ENTS, as New York state gets its first snow storm of the season - possibly 6-12 inches in the Catskills are predicated - it seems to me that trees with leaves on them are severely impacted by heavy wet snow - breaks many branches. So there would be a real advantage to losing the leaves before snow is likely, I think. Elisa
Edward Frank wrote: > 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 <mailto:[EMAIL PROTECTED]> > To: [email protected] <mailto:[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 -~----------~----~----~----~------~----~------~--~---
