsquos Jet Propulsion Laboratory constructed topographic maps of nearly all of Earth&rsquos land masses from 60 degrees north latitude to 60 degrees south.

By 2005, Kellndorfer deciphered signals (the scattering surfaces) in the electromagnetic waves detected by the radar&mdashdata that revealed the height of the vegetation. Subtracting the height of the treetops from the elevation of the land, the scientists could estimate the height and density of the woody plants, trees, and shrubs covering the surface.

But those numbers were only the beginning. Kellndorfer&rsquos team combined their data with the National Land Cover Database, which was built from Landsat satellite images of Earth&rsquos surface. They examined the biology and geology of their picture. How do different land elevations affect the height and thickness of trees? What can and cannot grow at certain elevations?

The last piece of the puzzle was ground truth. Kellndorfer enlisted the aid of Elizabeth LaPoint and colleagues in the Forest Inventory and Analysis program of the U.S. Forest Service. The federal foresters keep a census of the nation&rsquos trees, maintaining a survey plot for every 6,000 acres of woodland, and measuring the trees within that plot at least once every five years.

Those plots, however, are not available for direct survey or study by Kellndorfer or anyone outside the service&mdasha safeguard to protect the integrity of the data set and the rights of private property owners. So the Woods Hole team prepared thousands of data sets with 15 to 20 variables that LaPoint could compare to the forest inventory.

The NBCD is divided into 66 ecoregions. The zone corresponding to coastal Pacific Northwest has the densest biomass in the United States. (Map by Robert Simmon, based on data from Woods Hole Research Center.)

In the end, the research team was able to construct a map with higher resolution and more precise detail than any large-scale map of forest biomass ever made. The map reveals the checkerboard patterns of logging in the old growth of the Pacific Northwest and the highly managed tree farms of the Southeast. In the Midwest, trees outline the rivers and the edges between farms, while forests re-emerge on land that was once cleared for crops. In the Mid-Atlantic and New England, lands that were stripped bare in the early years of the nation are now tree-covered again&mdashthough with many urban developments amidst the forest.

At full resolution, the NBCD shows logging on the scale of individual plots. (Map by Robert Simmon, based on data from Woods Hole Research Center.)

&ldquoForests are a key element for human activity,&rdquo says Kellndorfer. &ldquoSo we have to know how much we have, and where, in order to conduct sound management and harvesting. This map gives us another tool to see our precious resource.&rdquo

Building a Better Measuring Stick

Lidar, radar, visible-light imagery, ground surveys, and computer models all bring slightly different answers to the same problem. Three different teams produced three different forest and carbon maps in a fifteen-month span. Groups at Stanford, the European Space Agency, Brazil, the U.S. Forest Service, and dozens of other institutions are pursuing similar questions, sometimes as competitors, sometimes as collaborators.

From a distance, the research can sometimes appear redundant. But parallel approaches and competition have always been the recipe for innovation and deeper understanding.

David Harding (left), Charles Gatebe (right), and Rafael Rincon (back) were three of the lead scientists on the Eco 3D field campaign. Each of the researchers was responsible for a different instrument. Understanding of the world&rsquos forests is improved by multiple groups looking at the problem from varying perspectives. (NASA photograph courtesy Jon Ranson, GSFC.)

&ldquoIt&rsquos similar to cancer research, where you have different laboratories and different countries pursuing the same problem,&rdquo said Jon Ranson. &ldquoEveryone is looking with a slightly different angle and methodology. Groups are collaborating as much as they can, and taking the data that are available and making the best of it. In the end, it&rsquos complementary and it improves the overall science.&rdquo

The ultimate prize is a uniform, standardized map of forest heights and carbon stocks on all continents at one time. And that map should be updated and revised as human activities renovate our planet.

&ldquoWe have a pretty good handle on forest area worldwide, but not as great a sense of the structure or the changes,&rdquo says Steve Running, a member of the Intergovernmental Panel on Climate Change. &ldquoWe need a better global, annual measure of our carbon stocks. We need to know how things change each year through fire, new growth and re-growth, desertification, and deforestation.&rdquo

&ldquoHow do we cover the whole world,&rdquo Running adds, &ldquoand do it every two to three years, which is what the science needs?&rdquo

The number of options for space-based mapping has gotten smaller. The ICESat mission ended in 2009. Its follow-on, ICESat II, is slated for launch in 2016, but will not necessarily be able to view forests in the same way as its predecessor. The synthetic aperture radar used for the Shuttle Radar Topography Mission provided a global picture of Earth&rsquos landscape structure in early 2000 but the space shuttle was retired in July 2011. A similar technology could provide forest structure and cover globally every year if launched on the space station or another satellite.

Many forest researchers and ecologists were counting on a mission that was proposed years ago and recommended by the National Research Council in 2007&mdashthe Deformation, Ecosystem, Structure, and Dynamics of Ice satellite. DESDynl would combine radar and lidar technologies to get a three-dimensional view of forests and their carbon stock. But that mission was put on indefinite hold in the spring of 2011 as the U.S. government made deep budget cuts. Researchers are now looking for other means to fly those instruments in space.

NASA researchers use instrumented aircraft&mdashsuch as the P3 Orion&mdashto make measurements that supplement and bridge the gap between satellite missions. (NASA photograph courtesy Jon Ranson, GSFC.)

Ranson and colleagues Doug Morton, Bruce Cook, Ross Nelson, and others at NASA Goddard have picked up the effort to find a way forward. Since August 2011, they have been flying developmental instruments on NASA research airplanes, crisscrossing the eastern United States and taking stock of everything from sub-tropical wetlands to boreal forests. The team has been flying over Forest Inventory and Analysis plots in Maine, New Hampshire, Pennsylvania, Maryland, Virginia, North Carolina, and Florida, while flying under the old satellite tracks of ICESat. The team intends to calibrate their data against measurements from ICESat, Cook says, &ldquoand see if we can detect changes as we re-fly over an area.&rdquo

In the summer of 2011, Ranson led the Eco-3D mission to measure forests in the eastern U.S. and Canada with three main instruments&mdashradar, lidar, and a radiometer. The Digital Beamforming Synthetic Aperture Radar (DBSAR) provides a broad, horizontal view, distinguishing forest from other land cover and giving a sense of the biomass density. The Slope Imaging Multi-polarization Photon-counting Lidar (SIMPL) measures the forest canopy height and structure, while also providing clues about the types of trees being measured. The Cloud Aerosol Radiometer (CAR) measures the light reflecting properties of the leaves and landscape, which tells researchers about the composition and health of the forest.

