DEAD THE HORSE MOUNTAINS, ANNOTATED VASCULAR FLORA OF ON WITH NOTES LOCAL VEGETATION BEND NATIONAL TEXAS, PARK, BIG AND COMMUNITIES REGIONAL FLORISTIC RELATIONSHIPS Michael Powell Fenstermacher Joselyn A. Sul Ross State University BoxC-64. BoxC-64 USA 79832-0001, 79832-0001 USA. Alpine, Texas Texas Alpine, [email protected] Martin Terry JoeSirotnak Box 29 Sul Ross State University P.O. BoxC-64 BoxC-64 USA. 79832-0001, Texas d National Texas 79834-0029, Alpine, Park, ABSTRACT 686 Journal of the Botanical Research Institute of Texas 2(1) INTRODUCTION The Dead Horse Mountains (DH) of Big Bend National Park (BBNP) create a remote and forbidding view- no scape on the West Texas park's eastern skyline The rugged limestone escarpments offer reliable (Fig. 1). being un- surface water, nor infrastructure allowing quick access to the interior, leading to claims of as it (Wood rugged topography and charted wilderness 1999). These logistical challenges, in addition to et al. extreme climate, have the area one of the least botanically understood areas in Texas and the northern left Much The 100 Chihuahuan Desert Region (CDR). collecting has taken place in the area over the past years. SRSU by came and 1950s-1960s, included master's thesis height of early scholarly investigations in the a by and by numer- Wells Rogers (1964), a short but excellently characterized field report (1965), collections Warnock. The (SRSU) Barton coherent ous professionals including Sul Ross State University botanist largest body of collections was made for a report to the Nature Conservancy (Amos and Giles 1992), which at the now Gap owned Texas Parks and Black Wildlife time part of the study area that part of the Wildlife's a is made came from more near The majority vouchers through these easily-accessible areas, of efforts and without widely sampling the range of niche habitats roads peripheral the heart of the range, to trails no characterization existing in the area. Despite a rather active historical interest in this area, overall floristic more made Dead than one use Big has been the Horse. Several of local flora exist, including in for for lists unknown Bend National Park; however these are based on sightings, literature reports and, to an degree, Worthington herbarium specimens (Mahler National Park Service 1996; Louie 1996; Clelland 2001; 1971; Alex 2001; 2006). etal. A Bend Dead Horse an important context Big regional analysis of the will create for floristics. floristic DH The Trans-Pecos Mountains and Basins vegetational area (Hatch 1990) but are located in the et al. High phytogeographic connections have been noted with other Texas areas including the Plains, floristic known Tamaulipan Thornscrub Edwards and South Texas the Rolling Plains, Plateau, the Plains, also as more evidenced by populations region (Powell 2000). Connections to northerly vegetational areas are the of Rocky Mountain growing and aspen other species (Populus tremuloides), Douglas-fir (Pseudotsuga menziesii), Madre and well south of their normal distributions. Floristic links also reach south to the Sierra Oriental CDR Mexico The graminoid even has an Occidental, expanding the greater of (Larke 1989). flora affinity to many the Great Plains grasslands (Powell 2000; Christie 2006). Because there are so regions intergrading to expected in the local area, there high potential in the study area to discover species out of their ranges. is DH may new complex and microclimates harbor species Furthermore, topographically the resulting the is known from few Already little-known Andrachne arida only a to science. the area shelters several species: is DH CDR Dead purported Horse in the and has not been seen in the since the 1960s, while the localities endemic Hedyotis pooleana has not been observed since the original 1985 collection. Other species are as- known known sumed occur study based on but are not well understood, being in the area their habitat, to One only from a few collections in a restricted area. such example is Bouteloua kayi; previous to this study known was not occur in the study area but was discovered during the current work. to it The environmental complexity, in both topography and regional climate regimes, no doubt has helped CDR, endemics mostly produce the numerous endemic species of the but instead of being widespread, are to numbers County locally distributed (Brown 1994). Indeed, in Trans-Pecos Texas, Brewster tallies the highest (TAM-BWG however, of endemic 2007) and rare plant species (Alex et al. 2006; Poole et al. 2007). Often, known beyond Thus, concern data taken original collection targeted field species of are at their site. little new Dead studies in Chihuahuan Desert areas like the Horse have a high potential for floristic discoveries. body work composi- The main was describing the objective of this project to create a collective of floral tion of the DH. Goals accomplish this objective included: developing an annotated flora for the study to (1) new and through area through documenting existing voucher specimens in regional herbaria, collections more knowledge from a wide variety of underrepresented areas and habitat niches in the range; gaining (2) known but not recorded about little-known species that occur in the range, including species regionally yet Fenstermacher et Vascular flora of the Dead Horse Mi al., The Dead Horse Mountains study area. Western slopes of central portion of the range, with Sue Peaks at left of center. Fig. 1 . 