The Importance of "Catastrophes"

 

Hurricane Idalia just passed us this morning and left our landscape intact.  Not the same for areas near Cedar Key and the Big Bend area of Florida which were hammered by 100+ mph winds and devastating high tides.  Large swaths of Florida were recently submerged in saltwater and likely will remain so for at least several days.  As most plants are not at all adapted to saltwater inundation, a great many landscape plants and vegetation in natural areas will perish.  

News reports often refer to such events as catastrophic ones, yet it is these very events that determine the ecology of an area. Wildfires, severe freezes, avalanches, and hurricanes are vital to the nature of plant communities everywhere.  They may be uncommon, but that doesn't diminish their importance.  They are so-called "keystone" events.  What we take as "normal" plant communities are their result.

Florida is a unique example - at least for North America.  We are shaped like an open sock.  Plants (and animals) work their way down from the north and move south to the "toe".  Plants (and animals) also wend their way across the Caribbean and find a foot hold in the Keys and extreme South Florida; all the while these two disparate communities of plants meet and fight for dominance somewhere in the middle.  What keeps them in their place are catastrophic events.  

Many of my favorite north Florida plants do quite well in my landscape.  I've planted  many of my favorites - species such as silverbells and native azaleas, in every one of my landscapes over the 36 years I've lived here in the Tampa/St. Petersburg area.  There is really no reason that they remain north of me naturally except for the fact that they don't reproduce without significant cold stratification.  Without cold temperatures, their seed does not germinate.  If that wasn't the case, you'd have species like serviceberry and southern crabapple all across the state. 

The same is true for many of the south Florida species naturally restricted to the lower 2-3 tiers of Florida counties - or that hug the coastline a bit further north.  When I first designed the native plant landscape 30+ years ago at the Pinellas County Cooperative Extension office in Largo, I had a bit of space left over that I had no plans for on paper.  I decided to plant it with south Florida natives with the idea that I could show folks what these plants looked like until we had a killing frost.  There was little in the literature at the time to tell me how they'd respond when temperatures dipped below freezing and I assumed it would kill most as none of them existed this far north naturally.  What I found over the course of all these years is that nearly every one of them is untouched by temperatures in the mid-20's F.  Temperatures that killed several native plants found here naturally caused no damage to plants not found naturally anywhere 100 miles south of me. The question then is why are these all restricted to extreme south Florida and my answer is that this is the result of catastrophes; temperatures like I saw in 1989 when it reached 19 degrees F for 3 consecutive nights.  I'm betting that this would have killed them all - and will someday in the future.

Rare catastrophic events are what cleans the slate of unadapted plants.  Saltwater and devastating  high winds like we just experienced in the Big Bend area of Florida are rare, but reoccurring events. They maintain the "purity" of a plant community by eliminating the species not adapted to it.  They are critical abiotic "disturbances", not something we should hope to eliminate if only we could. When we look out over a landscape following a natural catastrophe, we need to see it not as a disaster but as something rejuvenating even if that is difficult to do at the time. Catastrophes are devastating to private/personal property, but they are critical to the health of natural systems.