Lee and ENTS, I guess my thoughts were ill-formed when I first posed the question. What I am thinking is that there are two mechanisms that cause the leaves to change colors and fall. One is they are nipped by frost and drop. The other is that they drop because the process is triggered by the change in day length. One sort of backs up the other. If the cold doesn't get them, then the leaf change goes to its fail-safe option of change in day length. Why would the trees not simply wait until cold caused the leaves to die off? Why have this day-length mechanism at all?
There must be some disadvantage to allowing the leaves change and drop to be triggered by temperature change, or some advantage to the leaves being triggered by day length changes. What is it? On the face of it, it would seem it would be best overall for the trees to hang on as long as possible, to extend the growing season, but the day-length trigger must have some advantage that outweighs the gain from extending the growing season at the cost of the leaves freezing. This must be some specific ratio or formula balancing the benefits and costs of both options. Why is the change at a specific day-length? How specifically is this leaf change formula from day length change determined? It may be different for different species. Like now the black gum has long since fallen (thin leaves), the maples are mostly down, but the oaks and tuliptree leaves are still hanging on and to a large degree green. Why is there this pattern, and why is color triggered by these day length changes? It is a genetic mechanism. Clonal colonies all seem to change color at the same time. Trees transplanted from the north change colors sooner than southern trees. Is the time of nut production or fruit production triggered by the period since leaf-out or also by a change in day length? That would apply to blossoming in the spring - is it a certain time after leaf out or set by temperature or set by day length? I know blossoming can be delayed by weather, but what if the weather is good? I am just trying to understand the processes happening. Ed "Two roads diverged in a yellow wood, And sorry I could not travel both. " Robert Frost (1874–1963). Mountain Interval. 1920. ----- Original Message ----- From: Lee Frelich To: [email protected] Sent: Tuesday, October 28, 2008 7:02 AM Subject: [ENTS] Re: Fall colors and leaf drop Ed: Because both temperature and day length control formation of fall colors. Up here temperature used to be the primary controlling factor (it got cold enough to cause leaves to change color and drop before the days were short enough to do so), but now it doesn't get as cold as early, so day length has more chance to cause the leaves to change. Lee --~--~---------~--~----~------------~-------~--~----~ Eastern Native Tree Society http://www.nativetreesociety.org You are subscribed to the Google Groups "ENTSTrees" group. To post to this group, send email to [email protected] To unsubscribe send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/entstrees?hl=en -~----------~----~----~----~------~----~------~--~---
