Ouachita Highlands Research Articles

Biodiversity of Parasitic Hymenoptera Across Sky Islands of Arkansas, United States.

Sky islands are often areas of endemism and high species diversity around the world. In central North America, the Ozark and Ouachita Highlands contain numerous modestly high elevational islands that are slightly cooler and wetter than surrounding lowlands and these areas are known to contain many unique species. We studied parasitic Hymenoptera biodiversity on three sky islands in Arkansas, both in canopy and understory strata of mature post oak forests. We found that morphospecies diversity was high, and community structure varied both within (canopy versus understory) and between sky islands. Each mountaintop showed a high level of distinctiveness with few morphospecies found in multiple locations. The high intersky island variation indicates that individual sky islands in the region harbor unique Hymenoptera assemblages, a pattern that likely extends to the broader insect community. Our study suggests that these highland areas are important regions of North American biodiversity and that they should be evaluated individually for conservation efforts in order to preserve their distinctive community structure.

Population Characteristics of the Etheostoma pallididorsum Distler and Metcalf (Paleback Darter), a Narrowly Distributed Endemic in the Ouachita Highlands, Arkansas

Etheostoma pallididorsum (Paleback Darter) is endemic to the headwater reaches of 2 river systems in the Ouachita Highlands of Arkansas. Records of low abundance and habitat alterations have resulted in the species' imperiled conservation status and being petitioned for federal listing under the Endangered Species Act. The objective of this study was to conduct seasonal surveys across the Paleback Darter's distribution to better characterize growth, spawning patterns, and mortality using the seasonal von Bertalanffy statistic with an optimized electronic length frequency analysis (ELEFAN), as well as assess sex ratios throughout a calendar year to better inform future conservation management decisions for the species. We established seasonal survey collection sites at 4 localities and sampled with a backpack electrofishing unit and dip nets from January 2016 to October 2017. The study indicated relatively high abundance, based on catch per unit effort (CPUE), across all sampled localities throughout the duration of the study, with representation of the entire population from 3 age classes: 0, 1, and 2. Growth and coarse spawning patterns, based on the seasonal von Bertalanffy statistic, were comparable between the populations, suggesting similar and stable environmental factors throughout the distribution. Lastly, there was evidence of multiple spawn events occurring during winter and late spring or early summer that has not been documented for this species, warranting additional research. Collectively, this study, though narrow in scope and with limited data, suggest that the Paleback Darter populations assessed are not impaired. The endemic status and narrowly fragmented distribution of the Paleback Darter, however, still renders this species vulnerable to extirpation or extinction by stochastic events.

Drivers of ecosystem vulnerability to Corbicula invasions in southeastern North America

Invasive species introduction is one of the major ongoing ecological global crises. Identifying factors responsible for the success of invasive species is key for the implementation of effective management actions. The invasive filter-feeding bivalve, Corbicula, is of particular interest because it has become ubiquitous in many river basins across North America and elsewhere. Here we sampled bivalve assemblages, environmental indicators, and land cover parameters in the Ouachita highlands in southeastern Oklahoma and southwestern Arkansas, and in the Gulf Coastal Plain of Alabama to test three working models (using structural equation modeling, SEM) based on a priori scientific knowledge regarding Corbicula invasions. Our models tested three competing hypotheses: (1) Native mussel declines are related to land use changes at the watershed level and subsequent Corbicula colonization is a result of an empty niche; (2) Corbicula abundance is one of the factors responsible for native mussel declines and has an interactive effect with land use change at the watershed level; (3) Native mussel declines and Corbicula success are both related to land use changes at the watershed level. We found no evidence for the first two hypotheses. However, we found that environmental indicators and land cover parameters at the watershed scale were robust predictors of Corbicula abundance. In particular, agricultural land cover was positively related with Corbicula density. These results suggest that further improvement of conventional agricultural practices including the optimization of fertilizer delivery systems may represent an opportunity to manage this species by limiting nutrient inputs to stream ecosystems. Preservation of extensive floodplain habitats may help buffer these inputs by providing key ecosystem services including sediment and nutrient retention.

