Mangrove Disturbance and Response Following the 2017 Hurricane Season in Puerto Rico

Abstract

Mangrove ecosystem responses to tropical cyclones have been well documented over the last half a century, resulting in repeated measures of tree mortality, aboveground biomass reduction, and recovery by species, size, and geomorphology. However, no studies have investigated the role of urbanization in mangrove hurricane resistance and resilience, despite increasing urbanization of tropical shorelines. This study gauges the initial response and short-term recovery of Puerto Rico's mangroves along well defined and quantified urban gradients following the 2017 hurricane season. Survival probability of tagged trees decreased with time, and the mean mortality across all sites was 22% after eleven months. Mean canopy closure loss was 51% one month after the hurricanes, and closure rates also decreased with time following the storms. Aboveground biomass accumulation decreased by 3.5 kg yr -1 per tree, corresponding to a reduction of 4.5 Mg ha -1 yr -1 at the stand level. One year later, the mangroves have recovered to 72% canopy closure and to nearly 60% of their pre-storm growth rates. No connection to urbanization could be detected in the measured dynamics. Instead, species, size and geomorphology were found to play a role. Larger trees suffered 25% more mortality than smaller size classes, and Laguncularia racemosa suffered 11% less mortality than other species.Hydro-geomorphology was also found to play a role, with forests in tidally restricted canals experiencing more canopy loss but faster recovery than open embayment systems. These findings suggest size, species, and geomorphology are important in mangrove resistance and resilience to tropical storms, and that urbanization does not play a role. Managing mangrove ecosystems for optimal shoreline protection will depend upon knowing which forests are at greatest risk in a future of increasing urbanization..

Recent Carbon Storage and Burial Exceed Historic Rates in the San Juan Bay Estuary Peri-Urban Mangrove Forests (Puerto Rico, United States)

“…Tidal connectivity, flushing, temperature, salinity, and nutrient inputs are known to influence primary productivity and C sequestration in mangroves ( Krauss et al, 2006 ; Lugo and Medina, 2014 ; Lugo et al, 2014 ). These parameters in the urbanized SJBE have been heavily altered by bridge building, canalization, dredging, filling, and extensive shoreline development for more than two centuries ( Ellis, 1976 ; Cerco et al, 2003 ; Branoff, 2020a ). At the western end of the SJBE, repeated dredging of a portion of the Caño Martin Peña since the 1920s allowed for improved exchange between San Juan Bay and the western end of the canal, but the clogged eastern end of the canal [Martin Peña East (MPE)] prevents tidal connectivity into the eastern lagoonal systems of the SJBE.…”

The Role of Urbanness, Vegetation Structure, and Scale in Shaping Puerto Rico’s Acoustically Active Mangrove Fauna Communities

“…However, only three of the eight species missing from the November survey are migratory, suggesting the absence of the other five is due to something other than normal seasonal changes in presence and/or vocalization behavior. Thus, it may be due to the forest disturbance associated with hurricanes Irma and Maria, which passed near and over Puerto Rico 2 months before the November survey, causing significant canopy loss (Branoff, 2020a). This is corroborated by findings from a more generalized (not mangrove specific) census of birds that resulted in significantly fewer birds counted after the hurricane (Wunderle, 2017).…”

Beyond Tropical Storms: Understanding Disturbance and Forest Dynamics

“…Moreover, and beside storm events, other processes and dynamics in urban areas affect coastal forests, potentially reducing the services and diminishing their natural regeneration capacity. The forest context in this urban landscape setting must consider, consequently, a combination of disturbances in coastal areas such as urban encroachment, hydrological modifications, sea-level rise, floods, or storm surges (Branoff, 2019;Yu et al, 2019;Yu and Gao, 2020). Moreover, forest context in coastal urban settings includes a variety of conditions such as dry forest over karst substrates, mangroves, novel forests, and other brackish and freshwater wetlands.…”

“…An approach that considers studying separate and combined effects of both storm surge flooding and canopy foliage loss from hurricane winds is needed, both in forested and urbanized landscape settings. This would more efficiently guide management actions for coastal area forests, which may include the need for surface and hydrological modifications before vegetation restoration and tree planting activities (Branoff, 2019;Yu et al, 2019). Studies such as Campos-Cerqueira and Aide (2021) and Yu and Gao (2020) demonstrate the need to address and increase our knowledge of the effects and feedbacks of multiple disturbances in forest ecosystems, as well as in settings outside of forested landscapes.…”