Publications

Original field data show that forest species richness and tree density in the West African Sahel declined in the last half of the 20th century. Average forest species richness of areas of 4 km2 in Northwest Senegal fell from 64 ?? 2 species ca 1945 to 43 ?? 2 species in 1993, a decrease significant at p 0.001. Densities of trees of height ???3 m declined from 10 ?? 0.3 trees ha-1 in...

Mosses and lichens are important components of boreal landscapes [Vitt et al., 1994; Bubier et al., 1997]. They affect plant productivity and belowground carbon sequestration and alter the surface runoff and energy balance. We report the use of multiresolution satellite data to map moss and lichens over the BOREAS region at a 10 m, 30 m, and 1 km scales. Our moss and lichen...

The overarching goal of this project is to build a spatially distributed infrastructure for information science research by forming a team of information science researchers and providing them with similar hardware and software tools to perform collaborative research. Four geographically distributed Centers of the U.S. Geological Survey (USGS) are developing their own clusters of low...

Tampa Bay and its environs have experienced phenomenal urban growth and significant changes in land cover and land-use practices over the past 50 years. This trend is expected to continue, with the impact of human activity broadening geographically and intensifying throughout the region. One of the immediate impacts of urban growth is the creation of additional impervious surfaces, which...

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There are a number data set development, data dissemination, and applications activities at the U.S. Geological Survey (USGS) that contribute to the study of the water cycle in Africa. Some of these stem from global change research initiatives, while others are the result of technical assistance provided to international development and humanitarian assistance projects. Data themes...

Many digital elevation models (DEM) produced by the U.S. Geological Survey suffer from the presence of striping artifacts, which limit their utility. The most common approaches to filtering the affected DEMs rely on simple low-pass filters that blur fine details. A new filtering algorithm has been developed that isolates the stripes by applying a low-pass filter along the axis of the...

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Nitrous oxide (N2O) and nitric oxide (NO) are important atmospheric trace gases participating in the regulation of global climate and environment. Predictive models on the emissions of N2O and NO emissions from soil into the atmosphere are required. We modified the CENTURY model (Soil Sci. Soc. Am. J., 51 (1987) 1173) to simulate the emissions of N2O and NO from tropical primary forests...

Two experiments were conducted outdoors to investigate how bottom brightness impacts the spectral response of a water column under varied suspended sediment concentrations. A white aluminum panel placed at the bottom of the tank was used as the bright bottom, and a flat-black tank liner served as the dark bottom. Sixteen levels of suspended sediment from 25 to 400 mg litre -1 were used...