Genome-wide SNPs redefines species boundaries and conservation units in the freshwater mussel genus Cyprogenia of North America

Detailed information on species delineation and population genetic structure is a prerequisite for designing effective restoration and conservation strategies for imperiled organisms. Phylogenomic and population genomic analyses based on genome-wide double digest restriction-site associated DNA sequencing (ddRAD-Seq) data has identified three allopatric lineages in the North American freshwater mussel genus Cyprogenia. Cyprogenia stegaria is restricted to the Eastern Highlands and displays little genetic structuring within this region. However, two allopatric lineages of C. aberti in the Ozark and Ouachita highlands exhibit substantial levels (mean uncorrected FST = 0.368) of genetic differentiation and each warrants recognition as a distinct evolutionary lineage. Lineages of Cyprogenia in the Ouachita and Ozark highlands are further subdivided reflecting structuring at the level of river systems. Species tree inference and species delimitation in a Bayesian framework using single nucleotide polymorphisms (SNP) data supported results from phylogenetic analyses, and supports three species of Cyprogenia over the currently recognized two species. A comparison of SNPs generated from both destructively and non-destructively collected samples revealed no significant difference in the SNP error rate, quality and amount of ddRAD sequence reads, indicating that nondestructive or trace samples can be effectively utilized to generate SNP data for organisms for which destructive sampling is not permitted.

Conservation genetic assessment of the paleback darter, Etheostoma pallididorsum, a narrowly distributed endemic in the Ouachita Highlands, Arkansas, USA

Abstract The paleback darter, Etheostoma pallididorsum, is considered imperilled and has recently been petitioned for listing under the Endangered Species Act. Previous allozyme‐based studies found evidence of a small effective population size, warranting conservation concern. The objective of this study was to assess the population dynamics and the phylogeographical history of the paleback darter, using a multilocus microsatellite approach and mitochondrial DNA. The predictions of this study were that: paleback darter populations will exhibit low genetic diversity and minimal gene flow; population structure will correspond to the river systems from which the samples are derived; reservoir dams impounding the reaches between the Caddo and Ouachita rivers would serve as effective barriers to gene flow; and the Caddo and Ouachita rivers are reciprocally monophyletic. Microsatellite DNA loci revealed significant structure among sampled localities (global Fst = 0.17, P < 0.001), with evidence of two distinct populations representing the Caddo and Ouachita rivers. However, Bayesian phylogeographical analyses resulted in three distinct clades: Caddo River, Ouachita River, and Mazarn Creek. Divergence from the most recent ancestor shared among the river drainages was estimated at 60 Kya. Population genetic diversity was relatively low (He = 0.65; mean alleles per locus, A = 6.26), but was comparable with the population genetic diversity found in the close relatives slackwater darter, Etheostoma boschungi (He = 0.65; A = 6.74), and Tuscumbia darter, Etheostoma tuscumbia (He = 0.57; A = 5.53). These results have conservation implications for paleback darter populations and can be informative for other headwater specialist species. Like other headwater species with population structuring and relatively low genetic diversity, the persistence of paleback darter populations is likely to be tied to the persistence and connectivity of local breeding and non‐breeding habitat. These results do not raise conservation concern for a population decline; however, the restricted distribution and endemic status of the species still renders paleback darter populations vulnerable to extirpation or extinction.

Spatiotemporal population dynamics of the Caddo Madtom (Noturus taylori), a narrow-range endemic of the Ouachita Highlands

The Caddo Madtom, Noturus taylori, is endemic to three river drainages of the Ouachita Highlands in the southeastern United States. Conservation concern for N. taylori has been heightened by recent studies based on analyses of allozyme data suggesting population decline and a possible extirpation event, which lead to N. taylori petitioned for listing under the Endangered Species Act in 2011. The objective of this study was to determine if contemporary factors, historic processes, or a combination of both, using microsatellite DNA loci and mitochondrial (mt) DNA, have influenced patterns of genetic structuring for N. taylori to better inform conservation management strategies. Phylogeographic and Bayesian cluster analyses suggest that genetic structuring between Caddo and Ouachita river drainages was shaped by historical processes prior to construction of reservoir dams that dissect the drainages. We found no evidence that reservoir dams influenced contemporary patterns of genetic structure, thus it is likely that larger river courses, and life-history characteristics conducive to headwater habitats, play important roles in limiting gene flow between drainages, and to some extent within drainages. Genetic diversity of N. taylori was relatively high compared to other endangered madtom species; however, compared to the Ouachita River population, genetic diversity was significantly lower for the Caddo River population. Collectively, these results suggest that N. taylori populations are not heavily impaired, and the genetic variation and structuring is most attributable to historic processes. However, the endemic status and narrowly fragmented distribution still renders N. taylori populations vulnerable to extirpation or extinction by stochastic events.

