A question I've had in the back of my mind for a while; as one drives through various regions of the PNW, there seem to be noticeable differences in the growth habits of our native conifers - are these differences primarily the result of growing conditions or genetic variations within localized populations? Or perhaps the question needs to be applied on a case-by-case basis? Any pertinent (easy to read) studies?
Each specimen has its own history. This means that even the habit of an individual tree may be very different at different points in its life. For example, an Abies amabilis or a Sequoia sempervirens may spend centuries growing almost as a bonsai in the forest understorey, later to explode into much more rapid growth and zoom up if it lucks out and a gap appears in the canopy overhead. Old growth silver fir forests in particular have thickets of small, suppressed trees inside them. General site conditions will be shown the overall appearance of the stand. Dramatic events may also be shown by the composition of the stand. In extreme cases massive, ancient, fortuitously located individuals may occur by themselves or in small groups among many younger, smaller trees that date back to the last big blow or catastrophic fire.
With your local native species, you are seeing the full range of natural variability. With introduced species, very commonly all you see is clonally propagated cultivars, all genetically identical to each other, or at best only a small selection of the variation that species would exhibit in its homeland
Let me tell you about some seedlings raised from one cone from a Cork Bark Kuromatsu (Pinus thunbergiana) found in the wild in Japan. The cone was hand delivered to the US back in the late 50's. From the seed came 12 trees that made it to up to five years old. About the fourth year all but two started to develop the corking in the trunk like the parent plant had. The other two had no corking at all until they were roughly 20 years old and then one of them developed the corking to the trunk and some of the older branches, unlike the parent plant. The other tree never did and still does not produce any corking in the trunk and the oldest branches but will develop the corking in about the 4 year old wood. Many a people have been fooled by that tree when we called it a Cork Bark in the nursery when asked why did we keep that Japanese Black Pine considering where it was located and people immediately would look at the trunk and get angry at us and tell us we were playing with them. No matter, as all they had to was look elsewhere to see where the tree did produce the corking. Hey, I went through it also and even told Don he was nuts until I looked around and finally saw where it was happening. In all practical purposes that tree started producing the corking on the 4 year old twigs and branches after it was 20 years of age and it still does as I saw it almost five weeks ago. Was it genetic variance alone that causes this? Could it be an environmentally enhanced condition that could have caused it? A while back I wrote that the Pinus ponderosa seen in the Botany Photo of the Day differed from how ours are here in that our trunk color (I wrote bark) is much redder in color but it is the plates that is what differed the most in that the one shown in the BPotD had patchwork like plates being a square shaped overlapped patchwork quilt like shape and ours are elongated platelets. Ours are longer and narrower and do not overlap much, theirs have shorter much wider plates and definitely do overlap. Who would think they are the same Pine if we did not know it? Well, they are not the same Pine for the reasons I just stated but they are still both considered to be a Western Yellow Pine native to both areas. Why do you suppose they are different? What factors are at work to make their plates different and why do ours have much redder trunk color? Now we are into how the diversity in the trees are affected by the environments to which they have adapted to over time. One reason why ours have redder trunks is because we have more iron oxide in our soils but the presence or non presence of iron is not all of it as if we took seed from a Pine in Yosemite and planted the seedlings in Lake Tahoe those trees still will have reddish colored trunks even though the soils in and around Lake Tahoe do not have much iron in them. Sorry Michael but I was writing this as you made your post. Ask Michael F. sometime about the seed he has germinated from his collecting in Europe and elsewhere and ask him if the trees he has at home look the same as the parent plant did or does that he gathered the cones from? Jim
Thank you Ron & Michael. My original question, I guess, concerns not so much individual variation within a population, and not just whether genetic variation occurs between populations, but rather, refers to the old "nature vs. nurture" arguement. If we perceive variation within a species in its natural range, how much of this variation do we attribute to climate/growing conditions vs. the genetic variability that may have resulted from these growing conditions. I am wondering if there are genetic differences in plant populations geographically which are observable, measurable, and can be shown by example to be a response to environmental conditions.
Yes, there are. Some habit variations induced by environment become genetically fixed, so that when moved to a different location that form or race continues growing more narrowly, slowly, or lower than related ones from different environments.