Lidar instruments measure tree height by bouncing laser light off the canopy. (NASA image by Robert Simmon.)

Beyond Eco-3D, the Goddard team has been working with partners in Canada and Brazil to improve airborne forest mapping, which may be the best method the world will have until a space-based lidar and radar can be flown again.

What is it All Worth?

&ldquoIt&rsquos amazing how many people really need our data,&rdquo Saatchi notes. &ldquoI&rsquove been getting bombarded by emails from people who want these maps.&rdquo

Kellndorfer&rsquos inbox is full, too. Hundreds of ecologists, forest managers, academic scientists, city planners, land conservation groups, timber companies, climate modelers, civil engineers, biologists, and fish and game managers have sought maps on an almost daily basis. More are likely to come as international negotiators move closer to treaties and economic markets for managing carbon emissions and storage.

New information about forests around the world will help society predict and respond to climate change, both natural and man made. (Photograph ©2006 *clairity*.)

&ldquoThe work we&rsquore doing can help put an economic value on forests,&rdquo says Goddard&rsquos Doug Morton. &ldquoPolicymakers and economists want to know forest carbon stocks at very fine spatial scales, and countries naturally need to improve their assessment of stocks to participate in a forest carbon market. This is a high-stakes game in the policy realm.&rdquo

Developing countries are taking stock of the carbon in their forests as part of an effort in climate change mitigation called Reducing Emissions from Deforestation and Degradation, or REDD+. Scientific partners from the United States and Europe are often called on for technological assistance.

&ldquoCarbon trading markets are going to be partly based on selling credits for forests,&rdquo says Running. &ldquoIf there is going to be billions of dollars in carbon trading, then knowing where the carbon is and how much of it there is takes on huge political and economic importance. We need a coordinated, global monitoring plan in order to make it legitimate.&rdquo

Getting the dirt on carbon

As part of the carbon cycle, leaves decompose and the carbon in their bodies is broken down and recycled. Some of it is released into the air as carbon dioxide, or CO2. The rest moves into the soil.

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Each year, spring comes, plants bloom and the trees leaf out in their full green glory. Come fall, while diving into piles of fallen leaves, you may think the life cycle of the leaf has come to an end.

But that’s not so. Once a leaf hits the dirt, a new cycle begins. All those brightly colored leaves are like candy for fungi and bacteria on the ground. These decomposers, organisms that feed on dead matter, go to work breaking down leaves to create energy-filled food for themselves. In the process, decomposers also make nutrients available for other organisms.

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This recycling scheme is not just a plot to produce a mob of mushrooms and other eensy entities. It’s part of a complex chemical cycle that helps regulate the Earth’s climate. And it’s all based on carbon, a kind of element, or tiny substance.

Carbon is the building block for all life on Earth. Every single cell in every living thing — including plants, animals and humans — contains at least some of the stuff.

Carbon isn’t found only in living matter. It’s also found inside the Earth’s mantle, the layer between the crust and the core, and in seawater, air, rocks and soil. The planet’s carbon is constantly flowing from one of these to another, creating what is known as the carbon cycle.

Take those leaves, for example. As they decompose, or rot, the carbon in their bodies is broken down and recycled. Some of it is released into the air as carbon dioxide, or CO2. The rest moves into the soil.

Soil is a great place for carbon. There, it may remain locked up for hundreds, thousands or even millions of years, adding nutrients needed for growing food. Keeping carbon locked up in the soil also provides a way to keep it out of the atmosphere.

Dig in

Carbon has a very complicated cycle within the soil and in the atmosphere. The two cycles are intricately linked, says Patrick Drohan, a pedologist (scientist who studies soil) at Pennsylvania State University in University Park.

Though some of the carbon in soil comes from sedimentary rocks, such as limestone, most of it comes from organic matter, meaning waste from living organisms. Sounds a bit yucky, but it’s really cool. He explains the cycle like this:

A squirrel poops (or a plant or animal dies) and the waste then decomposes. Nutrients in the organic matter, including carbon, are released into the soil with the help of decomposers such as fungi and bacteria. Over the years, the nutrients are broken down further. Eventually, the nutrients get reabsorbed by a plant taking up water, or a human eating food grown in the soil or perhaps by a tiny organism called a microbe within the soil. When that microbe breathes, it releases CO2 into the atmosphere. Plants absorb the CO2 released from the microbe. From here, the cycle begins again.

Leaves on the ground are like candy for fungi and bacteria. These decomposers, organisms that feed on dead matter, go to work breaking down leaves to create energy-filled food for themselves. In the process, decomposers also make nutrients available for o

Concern over the rapid buildup of carbon dioxide in the atmosphere has prompted scientists to look at ways to sequester, or contain, carbon in the soil and plants. The key to doing this is plant production.

Scientists say promoting and protecting the growth of forests and other plants may boost plants’ capacity to take up CO2 in the atmosphere. Such practices may also increase soils’ capacity to store carbon for long periods of time.

The power of plants

Most of the carbon on Earth is stored in plants and soil.

Where does all this carbon come from? Plants get all of their carbon from carbon dioxide, or CO2, in the atmosphere. The leaves on trees and crops soak up CO2 during photosynthesis, a chemical process that converts sunlight into food. Then plants spit some of the CO2 back out during another process called respiration, the way plants “breathe.”

Plants, especially trees, are so efficient at pulling carbon dioxide from the air that they take in more carbon than they release. That’s why they’re called “carbon sinks.”

Trees grouped together in forests are even more efficient. Scientists estimate that the Earth’s forests currently store more than 75 percent of the planet’s aboveground carbon. And the forests store almost that much of the planet’s soil carbon.

