As a continuation from my last blog about place, the following is an entry from the Florida Keys, a place which recently suffered damage due to Hurricane Irma.
The Florida Keys is a long, 100 mile stretch of islands connected by a single road. The average height above sea level for most of the islands is 18ft, but many of them are lower than that.
Much of the Northern Keys are protected naturally by salt water growing trees called mangroves. These mangroves stretch for miles along the coastline helping to create small coves and inlets which take the brunt of wind and storms coming from the ocean side. The mangroves also exist at the tip of Florida bordering the Everglades National Park, but let’s stick to the Keys for now, as they are well developed and very vulnerable to Hurricane type storms.
(Mangroves along the ocean side of Key Largo)
Before continuing, let’s have a little background on the mangrove tree. Due to its southern location, the tree does not undergo seasonal changes as trees in the northeast do. Therefore, there are no growth rings, so understanding age is exceptionally difficult. The wood is so dense that it does not float, it sinks. The density of the wood gives it strength, while the tannins in its outer layer make the wood extremely resistant to bugs. The trees are extremely resilient, but when and if they die, due to this density and natural resin, they do not decompose like other trees. They typically stay in place for another hundred years.
(Inlet into the grove)
So back to the buffering. The trees grow very close together, constantly competing for sunlight and space. There are typically no other plants competing for space, as they grow in 100% salt water, a feat that most other tree type plants cannot handle. The root systems continue to grow throughout the life of the tree, and when a new branch grows out from the trunk, it sends a supporting root system down into the mud for vertical support.
(Mangrove root systems and supports + new growth)
So, when a category 1 or 2 hurricane hits, these mangroves barely even feel it, and anything behind them is extremely well protected. When the category 4 Hurricane Irma hit, the first few layers of mangrove were completely stripped of their leaves, but they still did their job of protecting the shore line.
When the 12ft storm surge hit, the mangroves took the initial impact, reducing the force by providing a semi permeable layer that the water had to pass through. This slows the wave down, and although the flooding still occurred, the devastating blow which takes out windows and doors, lifts cars, and plows through houses was greatly reduced. This natural barrier, coupled with a requirement that houses are built on 10ft concrete pillars, means that the houses faired much better than they might have otherwise.
(Houses along man made canals raised 10 – 12ft)
The story is not over however. Due to the resiliency of the mangrove tree even after it dies, the dead trees will stay in place. Over the next 30 years while the grove regenerates, the dead wood will continue to protect both the mangrove and the dry land behind it.
(Dead mangrove trees among new growth)
Mangroves cannot completely protect the islands from these weather events, but these and other natural systems have weathered these storms for thousands of years, and evolved to create layers of buffers against these storms. The natural environment knows how to protect itself. Let’s start listening.
-Nate
