Southern grasslands … with trees

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Learned and relearned some interesting things at the longleaf pine meeting. The keynote speaker was Reed Noss, who wrote a book that I bought (but admit I have not yet read) called “Forgotten Grasslands of the South.” He understands the longleaf pine ecosystem as much as a grassland as a forest and his point have merit. A natural longleaf ecosystem is a savanna, which is a bit of both and neither.

It stayed a savanna because of fire and grazing. If you exclude fire and grazing animals from an acre of land in the Southeast, it turns to thick forest in short order.

Noss referred the longleaf ecosystem as fire DEPENDENT. This is a slight difference from fire adapted. The fire dependent ecosystem does not exist in spite of fire but because of it. When fire is excluded, it dies.

The longleaf ecology is one of the oldest and most diverse in North America. Something like it originated Oligocene 33 million years ago and maybe in the Eocene more than 50 million years ago. It was not exactly like the pine today, but fossil record indicates it had similar services. (Note that paleontologists can recognize pine pollen, which they take from lake bottoms and they can generally tell northern from southern pine species, but cannot be more precise than that.) North America changed many times, of course. For part of the time the “coastal” plain was up around what is now Kentucky and Tennessee because of higher sea levels. At other times it was well into what is now the Gulf of Mexico from lower sea levels. What is certainly the longleaf pine biome is much more recent, after the last ice age, maybe 5-7000 years ago.

You have to think of the pine ecosystem like a pulse. It extends out or in depending on the changing climate conditions. North America has been much warmer than it is today and much colder, so the area adapted to southern pine is not the same.

Fire dependent pine species have two main strategies. Some, like jack pines or lodge pole pines, burn up entirely. Their cones will not open until they are burned and the progeny quickly recolonize burned over places. They need big, hot, crown fires. Others, such as longleaf and shortleaf, adapt by being fire resistant in their seedling stages and then develop thick bark to resist flames when they are older. They depends on frequent but not very hot surface fires. W/o fires they will disappear, out-competed by other species.
There is disagreement about when to burn. Foresters like to burn in winter because it is safer with cooler temperatures. This is not natural, however. Paleontological evidence indicates that fires were most common in May and June, when there were lightning strikes but before it rained very much. A winter fire does not kill hardwoods, while a growing season fire does and encourages grass and forbes.

Because of fire, not in spite of it, the southern pine ecosystem is one of the worlds most diverse. It is a global biodiversity hot spot that we need to work to maintain, using fire and grazing … and planting more longleaf.

At one time longleaf dominated 90 million acres of land in the south. It was down to about 3. We have brought it back to 4.5. We are planting 110 million longleaf pine seedlings every year and hope to cover 8 million acres with longleaf by 2025. We will not be able to restore it to its former glory, but we are making a good start.