South Texas Plains Research Articles

Using Geospatial Analysis to Identify Priority Communities for Cervical Cancer Prevention in Texas

Despite being almost entirely preventable, cervical cancer is the fourth most frequently diagnosed cancer among women worldwide. Cervical cancer incidence suggests missed opportunities for prevention. Geospatial analysis could strategically guide public health interventions. This study aimed to identify geographic clusters of cervical cancer incidence in Texas, a state with higher than national rates of cervical cancer incidence and mortality. In this population-based cross-sectional study, the authors analyzed incident cervical cancer data among Texas women aged 30-64 years, from 2014 to 2018. The authors conducted a purely spatial Poisson-based analysis function in SaTScan to examine geographic clusters of higher-than-expected proportions of cervical cancer incidence (i.e., hot spots) and adjusted for age. A total of 5,060 women aged 30-64 years with incident cervical cancer diagnosis (mean age: 45.7 years, SD=9.6), including 1,840 (36.4%) Hispanic, 591 (11.7%) non-Hispanic Black, 2,397 (47.4%) non-Hispanic White, and 232 (4.6%) other races, were analyzed. Spatial scan analysis detected 7 significant hot spots of cervical cancer incidence. Hot spots were identified in the South Texas Plains (near Mexico border), Gulf Coast (Houston), Prairies and Lakes (North Texas), Panhandle Plains (Northwest Texas), and Piney Woods (Southeast Texas) regions of Texas. Hot spots, compared with the rest of Texas, had higher proportions of Hispanic population and individuals with socioeconomic disadvantages. This study found spatial variation in cervical cancer incidence in Texas. The hot spot areas can benefit from targeted, novel, scalable, and cost-effective interventions to increase human papillomavirus vaccination and screening and early detection and treatment of precancerous cervical lesions.

Geographic Variation in Late-Stage Cervical Cancer Diagnosis

There are stark disparities in cervical cancer burden in the United States, notably by race and ethnicity and geography. Late-stage diagnosis is an indicator of inadequate access to and utilization of screening. To identify geospatial clusters of late-stage cervical cancer at time of diagnosis in Texas. This population-based cross-sectional study used incident cervical cancer data from the Texas Cancer Registry from 2014 to 2018 of female patients aged 18 years or older. Late-stage cervical cancer cases were geocoded at the census tract level (n = 5265) using their residential coordinates (latitude and longitude) at the time of diagnosis. Statistical analysis was performed from April to September 2023. Census tract of residence at diagnosis. Late-stage cervical cancer diagnosis (ie, cases classified by the National Cancer Institute Surveillance, Epidemiology and End Results summary stages 2 to 4 [regional spread] or 7 [distant metastasis]). A Poisson probability-based model of the SaTScan purely spatial scan statistics was applied at the census tract-level to identify geographic clusters of higher (hot spots) or lower (cold spots) proportions than expected of late-stage cervical cancer diagnosis and adjusted for age. Among a total of 6484 female patients with incident cervical cancer cases (mean [SD] age, 48.7 [14.7] years), 2300 (35.5%) were Hispanic, 798 (12.3%) were non-Hispanic Black, 3090 (47.6%) were non-Hispanic White, and 296 (4.6%) were other race or ethnicity. Of the 6484 patients, 2892 with late-stage diagnosis (mean [SD] age, 51.8 [14.4] years were analyzed. Among patients with late-stage diagnosis, 1069 (37.0%) were Hispanic, 417 (14.4%) were non-Hispanic Black, 1307 (45.2%) were non-Hispanic White, and 99 (3.4%) were other race or ethnicity. SaTScan spatial analysis identified 7 statistically significant clusters of late-stage cervical cancer diagnosis in Texas, of which 4 were hot spots and 3 were cold spots. Hot spots included 1128 census tracts, predominantly in the South Texas Plains, Gulf Coast, and Prairies and Lakes (North Texas) regions. Of the 2892 patients with late-stage cervical cancer, 880 (30.4%) were observed within hot spots. Census tract-level comparison of characteristics of clusters suggested that hot spots differed significantly from cold spots and the rest of Texas by proportions of racial and ethnic groups, non-US born persons, and socioeconomic status. In this cross-sectional study examining geospatial clusters of late-stage cervical cancer diagnosis, place-based disparities were found in late-stage cervical cancer diagnosis in Texas. These findings suggest that these communities may benefit from aggressive cervical cancer interventions.

