VARDAMAN VIRTUAL FORESTRY COMPANY

The Most Direct Link to Knowledge Workers in the Southeast Forest Economy

THE MOST INTENSIVE FOREST MEASUREMENTS THAT WE HAVE EVER SEEN AND WHAT THEY MEAN TO LANDOWNERS

The most intensive forest measurements that we have ever seen are taking place on the USDA-Forest Service Southern Global Change Research project in Scotland County, North Carolina. The project comprises 16 research plots containing a total area of about 10 acres in a nine-year-old loblolly pine plantation on soil so poor that the trees were only 15 feet tall at age eight. Four plots are fertilized and irrigated, four fertilized, four irrigated, and four not treated. The ground is covered with a network of pipes to deliver water and carbon dioxide (CO2), wires connecting computers with sensors underground, on the surface, and up in trees and observation towers, and structures to catch precipitation and leaf fall. All small buildings on the site are crammed with computers and wires leading to the hundreds of points that are being monitored.

Sixteen trees, one in each plot, resemble very ill patients in the intensive-care ward of a modern hospital. Mounted on a metal scaffold erected around each tree are three large, open-bottom, plastic chambers, each surrounding a branch; at the top of each chamber is a blower that constantly delivers air containing a precise percentage of CO2 inside the envelope. Scattered over the tree are little aluminum tags marking the locations where measurements are taken periodically. The tree can hardly do anything without a scientist measuring it.

The objective of such detailed study is to determine the effects of elevated CO2, water availability, and nitrogen availability on carbon and water fluxes from nine-year-old stands of loblolly pine. In simpler terms, the objective is to learn exactly how trees grow; such knowledge will be "portable" and can be used by all other landowners growing loblolly pine in the south. Cooperators are USDA-Forest Service, North Carolina State University, forest industry members of the NCSU Forest Nutrition Cooperative, Bowater, Inc., and Goldkist.

We recently visited the site with its two scientific leaders, Dr. Phillip M. Dougherty and Dr. H. Lee Allen. If you had been walking along with us, here is the conversation that you would have overheard:

