# 21st‐Century Mangrove Expansion Along the Southeastern United States

## TL;DR

Warming winters are causing mangroves to expand northward along the U.S. Atlantic coast, potentially reaching South Carolina by 2100, which could transform wetland ecosystems.

## Contribution

The study combines climate projections, dispersal simulations, and hurricane data to predict future mangrove expansion and its ecological impacts.

## Key findings

- Mangroves are projected to expand northward along the Atlantic coast, potentially reaching South Carolina by 2100.
- Hurricanes and ocean currents may facilitate long-distance propagule dispersal, aiding mangrove colonization.
- Mangrove encroachment into salt marshes could significantly alter wetland ecosystem structure and function.

## Abstract

Warming winter temperatures are driving range expansion of tropical, cold‐sensitive mangroves into temperate ecosystems. Along the Atlantic coast of North America, the mangrove range limit is particularly sensitive to climate variability and historical data demonstrate that the mangrove‐salt marsh ecotone on this coast has shifted recurrently during recent centuries. However, a comprehensive understanding of how this mangrove‐salt marsh ecotone may shift in the future remains lacking. Here, we combine ensemble forecasting of mangrove distribution for the next century with high‐resolution oceanographic dispersal simulations, phenological observations, and historical hurricane data to project future mangrove‐salt marsh dynamics at the rapidly changing range limit in northeastern Florida (USA). We show that warming winter temperatures will drive continued poleward expansion of mangroves along North America's Atlantic coast, potentially reaching South Carolina by 2100. With ongoing climate change, suitable mangrove habitat is projected to expand beyond the current range limit, and dispersal simulations suggest successful colonization of these sites from established mangrove populations. Additionally, patterns in hurricane directionality and intensity and field reports of propagule presence reveal that these high‐energy events may significantly contribute to future mangrove range expansion by facilitating long‐distance, storm‐driven propagule dispersal. The encroachment of mangroves in salt marsh‐dominated latitudes is expected to substantially modify wetland ecosystem function and structure, emphasizing how the identification of newly colonizable habitat can inform conservation strategies and site‐specific decisions on mangrove management.

Global warming is driving poleward range shifts worldwide, including the northward expansion of tropical mangroves along the Atlantic coast of North America. In this region, warming winters are enabling mangroves to encroach into salt marsh–dominated temperate latitudes, potentially transforming wetland ecosystem function and services. To assess future shifts in the mangrove–salt marsh ecotone, we projected mangrove habitat suitability under four IPCC SSP scenarios (2071–2100) and combined these projections with high‐resolution oceanographic dispersal simulations, phenological observations, and historical hurricane data to determine whether mangrove propagules can reach newly suitable habitats. Our results indicate that warming winter temperatures are likely to drive continued poleward expansion of mangroves along North America's Atlantic coast, potentially reaching South Carolina by 2100, facilitated by both oceanic and hurricane‐driven propagule transport from established populations. These findings are key for guiding conservation and wetland management decisions.