Genetic Diversity   wad-@comcast.net   Dec 22, 2005 07:11 PST  Bob I think that the structure of a tree is based more on environmental conditions than genetics. The amount of light, and nutrients. Trauma to the tree as it grows changes the course of which way and how it grows. Ultimately the tree that is damaged in it's younger years seems to have less of a chance of survival to a great age. Here at work, in the woods, I get to watch things happen. Often a small tree will be beat up by a male deer. Sometimes it will die outright, other times it is disfigured and continues to grow. It is no longer a single stem specimen, but may have an odd shape. If a limb falls from a larger tree and strips branches off a smaller tree, then that tree seems to focus energy to the healthy parts of it's system. This too will result in an atypical form. Often times in nursery stock the leader will die back to a point, but not kill the tree. It seems that the tree will cut it's losses and send out another leader when the conditions improve. There are millions of scenarios that change the structure of a tree that are environmental. If a tree was grown in a controlled space, without outside interference, I wonder if all tulip poplars would have the same habit (or any species) I do see genetic differences in trees also. Just yesterday a saw a red oak that was about 10"DBH that had a solid line of buds around about 1/3 of the root flare. I looked up at the tree to see many clusters of odd buds that didn't seem to be growing. I wondered if it was a genetic or environmental oddity. How diverse do you think the genetic makeup of a species is in a location? Is it more harmful or helpful to introduce plants of the same species from a different genetic pool? I think it is better for humans to be less genetically similar, but what about trees? Is it a case where over tens of thousands of years a genetic strain becomes dominant due to survival of the fittest? Does that in turn make them more susceptible as a group when a new threat is introduced (HWA)? I hope some of the science-types will chime in, as I would love to hear about research that has been done in these areas. Questions I have had for some time. Scott RE: Genetic Diversity   Darian Copiz   Dec 23, 2005 10:46 PST  Scott, ENTS, Although I don't qualify as a science-type, I find the topic very interesting, particularly in regard to genotypes. It is an issue that has occasionally come up at the Maryland Native Plant Society. For rare or endangered species it has been pointed out that one should not introduce plants of the same species from a different location because it may negatively impact the local genotypes adaptability to the site. It may also diminish aspects of the local population that make it unique. Of course with animals there are problems with inbreeding in an isolated population. I also wonder is this a concern with plant species as well? The question of whether it is better for a local population of a species to die out or for it to be augmented through additions of a "non-native" population is something that appears to be an area of current debate. For species that are common and not isolated, perhaps the issue is not as important. However, it does still have implications on how we use tree species from different locations. Many of us have seen planted trees that change leaf color or lose their leaves much later (or sooner) than the trees of the same species growing naturally in the area. The use of cultivars is very popular in the landscape industry. Although, as far as I know, it is not common in the forestry industry I imagine it is something that could occur. I think the results on ecological processes and the natural heritage of areas could be disastrous, or at the least saddening. In the landscape industry there is increasing homogenity - everything is becoming the same. I for one, would like to see plant and landscape diversity preserved. Whereas people used to plant a red maple from the local genepool, now everyone plants 'Red Sunset' or 'October Glory' or a few other cultivars. Although these may be fine trees, I think it is unfortunate that we lose the potential for the fine qualities that other trees may posess and the loss of uniqueness that every location has. As a landscape architect I try to avoid using cultivars when possible or try to use a cultivar that comes from the region that I am designing for. A phrase I sometimes like to quote from Aldo Leopold is "If the biota, in the course of aeons, has built something we like but do not understand, then who but a fool would discard seemingly useless parts?" Although this does not pertain directly to introductions it does relate to the question of how much we should tinker with natural processes. My opinion is that we should keep meddling to a minumum. On the other hand, we have altered some things so greatly that it might be necessary for us to actively meddle. Other thoughts on the issues? I think it's a great topic for discussion. Darian Genotypes and adaptability   Edward Frank   Dec 25, 2005 15:54 PST  Darian, A general population of a species contain a high degree of variability, only some of which is expressed in the general population. In an isolated population certain genetic characteristics tend to become concentrated. Those are the characteristics that represent the features that allow the best fit of the plant to the particular environmental characteristics of the site. If there is a free gene flow across the entire area then the plants populations tend to be more generalized in their general nature. Speciation occurs when the genetic characteristics of a particular population have become too different to allow viable interbreeding with the remainder of the population.   