Ecological Trauma                                                                                                                                                                                                                After each hurricane season, there is almost always something new to learn about the plants that make up our urban forests. Hurricane-force winds can be extremely damaging to the trees, palms and shrubs making up these communities. Most hurricanes are primarily wind events. Urban forest recovery often occurs within a year such that the casual observer would not recognize the ecological trauma of the last storm. Hurricane Ian, however, was an unfamiliar occurrence due to its significant Gulf surge that swept away structures and plant life alike. On September 28, 2022, Hurricane Ian made landfall near Cayo Casta State Park in Lee County as a dangerous Category 4 storm.

It is important to point out that in addition to the storm surge and wind intensity other factors influence the damage caused by hurricanes to urban forests. They include species, age, and health of the plants in the area. Also relevant are the site characteristics such as soil conditions, soil composition, and depth of water table. These factors determine whether plants will fail during heavy winds compounded by a surge of widespread proportion. Even surviving trees and shrubs may suffer short- and long-term consequences. Let us review some of the apparent outcomes that may not be unique to Hurricane Ian but were highlighted by this powerful Category 5 Hurricane and the accompanying surge.

Insect Pests                                                                                                                                                                                                                          Hurricane Ian stripped many trees of their foliage. Most trees quickly replenished their leaves, but the recovery of our native strangler fig (Ficus aurea) was significantly delayed due to a sudden increase in the population of Edwards wasp moths (Lymire edwardsii). The caterpillar of the moths has a special attraction to strangler figs. For several months after the hurricane, many strangler figs remain leafless due to feeding by the caterpillars. They ate leaves, stems, and bark of young twigs. There was fear that many of the affected trees would succumb to the intense feeding. This was not the case. Nature tends to put things back in their rightful cycle and thankfully our native strangler fig is back to its old glory.

Another native species that had a temporary setback was isolated populations of giant leather ferns (Acrostichum danaeifolium). Caterpillars of the Virginia tiger moth (Spilosoma virginica) for the first time were recorded feeding on these giant ferns. This might simply have been an alternative food source if their preferred meal was temporarily unavailable.

Uptick of Invasive Plants                                                                                                                                                                                                  Insects were not the only things moved around by Hurricane Ian. Two vines seem to have become more prevalent in areas where their populations were in check. The air potato vine (Dioscorea bulbifera) is a notorious invasive and has apparently now established additional headways on some of the barrier islands. The love vine (Cassytha filiformis) is a native, but its name denotes its intent as a parasitic vine. Driving along either side of I-75 in Lee and Collier Counties, it is seen hanging from all types of vegetations including palms, trees, shrubs, and invasives of whatever type. Love vine covers plants slowly and many of its hosts will persist for years without any significant decline.

Damage to Native and Non-Native Plants                                                                                                                                                                                   The dominant pine tree species in South Florida is slash pine (Pinus elliottii). Normally after a hurricane, they may look green and healthy. However, pines are notoriously sensitive to strong winds, thereby suffering unseen internal injuries. This usually leads to many dead trees over a period of 6 months to 2 years after windstorms. When decline occurs, needles suddenly turn yellow and quickly progress to brown in a very short period.  Beetles usually colonize these already stressed, declining, or fallen trees. Standing trees are usually left with powdery sawdust surrounding the trunks as the beetles work their way out of the trees.

Palms were not spared the effect of Hurricane Ian. Immediately following the hurricane most royal palms (Roystonea regia) were stripped of their leaves but within a year showed no ill effects. Royal palms in the most severely affected areas were left crownless and rapidly developed a withered trunk and decomposing interior. There were some outstanding hurricane resistance species, but depending on the area, Hurricane Ian often showed little favor decimating native and nonnative species alike. A large die-off of sabal palms (Sabal palmetto) occurred on Sanibel Island. Many surviving coconuts (Cocos nucifera), queen (Syagrus romanzoffiana), Bismarck (Bismarckia nobilis) and date palms (Phoenix spp.) displayed classical symptoms of boron deficiency. Increased palmetto weevil infestations were reported, particularly in Bismarcks, none was witnessed by the author as many of these palms were removed once diagnosed.

An occasional fallen gumbo limbo (Bursera simaruba) is nothing unusual in South Florida. Affected trees are rotted at the base of the trunks, undermining their ability to remain upright.  A year or so following Hurricane Ian, and continuing to today, unusually high numbers of trees, between, 20 to 30 feet tall, began toppling. They displayed the same rotted lower trunk as trees in the past. Many of the fallen trees were located along roadways or in managed areas. Trees toppled individually or in small, scattered groups. Galleries caused by beetles were found in the rotted area of some trees, but not in most, and no insects were found. It was quickly determined that insects were not responsible for the toppled trees. Several trees were examined for fungal pathogens. Almost all the results came back negative, and a fungal cause was ruled out at the time of this report. Speculation of saltwater intrusion from the surge seems unlikely since gumbo limbo is highly salt tolerant and the soil analysis showed no elevated salts. Linking this phenomenon to Hurricane Ian is purely speculative. Nevertheless, it is documented here since such large numbers of gumbo limbos have not failed in the collective memories of those familiar with such situations prior to Hurricane Ian.

Hurricane Ian laid waste to a large swath of mangroves heading into Sanibel Island and to a lesser extent on Fort Myers Beach. Some areas have slowly recovered, but large portions are indistinguishable from their appearance in the immediate weeks following the hurricane. Soil and water samples were taken in the worse hit areas. It appears that both high salinity and restricted tidal flow may be responsible for the decline of many mangroves.

This is just a brief snapshot on the horticultural impacts two years after Hurricane Ian. Hopefully this will serve as guidance to naturalists, master gardeners, homeowners, landscapers, pest control operators, and all those involved in support of our urban forests and greenspaces.

For an in-depth look at ‘What Made it Through the Strom,’ watch the Florida Master Gardener Volunteer Webinar on the aftermath of Hurricane Ian.  https://www.youtube.com/watch?v=YQtubV6-W-8                                                                                                                                                                  Check out the September 23 Instagram post at lee_ufifas on the lingering damage to mangroves caused by Hurricane Ian.

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