STATEMENT OF GREGG MARLAND, ENVIRONMENTAL SCIENCE DIVISION, OAK RIDGE NATIONAL LABORATORY; JIM L. BOWYER, PROFESSOR, DEPARTMENT OF FOREST PRODUCTS, UNIVERSITY OF MINNESOTA; STANLEY BULL, TECHNICAL DIRECTOR, TRANSPORTATION PROGRAMS, NATIONAL RENEWABLE ENERGY LABORATORY; GARY MOLL, VICE PRESIDENT, URBAN FORESTRY, AMERICAN FORESTS; AND JAMES R. BIRK, DIRECTOR, STORAGE AND RENEWABLE DEPARTMENT, ELECTRIC POWER RESEARCH INSTITUTE Mr. MARLAND. Thank you, Mr. Chairman, and members of the committee. I am delighted to have an opportunity to be here and express some views about tree planting. I guess it was in the 197779 Freeman, Dyston, and I published a couple of papers which I think was the first effort to ask what could be done with Mr. SHARP. Maybe you can pull that microphone closer. I am not sure people in the back of the room can hear. Thank you. Mr. MARLAND. Figure out the ethics of this survey. In 1977 and 1979 Freeman, Dyston and I published a pair of papers in which we made the initial computations on what it would take to confront the emissions of greenhouse gases, particularly CO2, from fossil fuel systems by planting trees. And that was the point at which we said, if you were to plant fast-growing trees over an area equivalent to the continent of Australia, you can in fact balance all the CO2 emissions and fossil fuel. It was interesting at that time because everybody reads a statement like that within their own context and some people were willing to start digging in Australia, and others thought we were nuts. And of course, over the intervening years, there has been a lot of thinking going on and the idea of some scale is taken seriously and I think that is good. I would like to make a couple of points from my written statement. First of all, we cannot plant enough trees. Planting Australia is absurd of course. We cannot plant enough trees to offset all of the fossil fuel and CO2 emissions, and it is also true that trees eventually mature and trees will not take up CO2 emissions forever, so we have to confront two issues. Since land is the limiting value, we have to ask how can we use land the most efficiently if we are going to plant trees to take up CO2. And we have to ask what to do as the trees mature. So I am going to consider both of those questions and in a context that we can use trees to offset emissions from fossil fuel or we can use them to replace emissions from fossil fuel. And if you read the summary statement, even I think as far as the atmosphere is concerned, it doesn't matter in terms of CO2 whether we burn coal and save trees or whether we burn trees and save coal. As far as the atmosphere is concerned, it is the same situation. Having said that, let me emphasize that the rest of my comments are based only on carbon balance and, obviously, that is not the sole reason one manages forests. There are a multitude of things that will enter into a forest management scheme, but I think carbon balance is a legitimate one and a new one, and my comments are limited strictly to carbon balance. The question then is, I think as a tree matures-well, as a tree is growing, we can match the number of trees to exactly offset a fossil fuel plant, for example, and we can take up in trees 1 kilogram of fuel for every-1 kilogram of carbon for every kilogram that is put off. But if we ultimately harvest that tree, what happens then? And the initial answer I think that people had was, carbon goes back into the atmosphere and we haven't gained anything. And I think that is a simplistic answer because, in fact, if you burn a tree, there is a certain amount of coal which is not burned. And one has to ask then, if we harvest this kilogram of tree carbon, how much coal carbon can we avoid burning? And it is not one for one for a variety of reasons. The cost of mining coal and transporting it to a power plant, because coal is a very high energy density, is really quite small. On the other hand, there is a relatively large cost in managing a tree plantation and harvesting and hauling it to a place to be burned, and we cannot burn at this point wood with the same efficiency that we can burn coal. So the answer is, there are some losses. And at best, I think if we harvest a kilogram of tree carbon, we can replace about three-quarters of a ton of coal carbon, so there is some loss. On the other hand, if I harvest a kilogram of tree carbon or a ton and replace coal carbon, you can then replant the tree and go on, and you get a second generation of trees and you replace another three-quarters of a ton of coal carbon. And it is a continuing process as long as one has a sustainable tree plantation. So to plant trees and let them grow one time, you get one chance to offset emissions from fossil fuels. And in a sustainable plantation, it can be a continuing process and we can get continual benefits. The three-quarters ton replacement is based on using coal forwood for electricity, and it assumes that we can burn wood with the same efficiency conversion to electricity as we could with coal. And at present, that is not the case, but there are things that are happening now, perhaps in the Electric Power Research Institute, for example, which are striving toward this. And I think one of the objectives right now has to be better technology to convert wood into electricity. The question I think one confronts then is, given the choice of either planting trees or harvesting for electricity, which is the better choice and I don't want to go through this, but I think it is captured in my written statement. There