JMV:	The objective of this study makes it appear to be more fundamental research rather than empirical research. Is this correct?
HLA:	Yes. Some landowners may ask, "Why do we need to know why? Why isn't empirical research good enough? Why can't we just go out and try a lot of different things to see what works?" That's what we've done for years. But the trouble always has been, and will be, that what works under specific conditions in this test won't work when these conditions change in some way. Once we thoroughly understand how trees grow, we'll be in better position to manipulate that growth. Then our knowledge becomes "portable," and we will be able to prescribe exactly how to produce the desired results on each site.
PMD:	Our objective in putting in the Scotland County Site is to determine the effects of elevated CO2 on the southern forest type, and we selected this site because it gives us an opportunity to manipulate water, nutrients, and CO2. What we hope to come up with is a data base with a very wide range of inferences that we can use to predict what might happen to other forests at other locations.
JMV:	Has this kind of research been done before?
HLA:	The first research of this kind was done in Sweden with Scotch pine in the 1970's. Similar research has been done with radiata pine in Australia and eucalyptus in Portugal, and they are working now with Norway spruce in northern Sweden. This is the first work with loblolly pine.
JMV:	Tell us more about elevated CO2.
PMD:	We know that CO2 is going up; it increases every year and has for many years. We also know that CO2 is limiting in all southern forests and that all southern species will respond to elevated CO2. If CO2 doubles by the third quarter of the next century, we would expect a 30% to 40% increase in the trees' ability to produce sugars for growth. But whether this will occur and whether it would result in a 30% to 40% increase in yield is another question. This will all depend on what happens if there are limitations of nutrients or water. That's what we're trying to learn here. The foliage contains stomata that open and close each day to let water vapor out and CO2 in. Two responses to elevated CO2 have been reported for plants. One is that it increases photosynthesis. The other is that it promotes stomatal closure, and this reduces the amount of water used in proportion to CO2 being fixed into sugars. We call this in increase in water-used efficiency. Even though rainfall might go down and evaporative demand go up, we could still possibly get an increase in the amount of carbon being fixed and thus an increase in productivity.
HLA:	If water and nitrogen are limiting in many of our ecosystems, increases in yields may not come with increased CO2. CO2 is like a fertilizer. If you add CO2 to a tree and get a growth response, you can say that the limiting factor on that tree was low CO2 and that you can increase growth by adding CO2. If low levels or water and nutrients on very poor sites like this one are most limiting, we may add as much CO2 as we want and yet see very little increase in yields because that's not what's limiting. When we irrigate and fertilize to eliminate these limitations, we would expect to get a very strong growth response to elevated CO2. Phil has been very careful to say that more sugars could be made in the foliage. We could get a lot more sugar fixed by the foliage and not wind up with more stemwood; it could wind up in lots of other places. In fact, only about 15 to 20 percent of the carbon fixed as sugars winds up in stemwood.
JMV:	Why is that?
HLA:	There are many points of carbon loss. The major one is respiration. Like us, trees must respire, and they use a lot of energy to perform life functions. Our best guesstimates for southern pine forests are that 50% or more of the carbon fixed as sugars is lost through respiration and goes back into the atmosphere. This is not just respiration of the foliage, but of all components, roots, branches, and stem. If we have a nutrient-poor or water-limited site, much of the sugars remaining after respiration, maybe as high as 75% of it, goes to produce roots. This reduces stemwood and foliage production, which in turn reduces the amount of sun energy that can be intercepted and made into sugars. Producing more foliage is a prerequisite to getting more growth. Thus what we need to know is how to get trees to produce more foliage.
PMD:	But we will also need to know this: "If we increase stand density and leaf area index through fertilization and irrigation, what changes will occur in the water balance?"
HLA:	On the plots receiving nothing but fertilizer, we have increased leaf area index by 60% to 70% in only one year. This site has an exhibited site index (base age 25) of 45. Phil and I predict that, with fertilizer and irrigation, we can raise it to 90.
JMV:	What happens to the rest of the carbon?
HLA:	It is used in producing foliage, and roots, which turn over every year, and branches. Probably as much carbon is used in producing roots as in producing foliage, but this is largely unknown for pines growing on upland sites.
PMD:	More may be used in producing roots. There is a general rule that, when water or nutrients are limiting on a site, the trees allocate more of the carbon to developing below-ground portions so acquisition of the limited resources can be enhanced.
JMV:	So what can a landowner do to increase stemwood growth?
HLA:	One of the biggest ways of increasing production of stemwood is to increase the availability of nutrients and water so that the trees don't allocate so much of the sugars to produce roots. A landowner can increase nutrients by adding fertilizer. This is a marginal site for loblolly pine. One of the things that has surprised us so far is the magnitude of response that we have received to nutrient amendments. We've added nitrogen, phosphorus, potassium, calcium, magnesium, boron, and copper. We are getting a bid response on this deep infertile sand that is droughty. To get maximum stemwood growth, we need to have a Leaf Area Index (LAI) of close to five, i.e., the area of leaves on the trees is five times the area of land under them. This site was so poor that LAI was 0.3. In just the first year of fertilization, we have pushed LAI almost up to 1.0; we expect to bring it up to 2.5 in the second year and to 4.0 or 4.5 in the third. We will get this increase first by producing more foliage on each branch and second, because the stand is understocked and does not occupy all the growing space, by crown closure. The needles may live longer on the tree, but we don't look for this to be a major cause of increased LAI or growth. By controlling competition from all undesirable vegetation, a landowner can increase availability of not only water, but also light and nutrients.
PMD:	He can increase water availability in two way. One is by eliminating unwanted competition; the other is by managing stand density from the beginning so that more water gets down into the soil. Trees intercept maybe 15% of precipitation, which is then lost to the atmosphere by evaporation.