Scientists are working to develop forest management strategies to help absorb some of the extra CO2 in the atmosphere. But this task isn’t as straightforward as it may seem.

Not all forests actually store carbon, says Peter Curtis, a forest ecologist at Ohio State University in Columbus who studies the role of forests in the carbon cycle. “Some forests experience a net loss.”

That doesn’t mean that the trees have stopped photosynthesizing. It simply means that the respiration part, the loss, is greater than the gain, he explains.

Accounting for carbon

Curtis works to measure how much carbon can be held in forests in the Midwest and Great Lakes region. Working from the University of Michigan Biological Station in northern Michigan, he has two ways of doing that.

First, he uses a high-tech approach: Information is collected on and around two meteorological, or weather-measuring, towers, which look a lot like cell phone towers. Standing 150-feet-tall — about as high as a 15-story building — the towers loom over the forest’s canopy.

Instruments on the towers measure how much CO2 is being taken up by the leaves on the trees. The instruments also measure temperature and moisture levels in the air, recording information up to 10 times per second.

The scientists also use some “low-tech” methods to collect data. In other words, researchers spend lots of time on the ground measuring the trees and collecting leaves to see how much debris has decomposed.

Using this information, Curtis tracks how much carbon the forests take in through photosynthesis, and how much they lose through respiration.

Carbon is the building block for all life on Earth. Every single cell in every living thing — including flowers, frogs and humans — contains at least some of the element.

“It’s like a bank account,” he says. “If you get $10 in allowance, but have $8 in expenses, then $2 is what goes into your account.”

The trees may take up a ton of CO2 per acre, but respire 1,500 pounds, leaving a “profit” of 500 pounds of carbon intake.

Fortunately, most forests take in more carbon than they loose. Generally speaking, the planet’s forests take in about 25 percent of the CO2 created by human activities, Curtis says.

Areas heavily populated with forests absorb even higher amounts of human-generated CO2. In some parts of Michigan or Maine, the oaks and pines found in hardwood forests take up about 60 percent of the carbon emitted by people that live in that area.

“A forest in one of these areas can soak up the yearly emissions of about 225,000 cars,” Curtis says. “We call that an ecological forest.”

But changes in rainfall and temperature can shift a forest’s ability to hold carbon from year to year. Unseasonably warm temperatures in a cool, wet forest, for example, can speed the rate of decomposition of soil matter. When that happens, carbon that has been stored in the soil for hundreds, even thousands of years, may be released back into the atmosphere.

Such changes have been documented in some Canadian forests, Curtis says. “This is one of the big worries with climate change. When temperatures increase, decomposition ramps up and the forest gets drier, and all that soil carbon starts to be lost.”

Small changes

Scientists don’t yet know all the effects climate change will have on soil’s ability to store carbon, Drohan says.

They do know, however, that even a small change in soil carbon storage can have a significant impact on the global carbon balance. To that end, researchers are looking at ways farmers might better manage their crops and soil.

Practices designed to keep carbon in the soil will benefit farmers, as well as the planet. Carbon adds organic matter, which helps soil retain nutrients and water. Soil carbon also improves the structure of soil, resulting in better drainage and aeration, or flow of gases, for roots. That means healthier plants and better yields for farmers.

You don’t have to be a farmer to benefit, or to help. Curtis spends some of his time working with government officials and landowners to help them manage forest areas for the benefit of the planet and its soil.

At Michigan Technological University, faculty and students are leading a community effort to return carbon to the soil. The group throws logs and other debris into a large container. These scraps are then burned slowly at a low temperature to create bioch

Even small-scale, community efforts can help. At Michigan Technological University, faculty and students are leading a community effort to return carbon to the soil. Instead of just letting agricultural and plant wastes degrade on their own, the group throws logs and other debris into a large container. These scraps are then burned slowly at a low temperature.

This smoldering process produces a substance called biochar that resembles the char left by a campfire. More importantly, the slow burn prevents much of the carbon from getting released back into the air, says Michael Moore, who’s leading the effort. The char can then be tilled right into the soil, where the carbon stays locked for years.

Amazonian natives have used this technique for centuries to fertilize their soil, says Moore, who teaches writing and poetry. He learned about it while traveling in Honduras.

Biochar isn’t ready for large-scale agriculture yet, but Moore says such community efforts provide a way for ordinary citizens to help the planet. And that has benefits for all.

What makes leaves sprout in the spring?

A spring sycamore with buds opened and flowers appearing. Credit: Albert Bridge,

If you’re in the lower latitudes of Canada right now, take a look outside.  Most trees are in the process of sprouting their 2011 crop of leaves.  Only a few weeks ago, they appeared barren – now there is an explosion of new life.

But how does this happen?  As internationally acclaimed plant biologist (and Vice-Principal, Research at U of T Scarborough) Professor Malcolm Campbell explains in this interview, this bursting of buds is the result of a complex program designed by the trees over tens of thousands of years.  It all depends on a number of factors occurring throughout the year – and variation in one factor can change the timing of trees’ buds bursting in the spring.

What is it about the spring that makes the new growth of leaves on trees occur, year in and year out?

Even though we’re in the spring now, the whole program that you’re observing was set up in the autumn.

As the days get shorter in the autumn and the temperatures decline, the tree sets itself up to go dormant and then in the same program sets itself up to burst bud in the spring.  And of the two components I mentioned, day length and temperature, the one in the autumn that’s most important is day length.

That functions as a signal for the plant to begin to shut down.  Actually, to put it another way, it’s night length that’s important.  As the nights get longer, the plant perceives the lengthening night or the shortening day and embarks on a program to shut down.

That said, even plants in tropical zones or in lower latitudes will still shut down in the winter months, even though the day length may not decrease as dramatically as what we experience in Canada.  And they do that by perceiving other cues.  Decreasing temperature is one cue.  Water availability is also important.  Take a look at forests that exist close to the Equator — they use signals that are derived from water availability.  So in late August and early September in the northern hemisphere, when precipitation rates drop, that can function as a cue and have the tree shut down and enter that dormant state.

