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by Ryan Bremen December 22, 2020 3 min read

Hurricanes, Good for Mangrove Forests...In Moderation

December 1st marked the end of hurricane season here in the Atlantic. And as with most things in 2020, it was far from normal. The busy Atlantic hurricane season saw a record 30 named storms, including 13 hurricanes, and 6 of the major variety. The western Caribbean and Gulf of Mexico were areas of especially high activity with Louisiana, Nicaragua, and the Yucatan Peninsula all being hit by multiple hurricanes.


We’ve talked before about one of the ecosystem services that mangroves provide - protecting the coastline and those that live near it from inclement weather. Along with coral reefs, fringing mangrove forests dramatically reduce wave energy, flooding, and strong winds associated with hurricanes. These storms can strip canopies, snap and uproot trees, and submerge smaller ones via high storm surge. While these initial impacts are clearly destructive, there is evidence that hurricanes also provide benefits to mangroves forests.


An essential nutrient for plant growth, phosphorous concentrations are low in karstic settings such as Florida, the Caribbean, and the Yucatan Peninsula. Karst is a topography consisting of porous rock, as in the limestone-dominated substrate of South Florida. As a result, growth of mangrove forests here and in areas of similar geology are limited by low concentrations of phosphorous in the soil. Here hurricanes can serve as a stimulus to the growth of mangroves. Powerful winds and waves of hurricanes bring phosphorous-rich marine sediments into the soils of coastal mangrove forests. The influx of phosphorous that hurricanes bring actually facilitates rapid forest recovery post-storm. Increases in tree area, recruitment, and density as a result of enhanced soil phosphorous will lead to increased structural complexity. All of these benefits will aid mangrove forests’ abilities to stand tall in the face of subsequent hurricanes.  

 

 

As sea-levels rise, mangroves, just like all other life, must find a way to combat this change. Perhaps counterintuitively, it seems that hurricanes will actually help mangroves stave off sea-level rise. The sediment displaced by hurricanes into coastal mangroves increases the elevation of the soil. For example, in 2017, soil accretion as a result of Hurricane Irma was up to fourteen times greater than the annual accretion rate of the prior 100 years in mangrove forests of the Florida Coastal Everglades. Furthermore, storm deposits from Irma extended ten kilometers inland from the Gulf of Mexico. Best estimates currently put the rate of sea-level rise at 0.36 centimeters per year, which is greater than the aforementioned annual accretion rate in the coastal mangrove forests of the Florida Everglades. Thus, increased elevation from sediment deposition is likely a critical factor for mangrove forest soil elevation to outpace sea level rise.


It is clear that hurricanes can have both negative initial impacts and positive subsequent effects on coastal mangrove forests. The phosphorous-rich sedimentation that Hurricane Wilma brought to the Florida Everglades in 2005 helped the forest recover in less than years. And researchers expect, and are currently seeing signs of, a similar recovery trajectory post-Irma.  However, the hyperactive hurricane season of 2020 should raise some concern for these vital forests. While intermittent hurricanes help to fertilize phosphorous-limited mangroves and build upon their elevation, too frequent of storms could prove disastrous. Due to our planet’s changing climactic conditions, scientists are predicting more seasons of frequent and powerful storms as we saw this year. If this becomes a reality, mangrove forests may not have the time necessary to recover from storms. Even despite the added nutrients and soil elevation, recurrent losses of tree biomass may prove too large a hurdle to overcome. Mangroves have long protected coastal communities from the devastating impacts of hurricanes. Now we must strive to turn back the clock on climate change in hopes of shielding mangroves from the destruction of overly frequent and powerful storms.
 

 

To read more about the busy hurricane season, check out Brian McNoldy’s blog at: http://bmcnoldy.blogspot.com/

 

 

 

References
14. How fast is sea level rising? (2020, March). Retrieved December 21, 2020, from https://royalsociety.org/topics-policy/projects/climate-change-evidence-causes/question-14/
Castañeda-Moya, E., Rivera-Monroy, V. H., Chambers, R. M., Zhao, X., Lamb-Wotton, L., Gorsky, A., ... & Hiatt, M. (2020). Hurricanes fertilize mangrove forests in the Gulf of Mexico (Florida Everglades, USA). Proceedings of the National Academy of Sciences117(9), 4831-4841.
Feher, L. C., Osland, M. J., Anderson, G. H., Vervaeke, W. C., Krauss, K. W., Whelan, K. R., ... & Cahoon, D. R. (2020). The long-term effects of hurricanes Wilma and Irma on soil elevation change in Everglades mangrove forests. Ecosystems23(5), 917-931.
McNoldy, B. (2020, November 30). Tropical Atlantic Update. Retrieved December 21, 2020, from http://bmcnoldy.blogspot.com/

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