JMV:	When you learn what you are going to learn here, you will know exactly how trees grow and thus know what levers to pull to produce the desired results. Right?
PMD:	That is the goal. To understand what tree and environmental levers control the things that we are really interested in. If we want more stemwood, for instance, we must know what lever to pull.
HLA:	We also want to study the nutrient budget, nutrients coming into the system and being cycled through it. One mechanism of nutrient flux is needle fall: needles drop to the forest floor, decompose, and thus release the nutrients in them. Roots also serve as a sink for nutrients. What happens to the nutrients in roots when the roots die? We don't know that. We do know that, just before needles drop off, the tree withdraws about 70% of the nitrogen in them; this illustrates that, once the tree takes up nutrients from the soil, it won't surrender them easily. We hypothesize that the same withdrawal takes place in roots that are about to die. Trees grow foliage and roots in the summer and continue to produce roots in the winter. We hypothesize that, when the roots begin to grow in the fall, that coincides with senescence of the needles so that nutrients are transferred below ground for storage and root growth and that the reverse process takes place in the spring. One objective of this study is to test this hypothesis. If the tree does not withdraw nutrients just before the roots die, the roots decompose, and the nutrients are returned to the soil where they are available to its other roots. But it will have to compete with other organisms for them, and it will also have to expend chemical energy to take that nutrient up again. It's not like sucking up Coke through a straw; it has to expend energy to get it across membranes and to transform it to the form in which it can be used. Therefore, it's smart for a plant to keep nutrients within its system once it get them.
JMV:	Why did you pick such an unproductive site for the study area:
HLA:	When we searched for a site for this study, we had to turn down several because they were old fields and the trees were growing very well on the residual fertilizer. The old fertilizer minerals, including nitrogen, were still there. Nitrogen was tied up in the organic matter and vegetation on the forest floor. About one or two percent of it is turned over annually and becomes available to the trees. Phosphorus was also there. About the only mineral you lose in such a situation is potassium, which is readily leached out, but even that will probably not move far down. This brings up another objective of this study. We've talked about two: the response to elevated CO2 and learning the fundamentals of tree growth and their implications for silviculture. A third is to determine the sustainability of forest production as we move to intensive forest management where we put tremendous demands on the site. We are trying to ascertain the key attributes of forest lands that will give them sustainability over time. The shifting of nutrients up and down in the tree each year is one key. Another is maintaining the soil organic matter because it is important for nutrition and moisture. How are we influencing it by fertilization and irrigation?
JMV:	What is your hypothesis about sustainability?
HLA:	This is an opinion and only that. We are developing the tools to allow us to maintain sustainability, i.e., to grow the same or larger timber crops "forever." If we do not add nutrients, are not careful in conserving organic matter, and just continue to remove, remove, remove, without adding anything, it's very clear that production of crops is not sustainable, particularly on poor sites like this one. I think that we can continue to improve productivity on all our lands if we do the right thing.
PMD:	I agree with Lee, in areas like the Piedmont where agriculture eroded away the soil horizon containing the original organic matter, we should be targeting not to sustain but to upgrade the system. Most of our forest practices are building the system back up. We use forests around the world to reclaim eroded land; one of the original goals of the U.S. Forest Service land in the southern U.S. was to use forests to reclaim eroded lands.
JMV:	Why are those two trees over there two or three time the size of all their neighbors?
PMD:	The answer could be partly genetics. Another part is probably organic matter. The mechanical site preparation before planting here moved a lot of organic matter around, and now the pockets of big trees are where they piled up organic matter. That tells you something about potential pitfalls of mechanical site prep on a fragile site like exists here.
HLA:	There are pockets here where the trees are growing well. If you go to them with a soil auger, you'll find out exactly why. A pile of slash was left there and is decomposing.
JMV:	Why are the needles on that tree so yellowish?
PMD:	Chlorophyll production and breakdown occur constantly. In winter it is not uncommon for chlorophyll breakdown to occur faster than production, so needles turn yellowish because chlorophyll is not masking the carotinoids in them. They will green up again when the tree starts taking up more nitrogen and conditions for chlorophyll production improve.
HLA:	One key reason for this chlorosis is that, with low soil temperatures, the turnover of nitrogen slows down. The tree is already limited by nitrogen, and it's not getting any from the soil.
JMV:	Does ozone have an effect on forest productivity?
HLA: I	n other work with pine needles, we have found that, at current atmospheric levels of ozone, pine needles live on the tree for only two years. When we removed ozone with charcoal filters in tests, the needles lived three seasons.
PMD:	These needles may become inefficient as they get older, but as long as they are green and stay on the tree, they are net contributors of sugars. If a needle can't take care of itself, the other needles won't take care of it, and the tree gets rid of it in a hurry. There are years now in which ozone may reduce the amount of carbon being fixed. These are years when it's fairly dry with high temperatures and radiation and ozone levels tend to be high. During 1992 I would say that ozone had a very minor effect on how trees functioned because ozone levels weren't that high. In 40- to 50-mile circles around large cities like Atlanta and Houston, where ozone levels are higher than in rural areas, forests and shade trees may already be impacted in years that are favorable for ozone formation.
HLA:	Although there may be an ozone effect, it is very small, a drop in the bucket compared to the increases we can get by silvicultural treatments. By these treatments, we can increase growth 100% or more; on this site we can increase it by 200% to 300%.
JMV:	You have mentioned "allocation" and "partitioning" of sugars. Do you expect to learn a lot about them?
