Louis R. Iverson

Modelling topographic potential for erosion and deposition using GIS

Modelling of erosion and deposition in complex terrain within a geographical information system (GIS) requires a high resolution digital elevation model (DEM), reliable estimation of topographic parameters, and formulation of erosion models adequate for digital representation of spatially distributed parameters. Regularized spline with tension was integrated within a GIS for computation of DEMs and topographic parameters from digitized contours or other point elevation data. For construction of flow lines and computation of upslope contributing areas an algorithm based on vector-grid approach was developed. The spatial distribution of areas with topographic potential for erosion or deposition was then modelled using the approach based on the unit stream power and directional derivatives of surface representing the sediment transport capacity. The methods presented are illustrated on study areas in central Illinois and the Yakima Ridge, Washington.

Land-use changes in Illinois, USA: The influence of landscape attributes on current and historic land use

The Illinois Geographic Information System was used to compare the soil and landscape attributes of the State with its historic vegetation, current land use, and patterns of land-use change over the past 160 years. Patch structural characteristics among land types in four geographic zones were also compared. The assessment of patch characteristics revealed a highly modified State with most land patches controlled by human influences and relatively few by topographic and hydrologic features. Correlation and regression analyses determined the relationships of land type and abundance within each of 50 general soil associations to properties of the soil associations - typically slope, texture, organic matter, productivity index, and available waterholding capacity. The distribution of the historic vegetation of the State and its current deciduous forests and nonforested wetlands related moderately (r2 ≥ 0.44) to various landscape attributes. Urban and other highly modified land types were less closely related.

Applications of satellite remote sensing to forested ecosystems

Since the launch of the first civilian earth-observing satellite in 1972, satellite remote sensing has provided increasingly sophisticated information on the structure and function of forested ecosystems. Forest classification and mapping, common uses of satellite data, have improved over the years as a result of more discriminating sensors, better classification algorithms, and the use of geographic information systems to incorporate additional spatially referenced data such as topography. Land-use change, including conversion of forests for urban or agricultural development, can now be detected and rates of change calculated by superimposing satellite images taken at different dates. Landscape ecological questions regarding landscape pattern and the variables controlling observed patterns can be addressed using satellite imagery as can forestry and ecological questions regarding spatial variations in physiological characteristics, productivity, successional patterns, forest structure, and forest decline.

Regional forest cover estimation via remote sensing: the calibration center concept

A method for combining Landsat Thematic Mapper (TM), Advanced Very High Resolution Radiometer (AVHRR) imagery, and other biogeographic data to estimate forest cover over large regions is applied and evaluated at two locations. In this method, TM data are used to classify a small area (calibration center) into forest/nonforest; the resulting forest cover map is then used in combination with AVHRR spectral data from the same area to develop an empirical relationship between percent forest cover and AVHRR pixel spectral signature; the resultant regression relationship between AVHRR band values and percent forest cover is then used to extrapolate forest cover for several hundred kilometers beyond the original TM calibration center. In the present study, the method was tested over two large regions in the eastern United States: areas centered on Illinois and on the Smoky Mountains on the North Carolina-Tennessee border. Estimates of percent forest cover for counties, after aggregating AVHRR pixel estimates within each county, were compared with independent ground-based estimates. County estimates were aggregated to derive estimates for states and regions. For the Illinois region, the overall correlation between county cover estimates was 0.89. Even better correlations (up to r = 0.96) resulted for the counties close to one another, in the same ecoregion, or in the same major land resource region as the calibration center. For the Smokies region, the correlations were significant but lower due to large influences of pine forests (suppressed spectral reflectance) in counties outside the hardwood-dominated calibration center. The method carries potential for estimating forest cover across the globe. It has special advantages in allowing the assessment of forest cover in highly fragmented landscapes, where individual AVHRR pixels (1 km2) are forested to varying degrees.

Processes and Lands for Sequestering Carbon in the Tropical Forest Landscape

Balancing the C budget in the tropics has been hindered by the assumption that those forests not undergoing deforestation are in C steady state with respect to their C pools and thus with the atmosphere. The long history of human activity in tropical forests suggests otherwise. In this paper we discuss the forest compartments into which C can be stored, what the likely rates of storage are and for how long, and over which areas of the tropical landscape these processes occur. Results of our analysis suggest that tropical forests have the potential to sequester up to 2.5 Pg C yr−1 from the atmosphere if human pressure could be completely removed. Addition of agroecosystems and degraded lands could increase this estimate markedly.

Estimating forest productivity with Thematic Mapper and biogeographical data

Abstract The usefulness of Landsat Thematic Mapper (TM) spectral data and biogeographical site characteristics for estimating forest productivity was investigated in three forest ecosystems in eastern North America — southern Illinois, the Great Smoky Mountains of Tennessee and North Carolina, and the central Adirondack Mountains of New York. TM data from the 1984 growing season were combined with ground-collected measures of forest productivity, along with additional biogepgraphic information, such as slope, aspect, elevation, and soil and vegetation types, in a geographical information system (GIS). Correlation, regression, and classification techniques were used to examine relationships of spectral and biogeographical variables to forest productivity. In general, the regression and classification models produced were highly significant (p

Analyzing long-term changes in vegetation with geographic information system and remotely sensed data

Abstract Geographic information systems and remote sensing techniques are powerful tools in the analysis of long-term changes in vegetation and land use, especially because spatial information from two or more time intervals can be compared more readily than by manual methods. A primary restriction is the paucity of data that has been digitized from earlier periods. The Illinois State Geographic Information System has a number of automated data sets containing land-use information, including original land survey plat maps that show the boundaries of forests, prairies, and wetlands as they existed prior to European colonization in the early 1800s. More recent data include the United States Forest Service inventories of 1948, 1962, and 1985; the United States Geological Survey Land Use Data Analysis; National High Altitude Program photographs of vegetation; and Landsat MSS and TM information. These data can be used to compare vegetation patterns and changes in land use over time and to suggest factors that may have caused or influenced these variations. Profound changes have occurred in the Illinois landscape since European settlement, primarily because of conversion to agricultural use; in certain parts of the state, however, urbanization has been the major factor contributing to changes.

Land-Use and Biomass Changes of Forests in Peninsular Malaysia from 1972 to 1982: A GIS Approach

Two maps depicting the forest resources of Peninsular Malaysia, one dated 1972 and the other 1982, were digitized into ARC/INFO for analysis of spatial and temporal trends. Estimates of 1972 and 1982 biomass density for each of 11 forest classes were also produced from inventory stand tables. These data allowed us to calculate changes in forest cover and biomass during the decade. Overall, forest area was reduced by 17%, and total biomass by 28%; however, this percentage varied among forest classes. For example, primary forest area declined by 23% while its biomass was reduced by 35%; disturbed forest area declined by 7% while its biomass was reduced by 19%. These data indicate that, in addition to loss of forest biomass because of changes in land use, biomass degradation was also occurring within the forests. Together, they represented a loss of 30 TgC/yr. Changes in perimeter area ratios were correlated with the degree of biomass degradation suggesting that the fragmentation of Malaysian forests, a process that increases their accessibility, was a cause of the degradation.