When the trees make that dormant bud, that hardened bud we see through the winter months that protects the growing tissues underneath from the foul weather, they are set up to grow again in the spring and to make sure they interpret the cues during the winter so that they don’t grow again in the spring at the wrong time.

Why is there variation in when the leaves sprout from year to year?   My wife noted in 2010 that all the leaves had come in on May 1.  This year, it’s mid-May and the trees are not fully in bloom yet.  Why?

Let me provide a bit of background first.

The program that is set up is contingent on having what’s called a “cold requirement”.  That is, having a minimum number of days of cold temperature.  After this critical number of cold days has passed and, provided the plants are warmed to an adequate temperature, they will burst buds in the spring.  Both factors are essential.

This explains why trees from lower, warmer latitudes don’t do well in cold climates. What will happen in cold climates is that their need for cold temperature or reduced water will be fulfilled very rapidly and you can imagine that you might have a very warm day in January and what will happen is that those trees will burst bud and then we’ll have a cold snap after that and it will kill them.

We’ve seen this before, even in Canada, for trees at lower latitudes, especially those running along the Canada-US border.  In the 1930s, the trees had their minimum requirement for cold days fulfilled and the temperature rose relatively early in the spring.  The trees burst bud and they were making leaves and then there was a cold snap and we had a catastrophic loss of trees due to fulfilling the cold requirement, having a warm time and then having a late spring frost again.

So, to answer your question, in 2010 the buds may have burst two weeks earlier than this year because the autumn of 2009 was cold enough for the trees.  So, once the night length got longer, the trees went into their dormant program, and then the tree was able to fulfill its cold days requirement and then there were enough warm days to allow the tree to say, “OK, timing is right, I can burst bud again.”

And what happened this year to make them burst bud later?

There could have been a warmer autumn last year.  Warm autumns can mess the plants up.  As I recall, it was a warm autumn last year.  This is one of the things that people are worried about with global climate change — if we have warmer autumns,  that cue won’t be there to tell the tree to go dormant in the autumn and they won’t have the necessary combination of day length and temperature to properly shut them down.

This is what could have happened this year.  The other cue is that we didn’t have sufficiently long enough numbers of warm days on the spring side to bring them out of dormancy.  So their cold requirement might have been met during the winter, but now we haven’t had enough warm days in a row to bring them out of dormancy.  So, everything is delayed.  Remember, trees won’t do anything until they get their cues.

Is it possible for trees to adapt to what we expect to be the vastly different climate conditions global warming will bring about?

It is true that trees can adapt and have adjusted to pretty significant climate changes in the past.

For example, during the last period of glaciation, we had many of the tree species familiar here in southern Canada pushed down into southwest  California and the Florida panhandle, as the ice sheet pushed from north.  That took 10,000 to 15,000 years.    Herein lies the problem today – while it is true that over long geological time scales plants and animals can adapt, if you’re talking about a tree that doesn’t have the capacity to pick up and move long distances, then climate change that takes place over a very compressed time scale can make it very difficult for the tree to contend with.

U of T is doing a lot of research in understanding life systems of trees and plants, isn’t it?

Yes, we’ve made some important discoveries.  One is by U of T professors Peter McCourt, Darrell Desveaux and Nick Provart of Cells and Systems Biology and a former U of T professor, Sean Cutler.  This group has reached an understanding, at a very detailed level, of the mechanism that perceives hormones that tell the plant “OK, now it’s time to shut down.”

My own lab has been working on understanding all the genes that are expressed in response to cues like that but we’ve been focused on a different cue — not temperature but water availability.  To put it more simply, we’re working to understand the molecular pathways that control the plant processes that we see change around us, like the leaves dropping and then growing again.

It’s interesting how this work, in the study of trees and plants, sounds similar to work done on human health.

Absolutely.  The tools we’re using to investigate personalized medicine or translational genomics, which are so important to humans, are the same tools being used to understand and protect forest and crop health.

A good time to fertilize trees in most Northern temperate climates is from fall to mid-spring. At these times the tree's roots take the nutrients from the soil and apply them to important health-promoting functions such as root development and disease resistance, rather than simply putting out new growth.

During the growing season, fertilizing can help a tree overcome mineral deficiencies and fight off infections. If you are fertilizing in mid- to late summer, avoid formulations high in nitrogen as this will just promote weak, new growth that may be easily damaged in the winter.

Where Do Rainbow Eucalyptus Grow?

Rainbow eucalyptus (Eucalyptus deglupta) is the only eucalyptus tree indigenous to the northern hemisphere. It grows in the Philippines, New Guinea, and Indonesia where it thrives in tropical forests that get a lot of rain. The tree grows up to 250 feet (76 m.) tall in its native environment.

In the U.S., rainbow eucalyptus grows in the frost-free climates found in Hawaii and the southern portions of California, Texas and Florida. It is suitable for U.S. Department of Agriculture plant hardiness zones 10 and higher. In the continental U.S., the tree only grows to heights of 100 to 125 feet (30 to 38 m.). Although this is only about half the height it can reach in its native range, it is still a massive tree.

Temperature and tree growth

Tree growth helps US forests take up 12% of the fossil fuels emitted in the USA ( Woodbury et al. 2007), so predicting tree growth for future climates matters. Predicting future climates themselves is uncertain, but climate scientists probably have the most confidence in predictions for temperature. Temperatures are projected to rise by 0.2 °C in the next two decades, then by 1.5–3.5 °C at the end of the century, depending on model and emissions scenario ( IPCC 2007). In this issue, Way and Oren (2010) provide a thorough, timely and important synthesis of the effects of temperature on tree growth. I will highlight some of their findings and think about some other ways to approach the problem.

