Jean Marie Hartman

Use of vegetation indices to estimate indices to estimate intercepted solar radiation and net carbon dioxide exchange of a grass canopy

Photosynthesis, respiration, and decomposition in terrestrial plant communities consume and produce large amounts of carbon dioxide (CO2) and play an important role in the global cycle of carbon. Recent studies have suggested that satellite remote sensing may be useful in providing the extensive data sets needed to quantify these processes over large areas, but many of the factors which potentially limit the accuracy of the analysis in natural vegetation have not been examined experimentally. We have conducted field experiments relating spectral reflectance to intercepted photosynthetically active radiation (PAR) and net CO2 exchange in a natural canopy composed of the tidal wetland grass Spartina alterniflora (marsh cordgrass). Reflectance measurements made by a hand-held radiometer with Landsat Thematic Mapper spectral wavebands were used to compute remote sensing indices such as the normalized difference vegetation index (NDVI). Net CO2 exchange was measured in a clear, climate-controlled chamber placed over square meter plots of the canopy. The NDVI was near-linearly related to the proportion of solar PAR intercepted by green plant material. The relationship was not as strong as has been reported for growing agricultural canopies, but the regression model form persisted throughout the growing season (March through October) and was applicable to a wide variety of growth forms exhibiting different proportions of green foliage. NDVI was also near-linearly related to net CO2 exchange rates throughout the growing season and in plots subjected to varying levels of chronic stress. However, significant uncertainty in the relationship was produced by changes in photosynthetic efficiency in response to varying environmental conditions. Estimates of CO2 exchange based on NDVI were improved if the effect of ambient air temperature on net photosynthesis was assessment of photosynthesis and net gas exchange in natural vegetation is feasible, particularly if the analysis incorporates information on biological responses to environmental variables.

The role of large rhizome dispersal and low salinity windows in the establishment of common reed,Phragmites australis, in salt marshes: New links to human activities

In spite of its long history,Phragmites australis’ (Cav.) Trin ex Stuedel invasion in tidal marshes defies explanation. Initial establishment in these systems is particularly perplexing, because seedlings and rhizome fragments do not perform well in poorly drained saline environments. We tested the possibility that dispersal and burial of large rhizomes, periods of low salinity, and localized, well-drained areas facilitate initial establishment in brackish marshes. In a greenhouse we exposed large and small rhizomes to two drainage treatments: mimics of poorly-drained, high marsh interiors and mimics of well-drained, mosquito ditch banks. In well-drained treatments we exposed rhizomes to one of three salinity treatments: fresh, natural salinity regime of an invaded brackish water marsh, and a 2-wk freshwater window followed by a natural salinity regime. Small rhizone fragments did not emerge in saline treatments or treatments with high water tables, while emergence was spotty in well-drained freshwater treatments. Large rhizomes emerged only in well-drained, treatments. For large rhizomes, growth, survival, and clonal spread decreased when exposed to the natural salinity regime, but improved with exposure to the 2-wk freshwater window. These results suggest that dispersal and burial of larger rhizomes, well-drained features, and low salinity windows following dispersal improve the chances of successful establishment. These results help explain case-specific historical links between establishment and such human activities as hydrological alterations, construction activities, and lowered salinity.

The Influence of Phragmites (Common Reed) on the Distribution, Abundance, and Potential Prey of a Resident Marsh Fish in the Hackensack Meadowlands, New Jersey

This study investigates the influence ofPhragmites australis (common reed) invasion on the habitat of the resident marsh fish,Fundulus heteroclitus (mummichog) in the Hackensack Meadowlands, New Jersey. These abundant fish play an important role in the transfer of energy from the marsh surface to adjacent subtidal waters and thus estuarine food webs. The objectives of this 2-yr study (1999 and 2000) were to compare the distribution and abundance of the eggs, larvae, juveniles, and adults of mummichog and their invertebrate prey inhabitingSpartina alterniflora-dominated marshes withPhragmites-dominated marshes, and to experimentally investigate the influence of marsh surface microtoprography on larval fish abundance withinPhragmites-dominated marshes. In 2000, we verified that egg deposition does occur inPhragmites-dominated marshes. In both years, the abundance of larvae and small juveniles (4–20 mm TL) inS. alterniflora was significantly greater than inPhragmites-dominated marshes, while larger juveniles and adults (>20 mm TL) were similarly abundant in both habitat types. The overall abundance of larvae and small juveniles was significantly greater in experimentalPhragmites plots in which microtopography was manipulated to resemble that ofSpartina marshes than inPhragmites control plots. Major groups of invertebrate taxa differed between marsh types with potential prey for larval fish being significantly more abundant inS. alterniflora marshes.Phragmites-dominated marshes may not provide the most suitable habitat for the early life-history stages of the mummichog. The low abundance of larvae and small juveniles inPhragmites marshes is likely due to inadequate larval habitat and perhaps decreased prey availability for these early life history stages.

