Abstract
Landscape-level shifts in plant species distribution and abundance can fundamentally change the ecology of an ecosystem. Such shifts are occurring within mangrove-marsh ecotones, where over the last few decades, relatively mild winters have led to mangrove expansion into areas previously occupied by salt marsh plants. On the Texas (USA) coast of the western Gulf of Mexico, most cases of mangrove expansion have been documented within specific bays or watersheds. Based on this body of relatively small-scale work and broader global patterns of mangrove expansion, we hypothesized that there has been a recent regional-level displacement of salt marshes by mangroves. We classified Landsat-5 Thematic Mapper images using artificial neural networks to quantify black mangrove (Avicennia germinans) expansion and salt marsh (Spartina alterniflora and other grass and forb species) loss over 20 years across the entire Texas coast. Between 1990 and 2010, mangrove area grew by 16.1 km2, a 74% increase. Concurrently, salt marsh area decreased by 77.8 km2, a 24% net loss. Only 6% of that loss was attributable to mangrove expansion; most salt marsh was lost due to conversion to tidal flats or water, likely a result of relative sea level rise. Our research confirmed that mangroves are expanding and, in some instances, displacing salt marshes at certain locations. However, this shift is not widespread when analyzed at a larger, regional level. Rather, local, relative sea level rise was indirectly implicated as another important driver causing regional-level salt marsh loss. Climate change is expected to accelerate both sea level rise and mangrove expansion; these mechanisms are likely to interact synergistically and contribute to salt marsh loss.
Highlights
Landscape-level shifts in plant species distribution and abundance can fundamentally change the ecology of an ecosystem
We focused on the Texas (USA) coastline because recent work has documented a number of “hot spots” of mangrove expansion on the portion of the Gulf of Mexico coast over the last 20 years [16, 19, 20]
The Landsat Thematic Mapper (TM) sensor is reliable for this type of wetland detection and classification [41]
Summary
Landscape-level shifts in plant species distribution and abundance can fundamentally change the ecology of an ecosystem. The boundaries between marsh and mangrove habitat fluctuate in response to environmental conditions, as cold-sensitive mangroves die back during freeze events and expand during warm periods, creating a dynamic ecotone [9] Vegetation composition within this ecotone is further influenced by a complex set of environmental and anthropogenic drivers, such as sea level rise, changes in rainfall, dredging and filling, structural development, shoreline stabilization projects, subsidence, and eutrophication [10, 11]. On Harbor Island (Aransas Bay, Texas), black mangroves (Avicennia germinans) more than doubled in area from 1930 to 2004 [20] These studies clearly demonstrate localized expansion, but it is not yet clear whether mangroves are displacing salt marshes at a larger, regional scale. We focused on the Texas (USA) coastline because recent work has documented a number of “hot spots” of mangrove expansion on the portion of the Gulf of Mexico coast over the last 20 years [16, 19, 20]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
