During the month of September we experienced one our annual
highest tides, sometimes called the King Tide. These are normally occurring
tides throughout the months of September, October, and November during the full
moon phase. This year, it was coupled with low-pressure systems bringing strong
northeast winds that impacted the flow of the Gulf Stream, causing it to
back-up water in the Keys and Florida Straits. There have been numerous flood
warnings this fall and there has been plenty of footage in the news of the
flooding in Ft. Lauderdale and Miami Beach.
Due to the unique, porous geology of the limestone in south
Florida, and especially in the Keys, which have formed on an ancient coral
reef, we cannot shore up our waterfronts with sea walls and levees; the water
will eventually come up from below. We also have very flat topography so once
the sea rises, it will not matter how far inland you are. What do botanic
gardens do in this situation? How do we effectively preserve our collections in
the face of sea level rise?
Currently, we have many native and exotic salt-tolerant
plants on our Florida Bay waterfront. Aside from sea level rise and extreme
high tides, this environment is tough for plants in general with salt spray
during winter storms that blow in from the north and full, hot sun throughout
the summer. Salt-tolerant plants, however, are just that, ‘tolerant’, and some
of our plants may soon reach their thresholds. One potential casualty from last
month’s high water is our Argusia
gnaphalodes, sea-lavender or beach heliotrope.
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| Our sea-lavender after this summer's high tides |
This evergreen shrub is highly salt-tolerant and extremely drought-tolerant once established. Our specimen is over 13 years old and has a 5-foot, gnarled trunk with branches sweeping down to the ground. Apparently, beach heliotrope is difficult to establish so I feel lucky to have such a mature specimen in our collection. Unfortunately, all the leaves fell off after the high water and we are waiting to see if it will regenerate. A similar situation occurred in 2011 and our BG-Base records indicate that it “came back well after storm damage” so my fingers are crossed.
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| Sea-lavender regrowth after 2011 storm damage |
Not only are we concerned with protecting our botanical
collections, but more importantly, we need to protect the rare plant
populations in the wild that are being affected by sea level rise. The
inhospitable conditions produced by salt-water make it impossible for many
species to survive in their present locations. Even common plants are unable to
deal with excess salt, their seeds unable to germinate, they will eventually be
displaced by mangroves or other salt-tolerant species. In this case, botanic
gardens and nurseries are their only hope for continued propagation.
In the Florida Keys, we have many rare species that have
been propagated for years by local conservation institutions such as Fairchild
Tropical Botanic Garden and a handful of local nurseries. Regional watchdogs
like the Institute for Regional Conservation have performed baseline
inventories for monitoring rare plant populations so we know how they are doing
over time. Without human intervention, these plants and their habitats will
disappear and we do not fully understand the implications of this on a local
level, and much less on a global scale.
After each storm and high tide, as I notice the multitude of mangrove
propagules deposited along the shoreline, I wonder how long it would take for
the trees to return our developed shoreline back into mangrove forest. I guess
we’ll see over the next 30 years! Hopefully, we will be able to change the way
we live and use our resources more sustainably so life in coastal areas may
continue and we will not have to relocate our garden to the Lake Wales ridge –
the previous shoreline of Florida.
Emily B. Magnaghi
Associate Director