This may be a result of simple concentration of certain genetic characteristics or mutations or both. In strict terms a Chihuahua and a St. Bernard are the same species, but they can no longer interbreed because of concentrations of genes responsible for the size of the organism. When a population from an outside area is introduced into a different area it can have an adverse effect. Essentially the native species have adapted to flourish best in that area, and introducing outside plants can dilute the gene pool. The concentration of characteristics that allow for the optimum characteristics for that specific area becomes lower as the native genes intermix with the external gene pool. A second effect is that an isolated population my not reproduce as rapidly as the introduced population. A lower reproduction rate may have an adaptive benefit for the local population. Introducing outside populations into an area, may not only dilute the local gene pool, but if they reproduce more rapidly they may replace the local population almost entirely. Faster reproduction may seen to be a good thing, but if the area is subject to stress, like drought, freezing weather, poor soils, a stressful situation may eradicate an introduced more rapidly reproducing population, whereas the local specimens may have survived the stress. Mono-culture is not a problem in natural populations like they are in a planted population. In a planted population the genes from a single specimen or small group of specimens is reproduced over and over again thousands of times. In a natural population the genetic variation is still retained, even within an isolated population. The general traits found in the general population are still present, although they be represented in by less frequent expression. Genetic characteristics or physical characteristics are not lost because they are useless or serve little function, they are lost because they have a detrimental effect. For example the eyes of the blind cave crayfish were not lost directly because they were useless in the dark, they were lost because it cost the organism large amounts of energy to grow and provided no benefit. In caves with restricted food supplies, eyeless organisms are more common. In caves, such as many in the tropics, where the food supply is not a limitation, there are fewer organisms without eyes. It doesn't cost them much to keep them if there is food available (Although genetic eye defects may be higher in troglobitic populations than the general surface populations). Back to the main point of discussion here.   The genetic characteristics typical of the general population tend to be retained in isolated populations because they cost the isolated populations little to retain. Therefore the isolated populations retain almost all of the genetic variability of the overall population. Hemlock from a variety of sites have been transplanted to farms and areas outside the areas affected by Hemlock Wooly Adelgid. One of my concerns I have expressed to Will and others working on studying these hemlock populations before they are destroyed, is that specimens and information from isolated populations or populations in extreme environments may not be being sampled as they should be. These populations have concentrated certain genetic characteristics that are more diffusely spread amongst the general population. Therefore even a systematic sampling of the general population may not include the genes and certainly not the genotypes represented by trees in these isolated and extreme environment populations. There needs to be a systematic sampling and collection of trees from these unique populations if there is to ever be a hope of reintroducing hemlock into its former range with specimens that are representative of the diversity of the species as a whole. I don't know under what circumstances that reintroduction might take place. Certainly the booming populations of the adelgid would need to be controlled if not eradicated. But if this diversity is to be preserved, even for research farms down the road, these populations need to be sampled now, when they are still alive. Ed Frank RE: plant genotypes   Lee E. Frelich   Dec 27, 2005 06:22 PST  Darian: I think we should do reciprocal transplants between neighboring populations of plants in fragmented landscapes--whether they are rare or not. It is one way of making the populations behave as if they are not in a fragmented environment. Landscape scale gene flow was an important process that we have eliminated on many landscapes for 100-300 years in the eastern U.S. I don't agree with those who think every little variation in genotype is worth saving. Many of the unique local genotypes could be artifacts of fragmentation caused by people. We need to restore landscape-scale gene flow or many species will go extinct. Lee Re: plant genotypes   Edward Frank   Dec 27, 2005 18:41 PST  ENTS, I have re-read my original comments after reading Lee's post. I still believe what I wrote previously but I could have been more articulate. Essentially I was talking about populations that are genetically different from the general population because of geographic or environmental isolation. The local plants are specialized for that environment, because for generations they have selected for characteristics best suited for growth in that environment. Plants form a longer distance away may grow if transplanted in that locality, but will not do as well in the long term as plants from the local area. The best option would be to try to encourage growth and somehow increase the rate of reproduction of the local plants. The second best would be to transplant plants from nearby locations to supplement the plants at the specific locality. Plants from the nearby area are more likely to have the same adaptive characteristics of the local plants and should do well. Plants from longer distances may present problems as I outlined in the initial post. If