People, I a sorry my suggestions last night were not better articulated. They were posted at 3 AM while I was up from not feeling well. There really are three suggestions I have made and there is some similar ideas posted by others today.
1) Perhaps the young rapidly growing trees slow down their growth rate or net growth may actually stop or decrease as their top is battered by weather and other elements. Bob Leverett said something similar this morning "Several years ago, Will and I begin talking about the possibility that many species appear to reach their greatest heights earlier than we would have thought and then stagnate or lose height in advancing age. Tuliptrees in the Smokies fit that profile well." 2) The second idea was that these early fast growing tall trees were over time replaced by longer lived, but shorter specimens over time resulting in the lowering of the net canopy height in subsequent generations. The idea essentially stated in another way is that the tallest stage of the forest is a passing phase in the sequence of forest development, but that a shorter forest, perhaps with longer lived trees, would form the canopy of a longer term more stable forest regime. We know that some of the oldest specimens for a species are often those stunted specimens clinging for life on a rocky cliff somewhere so maybe somewhat shorter trees would come to dominate a forest over time. I like this idea conceptually, but have no specific data that would either support or oppose it. 3) The third idea was that the circumstances of how the growth of the grove was initiated would play a role. There might be a difference in species composition and competition between those groves started from smaller openings within a forested setting, and those formed from a large scale disturbance such as a major fire or large scale blow down. The part left out of this idea was that the first generation after a large scale reset perhaps could grow taller than subsequent generations of replacement trees. This is similar to the second idea above, and both could work together. The difference is that in the second idea the second generation shorter trees may reflect an adaptive genetic component favoring longer lived trees, while the third idea postulates that different initial growing conditions may be reflected in different heights of trees. Again this is just speculation on how things might work, rather than interpretation of data sets. I an case, whether the ideas are valid or not, they do provide a different approach to the question. Ed Frank http://nature-web-network.blogspot.com/ http://primalforests.ning.com/ http://www.facebook.com/profile.php?ref=profile&id=709156957 ----- Original Message ----- From: Edward Frank To: [email protected] Sent: Tuesday, January 12, 2010 2:40 AM Subject: Re: [ENTS] Re: Projected heights Josh, Jess, Will, Gaines, Lee, ENTS, You are reporting these taller younger forests. I am wondering if these forests maintain their height or grow taller after this initial youthful exuberance of growth? Could it be possible that the upward growth slows or or stops and the trees over the course of time get beaten back down to lower levels by 100- 200 year storm events? Upward growth would not actually cease but if it fell below the rate of height loss from weather, the net result would be a decrease in the average height of the forest. Perhaps the taller younger trees tend to die off after a period of time and are replaced by longer lived, but shorter specimens of the same species. You know that slow growing stunted trees clinging to cliffs under poor conditions are often among the oldest for the species. This may not be the case for the forests you are observing, but it is an alternative to the idea that environmentally something must have changed, and certainly is an alternative to the idea that indigenous cultures somehow did something on a grand scale for which there is little or no evidence that made these original "old growth forests" be shorter than younger modern forests. The idea essentially stated in another way is that the tallest stage of the forest is a passing phase in the sequence of forest development, but that a shorter forest, perhaps with longer lived trees, would form the canopy of a longer term more stable forest regime. Another idea might be that the type of regrowth might play a role - the height of tree the forest in might reflect whether or not they grew from canopy gaps in a broad forest, or from a larger scale disturbance event - like a major fire or large area blow down. These could have different species recruitment, and certainly different competition between trees as they grew. I would think it might have an impact on the total height of the resulting forest. Perhaps both postulated mechanisms could play a role. I think at least the first idea has some merit and deserves consideration, it might not be correct, but gives another approach to the problem that may be useful even if wrong. Ed Frank http://nature-web-network.blogspot.com/ http://primalforests.ning.com/ http://www.facebook.com/profile.php?ref=profile&id=709156957