Way and Oren (2010) found that increased temperature generally increases tree growth, except for tropical trees. They suggest that this probably occurs because temperate and boreal trees currently operate below their temperature optimum, while tropical trees are at theirs. The response of growth to temperature was not simply accelerating the same trajectory of ontogeny achieved at current temperatures. Remarkably, temperature shifted the trajectory. Warmer trees were taller and skinnier, with more foliage and fewer roots! These changes were more pronounced in deciduous species than in evergreen species, as was the overall response of growth to temperature. Contrary to expectations in the literature ( Ryan 1991), plant respiration responded less than photosynthesis to increased temperature, because respiration acclimated while photosynthesis did not. Way and Oren (2010) also developed and tested general equations for estimating temperature effects on tree growth that should be useful for adjusting models. Because the literature was dominated by pot studies done with limitations to water and nutrients removed, they suspect that the equations might tend to overestimate the response of growth to temperature in ecosystems, especially where these are limiting. As a final comment, Way and Oren (2010) offer an excellent model of how to synthesize diverse studies, because the methods are clear and statistically rigorous and the limitations and potential confounding factors are identified and addressed.

How well can equations developed from a synthesis of studies across sites predict the response for an individual site? This is important to consider, because an individual site is where the equation will be applied. Problems with cross-site relationships might arise if the population at a specific site had a different response than the combined populations across sites. As an example, imagine if a cross-site relationship was developed from the 10 populations depicted in Figure 1 ( Rehfeldt et al. 2002). Since each of the populations are currently growing at their optimum temperatures, a cross-site relationship would show a response connecting the peaks (dashed line), but the response of any individual population would be much different. Indices of dispersion or overall model fit statistics for a cross-site model can help assess this. However, because the within-site data used for the cross-site relationship represent only a small fraction of the overall response, they sample only a small part of the population response. Way and Oren (2010) did test their cross-site relationship for a single species (Douglas-fir) and found that the more specific the cross-site relationship (for example, warming only for evergreens), the better it fit the individual site. That the projected increases in temperature over the next century ( IPCC 2007) are within the range for most of the experiments suggests that a cross-site relationship is a good initial estimate for the next century.

The response of tree growth to temperature differs among populations, where each population is found at the peak of its growth curve (black circles). A cross-site relationship for this data (dashed line) would poorly predict the response of any given population.

The response of tree growth to temperature differs among populations, where each population is found at the peak of its growth curve (black circles). A cross-site relationship for this data (dashed line) would poorly predict the response of any given population.

A mechanistic understanding of temperature effects on tree growth might also come from an understanding of the effects of temperature on cell division and expansion, which are generally more sensitive to environmental variability than are photosynthesis and respiration ( Hsiao 1973, Körner 2003). In many trees in many situations, photosynthesis does not control the tree’s carbon balance ( Körner 2003). Rather, the control over the sinks by growing cells does, and sink feedback can also regulate photosynthesis and respiration ( Cannell and Thornley 2000, Wiemken and Ineichen 2000). Moving towards a better understanding of the environmental controls over cell division, cell expansion and partitioning photosynthesis into various sinks might help achieve a better mechanistic understanding of how tree growth will respond in future environments.

Will faster tree growth in a warmer climate act to help mitigate CO2 release from fossil fuels and land-use change in the tropics? Tree growth is only a part of the equation for carbon stored in forests or available for use as low carbon biomass fuels or for substitution for concrete and steel (material with high carbon costs for manufacture). The other part of the equation, the response of rates of tree mortality to future climate, is unknown ( Ryan et al. 2010). Disturbances such as forest fires, insect outbreaks and storms may increase in a warmer world ( Ryan et al. 2008), and there are some suggestions that those increases may be occurring now ( Westerling et al. 2006). If disturbances do increase, any increase in forest carbon storage or availability from faster growth could be negated by disturbance losses unless tree mortality can be used quickly after it occurs.

Spring Lesson: Learning About Trees

EducationWorld is pleased to present this lesson shared by the Get to Know Program, which inspires youth to discover the natural world by providing innovative programs, resources and events. The original lesson plan was developed in consultation with acclaimed artist and naturalist Robert Bateman and science consultants from the California Department of Education. The lesson appears on the Get to Know Program’s Best Practices Resource Page, which provides teachers and parents with free, cutting-edge lesson plans, videos and interactive activities designed to connect children with nature through art, music, drama, writing, photography, video and nature journaling. Find more information, including a large selection of lesson plans, here.


--Science as Inquiry
--Life Science

Brief Description

In this hands-on science activity, students experience trees by using senses other than sight.

  • Learn to identify several tree species by sight, touch, and smell
  • Be able to describe several tree species based on features such as leaf shape and type, bark, growth form, and others
  • Describe the importance of trees to humans and to other species

Trees, science, ecosystem, ecology, environment, outdoor, nature, senses

Materials Needed

  • Tree tags (large recipe cards with strings taped or stapled to them)
  • Blindfolds for half of your class
  • Copies of the Blind Tree Discovery Worksheet (one copy per student)
  • Pencils, pens, or crayons
  • Student notebooks, journals, or sheets of drawing paper
  • Clipboards (optional, one per student group)

NOTE: This lesson requires 30 to 90 minutes, and access to the schoolyard or a nearby park is recommended.

Lesson Plan

Trees are a key component of any ecosystem, as they influence everything around them, including the local weather and the wildlife that lives in the region. Getting to know the trees in your area is a great place to start if you want to appreciate and understand the ecology of your state. This is true not only of rural areas, but also in cities where trees are an important part of the urban ecology.

In this activity, your students will become intimately familiar with trees by using senses other than just their sight. Your students will discover the features of local tree species that make them unique, and will make connections with trees that go beyond just knowing their names and what they look like. This is an activity you can do in any season, but the best time is in spring or early fall when deciduous trees still have their leaves.

In advance of your class, visit the field trip site and pick a gathering spot within a short walk of several trees. Pick out between three and six different species of trees that students will visit, and place nametags on them. Try this source or this source (or a library reference book) for helping identify different species.

These trees should be located within a short walk of the gathering spot, and be clearly visible so you can see your students at all times. If possible, choose trees that have branches your students can reach so they can check out the leaves. Give your trees short names like “Sam” or “Betty” so that you and your students will have a way to find individual trees in your field trip area. Write the common name on the back of the nametag.

To prepare your students for this activity, go over the Background Information: Get to Know Trees (at the bottom of this lesson).

