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Earth Sci. There is a rich historical aerial photographic record of the USGP which provides an unparalleled view of past landscapes and allows for evaluation of surficial response to drought beyond the satellite record, such as during the s Dust Bowl Drought DBD.
This study classified the extent and loci of surficial denudation from seamless mosaics of radiometrically corrected and georectified digitized aerial negatives acquired in the late s from six counties distributed across USGP ecoregions. The dominant sources of degradation found for sites east of the th meridian are cultivated fields and fluvial deposits, associated with woody vegetation response to water availability in uncultivated areas.
For sites to the west, denuded surfaces are predominantly eolian sandsheets and dunes, correlated with intensity of drought conditions and reduced plant diversity.
Discrete spatial signatures of the drought are observed not only within the classically recognized southern Dust Bowl area, but also in the northern and central plains. Statistical analyses of site variability suggest landscape response to the DBD is most strongly influenced by the arid—humid divide and severity of precipitation and temperature anomalies.
With a projected increase 21st century aridity, eolian processes cascading across western grasslands, like during the Dust Bowl, may significantly impact future dust particle emission and land and carbon storage management. However, grassland response to extreme drought is highly variable over space and time and remains a significant factor for adaptable land and carbon management during forecasted 21st century aridity Basara et al.
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Carbon flux is sensitive to precipitation on daily-to-seasonal timescales because shifting water availability, with associated plant physiological response and biomass changes, impact the fixation of carbon Sims and Bradford, ; Petrie et al. Disturbance-induced plant loss can amplify aridity Cook et al. The Dust Bowl of the s is a vivid example of such cascading landscape degradation and offers insight into potential land surface response, and dust sources during severe droughts, projected for the future across the Great Plains.
There exists a large archive of pre-satellite panchromatic aerial photography for the conterminous United States that provides an unparalleled network of images for historical landscapes coincident with large-scale human modification characteristic of the 20th century Redweik et al.
The USGP has a particularly rich photographic record beginning in the s, when the United States Department of Agriculture was tasked with reducing acreage under cultivation to stabilize crop prices during the Great Depression Leedy, ; Rango et al.
The resulting record, completed from to , covers approximately 7,, km2, or Recently a new historical image product was created from this record by applying advances in remote sensing and geospatial techniques to digital reproductions of original reel film Bolles et al.
Previous studies using early aerial photographs are typically focused on changes in the distribution and cover of vegetation cf. Carmel and Kadmon, ; Laliberte et al. However, heterogeneity is a significant concept in landscape ecology linked to ecosystem functioning, defined as the degree of spatial variability of a particular property within a scale-dependent system Turner, ; Wiens, ; Li and Reynolds, ; Pickett and Cadenasso, ; Morgan and Gergel, Heterogeneity of bare soil surfaces is an indicator of landscape sensitivity to aridity, with increased patchiness frequently correlated with degradation Schlesinger et al.
Patch size, condition, and landscape context are significant factors in determining ecosystem resistance and resilience to climatic perturbations Samson et al. Utilizing semi-automated image analysis techniques, these metrics can be quantified for historic landscapes to examine biotic and abiotic controls on land cover changes Browning et al. The resultant image products offer extended spatial scales to paleoarchives such as lake cores, stratigraphic sections, and tree-rings, and elucidate the interplay between climate, geomorphology, vegetation, and land use e.
There are well developed standards for manual interpretation of individual or stereoscopic pairs of aerial photographs with traditional photogrammetry.
However, methods are emerging for semi-automated radiometric and spatial homogenization and structure-from-motion SfM photogrammetry for large numbers of archival black and white photographs e.
Raw panchromatic aerial photographs are produced via black and white emulsions, where color is related to relative brightness of the visible light spectrum reflected from the surface Caylor, When digitized, photographs are displayed as a single-band, gray-scale image, wherein each pixel is assigned a digital number DN that is proportional to the brightness of that pixel. Surface brightness is potentially altered by several parameters, not limited to viewing angle, azimuth and intensity of radiation source, sample geometry i.
Therefore, surface roughness is an important determinant of the range of spectra expressed in aerial imagery Ben-Dor, ; Zhang et al.
The principal characteristics available for feature identification in panchromatic imagery are variation and relative differences in tone Morgan et al.
Classification of tonal variation assigns individual pixels a label based on a specific property Gennaretti et al. Relative differences in tone, also referred to as image texture, are determined by the spatial relationships between pixels within a defined area and directionality Morgan and Gergel, , ; Morgan et al.