are a variety of variables that go into that. One of the most important, which is what is the time horizon that one has in mind. If you have a very long time horizon, then it makes sense to recycle trees through several generations, harvest them, and turn them into electricity. If we are concerned about a very short time horizon, if we had an emergency, for example, and felt we had to take CO2 out of the atmosphere, one would just let the trees stand and store the carbon. So the time horizon is a very important variable. I think also important is how fast the trees will grow, what is the productivity of the given site one has in mind. If trees will grow very slowly, then to harvest the tree is going to take a very long RE. time to replace it and the benefits become very small. On the other hand, if we can go into an area where the rate of the growth is fairly high, then it makes sense to start to recycle. The other things that make a very large difference is how efficiently one uses those trees once harvested. If you can get 75 percent conversion efficiency, that is a tree will substitute for 75 percent as much coal carbon, then it is a very attractive opportunity. If we use the tree very inefficiently and get, say, only a 20 percent offset, then it becomes a very unattractive opportunity. To pass on it and sort of summarize-again, there are graphs which are a little complex, but I think they are comprehensible in my statement. My suggestion is that in areas and this is mathematically demonstrated in the little model we built in areas where trees grow very slowly. In areas where there are already mature forests, in areas where it is very expensive in energy terms to harvest and transport and use those trees, the most effective thing we can do is to leave those trees and let them store the carbon. If trees are going to grow very slowly and recycle very slowly, the best thing we can do is plant trees and let them store that carbon. On the other hand, in areas where we can get high productivity, and I think one has to debate at this point how much productivity it requires, the best choice is to plant-grow plantations, recycle the carbon, grow trees sustainably, then use them. And I think this starts to provide opportunities both in the United States and elsewhere. And the value of trees is, we get usable products from them, and in developing countries, there is local benefits from recycling, but the key is sustainable plantations. Thank you. [The prepared statement and attachments of Mr. Marland follow:] STATEMENT OF GREGG MARLAND, ENVIRONMENTAL SCIENCES It has been suggested that, since growing trees remove CO2 from the atmosphere, tree planting could be used to offset the CO, which is released to the atmosphere when fossil fuels are burned. Consider a quick calculation. U.S. emissions of carbon dioxide from fossil fuel burning amounted to about 1.3 billion tons of carbon in 1990. If we divide this by the average annual rate at which forests in the contiguous 48 U.S. states take up carbon now, about 1.2 tons of carbon per hectare per year (286 million tons of carbon per year divided by 243 million hectares of forest and woodland, numbers from Turner et al., 1993), we find that it would take 1.1 billion hectares of forest to take up in trees and forest soils the carbon we discharge from burning fossil fuels. This is about 40% larger than the land area of the contiguous 48 states. The U.S. is not going to balance all of its CO2 emissions by taking up carbon in forests resembling those we have now. We should also note that the uptake of 286 million tons of carbon per year in existing forests is possible only because of the continuous removal of carbon through harvests, and the re-creation of young, vigorously growing stands. To a first approximation, mature forests are no longer increasing in mass and hence are no longer taking up carbon. Acknowledging that land available will limit how much carbon can be taken up in growing trees and that the growth cycle of trees will limit the length of time over which this uptake can be maintained, we have to ask how best to use the land which is available, and how much might be accomplished. It is often assumed that trees grown to offset CO2 emissions need then to be preserved in order to keep the CO2 from returning to the atmosphere. My contention is that, in terms of atmospheric CO2 a tree performs equivalently if it stores carbon or if its conversion to CO2 displaces some other source of CO2 that would otherwise be released. There is no difference in atmospheric CO, if we burn coal and save trees or if we burn trees and save coal. I will compare the alternatives. Let me emphasize at this point that the rest of this discussion is focused primarily on carbon flows. I don't mean to imply that carbon management should be other than one of several criteria that influence land-use and forest-management strategies -- yet it is a new criterion, our concern here is with global climate change, and it is useful to isolate and examine the implications for net CO2 emissions. Figure 1 illustrates in simplest terms two fundamental tree-growing strategies that might be considered: using growing trees to offset emissions from the energy sector, and using trees to displace emissions from the energy sector. I consider some variations on these strategies below. Figure 1 is strictly schematic and doesn't allow us to make quantitative comparisons, but it does suggest some of the factors we ought to evaluate in making quantitative comparisons. In particular, time