Human facilitation of Phragmites australis invasions in tidal marshes: a review and synthesis.

Efforts to manage or prevent Phragmites australis invasion in salt and brackish marshes are complicated by the lack of a general causal role for specific human activities. The pattern of invasion within a marsh differs among sites, and each may have different causal histories. A review of the literature finds three establishment/invasion patterns: (1) from stands established on ditch- or creek-bank levees toward interior portions of high marshes, (2) from stands along upland borders toward high marsh interiors, and (3) centroid spread from high marsh stands established in ostensibly random locations. Each invasion pattern seems to have different anthropogenic precursors, therefore preventing generalizations about the role of any one human activity in all sites. However, historical and experimental evidence suggests that regardless of invasion pattern, establishment is much more likely at sites where rhizomes are buried in well-drained, low salinity marsh areas. Any human activity that buries large rhizomes, increases drainage, or lowers salinity increases chances of establishing invasive clones. To integrate these patterns and improve our understanding of the rapid spread of Phragmites, recent evidence has been synthesized into a dichotomous flow chart which poses questions about current site conditions and the potential for proposed activities to change site conditions that may facilitate invasion. This simple framework could help managers assess susceptibility and take preventative measures in coastal marshes before invasion occurs or before removal becomes very expensive.

Environmental constraints on early establishment of Phragmites Australis in salt marshes

Finding environmental constraints on the establishment in salt marshes of Phragmites australis may help elucidate human activities that facilitated its invasion. We tested the effects of rhizome burial, salinity, anoxia, and sulfides on emergence, survival, growth, biomass production, and spread. In greenhouse and field experiments, rhizome burial facilitated initial emergence in well-drained soils. Rhizome emergence was prohibited in poorly drained treatments, regardless of salinity or sulfide concentrations. Emergence in well-drained treatments was not affected by salinity or sulfides, but survival, growth, and biomass storage of the culms and rhizomes were diminished in salt treatments. Combined with other studies, these results indicate that Phragmites invasion is a multi-stage process, with emergence constrained by poor drainage and survival constrained by lack of burial opportunities and salinity. These conditions constrain early stages of the invasion only, as later stages of the invasion can spread into anoxic and high salinity areas. These results also suggest that the process of invasion is facilitated by different human activities at different stages. Emergence is facilitated by soil disturbance, rhizome burial, and altered drainage. Survival through the first season can be facilitated through activities that lower porewater salinity.

Characterization of polymorphic microsatellites for the invasive grass Microstegium vimineum (Poaceae).

PREMISE OF THE STUDY Microsatellite markers were developed for the invasive plant Microstegium vimineum (Poaceae) to assess its population structure and to facilitate tracking of invasion expansion. METHODS AND RESULTS Using 454 sequencing, 11 polymorphic and six monomorphic microsatellite primer sets were developed for M. vimineum. The primer sets were tested on individuals sampled from six populations in the United States and China. The polymorphic primers amplified di-, tri-, and tetranucleotide repeats with three to 10 alleles per locus. CONCLUSIONS These markers will be useful for a variety of applications including tracking of invasion dynamics and population genetics studies.

Genetic Variation of Spartina alterniflora in the New York Metropolitan Area and Its Relevance for Marsh Restoration

We examined the genetic population structure of Spartina alterniflora in Jamaica Bay, Queens, NY and the surrounding area in order to assist the ongoing restoration of Jamaica Bay. AMOVA (Analysis of Molecular Variance) indicated that population differences accounted for 15% of molecular variance (ΦPT = 0.15, p = 0.001). Observed heterozygosity (Ho) ranged from 0.61 to 0.73 among populations. A Mantel test indicated a weak and non-significant correlation between pairwise ΦPT and geographic distance matrices (r = 0.34, p = 0.12). A PCA revealed no obvious grouping pattern for sampled populations. Based on these data, we determined that the studied populations contained similar genetic variability to other populations in the New York vicinity and to those of the entire region. It seems likely that collection of germplasm from within the region will prove sufficient in maintaining overall genetic variation in restoration plantings. Given the small amount of genetic structure among populations within Jamaica Bay, however, it would be prudent to collect widely within the target marsh. We also recommend the practice of propagating plugs of S. alterniflora from wild seed, as opposed to using vegetative cuttings, when creating planting stock, in order to maximize genetic diversity in restored marshes.