Peanut Cultivar Response to Diclosulam in the Southwest Peanut Growing Region

Field experiments were conducted in the south Texas and Texas High Plains area during the 2018 through 2020 growing seasons and in southwestern Oklahoma in 2020 to evaluate runner peanut cultivars (Georgia-13M, Georgia-09B) and the Spanish cultivar (Ole´) tolerance to diclosulam at 0.026 (the manufacture’s recommended use rate) and 0.052 (twice the manufacture’s recommended use rate) kg ai/ha applied preemergence (PRE) or peanut cracking (CRACK). No diclosulam injury was noted in south Texas; however, in the Texas High Plains and Oklahoma locations significant stunting was noted with diclosulam applied PRE especially under sprinkler irrigation. In 2018 at the High Plains location, under furrow irrigation, no peanut stunting was noted. In 2019 and 2020, under sprinkler irrigation, diclosulam at 0.026 and 0.052 kg/ha applied PRE resulted in early-season stunting of 18 to 59% in both Oklahoma and the Texas High Plains. No late-season stunting was noted in Oklahoma; however, up to 20% stunting was still visible at the Texas High Plains location. No yield differences were noted in south Texas or the High Plains region in 2018 or 2020; however, in 2019 at the High Plains location, peanut yield decreased as diclosulam rate increased but application timing had no effect. At the Oklahoma location, application timing and rate effect were noted. Diclosulam applied PRE and the high rate of diclosulam reduced peanut yield. Issues still exist with diclosulam in the southwest peanut growing areas as seen previously in 2000 despite the different varieties planted. There may be opportunities to utilize diclosulam postemergence (POST) since peanut injury was 5% or less and yields were not reduced when applied CRACK.

A Simulation Model of Sustained-Yield Harvest for Northern Bobwhite in South Texas

Recommended sustainable harvest rates for northern bobwhite (Colinus virginianus) vary greatly and range from 25% to 70% of the prehunt population. Because northern bobwhite populations have declined across their geographic range, determining sustainable harvest levels is critical for effective management. Our objectives were to use simulation modeling to identify sustainable rates of bobwhite harvest, probability of population persistence, and minimum viable population estimates. We also conducted a sensitivity analysis to evaluate the impacts of harvest on northern bobwhite populations in Texas, USA. We constructed a simulation model using Program STELLA 9.0 for a hypothetical northern bobwhite population on 800 ha in the South Texas Plains USA and modeled population dynamics to 100 years over a range of harvest rates (0–40%). A 20% harvest rate produced the greatest average yields (mean ± standard error = 231 ± 10 bobwhites harvested/year). Given a quasi-extinction criterion of ≤40 bobwhites (≤0.05 bobwhite/ha), a 30% harvest rate resulted in a high probability of quasi-extinction (PE = 0.75) within 47.8 ± 2.3 years. A 40% harvest rate was not sustainable (PE = 1.0), with quasi-extinction occurring within 15.5 ± 2.6 years. Harvesting northern bobwhite populations in the South Texas Plains at rates of 20−25% of the prehunt population should maximize long-term harvest while minimizing the probability of population extinction. Spring densities of 0.60−0.80 bobwhite/ha may represent minimum viable spring densities for northern bobwhite populations in the South Texas Plains as these are the densities associated with sustainable 20-25% harvest rates. Harvest rates >30% are likely to be excessive with respect to long-term population persistence for northern bobwhite populations in the South Texas Plains.

Ecological risk assessment of the effects of neonicotinoid insecticides on northern bobwhites (Colinus virginianus) in the South Texas Plains Ecoregion.

