Ed:
Yes, its just as much about what's right as what's not wrong with a site.
The same argument can be made in natural selection--you can have selection
for certain adaptations, but also selection against others.
Lee
At 10:42 PM 11/26/2009, you wrote:
>Lee and Bob,
>
>Lee you spoke of the Kandiyohi Elm Forest:
>
>Lee Frelich, Nov 22, 2009
>At the Kandiyohi elm forest, for example, last September I found
>what I call the peach-leaf willow super site. Its a stand of peach-leaf
>willows 80-100 feet tall with some single trunks up to 40 inches dbh.
>Published descriptions of the species say it reaches a maximum height of
>40 feet.
>
>Lee Frelich, Nov 22, 2009,
>Its easy for that site{Kandiyohi elm forest]: the soils are nutrient-rich
>black silt
>at least 10 feet deep. The soil has a huge capacity to hold water through
>droughts that are common at the prairie-forest border. Super sites are
>always about how evenly water and nutrients are supplied to the tree.
>The more even an adequate supply (and the fewer episodes of flooding or
>drought), the better the site. That's why cobblestone sites at the base
>of slopes with trickling water and types of bedrock that weather into
>particles with with high nutrient abundance are also super sites.
>
>
>In this context a Super Site is one for which a particular species grows
>exceptionally large - peach leaf willow. That is a reasonable idea and I
>can't argue with the logic, but maybe I can suggest a variation of the
>concept of a Super Site. When I think of a Super Site I think of one in
>which the tree assemblage is pretty much the same as that of the
>surrounding forest, only the trees at that site are bigger for trees of
>the same age range. (generally old). The question is whether a Super
>Site as a concept should refer to site with respect to an individual
>species or should it reflect the relative size of general group of species
>found there in comparison to those in the surrounding forests? Maybe
>either one is appropriate.
>
>I am sure that a thick rich soil will tend to promote growth in most
>settings, with those areas with better soils tending to grow bigger trees
>than areas with poorer soils. I like the idea you seem to be suggesting
>in that these sites have a characteristics which helps mitigate some
>environmental factor that can limit growth on other sites. In this case
>the thick soil holds water that mitigates the drought limitations at the
>forest-prairie interface. Perhaps a slightly higher spot in wet areas,
>say flood plains or hummocks in swamps, may promote growth for species
>that are less water tolerant and yield taller trees relative to in the
>surrounding wetter areas.
>
>There are examples of disjunct populations of less heat tolerant species
>surviving at higher elevations in areas farther south than the main body
>of the population. These are certainly taller than the same species in
>surrounding areas - because there aren't any. The Kandiyohi forest
>represents an unusual assemblage of the dominant tree species because of
>its soil characteristics. It isn't really representative of the general
>forest types found in the region, so it doesn't have exceptionally large
>examples of trees of the species found farther away from the prairie
>boundary, but is a Super Site for the many of the individual species that
>are found there.
>
>What are some examples of Super Sites in which there is basically the same
>species assemblage, only the trees are bigger? And why are they
>bigger? You gave some examples: 1) rich, thick soils, 2) right balance
>of water neither too much nor too little, and 3) rocks that provide good
>mineral nutrients to the soil. All of these sound good. Perhaps we
>should look at other environmental conditions that are somehow limiting
>growth in a region and see if at sites with taller trees, these effects
>are in some way being mitigated. If calcium is a limiting factor in the
>soil, then trees growing in an area with limestone bedrock should grow
>better there than elsewhere in the region. If wind shear is limiting tree
>heights, then areas such as coves and smaller valleys may have higher
>trees because the topography provides some protection from the wind to
>these trees. Certain species combinations in certain proportions might
>yield taller forests than other combinations - and we could ask why is
>this combination growing in this area and not in others.
>
>The small point I am trying to make is that a Super Site for a species or
>a forest as a whole is not just a matter of what is great about the site,
>but also what is not wrong with it. What limitations are being mitigated
>by the specific site conditions? This is sort of a half full or half
>empty argument, but it would allow some one to look at the question from
>two different approaches and perspectives.- what is great about the site,
>and what problem is absent from the site?
>
>Ed
>
>
>
>Check out my new
>Blog:
><http://nature-web-network.blogspot.com/>http://nature-web-network.blogspot.com/
>
>(and click on some of the ads)
>
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