Before staring this activity, you'll also want to check with your students to see what they already know about trees. The following questions can help you assess your students’ prior knowledge:

  1. What makes a tree different from other kinds of plants? Trees have a thick woody stem, and are usually fairly tall (greater than 3 yards). Shrubs also have woody stems, but have many smaller stems that rise together from ground level. Other kids of plants lack the woody stems, and are usually much shorter in height.
  2. What trees grow in your neighborhood? Check for knowledge of accepted common names. Students may say “spruce”, or “pine”, or they may know the actual common names, like “aspen poplar”, or “jackpine.” If trees are visible outside the window of the classroom, ask your students if they know what kind of trees they are, and what their names are. Check to see if your students understand the difference between deciduous and evergreen trees.
  3. What animals live in trees? Let your students name as many as they can. This will help them think about trees as a part of the habitat for local animals. They may identify birds that nest and or feed in trees, and they should also be able to name some mammals, such as squirrels, that live mainly in trees.
  4. How do trees reproduce? Let your students name any of the ways they may be familiar with. Trees may reproduce by means of seeds (most common), but can also clone themselves through suckers (saplings that rise from the spreading roots of the parent tree). Do your students realize that many trees are either male or female?

Have students complete one or more of the following three activities:

Have your students work in pairs. Each group should have a blindfold and a copy of the Blind Tree Discovery Worksheet.

Allow one member of the pair to blindfold the other, and carefully lead him/her to one of each of the tagged tree species.

Once at the tree, the blindfolded student will explore the tree from the ground to as high as she/he can reach, and describe the texture, smells, shapes and other attributes of the tree. The partner will record these observations on the worksheet.

They will have five minutes to explore the tree before moving to the next one.

Before leaving the tagged tree, the blindfolded student must take a guess as to what kind of tree it is.

Visit at least three different trees and make blindfolded observations at each one.

Call your students back after 20 minutes, and have the partners switch roles and repeat the blind tree discovery.

When they have completed the activity, test your students' ability to identify the tree species. Ask them what features most clearly distinguish each species. Have them highlight these features on their worksheet.

Distribute plain paper and pencils to your class. Have them do any or all of the following:

  • Make a portrait of the whole tree as it appears in its habitat.
  • Make a rubbing of the bark of a tree
  • Make a rubbing of a tree leaf
  • Make a detailed sketch of just one branch with a few leaves and buds

C. Field Guide to Local Trees

When your students have identified trees in your field trip area, have them put together a several-page field guide to these tree species. Have them take a photo using a digital camera, or make drawings and diagrams that help identify the tree to include with the description.

Include details like the leaf shape and color, the arrangement of the branches, size of the tree, what habitat it seems to prefer, the texture and color of the bark, and other details. Divide your class into groups, and assign one tree species to each. They may use the Internet to gather additional natural history information they can summarize for their descriptions.

Indoor Option
If you are unable to bring your class outdoors to work with living trees, you can have fun with a version of this activity in the classroom. Simply find large samples (pruned branches will do, or potted domestic varieties from a greenhouse or nursery). Tag them and place them around the room, and conduct the blindfolded discovery activity with these materials.

Plan a tree-planting project. A wonderful way to reinforce the value of trees and to help your students develop personal connections with trees is to have them plant trees in the schoolyard, neighborhood, or on local public land. You will need to seek permission from a landowner or local authority to do this, but such permission is usually easy to get. Select a tree species that is preferably native to your region and which you know will grow well without much help. Enlist the help of parents if the project is out of the school yard and requires travel. If planting trees in the schoolyard, make sure the trees are planted in a place where they will get adequate sun and moisture, and where they will not be disturbed.

Multimedia: Instead of writing down student observations as they touch and explore trees blindfolded, have the partner shoot a video clip using a handheld camcorder, digital camera, or make an audio recording using a portable sound recording device such as a cassette recorder or digital voice recorder. Have your students transcribe their observations back in the classroom.

Social Media: Web sites like Flickr and Facebook are useful tools in constructing field guides, journals of observations and photographs of the trees studied. Some suggestions for their application: a class page where students are encouraged to share their observations a running update of trees discovered and where or a photo mural or montage of all the trees involved in your study.

Background Information: Get to Know Trees

Trees are simply large plants with thick woody stems. Wood is a tough material that trees make as they grow. It is the wood in their stems that lets trees grow to such large sizes. You can find trees pretty much everywhere—in our cities and parks, and as part of the landscape almost everywhere we go. They are extremely important in nature because they are the dominant living things in many ecosystems.

Broad-leafed trees have soft, flat leaves with branching veins. Broad-leafs include species like the Bigleaf Maple and the Blue Elderberry. Broad-leafed trees are also called deciduous, which means they lose their leaves each fall. Most of these trees have simple flowers, and produce seeds during the summer or fall. Some of their seeds are in the form of hard nuts, such as the acorns on oak trees, while others, like aspen and maple, make seeds that are carried on the wind.

The needle-leafed trees include spruce, pine, larch, fir, cedar and hemlock. The leaves of these trees are stiff and woody, and except for larch, stay on the tree year-round. All of these trees produce their seeds in cones, and so are also called coniferous trees, meaning “cone-bearing.” For the most part, conifers are evergreens, meaning they keep their needles year round.

  1. Leaves: Like other plants, trees use sunlight to make sugar from carbon dioxide and water in their leaves. This is called photosynthesis.
  2. Crown: The top of the tree is the crown. The tree grows taller by adding new branches and adding height to its crown.
  3. Branches: Branches support the leaves, spreading out so that the leaves can get sunlight.
  4. Trunk: The trunk is the thick, woody core of the tree. It is made of a tough material called cellulose, which is made from the same sugars trees make in their leaves.
  5. Bark: Bark is the rough outer covering of tree trunks and branches. It protects the growing tissues inside from drying out. Some trees have thick bark that resists insects, fungi, and fires.
  6. Base: The base of the tree is usually the widest part of the trunk, and often has the thickest bark.
  7. Roots: Tree roots do several important jobs. They anchor the tree in the soil so it stays upright, they bring water and minerals into the tree for use in the leaves, and they store sugars and starches over winter.

