In coastal wetlands, one of the most striking examples of climate change is the poleward range expansion of mangrove forests in response to warming winters. In North America, the Cedar Key region has often been considered the range limit for mangroves along the western coast of Florida (USA). However, within the past several decades, robust stands of Avicennia germinans and Rhizophora mangle have been observed in the Apalachicola Bay region, which is 200 km northwest of Cedar Key. Here, we combined field vegetation surveys, historical herbarium records, and analyses of past temperature data (station-based and gridded) to examine the distribution and structure of these two mangrove species in the Apalachicola Bay region. Historical records indicate that mangroves have been present for at least 150 years. However, our abundance and structural data indicate that mangroves are currently reaching heights, densities, and reproductive stages not historically reported. We found a surprisingly broad distribution and high number of R. mangle individuals, which is unlike A. germinans–dominated mangrove range limits in Louisiana and Texas. Using cold temperature tolerance thresholds and gridded temperature data, we show that A. germinans and R. mangle distributions can be influenced by spatial variation in the frequency of extreme freeze events, which can be used to spatially depict the risk of mangrove cold damage. Given the rapid pace of change and the potential for abrupt landscape-scale transformation, our findings reinforce the pressing need to advance understanding of mangrove expansion dynamics near northern range limits in the southeastern United States.

在沿海湿地，气候变化最显着的例子之一是红树林因冬季变暖而向极地扩张。在北美，Cedar Key 地区通常被认为是佛罗里达州（美国）西海岸红树林的范围限制。然而，在过去的几十年里，Avicennia Germanans和Rhizophora mangle 的健壮林分在雪松岛西北 200 公里的阿巴拉契科拉湾地区已经观察到。在这里，我们结合实地植被调查、历史标本馆记录和过去温度数据分析（基于站点和网格）来检查这两种红树林物种在阿巴拉契科拉湾地区的分布和结构。历史记录表明，红树林已经存在至少 150 年。然而，我们的丰度和结构数据表明，红树林目前正达到历史上未报道的高度、密度和繁殖阶段。我们发现了令人惊讶的广泛分布和大量R. mangle个体，这与A.germinans不同– 在路易斯安那州和德克萨斯州占主导地位的红树林范围限制。使用低温耐受阈值和网格温度数据，我们表明A.germinans和R. mangle分布会受到极端冰冻事件频率空间变化的影响，可用于在空间上描述红树林冷害的风险。鉴于变化的快速步伐和突然的景观规模转变的潜力，我们的研究结果强调迫切需要加深对美国东南部北部范围限制附近红树林扩张动态的了解。