Habitat Assessment and Range Updates for Two Rare Arkansas Burrowing Crayfishes:Fallicambarus harpiandProcambarus reimeri

Abstract The Ouachita Highlands Freshwater Ecoregion harbors the 6th-highest native crayfish species density in the US and Canada. Many of these species are understudied, and the burrowing crayfishes of this region are of particular interest. We conducted field surveys in the spring of 2014 and 2015 to assess the range and habitat preferences of 2 of Arkansas' rarest burrowing crayfishes: Fallicambarus harpi (Ouachita Burrowing Crayfish) and Procambarus reimeri (Irons Fork Burrowing Crayfish). Both crayfishes are currently of conservation concern—F. harpi is vulnerable and P. reimeri is endangered according to the American Fisheries Society. Our surveys detected new populations of both species and documented marginal and wider range expansions for F. harpi and P. reimeri, respectively. The preferred habitat for both species was characterized as wet seepage areas with an open canopy, low grasses, and abundant sedges. Our surveys support prior observations that these species are geographically constrained; ...

A New Species of Darter from the Ouachita Highlands in Arkansas Related toPercina nasuta(Percidae: Etheostomatinae)

Percina brucethompsoni, the Ouachita Darter, is described as a new species endemic to the Ouachita River system in the Ouachita Highlands of Arkansas. Bruce Thompson first noted the distinctiveness of the new species from the nominal P. nasuta distributed in the White River and Arkansas River basins in his 1977 doctoral dissertation. The new species is delimited through morphological comparisons with P. nasuta and a phylogenetic analysis of the Percina subclade Swainia using two mitochondrial genes. More than 385 specimens were examined for the morphological comparisons, and 54 specimens were sampled for mitochondrial DNA sequencing. Percina brucethompsoni is distinguished from P. nasuta by a shorter snout, a broader and deeper head, six versus seven branchiostegal rays and specific patterns of lateral pigmentation on the side of the body. Phylogenetic analysis of DNA sequences sampled from two regions of the mitochondrial genome indicate that P. brucethompsoni is the sister species of P. nasuta populations in the White River drainage. Neither P. nasuta nor P. phoxocephala are monophyletic in the mitochondrial DNA gene tree. Specimens of P. phoxocephala from the Red River drainage are resolved as the sister lineage of a clade containing all other sampled populations of P. phoxocephala, P. brucethompsoni and P. nasuta. Percina nasuta and P. phoxocephala sampled from the Arkansas River drainage form a clade that is the sister lineage of a clade containing P. brucethompsoni and P. nasuta from the White River drainage.

Isolation and characterization of 10 polymorphic microsatellite markers for the Ouachita Highlands endemic Notropis suttkusi (Teleostei: Cyprinidae)

Human pressures primarily associated with urbanization, forestry practices, over-mining of groundwater, and reservoir construction threaten the exceptional aquatic endemism of the Ouachita Highlands of southeastern Oklahoma and southwestern Arkansas, USA. At present, there is a need for hypervariable markers useful for understanding population structure and historical demography, thereby helping to provide a framework for conservation efforts. In this paper we describe 10 microsatellite markers for Notropis suttkusi (rocky shiner), a species endemic to the Ouachita Highlands. We characterize these markers on 40 individuals from Blue River in Oklahoma. The loci yielded 3–23 alleles per locus, with mean observed and expected heterozygosites of 0.679 and 0.729, respectively. The availability of these markers will facilitate studies of the conservation genetics of N. suttkusi and should be useful for other members of the Notropis rubellus complex.

Contrasting phylogeographic histories between broadly sympatric topminnows in the Fundulus notatus species complex

Sympatrically distributed closely related species provide opportunities for studying evolutionary patterns of diversification. Such studies must account for historical contingencies in interpreting contemporary patterns of variation. Topminnows in the Fundulus notatus species complex are distributed sympatrically across much of the southern and Midwestern United States. Throughout most of their ranges F. olivaceus is often found in headwater stream habitats, and F. notatus is more typically distributed along the margins of larger river habitats. However, in some drainages, ecological associations of the respective species are reversed, with F. notatus populations isolated in headwater streams and F. olivaceus in downstream river habitats. Phylogeographic analyses of AFLP marker and multi-locus sequence data detected historical isolation in F. notatus consistent with pre-Pleistocene drainage patterns. Four F. notatus clades corresponded to (i) the Western Gulf Slope, (ii) the southwestern Ouachita Highlands, (iii) the Mobile Basin, and (iv) central Coastal Plain and Mississippi River Basin. In contrast, a relative lack of range-wide geographic structure in F. olivaceus is consistent with recent range expansion over much of the same geographic area. The southwestern Ouachita Highlands and Mobile Basin F. notatus clades corresponded to regions where ecological associations between the two species are reversed, providing evidence of the independent evolution of variation in contemporary habitat associations. Fundulus olivaceus from several drainages demonstrated introgression of mitochondrial DNA from F. notatus, but none of the sites in this study included individuals with hybrid ancestry in their nuclear genome. Phylogenetic analyses that included only nuclear loci supported the reciprocal monophyly of F. notatus, F. olivaceus and a third narrowly endemic species, Fundulus euryzonus, and supported a sister relationship between F. olivaceus and F. euryzonus.

