Gaines, ENTS, This is why I don't think cutting has affected the genetics of the white pine population. The thing is to get a genetic shift, you need to be selecting for something or against something. Harvesting mature trees is not selecting anything, hence there is no genetic shift. How rapid the genetic change is dependant on the completeness of the selection process. If only a small percentage of the specific gene is either selected for or against, then the change is slow. High grading in which you selecting for the best trees does affect the genetic composition overall, but not by much. In any forest the majority of the trees are too small to be harvested, seedling to saplings - to small trees, thus the majority of the tree genetic variability is not found in the mature trees that are harvested.
The second factor to consider is that the size of the tree is not only dependant on the genetics of the tree, but on growing conditions at the specific location the tree is growing. side by side a tree with poorer genetics may be larger than one of similar age of better genetics because of variables like water. A small spring may feed one tree and not the other. Tree growth has been linked to some of the microbes in the soil, many things make it so that high grading will be taking the best trees, but also some of the poorer trees, and leaving some of the better genetic trees behind. The selection process is not specific enough to make much of a difference in a single generation or even several generations. At most sites we are looking at most the fourth generation since the initial harvesting. In most of those harvests mature trees were taken, and high grading would not have been even slightly biasing the genetics of the population. Looking at the redundancy of the genetic pool in terms of the large number of smaller trees, seedlings and saplings in relation to the large trees harvested in high grading, their removal does not have much of an effect at all.. Now you have brought up the idea of different pockets of genetics in the landscape. As you said white pine pollen is wind distributed which tends to make the populations in an area fairly homogeneous. There are variations between trees, but the variants exist in about the same proportion in the population throughout the region. You get pockets of species with a different genetic makeup, or with different proportions of certain traits based upon some degree of isolation. For example where there are disjunct populations - those physically isolated from the general population you tend to get some genetic shifts. Any uncommon traits that are more prevalent in the isolated population at the time of isolation may propagate through that population through inbreeding until it is represented in a different or higher proportion than in the general population. That is why if you are to try to get a representative sampling of the genetics of a species, then these isolated pockets should be sampled. An uncommon gene that you may not by chance sample in the contiguous population may be present in these isolated pockets at a higher percentage, therefore by sampling these isolated pockets you are more likely to sample the less common genetic characteristics of the population. A second form of isolation is simply one of distance. The variations found in a species population from one end of its range to the other are a result of genetic drift because of distance. The pollen from one end of the range does not reach the far end of the range so that local differences can develop on a broader scale. There are other types of filters which can effect the populations in different ways. Another consideration is that the trees appear to have the ability to take different forms depending on the conditions. There are options in how they grow. Look at the form of a tree grown in the open, compared to to what the form of the exact same tree would have been in a closed forested setting. Aside from the fact that there is no reason to think that given the lack of isolation that one population of pines would have within the general contiguous population had a different genetic strain that would have allowed them to grow taller than other pine trees, I don't see any reason why the same genetic ability would not also be present, even if less frequently within the broader population. I am not even sure that there is enough genetic variation in the white pine species for a 250 foot tall tree to even grow. It was suggested in another email that perhaps the overall canopy height was taller than it is today. An argument could be made that a tight stand of tall pine trees, grew in a narrow, deep, south facing valley, with lots of water, that had to compete with trees higher on the slope therefore they grew much taller than average, and because they were in a narrow valley surrounded on the sides by higher ground and trees, and that they were in a tight cluster of similar white pines with little space between them, so that they were not subject to severe wind sheer as they grew to these phenomenal heights, that some of them reached 250 feet. OK, maybe in the wildest imagination that would be possible, but I don't think it happened. The general canopy height, judging by how high white pines stick up above the general canopy in current old growth forests would need to be raised from maybe 150-160 to 210 feet. That would mean that the AVERAGE canopy height would need to be taller than ANY known trees in the eastern United States today. The only tree that even shows the potential to reach that proposed canopy height is white pine. You could argue that the area was covered by a white pine dominated forest and the canopy reached the heights of the tallest white pine we have accurately documented. But to me it seems unrealistic to even consider that the average canopy height at times in the past were higher than any living tree today. I just can't accept this argument. Ed Frank http://nature-web-network.blogspot.com/ http://primalforests.ning.com/ http://www.facebook.com/profile.php?ref=profile&id=709156957
