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Patterns of Reproduction at the Black Mangrove (Avicennia germinans) Range Edge After a Freeze Event
Abstract
Among mangrove species in North America, Avicennia germinans (black mangrove) is the most resistant to freezing temperatures and is the only species found in the northern Gulf of Mexico. Between range-limiting cold events, warmer winter temperatures permit A. germinans cover to increase, outcompeting and displacing salt marsh vegetation. After cold events, mangrove reestablishment occurs through vegetative regrowth of surviving belowground structures, followed by reproductive output. Patterns of vegetative recovery have been documented, but patterns of reproductive output following cold damage are relatively unknown. In February 2021, a deep freeze event caused more than 95% black mangrove mortality across the Texas coast. Surviving mangroves failed to reproduce in the summer following the freeze, likely due to the dedication of plant resources to above-ground recovery. In 2022, surviving mangroves began flowering and producing propagules. To assess patterns of mangrove reproduction after the freeze event, surveys were conducted at two sites with different levels of mangrove encroachment. A southern site (Port Aransas, TX) had dense mangrove stands prior to the freeze event, while at a northern site (Galveston, TX), mangroves were patchy and interspersed with marsh vegetation. Surveys of reproductive output (percent of live trees producing flowers and propagule size) were conducted at both sites. Trees at the southern site had 40% more reproductive branches relative to trees at the more northern, less encroached site. A subsequent greenhouse study determined that propagules from Port Aransas trees germinated at 2.8 times the rate of those collected in Galveston. These findings indicate that black mangroves may recover faster in the more southern site, despite having similarly high freeze mortality levels. The smaller propagules and lower germination rates of mangroves in Galveston, in combination with more stressful environmental conditions, suggest that recovery from disturbance events may be slower in mangroves closer to the range edge.
Subject
mangroveCollections
Citation
Palmer, Marissa Juliette (2023). Patterns of Reproduction at the Black Mangrove (Avicennia germinans) Range Edge After a Freeze Event. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /203058.