The importance of trees and forests

Trees play a vital role in ecosystems as one of nature’s most important food producers. Trees absorb vast amounts of carbon dioxide and water, and as part of the process, make oxygen and sugar. The oxygen is needed by animals so they can breathe. The sugar, called glucose, is used to make wood and other plant materials, which is also used by many animals as food. In this way, trees and other plants supply animals with both their oxygen and food.

Forest-covered lands supply water to rivers and lakes. Forests act like a sponge and a filter, absorbing water from rain and snowmelt, removing dirt and minerals from it, and releasing it slowly and steadily to streams.

Without forests, our fresh water supply would be further threatened. Forests also provide essential habitat for many kinds of animals. Animals such as lynx, bears, wolves, caribou, deer, mountain lions, and many others depend on forests for their survival. Destruction of forests through logging and agriculture is often the most serious threat to these species.

National Standards

Grades K-4
NS.K-4.1 Science as Inquiry
NS.K-4.3 Life Science- Characteristics of organisms, life cycles of organisms, organisms and environments

Grades 5-8
NS.5-8.1 Science as Inquiry
NS.5-8.3 Life Science - Structure and function in living systems, diversity and adaptations of organisms


We used repeated defoliation on one plot in a paired-plot design in five aspen clones in the San Juan National Forest in Colorado during the summer of 2010 (see “Materials and Methods”). A nearby (less than 10 km) and similar-elevation weather station to the research sites revealed that 2010 had a relatively dry spring, 90% of average snowpack, and average snowmelt around mid-May. During the summer of 2010, the San Juan National Forest received little measurable rain (less than 0.5 cm) between snowmelt and the onset of monsoonal rains in late July, resulting in a seasonal drought. After a strong monsoonal influx of rain, water year precipitation was still slightly below average for the region (36.8 cm 42.2 cm average). Water year precipitation for 2011 was barely below average (41.1 cm 42.2 cm average) with monsoonal influx in early July.

Canopy Characteristics of Carbon Stress

Defoliated plots flushed three canopies over the summer (natural leaf flush [C1] plus two canopies after 100% defoliation of three ramets [C2 and C3]). Leaf area index declined substantially between the three canopies (P = 0.0004), although this was largely driven by different factors in the second canopy (C2) versus the third canopy (C3 Fig. 1C). Average leaf area per leaf declined overall (P < 10 −6 ) and sharply between C1 and C2 but much less substantially between C2 and C3 ( Fig. 1A). Conversely, the number of leaves per branch declined moderately between C1 and C2 but greatly between C2 and C3 (P < 10 −4 Fig. 1B). None of these patterns differed between high and low branches in the canopy, suggesting little sun-leaf/shade-leaf differences in leaf size. We noted very few instances of whole branch die-back in defoliated ramet canopies. Average leaf net photosynthesis rates did not differ between first (natural) canopy and second (postdefoliation) canopy (Afirst, 8.4 ± 1.2 [ sd ] µmol m −2 s −1 Asecond, 8.7 ± 1.4 µmol m −2 s −1 ), which indicates that reflushed leaves functioned largely as well for carbon uptake as the initial leaves.

Canopy characteristics (mean ± se ) of defoliated ramets after first canopy flush (C1), second canopy flush (C2), and third canopy flush (C3). A, Average area per leaf (cm 2 ). B, Average number of leaves per branch. C, Leaf area index (LAI m 2 m −2 ).

Canopy characteristics (mean ± se ) of defoliated ramets after first canopy flush (C1), second canopy flush (C2), and third canopy flush (C3). A, Average area per leaf (cm 2 ). B, Average number of leaves per branch. C, Leaf area index (LAI m 2 m −2 ).

In contrast, ramets undergoing SAD exhibited strongly directional patterns in canopy die-back. These ramets had much higher rates of mortality in the top and south sides of the canopy ( Fig. 2). Our observations of ramets at different stages of canopy dieback suggest that canopy dieback during aspen decline generally starts on high and south-facing branches and proceeds downward and northward.

Distribution of average canopy mortality of SAD-affected ramets. Average height of mortality within the canopy (left) and direction of mortality (right) are shown.

Distribution of average canopy mortality of SAD-affected ramets. Average height of mortality within the canopy (left) and direction of mortality (right) are shown.

Carbohydrate Dynamics and Changes

At no point did carbohydrate concentrations in control ramets differ significantly from native control (untrenched) ramets, suggesting that root trenching had little effect on carbohydrate balance. Thus, we present here only carbohydrate data of trenched-control and defoliated plots. No carbohydrate concentrations differed between control, defoliated, and native treatments prior to the onset of the experiment. Additionally, no substantial changes were observed in tissue Glc levels thus, only starch and Suc concentrations are presented here.

Branch starch concentration changed significantly over time (P < 10 −5 ), between treatments (P < 10 −3 ), and differently between treatments over time (time-treatment interaction P < 10 −4 Fig. 3). In contrast, bole xylem starch levels changed significantly over time (P = 0.003), although not between treatments or time-treatment interactions (P = 0.45, P = 0.66). Bole bark starch concentrations changed significantly between treatments, and these differences varied over time (Ptreatment = 0.013, Ptime-treatment interaction = 0.016). Similarly, starch concentrations in roots changed significantly between treatments (P = 0.03) and time-treatment interactions (P = 0.003). Thus, repeated defoliation strongly influenced branch and root starch concentrations, moderately influenced bark starches, and had little effect on xylem starches.

Starch levels (mean ± se ) of branch, xylem, bark, and root tissues in control ramets (white bars) and defoliated ramets (gray bars) over the course of the experiment. Sampling events were preleaf flush (P-L), first canopy flush (C1), second canopy flush of defoliated ramets (C2), third canopy flush of defoliated ramets (C3), and the next year (N-Y) after defoliation. Note that next-year samples were not taken from xylem/bark tissues.

Starch levels (mean ± se ) of branch, xylem, bark, and root tissues in control ramets (white bars) and defoliated ramets (gray bars) over the course of the experiment. Sampling events were preleaf flush (P-L), first canopy flush (C1), second canopy flush of defoliated ramets (C2), third canopy flush of defoliated ramets (C3), and the next year (N-Y) after defoliation. Note that next-year samples were not taken from xylem/bark tissues.