Neonicotinoid insecticides are among the latest class of insecticides that can have harmful effects on birds. Approximately 30 000 kg of neonicotinoid insecticides are applied annually to 429 100 ha of row-crop fields within the South Texas Plains Ecoregion, Texas, USA. Various studies have demonstrated that treated seeds can be highly toxic to northern bobwhites, with the consumption of only 20 corn seeds causing a fatality. Similarly, other studies have indicated that neonicotinoid insecticides can reduce arthropod populations-a substantial prey base for northern bobwhites, especially during the breeding season-by approximately 60%. Our objective was to conduct an ecological risk assessment of neonicotinoid insecticides' impact on northern bobwhite (Colinus virginianus) populations in the South Texas Plains Ecoregion. We estimated that juvenile and adult northern bobwhites could intake from 7.32 to 27.0 mg/kg/day and from 10.0 to 37.5 mg/kg/day of neonicotinoid insecticides, respectively, which can cause adverse effects on growth, reproductive output, and long-term survival. Our study determined that the application of 30 000 kg of neonicotinoid insecticides annually in the South Texas Plains Ecoregion harms the region's northern bobwhite that are exposed to neonicotinoids. Integr Environ Assess Manag 2022;18:488-499. © 2021 SETAC.

Abundance and Species of Thrips1 in Cotton on the South Plains of Texas

Thrips (Thysanoptera: Thripidae) are the major insect pest of seedling cotton, Gossypium hirsutum L., on the Texas South Plains. The western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), has historically been the most abundant thrips species in cotton in the region. A field survey during the 2017 and 2018 growing seasons collected thrips from small-plot insecticide seed treatment research experiments at multiple locations across the Texas South Plains. Species composition of adult thrips from cotyledon to four true-leaf stages cotton was determined by morphological identification with the aid of a microscope. Of the species collected during 2 years of study, 64% were onion thrips, Thrips tabaci Lindeman, followed by F. occidentalis (23%), Frankliniella exigua Hood (10%), and tobacco thrips, Frankliniella fusca Hinds (1%). Relative abundance of species varied significantly across growing seasons. In 2017, T. tabaci was the most abundant species in cotyledon to four true-leaf stages of cotton. In 2018, F. occidentalis was more prevalent than other thrips species. The percentage of adults was significantly greater than that of immatures at the cotyledon stage while immature thrips were significantly more abundant during one to four true-leaf stages of cotton. The study indicated T. tabaci and F. occidentalis were the most prevalent thrips species on seedling cotton on the South Plains of Texas.

Quantifying the Impacts of Land-Use and Climate on Carbon Fluxes Using Satellite Data across Texas, U.S.

Climate change and variability, soil types and soil characteristics, animal and microbial communities, and photosynthetic plants are the major components of the ecosystem that affect carbon sequestration potential of any location. This study used NASA’s Soil Moisture Active Passive (SMAP) Level 4 carbon products, gross primary productivity (GPP), and net ecosystem exchange (NEE) to quantify their spatial and temporal variabilities for selected terrestrial ecosystems across Texas during the 2015–2018 study period. These SMAP carbon products are available at 9 km spatial resolution on a daily basis. The ten selected SMAP grids are located in seven climate zones and dominated by five major land uses (developed, crop, forest, pasture, and shrub). Results showed CO2 emissions and uptake were affected by land-use and climatic conditions across Texas. It was also observed that climatic conditions had more impact on CO2 emissions and uptake than land-use in this state. On average, South Central Plains and East Central Texas Plains ecoregions of East Texas and Western Gulf Coastal Plain ecoregion of Upper Coast climate zones showed higher GPP flux and potential carbon emissions and uptake than other climate zones across the state, whereas shrubland on the Trans Pecos climate zone showed lower GPP flux and carbon emissions/uptake. Comparison of GPP and NEE distribution maps between 2015 and 2018 confirmed substantial changes in carbon emissions and uptake across Texas. These results suggest that SMAP carbon products can be used to study the terrestrial carbon cycle at regional to global scales. Overall, this study helps to understand the impacts of climate, land-use, and ecosystem dynamics on the terrestrial carbon cycle.

Potential impact of neonicotinoid use on Northern bobwhite (Colinus virginianus) in Texas: A historical analysis.

The widespread use of neonicotinoid insecticides in recent years has led to increasing environmental concern, including impacts to avian populations. In Texas and across their range, Northern bobwhite (Colinus virginianus) habitat frequently overlaps cultivated cropland protected by neonicotinoids. To address the effects of neonicotinoid use on bobwhites in Texas, we conducted a historical analysis from 1978–2012 in Texas’ ecological regions using quail count data collected from North American Breeding Bird Survey and Texas Parks and Wildlife Department, and neonicotinoid use data from the U.S. Geological Survey. We considered bobwhite abundance, neonicotinoid use, climate, and land-use variables in our analysis. Neonicotinoid use was significantly (p<0.05) negatively associated with bobwhite abundance in the High Plains, Rolling Plains, Gulf Coast Prairies & Marshes, Edwards Plateau, and South Texas Plains ecological regions in the time periods following neonicotinoid introduction (1994–2003) or after their widespread use (2004–2012). Our analyses suggest that the use of neonicotinoid insecticides may negatively affect bobwhite populations in crop-producing regions of Texas.

