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Multi-Resolution Land Characterization 2001 (MRLC 2001) is a second-generation Federal consortium designed to create an updated pool of nation-wide Landsat 5 and 7 imagery and derive a second-generation National Land Cover Database (NLCD 2001 IntroductionConsistent, relevant land cover information at a national scale provides data for a wide variety of geographical analysis and applications. In the last decade, a major provider of land cover information within the Federal government has been the Multi-Resolution Land Characteristics Consortium (MRLC). The MRLC was originally formed in 1993, to meet the needs of several Federal agencies (U.S. Geological Survey (USGS), Environmental Protection Agency (EPA), National Oceanic and Atmospheric Administration (NOAA), and U.S. Forest Service (USFS)) for Landsat 5 imagery and land cover information (Loveland and Shaw 1996). One of the products of this consortium was the completion of a successful mapping of the conterminous United States into the National Land Cover Dataset (NLCD 1992) (NLCD 2001), which is being generated across all 50 States and Puerto Rico using Landsat imagery and ancillary data.The completion of the initial NLCD 1992 (Vogelmann et al., 2001A) created a TM pixel scale (30 m) data layer over the conterminous United States with approximately nine billion pixels. During the five years of mapping required to complete this prototype product, many lessons were learned about quality of source data, objectivity of methods, and flexibility of products. This feedback, coupled with new MRLC 2001 member requirements, provided the guiding principles and research direction that culminated in the NLCD 2001 design. Principles included: (a) develop land cover products flexible enough for multiple users, (b) provide users with increased access to intermediate database products and derivatives, enabling local application, (c) develop methods that are as objective, consistent, and repeatable as possible, resulting in standardized land cover products that can be quickly updated, (d) constrain methods to those that are intuitive, simple, efficient, and transferable to others, and (e) ensure that the design of a second-generation land cover product maintains reasonable compatibility with NLCD 1992.The NLCD 2001 foundation is a database approach to land cover (defined as multiple interlinked data layers that are useful either as individual components or in synergistic groupings) which builds upon past USGS database designs such as the global land cover database (Brown et al., 1999, Loveland et al., 2001, while providing the land cover data necessary to meet the vision of the The National Map (USGS 2001) currently being created by the USGS for the United States. PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING July 2004829 SAIC Corporation, USGS/EROS Data Center, Sioux Falls, SD 57198 (homer@usgs.gov).

In situ decomposition of above and belowground plant biomass of the native grass species Andropogon glomeratus (Walt.) B.S.P. and exotic Imperata cylindrica (L.) Beauv. (cogongrass) was investigated using litter bags over the course of a 12 month period. The above and belowground biomass of the invasive I. cylindrica always decomposed faster than that of the native A. glomeratus. Also, belowground biomass of both species decomposed at a consistently faster rate when placed within an invaded area consisting of a monotypic stand of I. cylindrica as opposed to within a native plant assemblage. However, there was no similar such trend observed in the aboveground plant material. The microbial communities associated with the invaded sites often differed from those found in the native vegetation and provide a possible causal mechanism by which to explain the observed differences in decomposition rates. The microbial communities differed not only compositionally, as indicated by ordination analyses, but also functionally with respect to enzymatic activity essential to the decomposition process. This study supports the growing consensus that invasive plant species alter normal ecological processes and highlights a possible mechanism (alteration of microbial assemblages) by which I. cylindrica may alter an ecosystem process (decomposition).

Cogongrass ( Imperata cylindrica (L.) Beauv.), an invasive C4 perennial grass, negatively influences native plant communities by forming dense monotypic stands that alter ecosystem properties and lower local species diversity. A hypothesized mechanism by which cogongrass achieves competitive dominance is a novel use of below-ground vegetative disturbance of neighboring vegetation (i.e. puncturing). However, very little empirical evidence is found in the peer-reviewed literature to quantify this phenomenon, much less establish it as a true form of competitive interaction. The present field study was conducted to quantify the occurrence of rhizome-mediated, below-ground vegetative penetration, both interspecifically and intraspecifically, document how this phenomenon is influenced by spatial location relative to the cogongrass stand, and determine the role that above-ground and below-ground biomass might have in the process. Analyses of 100 sod samples indicated that rhizome-mediated, below-ground vegetative penetration is a much larger intraspecific phenomenon than an interspecific one. The data also strongly suggested spatial location as a significant factor, with most penetrations occurring in the interior of a cogongrass stand as opposed to the advancing border. Significant correlations between rhizome-mediated, below-ground vegetative penetration and above-ground cogongrass biomass were found in the overall plot analysis and most strongly in the advancing border of the cogongrass stands.

Cogongrass is a highly invasive perennial grass that threatens agriculture, forestry, and native plant assemblages in many regions of the world. Cogongrass is a prolific seed producer, but the ecological importance of seeds as a vector of invasion has not been adequately addressed. Propagule pressure plays a key role in many successful invasions and the relative importance of propagule pressure across environmental gradients is an area of research that is quickly becoming important in understanding invasion success. The present study was conducted to test the effects of varying propagule density upon the ability of cogongrass seedlings to grow and establish across experimentally manipulated light and soil gradients. Seedlings growing in high-nutrient soil performed the best regardless of the amount of available light, but overall biomass was always greatest in high-light environments. Cogongrass showed a very strong trend in biomass allocation, with seedlings in reduced light environments partitioning more biomass to aboveground tissue. The data provided no evidence that initial propagule density affected the growth and establishment of cogongrass seedlings, but growth and biomass production were positively correlated with final seedling density.