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Floristic provinces/areas of endemism of North America. Regional schema adapted from Takhtajan (1986) as published in Thorne (1993). The areas were drawn in Photoshop by Alice Tangerini on a base map from ArcMap8.2 with a North American Lambert conformal conic projection. The map was published in Katinas et al. (2004) and is used with permission of Missouri Botanical Garden Press and the authors.
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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 Te...
Citations
... One of the major and long recognized biotic boundaries in North America is the east to west boundary (Katinas et al., 2004;Escalante et al., 2013;Gámez et al., 2016;Mishler et al., 2020). In the southern United States, it passes through Texas (Saghatelyan, 2009(Saghatelyan, , 2015(Saghatelyan, , 2017, where it separates almost adjacent floras (Supplementary Appendix S1), the flora of Big Bend National Park (BB) from the floras of Edwards Plateau (EP) and South Texas Plains (S TX). Texas lies on the intersection of the Madrean and Atlantic regions in Takhtajan's (1986) floristic system, as well as close to the Nearctic/Neotropical Mexican Transition Zone of Morrone (2010) and Halffter and Morrone (2017). ...
... Two areas in southern Texas (Supplementary Appendix S1), BB and S TX, represent the northern parts of the Chihuahuan and Tamaulipan subprovinces of Takhtajan (1986) respectively. S TX and EP (of the Prairie province) also represent an ecotone between the floras of the southwestern (Madrean) and eastern (Atlantic) regions (Saghatelyan, 2015(Saghatelyan, , 2017. The floras of the Sonoran and Mojave Deserts in southwestern Arizona, northwestern Mexico, and southeastern California represent the Sonoran province/subprovince of all authors. ...
The history and connections of the flora of south-central/southwestern (SC/SW) North America have been studied and summarized in biogeographic regionalization. However, some studies show contrasting delineations of the SC/SW North American provinces that could be better determined using quantitative methods. We aimed to find spatial patterns of a set of plants in the SC/SW United States by conducting endemicity analysis (EA) on different scales. We first built a dataset with 81,965 specimen point records of 400 species from 174 genera and 61 families of angiosperms and two genera of gymnosperms using digitized specimen data from iDigBio. We then performed EA at four different scales to identify the areas of endemism (AoEs). We obtained 28 AoEs with different cell sizes by selecting each AoE under the grid size that yielded the highest number of high-scoring species. The study region split into two significant centers of accumulation of nested or partially overlapping AoEs: the SW and SC consensus areas. In these parts of the Nearctic region, many genera/clades, among those in the dataset, showed a geographic split into western and eastern clades. The split corresponded to an environmental and physical barrier known as Cochise Filter Barrier. The Sonora–Mojave arid center, parts of South Texas, and the Chihuahuan Desert harbor basally branching taxa of several genera and even families, based on the observations of some species, which allowed identification of the AoEs.
... A second major boundary is east to west boundary (Katinas et al., 2004;Escalante et al., 2013, Gamez et al., 2016Mishler et al., 2020). In southern USA, it passes through Texas (Saghatelyan 2009(Saghatelyan , 2015(Saghatelyan , 2017, where it separates almost adjacent floras of Big Bend National Park (BB) and the Edwards Plateau (EP) (Map 1, Supplemental Information 1). In the floristic regionalization system of North America by Takhtajan (1987), BB falls in the Madrean region (MR) while EP falls in the Atlantic region (ER) of the Madrean and Boreal subkingdoms respectively. ...
... We compiled the database with 81,851records of 400 species in 174 genera and 61 families of angiosperms, and 2 genera in 2 families of gymnosperms. More than half of the species were selected, using the classification of geoelements (species with congruent distributions) from the checklists of BB, EP, and S TX (Saghatelyan, 2009(Saghatelyan, , 2015(Saghatelyan, , 2017 to represent the different floristic regions and provinces which intersect in Texas. Also included are species of the western parts of the Madrean region in the USA from the floras of southern 3 Arizona, New Mexico, and California (SENet Portal: http://swbiodiversity.org/seinet/; ...
Areas of endemism (AEs) are fundamental entities of analysis in biogeography and a key step for biogeographical regionalization. Even though many studies have contributed to the biogeographical knowledge of southern USA flora, no endemicity analysis (EA) has been conducted that would include a large number of native seed plant species from different families. A new analysis of plant spatial patterns is important as a first step for a future updated floristic regionalization of North America North of Mexico. It has become easier to accomplish owing to the increased availability of large-scale digitized distributional data and statistical methods of biogeographic analysis. Here we identify the AEs in SC/SW USA using digitized plant specimen data available from IDigBio. We built a database with 81,851-specimen point records of 400 selected mostly angiosperm species and applied the NDM/VNDM method of endemicity analysis. We then compare the established 26 AEs in the area of study with the floristic provinces in two comparatively recent regionalization systems of USA. To understand the spatial patterns, we also pay attention to the information on relationships of the endemic species found in phylogenetic literature.