Quantification of image texture can account for tonal heterogeneity and thereby, surface roughness Morgan and Gergel, , and is particularly useful for landform and land use classification where radiometric properties are being classified Morgan et al.
A significant assumption of this approach is that separate classes are represented by discrete differences between gray scale values and that these classes are spectrally independent Anderson and Cobb, Where vegetation cover is only partial, a mixed signal from soil and vegetation occurs, making extrication of overlapping soil—vegetation signals complex Ben-Dor, , but this can be addressed via geographic object-based image analysis GEOBIA; Morgan and Gergel, , ; Blaschke et al.
Herein, we present methods to analyze pre panchromatic aerial photographs along climatic gradients of USGP grasslands and evaluate landscape response to the s Dust Bowl Drought DBD. Specifically, we 1 identify representative study sites across various ecoregions of the USGP, 2 incorporate spectral, texture and object-based parameters to classify photo-mosaics and verify surface types of historic landscapes, and 3 quantify surficial heterogeneity and evaluate potential drivers of landscape response to drought.
This research will examine the indicators and extent of landscape sensitivity to precipitation variability prior to widespread irrigation of the USGP and address controls on ecosystem degradation during severe drought years in the DBD.
The latitudinal zonation of northern to southern ecoregions generally follows temperature trends Figure 2A ; the short-to-tall grass prairie transition parallels the strong west-to-east MAP gradient Figures 2B,C.
This gradient shifted about km eastward between and compared the prior MAP between and , encompassing the largest extent of previously recognized severe wind erosion during the DBD Figure 2D. Drought and land use directly impact grassland functioning via an increased risk of degradation, desertification, and subsequent reduction in stability and productivity, such as that observed during the DBD Cook et al.
However, the DBD was not a homogeneous event in time or space but consisted of several droughts and relative wet phases affecting different regions at different times Figure 3 Laird et al. Climate modeling studies of the DBD have found that land cover changes increased the intensity and altered the spatial footprint of drought across the USGP cf.
Cook et al. Reduced vegetation cover allows for enhanced wind erosion of soils, burying of adjacent grasses by the accumulation of eolian sediment and an increase in overland flow and riling from episodic and extreme rainfall events Schlesinger et al.
The subsequent recovery of plant communities may be delayed a decade or more, even with 5 years of precipitation above the historical average, as observed after the DBD Weaver and Albertson, , pp.
Ecological studies in the 20th century indicated that the diversity of grassland species decreased with drought, excessive grazing, and range fire Albertson and Weaver, ; Tilman and Downing, ; Collins et al.
In semi-arid regions such as the USGP, there are also apparent responses in eolian and fluvial geomorphic systems to extreme precipitation variability Ewing et al. The pattern of stabilized dunes is often linked to bioclimatic variations. Wetter spring and summer conditions and heavy winter snowfall provide excess moisture for eolian systems to stabilize more effectively, with colonization by climax vegetation assemblages Cordova et al.
Drier conditions are often correlated with decreased vegetation coverage and increased eolian activity, such as during the Medieval Climate Anomaly MCA when multiple, multi-decadal droughts propagated across the Americas with numerous presently stabilized eolian sand systems apparently reactivated, but to an unknown spatial extent e. Many periods of eolian reactivation exhibit discontinuous blow-outs, parabolic dunes and sandsheet accretion, often leaving a spatially heterogeneous landform assemblage Schlesinger et al.
Materials and Methods A standardized workflow Figure 4 was developed to select, process, analyze, and archive aerial photographs captured between AD and from counties across the USGP based on previously defined iterative analyses Okeke and Karnieli, ; Redweik et al. In brief, photogrammetric scans of original reel film are corrected for interior and exterior distortions of position and light exposure.
Surface properties are retrospectively verified using historical primary documentation, contemporary field surveys, and digital surface models DSMs derived with SfM photogrammetry, allowing for assessment of uncertainty of manual and automated classifications.
Spectral analysis of individual pixels, texture analysis of multiple pixels within a sliding window i.
