Research report: Drought and productivity trends in freshwater flooded forest swamps in the North American Coastal Plain

A satellite-based study of the 500 largest freshwater flooded forest swamps in the southeastern United States found no single region-wide relationship between long-term drought trends and vegetation productivity between 2000 and 2024. Associations were highly variable across locations: some coastal and southern areas experienced declining precipitation and drying conditions but had mixed productivity trends, whereas more inland and coastal northern areas showed increases in precipitation and wetness. The findings indicate that changes in cypress-tupelo swamp productivity cannot be attributed to a uniform coastal-wide response to drought.

Researchers used imagery from the Moderate Resolution Imaging Spectroradiometer, or MODIS, processed through Google Earth Engine to track changes across the 500 largest flooded forest swamps in the North American Coastal Plain. They examined three vegetation metrics—Leaf Area Index, Normalized Difference Vegetation Index and Enhanced Vegetation Index—and compared their trends with three commonly used drought indices. Seasonal decomposition and linear regression were used to assess long-term relationships, while local bivariate spatial associations examined how drought and productivity patterns varied geographically.

The overall correlations between drought trends and vegetation-productivity metrics were small, but that weak aggregate signal concealed substantial spatial variation. Coastal and southern regions, including parts of Texas, Florida and Louisiana, were experiencing decreases in precipitation. Their productivity trends were mixed rather than consistently declining.

In more inland and coastal northern areas, precipitation and wetness were increasing. These contrasting patterns show why geographic contrasts alone do not demonstrate a uniform decline in productivity or establish that drought caused the observed vegetation changes. The study supports a more complex interpretation of cypress-tupelo swamp productivity.

Precipitation and drought were among the factors associated with differences among swamps, but the results indicate that these hydroclimatic conditions do not explain productivity patterns uniformly across the Coastal Plain. The analysis is observational and is based on remotely sensed vegetation indicators rather than direct measurements of plant growth, so it does not establish the biological or environmental mechanisms behind individual local patterns. The supplied findings also do not show that wetter areas always became more productive or that drying areas always became less productive.

The authors warned that some areas may be at risk of further degradation if drying trends become more frequent under future climate change. That statement describes a potential risk rather than a demonstrated outcome, and the study did not show that drought caused ecosystem degradation at any particular site. Additional research on individual swamps is needed to determine how their vegetation productivity responds to changing environmental conditions.

Overall, the study documents heterogeneous relationships between hydroclimatic trends and productivity across the largest flooded forest swamps of the southeastern United States, underscoring the limits of treating the region as a single ecological system.

Subject of Research: Drought and vegetation-productivity trends in North American Coastal Plain flooded forest swamps

Article Title: Drought and productivity trends in freshwater flooded forest swamps in the North American Coastal Plain

Article References: Holland, I. R., Stan, K. D., & Tucker, C. S. (2026). Drought and productivity trends in freshwater flooded forest swamps in the North American Coastal Plain. Regional Environmental Change, 26(4), Article 217. https://doi.org/10.1007/s10113-026-02708-6

Image Credits: AI Generated

DOI: 10.1007/s10113-026-02708-6

Keywords: drought trends, wetland productivity, flooded forest swamps, North American Coastal Plain, cypress-tupelo swamps, MODIS, vegetation indices, precipitation, satellite imagery, southeastern United States, Drought, productivity