HLA:	Yes: We measure stemwood growth and LAI of every tree out here. Inside the chambers, we measure individual branches and then individual needles. We've talked about carbon or sugars being partitioned between foliage, branches and roots. We've talked about a tree being able to sense that the site is nutrient-poor or water-limited so it sends more of the energy down to producing more roots. How does the tree do this? What signal is sent from the roots to the shoots that changes the flow of sugars? We don't know this, but here we will take a step toward finding out.
PMD:	In this set-up, we have created the extreme conditions for altering allocation. One would hypothesize that, when nutrients or water are limited, there would be a greater proportion allocated below ground. With plenty of nutrients and water, one would hypothesize that the greater proportion would be allocated above ground. We should be able to document what are the sideboards for loblolly pine from an allocation standpoint. At many locations throughout the study area, we have probes that are mounted horizontally at various depths throughout the soil profile, and Michelle Rymond reads the soil moisture at each level every two weeks. We bring all the data from light and temperature sensors from the chambers, soil temperatures, and heat flux into a computer for the four plots in this block, and we do the same for the other three blocks. All four data loggers are tied together, and we address them from Research Triangle Park by telephone and modem. Quite a bit of effort is involved in environmental monitoring because, when we develop our process models, we must have good measures of the environmental variables that will drive these models.
JMV:	What causes CO2 to come out of the ground?
PMD:	One source is live roots; they must respire to live, just as you and I must. The other source is the soil organisms; organic matter is their food source, and they break it down and convert it back to CO2. At night CO2 levels in a plantation get very high. Chris Maier is working on soil respiration losses. We want to be able to say, for the whole system and not just for the trees, what was the upward flux of carbon from the trees and the soil, what was the downward flux of carbon (that taken up by the trees), and finally what was the net effect. Did these trees contribute to the elevated CO2 problem or reduce it? The answer will give us an insight into how we can use forests to handle the problem.
JMV:	Aren't you also interested in the effect of global climate change?
PMD:	There's a lot of uncertainty about climate change - whether it's going to occur at all and to what extent the various elements will change. Many persons running global circulation models are saying that we might get from one to four degrees of temperature increase over the next 50 or so years. Whether we get one degree or four degrees will make a lot of difference in how these forests will function. But there is a lot of uncertainty about whether we will get any elevated temperature. Changes in rainfall patterns (percent of cloudiness, amount of rainfall, etc.) are even more uncertain. We are concerned about elevation of temperatures because respiration will increase greatly when this happens. If trees are already losing 50% or more of carbon at current temperatures and temperatures rise, they will lose even larger percentages for respiration and have less to grow on and survive. From the global climate change standpoint, we also want to know how the water balance of southern forests will change. "If temperature rises, if the demand for water rises, if the supply of water is altered, how will the balance between how much water will be used here and how much will be left for run off change?" In the future we will be concerned about timber production, but we will also be concerned about water production from forests. Here we will measure all components of the water balance - incoming precipitation, throughfall, interception, stem flow, and soil moisture.
JMV:	Some urge the planting of trees to reduce CO2 and prevent global warming. Are they on the right track?
PMD:	Some scientists work on doing a global carbon balance. When they recently completed their last go-around at this, they found a big unknown or gap in either where carbon is coming from or where it's going to. They think that the gap is related to the terrestrial ecosystem, to not having a good understanding of the vegetation's ability either to fix or to give off carbon. Our work here will help to fill this gap in the terrestrial component's contribution to the global carbon balance. We believe that plantation forests, which are in a vigorous growth stage, cause a net carbon uptake, that such forests are reducing the carbon problem, and that tree planting across the U. S. will help to control it. If trees are manufactured into structural material that later becomes part of a building that lasts 100 or so years, this is a form of carbon storage and helps alleviate the CO2 buildup. If the trees are used to make paper that is no recycle, the carbon returns to the atmosphere as the paper decomposes. Forests that are old and falling apart are probably net contributors to the problem.
JMV:	Will your findings help us with decisions about the future?
PMD:	We know that CO2 is going up and will likely continue to do so. If it does and climate change does not occur, where should you be practicing forestry in the future to make the most profit? My hypothesis would be, "Get on the good sites where there are plenty of nutrients and water so that the trees could utilize the added resource being placed in the atmosphere." We also want to look at what I consider advanced silviculture. What are we going to be trying to manipulate in the future? We will need to know how to manipulate leaf area, capture of light, and allocation. These things are feasible. It's just a matter of understanding how to do them. Another area of focus here is understanding how we are changing the functioning of the system when we manipulate these things. Society wants us to answer these questions: Are you taking the system apart? Are you being ecologically correct in your actions? Are you maintaining productivity? Here we are trying to develop enough understanding of community functioning that we can answer these questions with confidence.
JMV:	Do we really know yet whether elevated CO2 is good or bad?
PMD:	No, we don't. As a plant physiologist, I would say that we should be seeing an increase in productivity due to the elevation of CO2 unless substantial changes in temperature and rainfall occur. Even if CO2 doubles, we should definitely see increases in productivity. There could be a point where the stomata were closed so much that the plant really couldn't benefit from elevated CO2. That point, if it ever comes, may be 100 or more years from now. We usually underestimate how good a buffering system is in place on the planet.
HLA:	Over geological time, CO2 has been much higher and much lower in the past. Some persons are scared because the rate of change in CO2 and the possible change in annual temperature are much faster than in the past; they fear that many species will not be able to adapt the changes. But there's a lot of controversy on that.
PMD:	There sure is.