Explore Texas: A Nature Travel Guide by Mary O. Parker

Reviewed by: Explore Texas: A Nature Travel Guide by Mary O. Parker Michelle M. Haggerty Explore Texas: A Nature Travel Guide. By Mary O. Parker. Photographs by Jeff Parker. Foreword by Carter P. Smith. College Station: Texas A&M University Press, 2016. xi + 302 pp. Illustrations, maps, index. $28.00 paper. Explore Texas: A Nature Travel Guide is a wonderful companion for the naturalist and nature enthusiast taking a trip across Texas. Author Mary O. Parker focuses on nearly 100 nature-related venues and events statewide organized by the seven official regions of Texas: Big Bend Country, Gulf Coast, Hill Country, Panhandle Plains, Piney Woods, Prairies and Lakes, and South Texas Plains. This guide serves as a sort of life list for what to see, when to see it, and why we should take the time to explore the natural landscapes, destinations, and events of each Texas region. Beautiful photographs by Jeff Parker [End Page 93] enhance each section. Each entry contains a map, travel directions, and tips for how to make the most of your adventure. Helpful activity icons like "wildlife watching," "geology gems," and more accompany each venue to help you see which nature activity is available. But what sets this book apart from other nature travel guides is the excellent education sections for each venue. It offers fascinating facts and intriguing details about specific aspects of each particular location. For example, the entry for the Brazos Bend State Park and George Observatory details the site's American alligators, Anhinga birds, and northern raccoons. This serves to enhance the explorer's experience and, one hopes, spark in that person an appreciation of the need for continued conservation and protection for these areas. Michelle M. Haggerty Texas Master Naturalist State Program Coordinator Texas Parks and Wildlife Department Copyright © 2018 Center for Great Plains Studies, University of Nebraska–Lincoln

Phytogeographical relationships and analysis of the flora of South Texas Plains

The southernmost tip of Texas is a part of the Tamaulipan Province of northeastern Mexico which some authors consider in the Madrean Subkingdom of the Holarctic Kingdom, while others the “Xerofitica Mexicana” of the Neotropical Kingdom. To shed more light on this question, a natural flora of fourteen counties in the S TX Plains ecoregion, South Texas Plains flora (S TX), was compiled, studied from a biogeographical perspective, and analyzed in this work. The analysis was based primarily on the species and genera distribution outlines. Phylogenetic literature was searched to find relationships, patterns of migrations, and geographical connections of the species of major clades. Taxonometric and geographic spectra of the S TX flora were obtained and compared with those of two other floras in southern Texas: SC Texas (EP, or Edwards Plateau) and Big Bend Region (BB). There are 1250 native species in 553 genera and 117 families in the S TX flora. These species were classified into 25 geographic (floristic) elements. Herein is presented a checklist of S TX accompanied by the geoelement descriptions, a comparison of geographical spectra of the species and genera in all three floras, and the biogeographical analysis of the S TX flora. South TX, having a flat topography and being on the crossroads of migration routes, has multiple connections with adjacent floristic centers. The Tamaulipan endemism is not particularly high (8% in S TX) in comparison with much higher Chihuahuan endemism in BB (23% in BB; 10% in S TX). Proportions of taxa of the largest families in the three southern Texas floras show much higher numbers of tropical-subtropical, Tamaulipan, Gulf Coast, and Mesoamerican (coastal) species in the S TX flora in comparison with those of EP and BB. North temperate, E North American, and Prairie species are best represented in EP (47%), followed by S TX (36%), with only 17% in BB. The majority of the BB differential species are in the Chihuahuan, SW N American, Sonoran/Apachian, and the Madrean geoelements. The genera of the largest family, Asteraceae, that are differential among the three floras show importance of the Mexican (Madrean) centers of diversity as well as migrations from the Tethyan Subkingdom in the assembly of the S TX flora. Tethyan connections are also evident among the Boraginaceae s. str. and some other groups found in the flora. The spectra of generic and specific geographical elements of S TX illustrate transitional position of its flora. It represents an ecotone between the Western (Madrean) and the Eastern (Atlantic and Gulf Coast) N American Regions, with a very high influence of the various Neotropical elements and a higher affinity to the EP flora than to that of BB.