Phylogeography of the Bluegill Sunfish,Lepomis macrochirus, in the Mississippi River Basin

The Mississippi River Basin supports the richest fish fauna in eastern North America and has played a key role in the maintenance of fish biodiversity, especially as a refuge for freshwater fishes during glaciations. In this study, we investigated the phylogeography of the bluegill sunfish, Lepomis macrochirus, in eastern North America, using complete sequence of the mitochondrial ND1 gene from 369 samples collected at 15 sites. Phylogenetic analysis revealed two major lineages (northern and southern clades) in a parsimony network. A sympatric distribution of the lineages was widely observed in the Mississippi Basin. Sequence diversity in the two lineages was significantly lower in glaciated regions around the Great Lakes than in unglaciated regions. The two lineages were estimated to have diverged in the Kansan glaciation, and refugia for both existed around the Ouachita Highlands. The southern clade dispersed during the Yasmouth Interglacial, prior to the dispersal of the northern clade during the Sangamon Interglacial. In the northern clade, low genetic diversity and population fragmentation inferred by nested clade analysis (NCA) were considered due to bottleneck events in the Wisconsin glaciation, while the southern clade showed isolation by distance in a Mantel test. A difference in demographic fluctuation suggests that sympatry of the two lineages has resulted from recent secondary admixture through the range expansion of the northern clade in the post-Pleistocene. Large-scale admixture of multiple mtDNA lineages in L. macrochirus, which has not been recorded in other fishes in the Mississippi River Basin, may result from their high vagility.

Systematics and Zoogeography of the Rock Basses (Centrarchidae: Ambloplites)

This study examines the role that historical events have played in the diversification of members of the genus Ambloplites by estimating divergence times of clades within the genus. DNA sequences of the mitochondrial cytochrome b gene were used to develop phylogenetic hypotheses for Ambloplites using maximum parsimony and Bayesian methods. The timing of diversification within and between species of Ambloplites was estimated using nonparametric rate-smoothing and penalized likelihood methods calibrated by fossil dates. Monophyly of three of the four species was supported. The ages of the most recent common ancestors of species of Ambloplites estimated in this study confirm earlier estimates that in most instances, their origins occurred prior to the Pleistocene. A comparison of estimated divergence times of lineages to sea level fluctuations indicates a correspondence to extremely high or low sea stands throughout the Neogene Period. Populations of Ambloplites in the Ozarks and Ouachita highlands previously assigned to A. ariommus appear to have either been introgressed by A. rupestris or were misidentified as A. ariommus. Ambloplites rupestris displays low genetic divergence throughout its range and is consistent with a re-colonization of previously glaciated areas following the Pleistocene.

Crane Flies of the Ouachita Highlands of Arkansas (Diptera: Tipulidae). II

Sixty-two species and subspecies of Tipulidae are reported from the Ouachita Highlands of Montgomery and Polk counties of Arkansas. Several constitute new regional records. Habitats at collection sites are briefly described. Dates of collection are provided for each species.

Development of a Satellite-Based Hazard Rating System for <I>Dendroctonus frontallis</I> (Coleoptera: Scolytidae) in the Ouachita Mountains of Arkansas

The southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), is the most damaging forest insect pest of pines (Pinus spp.) throughout the southeastern United States. Hazard rating schemes have been developed for D. frontalis, but for these schemes to be accurate and effective, they require extensive on-site measurements of stand attributes such as host density, age, and basal area. We developed a stand hazard-rating scheme for several watersheds in the Ouachita Highlands of Arkansas based upon remotely sensed data and a geographic information system. A hazard model was developed using stand attributes (tree species, stand age and density, pine basal area, and landform information) and was used to establish baseline hazard maps for the watersheds. Landsat 7 ETM+ data were used for developing new hazard maps. Two dates of Landsat imagery were used in the analyses (August 1999 and October 1999). The highest correlations between hazard rating scores and remotely sensed variables from either of the dates included individual Landsat 7 ETM+ bands in the near- and mid-infrared regions as well as variables derived from various bands (i.e., Tasseled cap parameters, principal component parameters, and vegetation indices such as the calculated simple ratio and normalized difference vegetation index). Best subset regression analyses produced models to predict stand hazard to southern pine beetle that consisted of similar variables that resembled but were more detailed than maps produced using inverse distance weighted techniques. Although the models are specific for the study area, with modifications, they should be transferable to geographically similar areas.

Development of a Satellite-Based Hazard Rating System for Dendroctonus frontallis (Coleoptera: Scolytidae) in the Ouachita Mountains of Arkansas

The southern pine beetle, Dendroctonus frontalis Zimmermann (Coleoptera: Scolytidae), is the most damaging forest insect pest of pines (Pinus spp.) throughout the southeastern United States. Hazard rating schemes have been developed for D. frontalis, but for these schemes to be accurate and effective, they require extensive on-site measurements of stand attributes such as host density, age, and basal area. We developed a stand hazard-rating scheme for several watersheds in the Ouachita Highlands of Arkansas based upon remotely sensed data and a geographic information system. A hazard model was developed using stand attributes (tree species, stand age and density, pine basal area, and landform information) and was used to establish baseline hazard maps for the watersheds. Landsat 7 ETM+ data were used for developing new hazard maps. Two dates of Landsat imagery were used in the analyses (August 1999 and October 1999). The highest correlations between hazard rating scores and remotely sensed variables from either of the dates included individual Landsat 7 ETM+ bands in the near- and mid-infrared regions as well as variables derived from various bands (i.e., Tasseled cap parameters, principal component parameters, and vegetation indices such as the calculated simple ratio and normalized difference vegetation index). Best subset regression analyses produced models to predict stand hazard to southern pine beetle that consisted of similar variables that resembled but were more detailed than maps produced using inverse distance weighted techniques. Although the models are specific for the study area, with modifications, they should be transferable to geographically similar areas.

GENETIC DIVERSITY OF THE CADDO MADTOM, NOTURUS TAYLORI, WITH COMMENTS ON FACTORS THAT PROMOTE GENETIC DIVERGENCE IN FISHES ENDEMIC TO THE OUACHITA HIGHLANDS

Abstract We studied allozyme diversity of the endemic Caddo madtom, Noturus taylori, over its small geographic range (<2,000 km2) in the Ouachita Highlands of southwestern Arkansas. This small catfish species exhibited marked genetic divergence among rivers and low levels of genetic variation within sampling localities. The more widely distributed brindled madtom, Noturus miurus, exhibited nearly identical patterns of genetic divergence among river localities separated by similar geographic distance, and similarly low levels of variation within localities were observed. We compared genetic results from madtoms to those obtained in a previous study of 2 co-distributed, endemic darter species and found that habitat specialists, especially those restricted to head-waters, are likely to show high levels of genetic divergence at relatively small spatial scales. Comparative genetic and ecological study of these endemic species suggests that an interaction of extrinsic (larger rivers with higher silt loads) and ...

Unionid mussels influence macroinvertebrate assemblage structure in streams

Unionid mussels often occur as multispecies aggregates called mussel beds and in dense patches within the mussel beds themselves. Thus, their distributions are patchy at 2 spatial scales. We examined the association between mussel assemblage structure and macroinvertebrate assemblage structure at these 2 spatial scales in rivers of the Ouachita Highlands, Arkansas and Oklahoma, USA. We used multivariate variation partitioning techniques to relate variation in benthic macroinvertebrate distribution and abundance to variation in mussel assemblages, environmental variables, spatial variables, and overlapping or shared variation between these components. At the patch scale, total densities of macroinvertebrates and dominant groups (Oligochaeta, Chironomidae, Ephemeroptera, and Trichoptera) were significantly higher in patches containing mussels than where mussels were absent, and densities of macroinvertebrates were positively correlated with unionid density. In variation partitioning analyses, mussel assemblages explained almost ½ of the variation in macroinvertebrate assemblages at both spatial scales, even after removing effects of similar habitat (environmental variables) and biogeographic history (spatial variables).