... It is located to 50-75 km north of the river in Texas (Blair, 1950), and into the states of Coahuila, Nuevo Leon and Tamaulipas (Pérez et al., 2013). It supports a host of flora and fauna comprising 1200 plant, 700 vertebrate, and 300 butterfly species, including 17 federally listed endangered and threatened species (Jahrsdoerfer and Leslie, 1988;Saghatelyan, 2017). However, agricultural expansion and urbanization led to the removal of 90-95% of the original vegetation (Tremblay et al., 2005;Jahrsdoerfer and Leslie, 1988). ...
In the Lower Rio Grande Valley (LRGV) of south Texas, native thornscrub forest restoration has been ongoing for the past four decades, yet few assessments of their efficacy exist, and no study has yet quantified species-specific responses. Seedling transplantation in conjunction one or more restoration interventions (RIs) remains the method of choice at most sites, and thus the initial months following transplantation, when seedlings are especially vulnerable to drought and animal damage, are a critical time for determining restoration success. To this end, we evaluated the survival, growth, and animal damage of 3600 native seedlings of 24 thornforest species in response to RIs incorporating a combination of seedling shelters and slow-release moisture, as well as a mycorrhizae-biostimulant admixture (MBS). We surveyed seedlings on a bi-monthly basis over one year following planting at a semi-arid upland site in the LRGV. We found that while shelters had a pronounced and lasting impact on height growth (increased by 15–27% on average), reduction of mortality by seedling shelter RIs was only modest (reduced on average by 5–12% per species), with significant benefits accruing from cocoon shelters only, which provide slow-release moisture to the seedling roots during the initial month after planting. Species-specific responses were the most variable, with mortality ranging from 8 to 69%. While shelters in some cases reduced mammalian herbivory, the growth of leggier stems and degradation of biodegradable shelters may reduce their overall efficacy. We conclude that thornforest restoration may be most effective when seedling performance is considered in species selection and costly restoration interventions are applied on species-specific basis. These results contribute an important first step towards optimizing forest restoration efforts in the LRGV on the basis of species identity and kickstart a species-specific database of seedling demographic responses in semi-arid forest restoration.
Reforestation in the Lower Rio Grande Valley (LRGV) of Texas began in the 1960s and to date over 6,475 ha of land has been reforested. However, there has been minimal assessment to understand differential species success, compositional trends, and the aboveground C sequestration potential of these developing forests. We coupled quantitative planting information of >50 native woody tree and shrub species with surveys of 5,223 stems of 4,606 individuals in a chronosequence of restored forests ranging in age from 1 to 33 years to estimate species-specific mortality rates, biomass accumulation and recruitment, as well as compositional trends in the herbaceous understory. We show that 7–15 years are required for mortality rates of the transplanted cohort to stabilize to background levels observed in other dry forests. A small number of species, mostly N-fixing trees with a deep rooting habit, persisted on the landscape beyond 15 years. Even so, aboveground biomass (corrected for differences in initial planting density) accumulated at an average rate of 1.41 Mg ha⁻¹ yr.⁻¹ compared to 0.35 Mg ha⁻¹ yr.⁻¹ for a fallow old-field. Species biomass growth rates increased with decreasing mortality, as did the abundance of recruits, suggesting a degree of reproduction by initial planted cohorts. However, a suite of highly competitive exotic grasses increases in density over a 25-year period, which we link to suppressed seedling recruitment. This poses a serious challenge to the long-term sustainability of planted forests in the LRGV. We highlight potential avenues of research and modification to restoration methodologies.
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A noted impact of urbanization is the tendency for biotic homogenization, or the increase of similarity of geographically disparate communities. On the other hand, some urban habitats harbor biodiversity native to their region, a role potentially important in xeric landscapes, with irrigation increasing the coverage and availability of mesic habitats in an otherwise water-limited landscape. We assessed the relative importance of urban yards as agents of biotic homogenization or riparian refugia by characterizing community composition of Tamaulipan thornforest land snail assemblages across a pronounced precipitation gradient in far south Texas, USA. We quantified α- and β-diversity and assessed whether the land snail fauna of urban yards are more similar to each other across a precipitation gradient than they are to their wild counterparts, as well as determined the significance of moisture in driving Tamaulipan thornforest β-diversity, both in terms of turnover (changing species composition) and nestedness (species loss). Sites with both the wild and wet conditions had the highest values of species richness and abundance. Urban land snail communities were significantly homogenized, outweighing the influence of the precipitation gradient. We did not find urban yards served as a refuge for native, moisture-dependent, riparian snails. Our analyses find that turnover, not nestedness, is the largest contributor to β-diversity in these assemblages. Studies of urbanization should address regional spatial scales to quantify how urbanization modifies regional biodiversity arising from background environmental gradients. Such an approach could lead to improved understanding of how large metroplex areas could be used to maintain and even promote biodiversity.