Field Application of Sustained-Yield Harvest Management for Northern Bobwhite in Texas

Sustained-yield harvest (SYH) is considered a potentially viable strategy for managing harvest of northern bobwhites (Colinus virginianus). However, application of SYH has not been evaluated for northern bobwhites. We evaluated the application of using SYH as a harvest management strategy for bobwhite during the 2007 2008 and 2008 2009 hunting seasons in 2 ecoregions of Texas (Rolling Plains, South Texas Plains). We collected field data at 3 study sites/ecoregion (900 1,900 ha each; 2 hunted sites and 1 control) to estimate 4 demographic parameters (fall and spring density, overwinter survival in the absence of hunting, and harvest rate). We used these data to parameterize the additive harvest model for bobwhites and compare predictions of spring abundance of the model with field estimates. The additive harvest model, compared to field estimates, consistently underestimated spring population density (mean 6 SE) by 55.7 6 17.8% (2007 2008) and 34.1 6 4.9% (2008 2009) in the Rolling Plains, and by 26.4 6 25.3% (2007 2008) and 49.1 6 2.1% (2008 2009) in the South Texas Plains. Implementing SYH in the field, despite its potential benefits, will be challenging given the need for reliable estimates of 3 key population parameters (fall and spring density, and natural mortality in the absence of hunting) and the high variation often associated with them. Conservative harvest prescriptions based on the lower 95% CIs of fall density estimates may permit sustainable harvest despite variation in density estimates.

Landscape-Scale Land-Cover Change and Long-Term Abundance of Scaled Quail and Northern Bobwhite in Texas

Between 1978 and 1998, scaled quail (Callipepla squamata) abundance in the Rolling Plains ecological region declined (r1 = -0.85, P < 0.001), while no trend (P = 0.74) was exhibited in the South Texas Plains. Northern bobwhites (Colinus virginianus) exhibited no trend (P > 0.10) in either ecological region. Changes in land-cover between 1976 and 1998 indicated a loss of Savannah and Shrubland and an increase in Parkland cover types in the Rolling Plains. In the South Texas Plains, Woodland and Brush/Shrubland decreased between 1976 and 1998, whereas Brush/Shrub Parkland and Parkland increased. We examined land-cover change as a possible component in the scaled quail decline in the Rolling Plains. Loss of the Shrubland cover type may explain the decline of scaled quail in the Rolling Plains. Our results further suggest intraspecific spatial usability boundaries. These boundaries differed by species, with scaled quail associated with dense structure near the ground, whereas northern bobwhite were less abundant in areas dominated by scattered shrubs and trees, and large expanses of short, close-canopy cover types. A method is proposed for quickly obtaining data on land-cover changes on time.

Seroprevalence of Borrelia burgdorferi antibodies in white-tailed deer from Texas.

Lyme Disease is caused by the bacterial pathogen Borrelia burgdorferi, and is transmitted by the tick-vector Ixodes scapularis. It is the most prevalent arthropod-borne disease in the United States. To determine the seroprevalence of B. burgdorferi antibodies in white-tailed deer (Odocoileus virginianus) from Texas, we analyzed serum samples (n = 1493) collected during the 2001–2015 hunting seasons, using indirect ELISA. Samples with higher sero-reactivity (0.803 and above) than the negative control group (0.662) were further tested using a more specific standardized western immunoblot assay to rule out false positives. Using ELISA, 4.7% of the samples were sero-reactive against B. burgdorferi, and these originated in two eco-regions in Texas (Edwards Plateau and South Texas Plains). However, only 0.5% of the total samples were sero-reactive by standardized western immunoblot assay. Additionally, both ELISA and standardized western immunoblot assay results correlated with an increased incidence in human Lyme Disease cases reported in Texas. This is the first longitudinal study to demonstrate fluctuation in sero-reactivity of white-tailed deer to B. burgdorferi sensu stricto antigens in southern United States. Future ecological and geographical studies are needed to assess the environmental factors governing the prevalence of Lyme Disease in non-endemic areas of the southern United States.

