Leaf area index (LAI) is an extremely important structural characteristic of vegetation because it is directly related to the exchange of energy, CO
2 and mass from plant canopies at a variety of ...scales. Research investigating the relationship between forest LAI and satellite data for hardwood and mixed conifer-hardwood forests is lacking, however. The objective of this study was to explore the utility of Landsat-5 Thematic Mapper (TM) data for accurately estimating the LAI of conifer, hardwood, and mixed conifer-hardwood forests in north central Wisconsin. Individual bands and vegetation indices (VIs) calculated from satellite measures of exoatmospheric reflectance were related to the litterfall-estimated LAI of 24 stands. The results showed that individual bands or VIs containing at least one infrared (IR) band (either near- or mid-infrared) or a strong IR component divided data into at least two groups, with each group requiring a different regression line. The primary division was between conifer-dominated and hardwood-doin inated stands. Of the individual bands and VI.s considered, seven were strongly correlated to the LAI of conifer stands (
r
2
=0.69–0.73). For the hardwoods, the best individual band or VI was Green/mid-IR#1 (
r
2
=0.35), although an additional individual band and two VIs did much better using re subset of lower LAI stands (
r
2=0.60–0.75). For individual bands and VIs not requiring a conifer-hardwood distinction, the sixth Tasseled Cap component was most closely related to LAI (
r
2
=0.60). Multiple-variable models (using LAI as the dependent variable) were found to offer substantial improvement over single-variable models, especially for hardwood stands. We recommend for further consideration a four-variable model for the conifers, and one four-variable and two eight-variable models for the hardwoods.
Remotely sensed ice breakup dates for 62 lakes on the Laurentian Shield were analyzed to preliminarily assess determinants of the mean breakup date and to identify determinants of temporal coherence ...of lake-ice breakup. Correlations beteween mean breakup date and the explanatory variables (surface area, maximum depth, surface area: maximum depth ratio, latitude, longitude, and elevation) revealed that only latitude (r=0.96) and surface area (r=0.45) were significant at P ≤ 0.05. Latitude and surface area were significantly correlated (r=0.42). The temporal coherence of breakup dates between each pair of lakes was calculated by taking the product-moment correlation between their 8-yr time series (1987-1994) of breakup dates. There is a general lack of strong temporal coherence between lakes, implying that no lake in this study area is representative of the entire region. The significant (P ≤ 0.05) correlates of the temporal coherence of breakup dates were difference in mean breakup date (-0.49) and difference in latitude (\gamma= -0.51), themselves significantly correlated (\gamma=0.89). The differences in surface area, maximum depth, surface area: maximum depth ratio, longitude, and elevation were not significant. The general lack of strong temporal coherence between lakes and the significant correlation between coherence and mean breakup date are further confirmation that breakup dates for different lakes may be reflections or (and indicators for) different periods of meteorological forcing.
Landsat Thematic Mapper (TM) data were the basis in production of a statewide land cover data set for Wisconsin, undertaken in partnership with U.S. Geological Survey's (USGS) Gap Analysis Program ...(GAP). The data set contained seven classes comparable to Anderson Level I and 24 classes comparable to Anderson Level II/III. Twelve scenes of dual-date TM data were processed with methods that included principal components analysis, stratification into spectrally consistent units, separate classification of upland, wetland, and urban areas, and a hybrid supervised/unsupervised classification called “guided clustering.” The final data had overall accuracies of 94% for Anderson Level I upland classes, 77% for Level II/III upland classes, and 84% for Level II/III wetland classes. Classification accuracies for deciduous and coniferous forest were 95% and 93%, respectively, and forest species' overall accuracies ranged from 70% to 84%. Limited availability of acceptable imagery necessitated use of an early May date in a majority of scene pairs, perhaps contributing to lower accuracy for upland deciduous forest species. The mixed deciduous/coniferous forest class had the lowest accuracy, most likely due to distinctly classifying a purely mixed class. Mixed forest signatures containing oak were often confused with pure oak. Guided clustering was seen as an efficient classification method, especially at the tree species level, although its success relied in part on image dates, accurate ground truth, and some analyst intervention.
Landsat thematic mapper (TM) and enhanced thematic mapper plus (ETM+) images are being used to map lake water clarity region-wide in the Upper Midwest states of Minnesota, Wisconsin, and Michigan ...using a standardized image processing protocol. In Wisconsin, lake clarity estimates have been produced for 8645 lakes in the 1999-2001 time period. In addition to satellite imagery, the protocol relies on Secchi disk data collected by a network of citizen volunteers for development and validation of models. The most significant term in the regression model relating the satellite imagery to the field data is the ratio of spectral radiance values in the blue and red bands (ratio of Landsat band 1 to Landsat band 3). The resulting database of satellite-derived lake water clarity estimates represents an important new resource for lake managers in the region, and for those studying the linkages between lakes and their surrounding landscapes.
Landscapes result from the interaction between nature and society. To understand current landscapes, it is essential to disentangle this interaction; to accomplish this, an historical approach is ...necessary. Here we focus on the interaction between humans and lakes during the last century in two sites in Wisconsin, USA, a state where lakes, in excess of 10,000, have played an important role in the evolution of the landscapes they belong to. We draw contrasts between the two localities, which are set in landscapes that differ in their physiographic setting, environmental history, and current structure. One, in northern Wisconsin, is a forested recreational lake district; the other, in southern Wisconsin, is dominated by agricultural uses and urban and suburban development. We contend that a common development in both localities has been the increase in the value that society attaches to lakes. As a consequence, lakes are playing a bigger role in the evolution of the terrestrial landscapes surrounding them.
The existence of large-scale spatial and temporal trends in Wisconsin's lake water clarity is a topic that has not been thoroughly investigated. This study is an effort to reliably detect these ...trends by utilizing three inventories of satellite-derived lake water clarity predictions for over 2,000 lakes statewide. The data were analyzed statistically on a statewide, regional, lake type, and lake area basis. Statistically significant trends in clarity were found for the state overall, as well as for particular U.S. Environmental Protection Agency Ecoregions, Wisconsin Department of Natural Resources hydrologic lake types, and lake area categories. Results will aid in the establishment of a statewide lake water clarity database and demonstrate the effectiveness of satellite-based assessments in detecting trends in water transparency over the past three decades and into the future. Documenting such trends is essential to targeting and evaluating lake management practices as well as raising public awareness of lake clarity conditions throughout the state.
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