Gulf Coast Mangroves

[AnTonY]

I found some cool videos from a user who documents a mangrove colony on Galveston Island, TX (specifically the black mangrove):
https://www.youtube.com/watch?v=RnePfp5GFGc
https://www.youtube.com/watch?v=yosODeD7Rok

Furthermore, I found a text that discusses the potential for biomass energy generation on Galveston, using mangrove cultivation:
https://books.google.com/books?id=1T5tAwAAQBAJ&pg=PA108&dq=mangrove+galveston+biomass&hl=en&sa=X&ved=0ahUKEwiy2sL_-aLSAhVHiFQKHdeUCmsQ6AEIGjAA#v=onepage&q=mangrove%20galveston%20biomass&f=false

Now, these mangroves are said to be "freeze-stunted" compared to those in tropical Florida. But... the thing with freezes in the coastal US South is that they are intermittent/not constant. Then the rest of the year (spring, fall, and especially summer) is essentially warm, with no freezes. Thus, I wonder why just a handful of freezes in winter at the South is enough to stunt mangroves into looking like shrubs, when the vast majority of the year features warm conditions that they can thrive in; it is possible that these may just be young specimen, which have yet to grow tall, but still, just wondering.

What's also interesting is that mangroves just turn into marshes just with temps being cold enough; literally no type of species that can "take" the cold. So the difference between an entire coastal forest, and just grasses is simply cold that comes a few days of the year...

Edited February 22, 2017 by AnTonY

[Botanicus]

On the gulf coast of Florida mangroves make it just to Cedar Key, north of that is salt-marsh with grass/rush vegetation. Red and black mangroves occur there, but are regularly pruned back by the cold, they will keep growing through mild winters, but inevitably get frozen back and never achieve tree size. 

[AnTonY]

14 hours ago, Botanicus said:

On the gulf coast of Florida mangroves make it just to Cedar Key, north of that is salt-marsh with grass/rush vegetation. Red and black mangroves occur there, but are regularly pruned back by the cold, they will keep growing through mild winters, but inevitably get frozen back and never achieve tree size. 

If it is just the foliage that is damaged with cold snaps, then I don't see how the freezes would prevent tree-sized specimen. If the freezes aren't constant, then you have long hot, rainy summers, falls, and springs, then is that not a large period of the year a mangrove can grow and grow?  No, I don't see them looking as good as in frost-free areas, but I don't see how they can't get, at least, some size.

This, of course, is with the level of freeze set at the light range (29-32F); of course, the trees will be wiped out by deep low 20s/teens.

[Botanicus]

I'm not sure at what temp damage to the woody tissue occurs, I imagine that light frost/freeze does just damage the foliage & small branches, but much lower than that freezes back larger limbs/trunks often enough to keep them stunted.