Scale-dependent associations between native freshwater mussels and invasive Corbicula

In North America there is conflicting evidence concerning whether the invasive Asian clam, Corbicula fluminea, and native mussels (Unionidae), can successfully co-exist. One reason underlying disparate conclusions may be the different spatial scales at which data have been collected. We compared the distribution and abundance of native unionid mussels and Corbicula at two spatial scales, stream reaches and 0.25 m 2 patches, within one biogeographic region, the Ouachita Highlands, of the south central U.S. We found that Corbicula abundance was negatively related to native mussel abundance at small spatial scales. While Corbicula densities varied widely in patches without native mussels, and in patches where mussels occurred at low abundance, Corbicula density was never high in patches where mussels were dense. We hypothesize that the likelihood of successful Corbicula invasion decreases with increasing abundance of adult native mussels. Several mechanisms may potentially drive this pattern including lack of space for Corbicula to colonize, physical displacement by actively burrowing mussels, and locally reduced food resources in patches where native mussels are feeding. In addition, Corbicula may be unable to withstand environmental bottlenecks as readily as unionids. When patch-scale density and biomass information were pooled to represent entire stream reaches, the negative relationship between native mussels and Corbicula was no longer as apparent, and there was not a significant relationship between native mussels and Corbicula. These results point to the importance of appropriate sample scale in examining potential associations between species.

Impacts of Shortleaf Pine-Hardwood Forest Management on Soils in the Ouachita Highlands: A Review

Abstract Shortleaf pine (Pinus echinata Mill.) is the most ecologically and economically important tree species in the Ouachita Highlands of the southcentral United States. This species can occur in relatively pure stands but most frequently exists in mixed stands with various hardwood species. Because of the diversity of land ownership, public concerns about forest management, and increased intensity of forest practices, the Ouachita Highlands have been a focal point for numerous research projects over the past 20 yr that have studied how forest management affects soils. We summarized information in four fundamental areas: (1) compaction, (2) soil loss, (3) organic matter, and (4) nutrients to better evaluate if and to what degree management practices such as harvesting and prescribed fire modify the productivity and sustainability of soils in this region. The review indicated that soils with less than 15% rock content or sandy loam textures were susceptible to compaction when harvested during wet weather conditions. Although partial harvesting techniques, such as single-tree or group selection, tended to reduce overall soil disturbance in a stand, it increased soil compaction on primary skid trails by concentrating traffic on fewer skid trails. Compaction on skid trails frequently elevated bulk density to levels that could reduce regeneration success or seedling growth. Using current harvesting systems, soil losses and displacement to streams after harvesting appeared to have little or no effect on long-term soil productivity. Harvesting and prescribed fires significantly altered nutrient and organic matter contents of the forest floor and mineral soil. However, recovery of these nutrient or organic pools often occurred rapidly after these cultural practices occurred. Little information was available for determining how repeated silvicultural practices over multiple rotations would affect long-term soil productivity in the Ouachita Highlands. South. J. Appl. For. 26(1):43–51.

The Eternal Frontier: An Ecological History of North America and Its Peoples

<dm:abstracts xmlns:dm="http://www.elsevier.com/xml/dm/dtd"><ce:abstract xmlns:ce="http://www.elsevier.com/xml/common/dtd" view="all" class="author" id="aep-abstract-id1"><ce:section-title>Publisher Summary</ce:section-title><ce:abstract-sec view="all" id="aep-abstract-sec-id1"><ce:simple-para id="fsabs007" view="all">The Arkansas and the Red—two large, separate river basins—drain the southern Great Plains region of the US south of the Kansas River and north of the Texas–Gulf coastal drainages. Rivers of the region flow through the Southern Plains, Central Prairie, Ozark Highlands, Ouachita Highlands, and Mississippi Embayment “freshwater ecoregions.” The rivers of the region fall into two different groups based on their upland versus lowland characteristics. The group including the Arkansas, Canadian, Red, Washita, and Cimarron rivers represents typical large to medium-size low-gradient prairie main stems with wide, shallow, braided, unstable sand-bed channels, often carrying heavy loads of large wood snags washed in by floods. Late-summer drying of streams in the region is a function of both evapotranspiration and lowered rainfall. Extreme rainfall events result in annual or more frequent bankfull spates and streambed scouring in many of the smaller tributaries to the main rivers. Clearing and snagging rivers for boat passage, contamination by salt water from oil production, and interbasin water transfers have altered the rivers over the years.</ce:simple-para></ce:abstract-sec></ce:abstract></dm:abstracts>