VARDAMAN VIRTUAL FORESTRY COMPANY

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

CLONAL FORESTRY: WHAT IT IS, WHAT IT CAN DO FOR YOU

We have been looking at, reporting, and taking video shots of plantations for years now and have often been struck by the wide variation in development of seedlings that looked exactly the same when we planted them. You could see this clearly in our first publication of the stand table in the Leland Speed Plantation, and its quite visible in every plantation even as early as age one or two. We suspected that much of this variation was due to genetics and that we could eliminate it if we utilized clones in our management plans. Then we realized that we knew very little about clones. To eliminate our ignorance, we interviewed Dr. Henry E. Stelzer, Research Geneticist, Southern Forest Experiment Station, USDA Forest Service. Here's What we learned:

JMV:	When we inspect a row of seedlings in any one- or two-year-old plantation, we always see that some are much larger than others even though they were virtually identical when planted. We understand that the difference is due to both genetics and life history. What percentage would you guess is due to genetics?
HES:	The results of forest tree improvement to date indicate that between 25 and 50 percent of the variation we observe in a plantation is attributable to the genetic component. Forest geneticists come up with these estimates by determining how much of a parent's traits are passed onto its offspring. This percentage will vary from species to species. For example, red pine that is found in the Lake States produces very uniform stands regardless of where it is grown within its natural range. With this species, the genetic component is considered to be very strong because no matter on what site we plant it, the resulting stand will be similar to one that is planted on a different site. Unfortunately, we do not see this uniformity in the southern yellow pines. In the South, the genetic component is in the 25-50 percent range that I mentioned. It will also depend upon the particular trait one is interested in. Simple traits, that are controlled by one or two genes, tend to be influenced more by genetics than the environment. The color of the seed coat in pea is controlled by a single gene and the environment that the plant grows in has no bearing on the color. That single gene determines the outcome. On the other hand, tree volume or fusiform rust resistance is regulated by many genes, and expressions of these genes are modified by the environment that the tree grows in.
JMV:	As long as we utilize seedlings, genetically-improved or otherwise, won't we always have some "runts" in every batch?
HES:	Yes. Seed are the products of sexual reproduction, and each individual seed produces a plant with unique characteristics. The average will be better with genetically-improved seedlings, but the key word is average. You will always have poor performers along with outstanding individuals in any population. That's just the natural world. But this variability is not a bad thing from the geneticists point of view, because if we didn't have the runts, we couldn't identify the winners. Every tree would look like every other tree, and any effort at improving the species would have as much chance as you or I winning at the lottery.
JMV:	But isn't there a limit to the improvement that can be made by turning out one generation of improved seedlings after another?
HES:	Not really. As long as tree breeders maintain genetic diversity in the breeding population and can select the superior individuals in the resulting progeny tests, we will see a continued improvement in the species for the traits we want to improve. You can see this in agronomic crops. Man has been improving corn ever since the first farmer saved some seed from a high-yielding field for the next planting. Even though this "improvement" began several hundred years ago, they are still making gains today. But in every round of breeding and testing, we are unable to capture the exact package of genes found in a superior tree and give this to the landowner in the form of a seedling. The reason for this is that we had to go back to a seed. Every time we go back to a seed, we encounter what is called random mating. Even when we know that both parents are superior trees, the scrambling of genes in sexual reproduction will never reproduce an exact copy of a superior individual from the preceding generation.
JMV:	So you turned to vegetative propagation to capture more improvement?
HES:	Yes. There are several ways to vegetatively propagate trees. Horticulturists use grafting to propagate species like apple and pecan. A shoot from a desired apple tree, like a Red Delicious, is grafted onto the stump of another apple tree; then everything above the graft will produce Red Delicious apples. Forest geneticists use this technique when they identify superior individuals in the field and bring them all together in a common area called a seed orchard. The concept is like an apple orchard, only the fruit we produce is pine seed. But grafting is very expensive and is only cost effective for a high value tree such as apple or pecan. Furthermore, grafting only propagates the shoot and not the root system of a superior tree. Scientists know that there is communication of sorts between what grows above ground and what grows below the soil surface. Back to apples. If we graft that same Red Delicious onto a known dwarfing rootstock, all the apples will be Red Delicious, but the tree will be only ten feet tall. That may be okay for apples, but not for pine trees. Another way to vegetatively propagate plants is rooted cuttings. We simply stimulate a shoot we have cut from the superior tree to form roots in its own right. In this way, we haven't lost anything to random mating and don't have to worry about shoot growth being influenced by the roots. We have captured 100% of the superior tree's genetic potential.
JMV:	So, What's the next step?