Branch Suc levels exhibited significant differences between treatments, although these differences varied over time (Ptreatment = 0.002, Ptime-treatment interaction = 0.01 Fig. 4). Bole xylem Suc, however, showed significant changes only over time (P = 0.02), and bark Suc showed no significant changes across time, treatment, or their interaction. Root Suc changed significantly only in the time-treatment interaction (P = 0.02). This suggests that repeated defoliation only decreased branch and root Suc levels. We explore specific canopies and tissue-level changes below.

Suc levels (mean ± se ) of branch, xylem, bark, and root tissues in control ramets (white bars) and defoliated ramets (gray bars) over the course of the experiment. Sampling events were preleaf flush (P-L), first canopy flush (C1), second canopy flush of defoliated ramets (C2), third canopy flush of defoliated ramets (C3), and the next year (N-Y) after defoliation. Note that next-year samples were not taken from xylem/bark tissues.

Suc levels (mean ± se ) of branch, xylem, bark, and root tissues in control ramets (white bars) and defoliated ramets (gray bars) over the course of the experiment. Sampling events were preleaf flush (P-L), first canopy flush (C1), second canopy flush of defoliated ramets (C2), third canopy flush of defoliated ramets (C3), and the next year (N-Y) after defoliation. Note that next-year samples were not taken from xylem/bark tissues.

Canopy 1 (Natural Leaf-Out)

Starch concentrations in branches plummeted after initial leaf-out of ramets (P = 0.0007 Fig. 3). This indicates that primary reserves for canopy production in aspens likely come from branches. Bole xylem and bark starches declined significantly as well (Pxylem = 0.004, Pbark < 10 −5 ), while root starches remained steady or increased. Suc levels in xylem, bark, and roots all decreased slightly ( Fig. 4).

Canopy 2

After experimental defoliation, newly flushed leaves did not differ in any respect from previous leaves (starchnew, 11.3% ± 1.1% Sucnew, 12.8% ± 1.4% starchprevious, 11.6% ± 1.2% Sucprevious, 13.5% ± 1.1%). Branch starch concentrations remained low in defoliated ramets compared with substantial recovery in control ramets (P = 0.02), but they did not decline lower ( Fig. 3). Bark starch concentrations exhibited the same pattern as branches with control plots, increasing significantly from defoliated plots (P = 0.005). Root starch levels exhibited the largest declines (P = 0.003). This suggests that the reserves for a second canopy came largely from roots. Suc levels declined in roots, bark, and branches in defoliated ramets, but the declines were not significant after the Bonferroni correction ( Fig. 4).

Canopy 3

After the second experimental defoliation, branch starch concentrations remained significantly lower in defoliated plots (P = 0.0007) but did not decrease in C3, while root and bark starches recovered to where they were no longer significantly different from control plots (Proot = 0.07, Pbark = 0.052). Branch and root Suc continued to decline, remaining significantly lower in defoliated plots (P = 0.0005), while xylem and bark Suc largely recovered to control levels.

Next Year

By July 2011, branch starch concentrations remained significantly lower in defoliated plots than in control plots (P = 0.002), but they had recovered in roots to where defoliated root starch concentrations exceeded those of control plots (P = 0.47 Fig. 3). Similar recovery and higher levels was observed in branch and root Suc levels.

Infestation Vulnerability

One year after defoliation, rates of infestation increased substantially in defoliated ramets ( Fig. 5). Frequency of infestation by Cytospera canker and black canker increased significantly (P = 0.004 and P = 0.04, respectively). Although lower levels of infestation occurred with poplar borer and aspen bark beetle, control ramets experienced no infestation by these agents at all.

Frequency (mean ± se ) of fungus or insect attacks in control (white bars) and defoliated (gray bars) ramets 1 year after defoliation for Cytospera canker, black canker, poplar borer, and aspen bark beetle.

Frequency (mean ± se ) of fungus or insect attacks in control (white bars) and defoliated (gray bars) ramets 1 year after defoliation for Cytospera canker, black canker, poplar borer, and aspen bark beetle.

Hydraulic Vulnerability

Hydraulic conductivity did not differ prior to defoliation in 2010, yet measurements in 2011 indicated large shifts in hydraulic capability. By July 2011, defoliated ramets had significantly lower levels of refilled basal area-specific hydraulic conductivity (P = 0.007 Fig. 6). This held true for native (unrefilled conductivity) as well (P = 0.003) thus, the treatments had no significant difference in percent loss of conductivity (P = 0.15). Vulnerability curves indicated a slight increase in vulnerability (higher levels of percent loss of conductivity at less negative water potentials), but this was not significantly different for any water potential (P > 0.17 Fig. 6).

A, Refilled basal area-specific hydraulic conductivity (mean ± se g mm −1 kPa −1 s −1 ) in control (white bars) and defoliated (gray bars) ramets in 2010 prior to defoliation and in 2011. B, Percent loss of conductivity of control (white circles) and defoliated (black circles) ramets as a function of branch water potential.

A, Refilled basal area-specific hydraulic conductivity (mean ± se g mm −1 kPa −1 s −1 ) in control (white bars) and defoliated (gray bars) ramets in 2010 prior to defoliation and in 2011. B, Percent loss of conductivity of control (white circles) and defoliated (black circles) ramets as a function of branch water potential.

Temperate Deciduous Forest Climate

1. Temperate deciduous trees lose their leaves in which season?
A. Winter
B. Summer
C. Spring
D. Fall

2. Which layer of the forest has soft-stemmed plants?
A. The herb layer.
B. The canopy.
C. The forest floor.
D. The emergent layer.

3. Temperatures in temperate deciduous forests range from ___________________.
A. -22°F to 86°F
B. 65°F to 75°F
C. -5°F to 70°F
D. None of the above.

Watch the video: Können Bäume das Klima retten? 205 Gigatonnen Kohlenstoff können gespeichert werden l. Breaking Lab (September 2022).


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