is important. Looking at the figure as drawn, we would conclude that, over short time intervals, path B was to be preferred to path C, whereas when evaluated over longer times, path C appears to be the better choice. Also, paths C and D imply use of larger land areas than does path D because part of the energy contained in the harvested wood (or energy from fossil fuels) needs to be used when the trees are maintained, harvested, hauled to market, and prepared as fuel. The rate at which trees take up carbon, that is their growth rate or productivity, is also a very important factor. We have built a mathematical model of carbon flows in a forest in order to compare different management strategies (see Marland and Marland, 1992). The model is very simple and the results should be taken as indicative rather than demonstrative, but it does allow us to contrast the alternatives. Consider four possibilities: 1.) trees are planted where trees did not previously exist and are left in place to sequester carbon, 2.) trees are planted where trees did not previously exist but are managed for rapid growth and are harvested regularly to be used as a fuel, 3.) standing forests are cut and replaced with plantations which are managed for rapid growth and are harvested regularly to be used as a fuel, and 4.) standing forests are preserved and managed to store carbon. I should make clear that my reference to using wood as a fuel does not suggest fireplaces and wood stoves. To make a meaningful impact on atmospheric CO2 emissions, wood (or biomass generally) has to be used with high efficiency to supply a modern energy carrier such as electricity or a liquid transportation fuel like ethanol. If a tree takes up 1 kg of carbon, it has offset 1 kg of carbon discharged from, say, a coal-fired power plant. If we harvest that 1 kg of "tree carbon" and use it to supply energy, how much "coal carbon" or "oil carbon" can we leave in the ground, how much can we displace? Not much unless we are able to convert the "tree carbon" to useable energy with high efficiency. Our model considers how much carbon in the trees is lost during the harvest, how much fuel is needed to manage and harvest the trees and haul them to a power plant, and how efficiently wood can be converted into electricity. If we could convert wood to electricity with the same thermal efficiency as we do now for coal (such processes are being developed but for now the conversion is generally much less efficient, largely because of the high water content of wood), a kg of carbon in the forest could displace about .75 kg of carbon in coal. If we look at the energy losses encountered in converting wood to ethanol, it is more likely that a kg of "wood carbon" would displace only about half of this much "oil carbon" when used as a transportation fuel. The bottom line of this discussion is that carbon taken up in a tree to be left in the forest provides an essentially full offset of CO2 emissions, but the rate of this offset will shrink as the tree matures. On the other hand, carbon taken up in a tree to be harvested for fuel provides only a partial (depending on the efficiency of conversion to useful energy) offset, but this offset can be continued indefinitely as long as we maintain the forest plantation. The rate at which trees grow (i.e. take up carbon) is another important consideration. Harmon et al. (1990) examined the fate of the forest carbon when an old-growth forest was harvested. They showed that although some of the carbon ends up in long-lived products like construction lumber, the net amount of carbon stored in the living forest plus long-lived wood products did not recover for at least 250 years to the pre-harvest level, because of the slow growth of the forest toward its preharvest state. Although I would change their numbers a bit, because they did not give credit for the fossil fuel which was displaced by burning some of the forest products (Marland and Marland, 1992), the point is well made that it can take a very long time to get back to the starting point when the growth rate is slow. Figure 2 shows some of the output from our model. Again, I would emphasize the qualitative conclusions of the model without belaboring the details of the input assumptions or the numeric output. The figure does make clear that there is not a single answer for managing forests to minimize net CO2 emissions. The best choice for any given area depends on the characteristics of the area: whether it is already forested, what level of productivity can be expected, how much energy does it cost to manage the forest and convert the product into useful energy, how long a time perspective do we have. The figure is based on the average carbon saving per year when averaged over 50 years and both the carbon offset and the carbon displacement are counted. For areas not now occupied by forest, the maximum carbon benefit is achieved by simply planting trees and allowing them to stand and sequester carbon- when the expected productivity is less than about 4 tons carbon per hectare per year. For higher productivities, greater carbon benefit can be achieved by harvesting the trees and using them to displace fossil fuels, although very high productivity is required unless conversion from standing trees to useful energy is accomplished with high efficiency. If we were to average over longer times, the crossover point would move toward lower productivity because even the slowgrowing trees would begin to mature and take up carbon less rapidly. for areas with pre-existing |