Field-Based Radiometry to Estimate Tidal Marsh Plant Growth in Response to Elevated CO2 and Nitrogen Addition

Abstract

Plant growth is one of the most important variables to measure in long-term research plots, but the negative effects of labor-intensive and destructive sampling can restrict frequent assessment of plant biomass. Here, we used field-based, active radiometry to assess plant biomass in an ongoing, experimental manipulation of atmospheric CO 2 and soil nitrogen availability in a tidal wetland. We compared the ability of several radiometric vegetation indices (VIs) to predict total plant biomass and that of two plant functional groups, sedges and grasses. All VIs estimated total biomass better in July than in October, when senescence had begun. All VIs correlated strongly and positively to grass biomass (average r00.83) and weakly or negatively to sedge biomass (r0−0.30). Modified soil-adjusted vegetation index (MSAVI2) performed well through space (average July total biomass r 00.83) and time (across four sampling times r00.83) and predicted CO 2 and nitrogen treatment effect sizes. In conjunction with conventional biomass measurements field-based, active radiometry provides (1) a frequent estimate of biomass that can reveal plant responses to environmental stimuli that would otherwise escape detection, and (2) a viable alternative to frequent destructive sampling for assessing growth of fine-stemmed species such as Spartina patens and Distichlis spicata.

A Model for Estimating the Vegetation Cover in the High-Altitude Wetlands of the Andes (HAWA)

“…One of the most important and extensive plants in the salt meadows of Tilopozo is S. americanus. However, Langley and Megonigal [49] indicated that determining the phenological stage of S. americanus using NDVI is very complex, because the biomass is brown, and this generates very low NDVI values, which can be interpreted as bare soil. In addition, as S. americanus plants increase in height, their leaf areas decrease, which impacts NDVI in a counterintuitive manner, because higher biomass leads to lower NDVI values [50].…”

Evaluation of Approaches for Mapping Tidal Wetlands of the Chesapeake and Delaware Bays

“…Kirkpatrick Marsh, in the Rhode River sub-estuary along the northwestern shoreline of the Chesapeake Bay, is classified as an estuarine, emergent, persistent, and irregularly flooded marsh (E2EM1P) according to the National Wetlands Inventory (NWI) 2013 update. Kirkpatrick Marsh is noted as being high elevation by previous studies [46][47][48]. The vegetation composition is typical of a high elevation marsh in the Mid-Atlantic region of the United States with dominant species including: Scirpus americanus (also known as Shoenoplectus), Spartina patens, Iva frutescens, and Phragmites australis.…”

“…To evaluate how differences in geomorphology (i.e., marsh elevation) impact marsh inundation regimes and our ability to detect inundation using different remote sensing tools, our remote sensing assessment and mapping of marsh inundation focused on Kirkpatrick Marsh and Blackwater NWR. Kirkpatrick Marsh consists of almost entirely high marsh, is less frequently inundated than low marsh systems, and the mean tidal amplitude of the adjacent Rhode River sub-estuary is 0.3 meters [47,58,59]. This presented a unique opportunity to determine how effectively inundation events of low water depth (less than 0.5 meters) that occurred below dense vegetated canopies could be detected using satellite imagery, particularly in regions dominated by the high biomass and densely growing Phragmites australis.…”

“…NDVI is one of the more commonly used indices for characterizing wetland vegetation [25,47,49]. TVI is less commonly utilized but it has been demonstrated to be more effective for characterizing vegetation in high biomass ranges in agricultural studies.…”

“…NDVI captured a predictable greenness phenology for two full growing seasons. Scirpus americanus (also called Shoenoplectus) vegetation exhibited a lower NDVI than the other species, likely owed to its more vertical structure and more open canopy [47]. Spartina patens, which is the most horizontally oriented vegetation and forms dense mats of many small stems and leaves, had a consistently higher NDVI than even Phragmites australis and Iva frutescens, despite having a lower biomass.…”