Kelly L. Lucas

Remotely Sensed Spectral Heterogeneity As a Proxy of Species Diversity: Recent Advances and Open Challenges

Abstract Environmental heterogeneity is considered to be one of the main factors associated with biodiversity given that areas with highly heterogeneous environments can host more species due to their higher number of available niches. In this view, spatial variability extracted from remotely sensed images has been used as a proxy of species diversity, as these data provide an inexpensive means of deriving environmental information for large areas in a consistent and regular manner. The aim of this review is to provide an overview of the state of the art in the use of spectral heterogeneity for estimating species diversity. We will examine a number of issues related to this theme, dealing with: i) the main sensors used for biodiversity monitoring, ii) scale matching problems between remotely sensed and field diversity data, iii) spectral heterogeneity measurement techniques, iv) types of species taxonomic diversity measures and how they influence the relationship between spectral and species diversity, v) spectral versus genetic diversity, and vi) modeling procedures for relating spectral and species diversity. Our review suggests that remotely sensed spectral heterogeneity information provides a crucial baseline for rapid estimation or prediction of biodiversity attributes and hotspots in space and time.

Remote Sensing and Mapping of Tamarisk along the Colorado River, USA: A Comparative Use of Summer-Acquired Hyperion, Thematic Mapper and QuickBird Data

Tamarisk (Tamarix spp., saltcedar) is a well-known invasive phreatophyte introduced from Asia to North America in the 1800s. This report compares the efficacy of Landsat 5 Thematic Mapper (TM5), QuickBird (QB) and EO-1 Hyperion data in discriminating tamarisk populations near De Beque, Colorado, USA. As a result of highly correlated reflectance among the spectral bands provided by each sensor, relatively standard image analysis methods were employed. Multispectral data at high spatial resolution (QB, 2.5 m Ground Spatial Distance or GSD) proved more effective in tamarisk delineation than either multispectral (TM5) or hyperspectral (Hyperion) data at moderate spatial resolution (30 m GSD).

Barrier Islands: Coupling Anthropogenic Stability with Ecological Sustainability

Abstract Barrier islands provide a host of critical ecosystem services to heavily populated coastal regions of the world, yet they are quite vulnerable to ongoing sea level rise and a potential increase in the frequency and intensity of oceanic storms. These islands are being degraded at an alarming rate, in part because of anthropogenic attempts at stabilization. In this article, we outline a possible sustainability strategy that incorporates the natural degree of substrate instability on these sedimentary landscapes. We recommend placing the focus for managing barrier islands on maintaining ecosystem function and process development rather than emphasizing barrier islands as structural impediments to wave and storm energy.

Decadal Changes in Habitat-Type Coverage on Horn Island, Mississippi, U.S.A.

Abstract Barrier island geomorphic features change over relatively brief timescales in response to the combined effects of wind, waves, currents, sediment supply, coastal subsidence, sea-level rise, and tropical cyclones. Consequently, alterations in the vegetation composition occur with these physiographic changes. A greater understanding of the extent to which such changes have occurred in recent decades may indicate the likely response of barrier islands to the currently anticipated acceleration in sea-level rise and increase in tropical storm frequency and severity under a climate-warming scenario. Using ground data in conjunction with hyperspectral, Light Detection and Ranging (LIDAR), and historical data, this study classified and mapped vegetation on Horn Island, Mississippi, and compared the island land area and habitat-type distribution in 2004 vs. 1978. Total vegetation cover as a percentage of total land area remained virtually unchanged during the 1978–2004 period. However, the relative coverage of wetland habitat types increased, whereas coverage of drier habitat types declined from 1978 to 2004, suggesting an overall modification of island communities in response to relative sea-level rise, storm events, and reduced sediment availability. A noticeable portion of the loss of drier woodland and stable dune habitats was a consequence of changes in land area and elevation on the eastern end of the island.

Historical changes in seagrass coverage on the Mississippi barrier islands, northern Gulf of Mexico, determined from vertical aerial imagery (1940–2007)

Vertical aerial image data were used with an edge-detection procedure and visual image interpretation to determine yearly to decadal changes in seagrass (predominantly Halodule wrightii Ascherson) coverage on the Mississippi barrier islands. On Horn Island, seagrass coverage declined from 77 ha in 1940 to 19 ha in 1971, but returned to its 1940 value by 2006. Coverage on Petit Bois declined from 54 ha in 1940 to 8–19 ha from 1952 through 2007. On East Ship, seagrass coverage varied at 2–19 ha from 1963 to 2007. On West Ship, coverage dropped to zero in 2003, but by 2007 it had increased to approximate its 1975 value of 1.8 ha. On Cat Island, coverage increased from 22 ha in 2003 to 71 ha in 2007. There was no apparent negative impact of Hurricane Camille or Hurricane Katrina on seagrass coverage, which could vary annually by a factor of two or more.

Estimating vascular plant species richness on Horn Island, Mississippi using small-footprint airborne LIDAR

Most remote sensing studies of species diversity have been based on the use of passive imagery representing the horizontal dimensions of ecosystems. However, LIDAR (light detection and ranging), provides a means to accurately quantify vertical structure. The goal of this study was to evaluate vascular plant species richness on a coastal barrier island using indicators of community vertical structure derived from airborne, multiple-return LIDAR data. Returns from a 3 m buffer area surrounding each of 90, 15 m vegetation line transects were extracted from LIDAR data of Horn Island, Mississippi, acquired in April, 2004. LIDAR indices did not correlate with richness when data for all habitats were combined. When habitats were considered separately, several LIDAR indices correlated significantly (p ⩽ 0.05) with richness in marsh, meadow and woodland habitats. Best-fit indices indicated the importance of vegetation height and structural complexity in estimating plant species richness.

Effects of Annual Droughts on Fish Communities in Mississippi Sound Estuaries

The Mississippi coastal region has two major rivers and four smaller rivers influencing the estuaries that make up the Mississippi Sound. The islands off Mississippi create a barrier which allows the area to be a widespread, productive estuarine region. With such a dependence on discharge from the drainages, it is important to understand the effect of salinity regimes on fish communities. Drought conditions in other regions have been shown to dramatically change the fish community structure. We used the long running Interjurisdictional Fisheries Program database (2006–2014) within Mississippi state waters and compared yearly fish communities between drought and non-drought years. Non-metric Multidimensional Scaling (nMDS), Analysis of Similarity (ANOSIM), and Indicator Species Analysis (ISA) were used to compare drought and non-drought conditions in the Mississippi Sound. During 2006 and 2007, which were identified as drought years by the Palmer Drought Severity Index (PDSI), differences in fish community structure were identified and compared to non-drought years (2008–2009 and 2011–2014). The ISA identified a total of eight species that were significantly influenced by drought years. Of the eight species, the abundance of seven species significantly decreased while the abundance of one species significantly increased. With an increasing human population in central and south Mississippi, pressure on freshwater resources is likely to increase, resulting in possible changes in the fish community dynamics of the Mississippi Sound. Understanding the influence of decreased river discharges will assist managers in determining the impacts of freshwater withdrawals during base flow periods.