HES:	In the near future, we must focus on reducing the cost of cutting propagation. Current production costs are in the neighborhood of $350 per thousand cuttings. Some economic analyses that I have seen indicate that to get an incremental rate of return of eight percent, the cost will have to be around $75 per thousand cuttings. This can be done in a couple of ways. First, we can better define the environmental parameters that play a part in the rooting process in order to increase rooting success. At present, the rooting success rate for loblolly is 60 percent. Increasing that rate to 80 percent would go a long way in reducing production costs. Second, by adapting automated systems that are currently being used in ornamental horticulture to forest tree species, we will be able to lower the costs further. Down the road, another form of vegetative propagation will probably come of age. It's called somatic embryogensis. But, don't let its high-tech name scare you. The process takes selected tissue from a superior tree, and through supplying that tissue in the laboratory with hormones and nutrients, we stimulate it to produce embryos just like Mother Nature. Only instead of producing just one superior embyro with the right combination of genes, this process will produce millions of embryos. Then we pluck off the superior embryos and surround them in an artificial seed coat made of starch polymers. These artificial seeds can then be grown in traditional bare-root nurseries just like normal seeds, but they will produce plants that are identical to the one the tissue came from, thereby capturing 100% of the gain in the parent. This technology has been successfully developed for crops like tomato and carrot. It's just a matter of time for the southern yellow pines.
JMV:	Let's back up a bit for some definitions. Each seed produces a unique individual, so that individual is a clone. Right? Then the little trees that we plant in the field are rooted cuttings, not clones. And if this is correct, you scientists work with only a limited number of clones that have special characteristics. How many clones are there in, say, loblolly pine, and how do you designate them?
HES:	You are right about the definitions. Each seed produces a unique individual. If a tree is one day selected from the population because it exhibited some superior trait, say resistance to fusiform rust, then that tree would be called a superior selection. That superior tree would then be vegetatively propagated by the rooted cutting process I described earlier. All the individual rooted cuttings produced from that superior tree would be clones of that original individual. Think of clones as xerox copies of the original. In loblolly pine, the potential number of clones that we can work with is unlimited. Over the years, tree breeders have made hundreds, if not thousands, of crosses between individual loblolly pine trees. Each cross has produced a family consisting of hundreds of seeds. Each seed is a potential selection to be propagated via rooted cuttings. There are several private industrial forest companies currently working on clonally propagating loblolly pine. The number of clones they possess and how they chose them are proprietary, so I can't give you an exact number. But just to show you that this number is very large, let me give you some figures that I have access to. International Forest Seed Company (IFSCO) of Odenville, AL, has made over 237 crosses between parents that were selected for fusiform rust resistance and good growth. Those 237 crosses have resulted in over 4,700 individual trees that have been propagated through rooted cuttings. That's 4,700 different clones.
JMV:	When we make growth predictions with PTAEDA2V, the consensus of our scientific advisors is that, if we plant genetically-improved seedlings, we can raise the input for site index by 5% when we use an orchard mix and by 8% when we use a family specially adapted to the site. What modifications might be appropriate when we use specially-adapted clones?
HES:	Your improvement figures for genetically-improved seedlings are in the ballpark. My guess is that clonal material could increase gain by five percent for height and nine percent for volume, over the expected gains from the improved planting stock that is currently available.
JMV:	We have agreed to install on our land in Louisiana a study of ten clones of five different sizes (groundline diameters of 4.5mm, 6.5mm, 8.5mm, 10.5mm, and 12.5mm). The study was designed by Dr. David South, and you selected the clones to study. Why were ten clones needed?
HES:	The clonal test is an extension of Dr. South's research on morphologically superior seedlings. One of the objectives of the study is to determine if there is a clone-by-diameter interaction with regard to early height growth rooted cuttings of loblolly pine. We chose to evaluate ten clones because we wanted to get a handle on any variability that we might see in the growth and development of the individual clones. If the ten clones end up ranking in the same order regardless of the diameter class, then there is no interaction, and life for scientists and landowners will be simple. However, if clone#1 ranks best in the 4.5mm class, but ranks dead last in the 10.5mm class, then we will have to seriously consider stem size when we produce clonal material. By the way, what do you plan to do with the excess clonal material from this study?
JMV:	We will plant them on our cutovers so that everyone can see what forests of rooted cuttings from various clones look like. IFSCO will produce these cuttings on special order for us. Who else is producing cuttings, and what other species are available to landowners?
HES:	The use of clones is not new in forestry. Poplars, such as cottonwood, have been traditionally regenerated by planting either rooted or unrooted cuttings directly in the field, in America as well as Europe. Norway spruce in Europe, radiata pine in New Zealand and Australia and Eucalyptus throughout the tropics have been planted extensively using rooted cutting technology during the past 20 years. Several conifers in North America have been targeted for research leading to clonal reforestation. Douglas-fir and western hemlock in the Pacific Northwest; both white and black spruce in Canada; and loblolly, slash and Virginia pines in the Southeast have received most of the focus. IFSCO was the only private enterprise that was developing clones of the southern yellow pines for commercial retail. However, the market has been slow to develop, and the company has moth-balled its research program. That is not to say that it would not get back in the game if demand picks up. In the meantime, it is producing rooted cuttings of loblolly, slash, and longleaf pine on a contract basis. In addition, the development of its propagation facility has allowed it to produce rooted cutting of Leyland Cypress, an ornamental tree, on a commercial basis. Let's hope that the clonal field trials we have established over the last few years and the demonstration plantings you will be establishing will help landowners see for themselves the benefits of clonal forestry.