In several places around the world, coastal marsh vegetation is converting to open water through the formation of pools. This is concerning, as vegetation die‐off is expected to reduce the marshes' capacity to adapt to sea level rise by vegetation‐induced sediment accretion. Quantitative analyses of the spatial and temporal development of marsh vegetation die‐off are scarce, although these are needed to understand the bio‐geomorphic feedback effects of vegetation die‐off on flow, erosion, and sedimentation. In this study, we quantified the spatial and temporal development of marsh vegetation die‐off with aerial images from 1938 to 2010 in a submerging coastal marsh along the Blackwater River (Maryland, U.S.A). Our results indicate that die‐off begins with conversion of marsh vegetation into bare open water pools that are relatively far (> 75 m) from tidal channels. As vegetation die‐off continues, pools expand, and new pools emerge at shorter and shorter distances from channels. Consequently larger pools are found at larger distances from the channels. Our results suggest that the size of the pools and possibly the connection of pools with the tidal channel system have important bio‐geomorphic implications and aggravate marsh deterioration. Moreover, we found that the temporal development of vegetation die‐off in moderately degraded marshes is similar as the spatial die‐off development along a present‐day gradient, which indicates that the contemporary die‐off gradient might be considered a chronosequence that offers a unique opportunity to study vegetation die‐off processes.

Uncontrolled, large fires are a major threat to the biodiversity of protected heath landscapes. The severity of the fire is an important factor influencing vegetation recovery. We used airborne imaging spectroscopy data from the Airborne Prism Experiment (APEX) sensor to: (1) investigate which spectral regions and spectral indices perform best in discriminating burned from unburned areas; and (2) assess the burn severity of a recent fire in the Kalmthoutse Heide, a heathland area in Belgium. A separability index was used to estimate the effectiveness of individual bands and spectral indices to discriminate between burned and unburned land. For the burn severity analysis, a modified version of the Geometrically structured Composite Burn Index (GeoCBI) was developed for the field data collection. The field data were collected in four different vegetation types: Calluna vulgaris-dominated heath (dry heath), Erica tetralix-dominated heath (wet heath), Molinia caerulea (grass-encroached heath), and coniferous woodland. Discrimination 1804 between burned and unburned areas differed among vegetation types. For the pooled dataset, bands in the near infrared (NIR) spectral region demonstrated the highest discriminatory power, followed by short wave infrared (SWIR) bands. Visible wavelengths performed considerably poorer. The Normalized Burn Ratio (NBR) outperformed the other spectral indices and the individual spectral bands in discriminating between burned and unburned areas. For the burn severity assessment, all spectral bands and indices showed low correlations with the field data GeoCBI, when data of all pre-fire vegetation types were pooled (R 2 maximum 0.41). Analysis per vegetation type, however, revealed considerably higher correlations (R 2 up to 0.78). The Mid Infrared Burn Index (MIRBI)had the highest correlations for Molinia and Erica (R 2 = 0.78 and 0.42, respectively).In Calluna stands, the Char Soil Index (CSI) achieved the highest correlations, with R 2 = 0.65. In Pinus stands, the Normalized Difference Vegetation Index (NDVI) and the red wavelength both had correlations of R 2 = 0.64. The results of this study highlight the superior performance of the NBR to discriminate between burned and unburned areas, and the disparate performance of spectral indices to assess burn severity among vegetation types. Consequently, in heathlands, one must consider a stratification per vegetation type to produce more reliable burn severity maps.

Coastal marshes and their valuable ecosystem services are feared to be lost by sea level rise, yet the mechanisms of marsh degradation into ponds and potential recovery are poorly understood. We quantified and analyzed elevations of marsh surfaces and pond bottoms along a marsh loss gradient (Blackwater River, Maryland, USA). Our analyses show that ponds deepen with increasing tidal channel width connecting the ponds to the river, indicating a new feedback mechanism where channels lead to enhanced tidal export of pond bottom material. Pond elevations also decrease with increasing pond size, consistent with previous work identifying a positive feedback between wind wave erosion and pond size. These two positive feedbacks, combined with bimodal elevation distributions and sharp topographic boundaries between interior ponds and the marsh platform, indicate alternative elevation states and imply that marsh loss by pond formation is nearly irreversible once pond deepening exceeds a critical level. Plain Language Summary Coastal marshes are highly valued ecosystems, but in some areas with increased sea level rise these vegetated marshes disappear and convert into large ponds. Currently, we do not fully understand how these ponds are formed and why marsh vegetation is not recovering in these areas. In this study we measured the soil elevation of marshes and ponds in an area where large marsh surfaces have converted to ponds (Blackwater River, Maryland, USA). We found that ponds are generally deeper when the connection of the ponds with the tidal channels is wider. This indicates that pond sediments can be exported through these channels, and the wider the channel, the easier sediment is exported, leading to deeper ponds. Larger ponds are also deeper because larger waves can develop there, resulting in more wave erosion. These two processes both lead to deeper ponds. Furthermore, we found that there is a sharp elevation drop from the marsh platform into ponds, and that intermediate elevations rarely occur. These all suggest that ponds, once they are formed, are very difficult to recover into marsh vegetation.