Cotton Irrigation Timing with Variable Seasonal Irrigation Capacities in the Texas South Plains

Abstract. Within the Ogallala Aquifer Region of Texas, the irrigation capacity (IC) for a given field often changes within a growing season due to seasonal depletion of the aquifer, in-season changes in crop irrigation needs in dry years, or consequences of irrigation volume limits imposed by irrigation district rules. Irrigation planning is further complicated by erratic seasonal rainfall. A field experiment was conducted from 2010 to 2013 to determine cotton ( L.) irrigation productivity using a range of ICs common to the Texas South Plains during three irrigation periods. The treatments included in-season ICs (maximums of 0, 3.2, and 6.4 mm d-1) in combination with irrigation periods determined by accumulated growing degree days (GDD15.6) and were designated as period 1 (P1= emergence to 525 GDD15.6), period 2 (P2= 525 to 750 GDD15.6), and period 3 (P3>750 GDD15.6). Combinations of these factor levels resulted in 27 irrigation treatments with applications made by the low energy precision application (LEPA) method. Annual rainfall totals ranged from 137 to 557 mm over the four years. In all years, results indicated that attempting to store water in the soil profile, or irrigating in excess of the cotton evapotranspiration rate, early in the growing season reduced seasonal irrigation water use efficiency (SIWUE), and sometimes yield, compared to treatments with limited or no early irrigations. Treatments with 0 and 3.2 mm d-1 ICs during P1 used up to 20% less seasonal irrigation with minor yield loss (

Sustainability Atlas of Texas Ecoregions

Since the introduction of the triple bottom line sustainability assessment accounting, a variety of approaches have been developed to quantify sustainability using the three axes of social, economic and environmental sustainability. The aim of this atlas is to assess the sustainability of Texas natural ecoregions: the Piney Woods, the Gulf Prairies and marshes, the Post Oak Savanah, the Blackland Prairies, the Cross Timbers, the South Texas Plains, the Edwards Plateau, the Rolling Plains, the High Plains and the Trans-Pecos, by identifying a set of indicators. These are unemployment, children in poverty, severity of housing problems, daily PM2.5 concentrations, population affected by drinking water violation, total water use, organic production, non-obesity and attainment of post-secondary education. Despite the limitations of inherent inaccuracies and temporal limitation, the assessment points to issues that negatively affect the environmental sustainability of Texas ecoregions. Continual assessment is recommended to optimize the atlas.

Deflation Troughs, Water, and Prehistoric Occupation on the Margins of the South Texas Sand Sheet

Within the South Texas Plains, the area broadly defined by the Rio Grande to the south and the Nueces River to the north, a distance of ca. 175 km, evidence of open human occupation is remarkably abundant. Because it is predominantly a region of loose, sandy soils and active and relict sand dunes where wind processes dominate, the area is known as the South Texas Sand Sheet (STSS). There is no running water within the STSS and all streams are ephemeral. Existing drainage systems are small, localized, and not integrated, carrying water for a few days and up to two weeks after the passage of a storm. The lack of running water makes human occupation on this semi-arid area even more remarkable. The STSS and the adjacent wind deflated areas have hundreds of small and shallow elongated deflation troughs. Most of these poorly drained swales retain seasonal fresh water that sustain high moisture plants and are ephemeral wetlands; a small percentage of them hold water year round. As a result, the long history of human occupation of the STSS was possible due to the presence of the deflation troughs. This study explores the connection between human occupation of the STSS and deflation troughs at four previously unreported archeological sites in northern Hidalgo County using a combination of intensive archeological and geological survey, oral history, GIS technology, and existing soil maps.