a species has become functionally extinct from an area, I see no problem from replanting the area with specimens from other locations. I don't believe, as Lee sugests, that the unique local genotypes are an artifact of human cause forest fragmentation. I must agree fully with Lee concerning the need to transfer species between areas that have become fragmented by human activities. Human driven change often occurs rapidly. With intervening highways, suburban areas, farms, and cities the plants and animals can no longer travel or migrate between these forested fragments. Over time the populations will become increasingly depauperate in fragmented forest pockets. I am not one who believes that the best way to manage a forest for posterity is to leave it completely alone. I think humans must intervene in some ways to help offset the effects of human activities, invasive species, and forest fragmentation. I would support the reintroduction of species that are lost or are all but gone from the original forest setting. With global warming there may be a need in the future to do more. Lee presented arguments at the last Forest Summit that the rate of global warming may shift the local climate at a faster rate than the tree can migrate northward, especially in light of the fragmented state of the forests throughout much of the country. We may need to develop seed banks and replant southern species farther northward. Otherwise these species may be all but lost in the future forests. I must strongly disagree with Lee about the importance of these "little variations" with the genotype. We have a chance to preserve these variations within the hemlock populations before they are destroyed by the Hemlock Adelgid, and we should do so. I think these pockets represent an important element of the genetic make-up of the entire species. Currently we as a planet are undergoing a major extinction episode. The greatest extinction ever on the planet was not the death of the dinosaurs but the extinction at the end of the Permian period between the Permian and Triassic Periods. During this extinction over 90% of the species on Earth went extinct. How many species of vertebrates do you think made it through this extinction event? In the late Permian there were literally thousands of species of fish, amphibians, reptiles, and therapsids.   At the beginning of the Triassic Period only twenty vertebrate SPECIES had survived. Most of these were fish species. Some may have survived because of chance of location, but most survived because there was something in the genetic make-up of each of their sub-populations that enabled them to survive. The key to the eventual survival of a species, like hemlock, may very well be in these sub-populations.   In any case they should be preserved, just because we can, if for no other reason. Ed Frank Re: plant genotypes    Lee E. Frelich    Dec 28, 2005 06:09 PST  Ed: We probably don't disagree as much as you might think. I meant my comments to apply mostly to areas that had been heavily impacted by humans for a long time, but was in a hurry and sloppy with the explanation, so it didn't sound that way. Sorry about that. I support efforts to save natural genotypes that have developed in areas with unique climate or physiography, as well as populations near the edge of the range that are isolated as a result of natural processes, where we are sure we are saving genetic variation useful to future generations, and not meaningless founder effects caused by human impact. The officially sanctioned (by the state government, timber companies and environmental groups) guidelines for timber harvest (also called best management practices, or BMPs) have incorporated my thoughts on this issue. While writing the Generic Environmental Impact Statement on Timber Harvesting in MN, which guides forest management in the state through the year 2040, I listed all the species that have populations near the edge of their range in MN, and listed that rare forest types, and said that special care should be taken to make sure these populations are regenerated and maintained over time. Next thing you know, the new BMP book showed the range maps for all these species, and also listed the rare plant communities. Now any timber company or agency that wants to claim they are managing their lands in an environmentally acceptable way, and/or wants to get FSC certification, has to follow these guidelines. Of course, I had no idea that what I said was going to become policy and be carved in stone for eternity. You have done a great job of summarizing the issue in your post below. The only thing I would add is that we should see natural selection as more dynamic than most people think it is. Trees actually evolve faster than other organisms in terms of generation numbers. That is because for most trees, a million or more seeds fall on the forest floor for each seed that becomes a successful tree, leading to very strong selection. This means that trees can adapt to changing climate through evolution, rather than migration as they have in the past. The only reason trees migrate when the climate changes is that other trees more efficient in the new climate out compete them before they have a chance to evolve (2 or 3 generations). Also, trees have a very large proportion of total genetic variability for the species within individuals and small populations. Therefore, it is possible to allow mixing of genes from different populations, and build a lot of variability into one population, and let natural selection decide which genes should be expressed on a given site. This may be a good strategy given that we don't know exactly what the climate will do (although there should still be a series of stands that are kept genetically pure, so to speak, that represent the variations of each species throughout its range). Lee   Home