by Greg Mayer
There are some interesting comments on live oaks, their distribution, and resistance to hurricanes in the discussion (see #5) of my post on Long Beach, MS and its cuisine. One thing I’ve noticed is the striking zonation of the vegetation on the Mississippi Gulf Coast. Just a few miles inland, the live oak forest along the coast gives way to a forest strongly dominated by pine. Here’s a pine forest, less than two miles north of the water.
This pine forest continues considerably far inland, becoming mixed with broadleaved deciduous trees around Hattiesburg.
The live oaks dominate in a narrow strip along the coast.
And the beach itself supports grasses.
While never having been anywhere near there (eastern TX is the closest), I’m going to guess there are other factors involved in the zonation besides hurricanes slamming the place periodically.
While hurricane winds doubtless are powerful shapers of vegetation stands, I wonder if only two miles inland the winds are much weaker than they are right on the coast. They’re probably still easily strong to break trees. But, inundation by storm surges would be much less and maybe the Q. virginiana is more tolerant of periodic salty flooding than whatever the local pines are.
I wonder too about soil changes and whether the vegetation bands are related to substrate. Plants can be quite finicky about substrate characteristics and things like soil texture, moisture, and organic content/nutrients might well change as one moves inland.
There’s a tremendous book, Oak: the Frame of Civilization (Wm Bryant Logan) that cuts an amazing swath across biology, ecology, history, anthropology and probably a few more that I’ve forgotten, all as concern/intersect with oaks. I liked it so much I bought a dozen copies a couple yrs ago and sent them out as solstice presents. Everyone loved it. Highly recommended! Alibris has a number of cheap copies at the moment.
Thank you, I love to get such book recommendations!
Hydric versus non-hydric is my first reaction – then, upon further looking – salt talerance of most oaks is fairly high and pines are sensitive to salt intrusion at the roots. This, coupled with elevation, soil conditions, and water table – go together to make vegetative communities varied in such a coastal environment. Very few trees can survive tidal beaches anywhere! If you want to learn more – you can visit Plant Atlas and there is a wealth of information
An additional factor that keeps the live oaks (Quercus virginiana) restricted along the coast is they tend to prefer moister soils, mainly because they are intolerant of the periodic fires that the various pines can withstand. Live oaks are also more resistant to salt spray.
The various pines, loblolly, shortleaf, slash, longleaf, and Virginia are tolerant of fire and can thrive in sandy soils, but, being intolerant of shade, they quickly give way to taller deciduous species, like sweetgum and tuliptree.
For the role that fire plays in the Southern Pine-Oak Forests, I would highly recommend, “Looking For Longleaf, The Fall and Rise of an American Forest” by Lawrence S. Earley.
There’s interesting information on the fire ecology of the live oak at: http://www.fs.fed.us/database/feis/plants/tree/quevir/all.html#FIRE ECOLOGY. It appears their tops fire kill easily but they re-sprout vigorously from the roots. They also produce a microclimate that’s less conducive to fire and suppress understory vegetation that could serve to bring fire into the crowns. They may also be able to gain dominance in areas with less frequent fires by shading out pines.
If you look at a map of the surface geology of the Gulf Coast, you will see outcrops of different natures paralleling the coast. When I did a geology field class in East Texas, a remark, somewhat in jest, was made that one could do geologic mapping just by looking at names on mail boxes. German settlers were first in the area and settled on fertile clay soils. English speaking settlers came later and settled on less productive sandy soils.
I love that kind of analysis. One of the best courses I ever took was Agronomy, at Cornell. How closely our history maps to our soils!
Live Oak is very common near the beaches of SE Texas. Water oak is common too. But a little bit inland loblolly pine, sweetgum, green ash, water oak, and white oak dominate.
Galveston’s seawall held against Ike, but there was a backwash storm surge that dumped brackish water from the bay side. Almost every tree has been dying since 2008. But the live oaks are doing Ok. I think they must be salt tolerant.