Trends in vegetation and height of the topographic surface in a tidal freshwater swamp experiencing rooting zone saltwater intrusion. (December 2022)

• Record Type: Journal Article
• Authors: Middleton, Beth A.; David, John L.
• Is Part Of: Ecological indicators. Volume 145(2023)
• Publication Date: 2022-12
• Subjects: Climate change -- Drought -- Forested wetland -- Freshwater swamp -- Global warming -- Peat collapse -- Regime shift -- Relict forest; Environmental monitoring -- Periodicals; Environmental management -- Periodicals; Environmental impact analysis -- Periodicals; Environmental risk assessment -- Periodicals; Sustainable development -- Periodicals; 333.71405
• DOI: 10.1016/j.ecolind.2022.109637
• Languages: English
• ISSNs: 1470-160X

Abstract

Graphical abstract: Highlights: Offshore storms drive salinity spikes in rooting zone of freshwater tidal forests. Regional spikes of salinity are pushed inland for many kilometers during storms. Foundational forest species are shifting toward more salt-tolerant cattail and reed. Elevated rooting zone salinity, tree stress, and elevation loss portend transition. Abstract: A decrease in the ground surface height of coastal wetlands is of worldwide concern because of its relationship to peat loss, coastal carbon, and biodiversity in freshwater wetlands. We asked if it is possible to determine indicators of impending transitions of freshwater swamps to other coastal types by examining long-term changes in the environment and vegetation. In a tidal Taxodium distichum swamp in Hickory Point State Forest, Maryland, the topographic surface height (ground surface height) decreased by as much as 25.6 ± 2.2 to 50.8 ± 3.8 cm at two Surface Elevation Tables from 2015 to 2021 following salinity intrusion events related to hurricanes and offshore storms (e.g., Hurricane Melissa). In 2019, rooting zone salinity exceeded 5 ppt for >24.9 % of the time, with a maximum salinity level of 12.5 ppt. Tree growth of T. distichum trees declined and 60 % of these trees died along a 4 m wide × 125 m transect in 2014–2016. Root biomass and ground surface height decreased roughly in conjunction with a salinity pulse in the rooting zone during Hurricane Melissa in 2019. Saplings survived but T. distichum seedlings were uncommon and did not survive in the study area. Typha × glauca increased in cover (0.2 to 5.6 % cover plot −1 ) from 2014 to 2016 so a vegetation shift toward T. × glauca was apparent by 2021. This work captures a multi-year trend of decreasing ground surface height, tree growth and health, and freshwater status in the rooting zone that may be an indicator of impending vegetation transition.