Image and verified data are combined to classify objects based on surficial properties, including soil texture, land cover, land use, and geomorphic form, and classification results are statistically analyzed. Outline of semi-automated analysis of historical panchromatic aerial photographs used in this study with illustrative example: A diagrammatic workflow of methods used, B raw scan of original negative reel film of frame CCT from Syracuse, Hamilton County, KS taken March 22, , C oriented, radiometrically corrected, and resampled image, D digital surface model DSM generated from multi-view stereoscopy, E results of unsupervised spectral classification of pixel digital numbers DN with box and whisker plot of cluster distribution, where the gray-scale color of the box in the plot corresponds to the mean DN of the cluster; refer to Table 4 for legend description, F results of principal component analysis of image texture layers to delineate image objects, G soil surface texture gathered from the Web Soil Survey Soil Survey Staff [SSS] et al.
Study Site Identification and Photograph Reproduction A multi-criterion, spatially explicit weighted overlay is employed to identify USGP counties that are representative of the broader landscape for the time and place of negative acquisition and to minimize subjectivity in site selection Table 1.
We include three climatic parameters to estimate the magnitude of anomalies in each county between and , with larger deficits given greater weight: percent change in maximum MAT and MAP relative to the preceding year period — , and the central tendency of evapotranspiration as expressed by the mid-range Palmer Drought Severity Index PDSIMR; Figures 5A—C.
These criteria are standardized to a scale of 1—9 and given equal influence in an overlay to assign each county a final rating that reflects the intensity of drought conditions and similitude of surficial properties to the broader ecoregion Figure 5G.
A fishnet of 1, km2 cells is created across counties within USGP ecoregions, and a random sample of cells distributed across the precipitation and temperature gradients is selected for acquisition of aerial photographs.
Criteria included in the weighted overlay for site identification with Figure 5.
Layers included in the multi-criterion site selection scheme, including climatic factors A—C and surficial properties aggregated at the county-level D—F : A percent change in mean annual maximum temperature MATMAX during — in comparison to preceding year period — , B percent change in mean annual precipitation MAP during — in comparison to preceding year period, C mid-range Palmer Drought Severity Index PDSIMR during —, D average percent sand, silt, and clay content of soil, E average drainage density DD expressed as a ratio of total length of linear water features to county area, and F the percent of acreage under cultivation at the peak of agricultural expansion in Development of new magneic resonance acquisition concepts for magnetization transfer and oscillating steady state imaging.
Scheffler , Ph. Cattin Franz Pfeiffer. High-resolution 3D imaging of the human brain post mortem. Becker, K. Scheffler, S. Terraz, Ph. Cattin, R. Salomir, K. Haller S. Clinical applications of real time functional magnetic resonance imaging rtfMRI biofeedback. Scheffler, C. Stippich, C. Beglingen, A. Computer aided and image guided medical interventions.
Cajochen, K. Cerebral mechanisms underlying the influence of age-related changes in circadian and homeostatic processes on cognition: a functional neuroimaging approach. Scheffler Advanced biochemical Magnetic Resonance Imaging on high and ultrahigh magnetic field strength 3 and 7 Tesla : Visualization of early degenerative cartilage disease in the knee joint by means of noncontrast glycosaminogylcan specific multi-parametric MR imaging.
Hennig, K. Korvink, S. Popovic, A. Jasinski, H. Support total EUR Henning, G.
Lohmann, K. Support total EUR 2.
Golay, G. Navon, S. Aime, K. Axesson, A. Mitulescu, S Grimm, G Crelier. Grant Support total: EUR 6. Mapping of neuronal currents be means of T1r-sensitive magnetic resonance imaging.
Lerche, Preissl, Scheffler.
Himmelbach, Ethofer, Hagberg. Position No K Cattapan-Ludewig, E. Seifritz Scheffler K. Bieri, S. Hofmann, H. Schmid, K.The result is a fully loaded touch PC that youll want to get your hands on.
Wetzel, P. The open-source, python-based GNU Image Manipulation Program GIMP is utilized to normalize the histogram of each frame individually, then to gamma-balance across frames so overlapping features are displayed along the same radiometric range Kadmon and Harari-Kremer, ; Murray et al. Much of the vegetation present are grasses on alluvial surfaces and sparse cover on sandsheets, with the densest vegetation along fluvial channels. Position No Where vegetation cover is only partial, a mixed signal from soil and vegetation occurs, making extrication of overlapping soil—vegetation signals complex Ben-Dor, , but this can be addressed via geographic object-based image analysis GEOBIA; Morgan and Gergel, , ; Blaschke et al.
For example, an unpaved road, eroding field, and migrating dune are clustered together given similarities in surficial brightness.