The Botany of Hurricanes

It was bound to happen sooner or later.  After living in Miami for three years, a major hurricane finally struck South Florida, upending life as usual and downing trees and powerlines all over the region.  Lucky for me, the arrival of Hurricane Irma coincided with a workshop on science communication at Phipps Conservatory in Pittsburgh, Pennsylvania, so I was spared from experiencing this disaster first-hand.  As I spoke with visitors at Phipps about my research on the myrtle family in the Caribbean, one question kept recurring:  “How has the hurricane affected your work?”  Indeed, Florida was just the last stop on this massive storm’s path of destruction across the Caribbean, and both the people and the natural environment of the region were heavily affected.  And while we rightly focus on the people whose lives were significantly impacted by Irma, one may also wonder how wild plants and animals fared.  Evidently, Phipps guests aren’t the only ones wondering either, as shown by this article in the Wall Street Journal:  Hurricane Irma Wreaked Havoc on Caribbean Ecology.  I will venture to answer this question from the standpoint of a botanist by addressing how plants have been affected.

The best answer to this question may simply be, “It’s complicated.”  During a hurricane, plants can be damaged by water (and the resulting mudslides), wind and salt.  The extent to which a plant is affected by these factors strongly depends on its location (proximity to coast, elevation, exposure, etc.) and physical characteristics (height, structure, flexibility, salt-tolerance etc.).  Plants can survive by resisting damage, resprouting or regenerating from seed.  Some plants may even be adapted to hurricanes.  In 2005, scientists at the Montgomery Botanical Center in Coral Gables, Florida studied the impact of Hurricane Wilma on their collection of palms from the New World tropics1.  They found that palms that originated in the Caribbean, where hurricanes are common, were about 10x less likely to have died during the storm than those from South America, which are almost never affected by hurricanes.  These results strongly suggest that Caribbean palms are adapted to hurricanes.  It’s not clear what makes these palms hurricane-resistant, but they may have more flexible stems or a greater tendency to lose their leaves in high winds.  If palms are adapted to hurricanes, perhaps other Caribbean plants are as well.

The effects of hurricanes on vegetation aren’t all bad though.  Downed trees result in gaps in the forest canopy that provide opportunities for other trees to compete for light and grow to maturity.  Periodic disturbance of the dominant vegetation by hurricanes is probably an important factor shaping the composition of plant communities in the Caribbean over the long term.  Hurricanes can also allow plants to colonize new areas by spreading seeds and spores.  For a rundown of the winners and losers in nature after a hurricane, see the following site by the National Wildlife Federation: Hurricanes and Wildlife

And so life goes on – unless, of course, it goes extinct.  As a hotspot of biodiversity, the Caribbean is characterized by a large proportion of species found nowhere else in the world.  When a species has a restricted distribution and few remaining individuals, it is especially vulnerable to extinction by natural disasters.  Even if the species isn’t completely wiped out, further reduction in the gene pool may limit the long-term viability of the remaining populations, putting the species on a path to inevitable extinction.  I wouldn’t be the first blogger to suggest that Irma could cause extinctions in the Caribbean (see Is Irma an Extinction Level Event?), but I will highlight a little-known species of concern in the family I study, Eugenia earhartii.  This species was described as new to science in 1993 and is only known to occur in two small populations within Virgin Islands National Park on the hard-hit island of St. John.  How it fared during Irma remains to be seen.  Though rarer than most, Eugenia earhartii is not unique in its vulnerability to extinction among the approximately 500 species of the myrtle family limited to the Caribbean.  With regard to these species, I suggest that the next question ought to be, “Now that we know they’re there and vulnerable, what should we do about it?”

 

1Griffith, M.P., Noblick, L.R., Dowe, J.L., Husby, C.E. and M.A. Calonje. 2008. Cyclone tolerance in New World Arecaceae: biogeographic variation and abiotic natural selection. Annals of Botany 102: 591-598.

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