Tests of an additive harvest mortality model for northern bobwhite Colinus virginianus harvest management in Texas, USA

We evaluated the application of using an additive harvest mortality model (AHMM) as a harvest management strategy for northern bobwhites Colinus virginianus during the 2007/08 and 2008/09 hunting seasons in two ecoregions of Texas: the Rolling Plains (RP) and the South Texas Plains (STP). We collected field data on three study sites/ecoregion (of 400‐1,900 ha each; two treatment and one control) to estimate four demographic parameters (i.e. fall and spring density, overwinter survival in the absence of hunting and harvest rate). We used these data to parameterize an AHMM (a theoretical component of sustained‐yield harvest; SYH) for bobwhites and compare model‐based predictions of spring bobwhite populations with field estimates. Our goal was to compare predictions from the AHMM to field estimates of spring density based on known rates of harvest. Compared to field estimates, the AHMM consistently underestimated spring population density (mean % ± SE) by 55.7 ± 17.8% (2007/08) and 34.1 ± 4.9% (2008/09) in the RP and by 26.4 ± 25.3% (2007/08) and 49.1 ± 2.1% (2008/09) in the STP. Prescribing a fall bobwhite harvest to achieve a specific, target spring density may be difficult given the wide variation in the model parameters (i.e. fall and spring density, and natural mortality) that we observed.

Historical Changes in Stocking Densities on Texas Rangelands

Stocking density, both current and past, is a major determinant of the nature and condition of rangelands. Despite this fact, there have been few detailed examinations of historical trends in stocking density. We used data from the U.S. Census of Agriculture to track the density of domestic livestock from the early 1900s to the present, for six rangeland regions in the State of Texas: (1) the Edwards Plateau; (2) the Trans-Pecos; (3) the Lampasas Cut Plain; (4) the South Texas Plains; (5) the Rolling Plains; and (6) the High Plains. We find that stocking densities have declined across the state—ranging from a decline of about 40% in some regions to as much as 75% in the Trans-Pecos and Edwards Plateau regions. The period of sharpest decline, which began in the middle of the last century, reflects important, but not fully understood, socioeconomic changes. These most likely include changing land ownership, fragmentation of land holdings, and increasing emphasis on wildlife conservation. Other factors potentially contributing to the destocking of Texas rangelands include woody plant encroachment and a rise in predation. We argue that the dramatic reduction in stocking densities documented here has profound socioeconomic, ecological, and hydrological implications that need to be better understood.

Long-Term Effects of Aeration and Fire on Invasion of Exotic Grasses in Mixed-Brush Plant Communities

Abstract Invasion of exotic grasses into grasslands dominated by native plants changes fire cycles and reduces biodiversity. Brush management practices that create soil disturbance, such as aeration, may potentially result in invasion of exotic grasses and replacement of native vegetation. We tested the hypothesis that a long-term effect of aeration and prescribed burning is an increase in exotic grasses. The study was conducted at the Chaparral Wildlife Management Area in the western south Texas plains where four treatments were evaluated: aeration, warm-season burn, aeration followed by a warm-season burn, and no treatment (control). The experimental design was a randomized complete block with four replicates. We estimated percentage canopy cover of exotic grasses, native grasses, forbs, litter, bare ground, and woody and succulent plants in 2007. There was a multivariate main effect among treatments for the dependent variables absolute canopy cover of exotic grasses, native grasses, forbs, litter, and ...

An Economic Comparison of Prescribed Extreme Fire and Alternative Methods for Managing Invasive Brush Species in Texas: a Modeling Approach

This article presents the results of a study to determine the economic feasibility of using prescribed fire as a rangeland restoration practice on private land when ambient air temperature is greater than and humidity less than the standards endorsed by the United States Department of Agriculture (USDA) Natural Resource Conservation Service (NRCS). The objective of this study was to evaluate the economic effectiveness of using prescribed summer burns compared to more commonly used practices for managing invasive woody plants. The research incorporates four contiguous counties in the Rolling Plains, Edwards Plateau and South Texas Plains eco-regions in Texas. Focus group meetings were held with landowners and NRCS and Texas AgriLife Extension personnel to obtain information about the most common economic uses of rangeland resources by landowners, the dominant invasive brush species, and the most commonly used practices and associated costs for controlling these invasive plants. An investment feasibility model was used to compare the economic efficacy of applying extreme fire and other commonly applied treatments to manage invasive brush species in the three Texas eco-regions. The economic analysis indicated that extreme fire was economically superior in all three regions and was the only treatment alternative that resulted in positive returns on investments in the treatments. The analysis included cost-share, which indicated increased returns for extreme fire and less negative returns for alternative treatments. The results of our study have implications for the review of current NRCS technical standards with respect to prescribed fire.