green "autumn" leaves

[dosmann at IASTATE.EDU]

I think you hit the nail right on the head.  Provenance and genetic 
source are a primary reason for the variability in autumn leaf 
coloration.  Here on the ISU campus, there is extreme variability both in 
time of senescence and color.  A majority of the 'hard maples' on campus 
are Acer nigrum, the black maple (A. saccharum ssp. nigrum for you 
lumpers out there!), while there are some selections of true sugar maple 
(A. saccharum) also on campus.  Since the black maples are primarily all 
native or from native source, time of color development is pretty 
synchronized.  Sugar maples, though, have been unpredictable, some still 
green, others already defoliated.  Regarding trunk damage and coloration, 
it has been my observation that some of the best color I have seen is 
often associated with stressed trees.  Don't forget microclimate, 
either.  While light intensity and photoperiod are relatively the same in 
a localized area, microclimate (and evening temperatures) can vary 
dramatically, also contributing to variable coloration.

Hope this helps,
Michael

---
Michael S Dosmann                    
dosmann at iastate.edu             . . .  
Graduate Research Assistant      . . 
Department of Horticulture      . . . 
Iowa State University          



> Hi,   
> 
> One of my students noticed that although most of the sugar maples here
> in northern Ontario have turned gold and red (and have since dropped
> their leaves), some of the sugar maples in town are still green. Someone
> told her that it was due to the trunks being damaged, but I think it
> probably is the source of these maples.  Trees planted in the city are
> often garden stock from southern Ontario, where leaves don't turn as
> early (southern ecotypes).  We've already had several frosts and 10 cm
> of snow last week, so these city maples now have dead green leaves
> hanging from the twigs. Does anyone have an accurate explanation for
> this phenomenon?
> 
> Thanks,
> 
> Sue Meades
> Sault Ste. Marie, ON
>