688 Journal of the Botanical Research Institute of Texas 2(1) whether within the study and documenting the occurrence of novel species for the study area, rare, area; (3) and new and requirements. Subsequent disjunct, or invasive, providing insight into their distributions habitat was used Dead Horse regional context within the Trans-Pecos and analysis to interpret the flora in a larger MS also the larger southwestern United States. The study was conducted as the first author's thesis research m The (Fenstermacher 2007). thesis full photos can be found on Cactus Cons the CCI/botany/fdhm.html. DH mi The are located in the Big Bend region of western Texas, in southern Brewster County about 80 south of the town of Alpine (Figs. The study area boundary starts in the northeastern part of the national park 1, 2). Dog DH, and Canyon, continues south along the western foothills of the extends east into a portion of at (BGWMA), Texas Parks and Wildlife's Black Gap Wildlife Management Area including a few parcels of private DH ranchland The Rio Grande marks the southern The are a smaller, northern extension of limit. (Fig. 3). Carmen the impressive Sierra del of northern Mexico, exhibiting similar physical characteristics: northwest- with and rugged, rocky Extending 31.5 trending ridges alternating alluvial basins, generally arid, terrain. mi (51 km) N/S and an average of 8.5 mi (14 km) E/W, the study area covers approximately 176,800 acres km 276 mi2 715 2 and from 1800 (549 m) the Rio Grande 5840 (71,548 ha; ranges in elevation at to ft ft ), , m) (1780 Sue Peaks in the heart of the range. at Canyon The only major physical feature that trends east-west in the study area besides Boquillas along DH. the Rio Grande the 14-mile-iong (22.5 km) Telephone Canyon that bisects the There are several major is Any no permanent occurs usually drainages in the study area, but there surface moisture. precipitation that is flows overland into the dry arroyos, creating powerful but temporary floods draining towards the Rio Grande. Away eroded from the surface water found only unreliably in tinajas, stone basins usually out river, is i.e., summers and The of arroyo or canyon beds with bedrock outcrops. study area experiences hot cool-to-cold maximum winters. The average annual high 85°F while the low averages 53°F with an average annual of is C minimum common, mean 100° F/38° and of 33° F/l° C. Large diurnal temperature ranges are with a of maximum May 32° C and 50° peaks between and October, the about F/0° of about F/10° C. Precipitation a cm and 10 in/25 yearly average falling usually as late afternoon thunderstorms that range in intensity often Bend unpublished create hail (temperature data from National Park Service, Big National Park, data). DH The are composed primarily of lower Cretaceous limestone deposited in a deep sea environment As was and ca. 180 mya. the area close to the shoreline of the great interior sea, as sea levels fluctuated, some and were changing environment. During the Cenozoic 30 shales clays deposited, reflecting the (ca. mya), massive blocks of Del Carmen and Santa Elena Limestone were uplifted and tilted along fault lines, resulting in the basin and range morphology seen today: gradual western slopes and steeper escarpments DH with between (Maxwell mostly shallow with basins are a to the east, alternating alluvial in 1979). soils Rock and most high percentage of rock fragments (mostly calcium carbonate). outcrops are frequent slopes are steep. There are small, localized areas on alluvial uplands where the soils are slightly deeper, while deep, The loamy can be found in some basins and near the Rio Grande. highest elevations have soil darker in soils & may because high organic content and be moist more often than dry (Cochran Rives 1985). color of its Human and Disturbance Regimes History (12,000-6500 BC) and were Bend Paleo-Indian period there People living in the Big area as early as the late AD; abundant evidence of habitation in the Dead Horse dating from the Archaic period (6500 BC-ca. 100 is DH Alex 1990). The periphery of the was most probably used as a travel corridor throughout history until AD- from more permanent settlement occurred in the Historic era (1535 present); after the threat hostile Indians was removed, ranching and mining increased substantially (Tyler 1975). activities DH Human-induced disturbance regimes that have affected to a small degree include grazing, natural- and developments resource harvesting of Euphorbia Bouteloua ramosa, infrastructure related to antisyphilitica cinnabar ore mining, and recreational pursuits such as hiking, camping, and river rafting. However, the fire, Fenstermacher et Vascular flora of the Dead Horse Mountains al., Journal of the Botanical Research Institute of Texas 2(1) Mixed Desert Scrub lower Telephone Canyon itudy area. A. (dsc), upper Telephone Canyon Sotol-Yucca Grassland B. trail ;a. (syg), Fenstermacher et Vascular flora of the Dead Horse Mountains al., Journal of the Botanical Research Institute of Texas 2(1) Dead Mountains Fenstermacher et Vascular flora of the Horse al., Sue Sue 4g-h. Examples of vegetation zones within the Dead Horse Mountains study area. G. Sotol-Yucca Grassland, Peaks. H. Chaparral, different Fig. 694 Journal of the Botanical Research Institute of Texas 2(1) most damaging and far-reaching would likely be the increased distribution and dominance of invasive plant and Jamarix and Arundo donax have expanded range along the Rio Grande, creating miles their species. spp. lower miles of dense thickets lining the riverbanks. Pennisetum ciliare is well established in the elevations of become BBNP, including the extreme southern end of the study area. However, not as dense as has in is it it and The other low-elevation perhaps being held in check by other non-native species, burros horses. areas, up park from Mexico, trampling vegetation and breaking biological crusts, increasing livestock enter the many the erosion potential in places along the river corridor. may Fire be a significant natural factor driving the study area ecology, creating the characteristic Human-caused limited the developed areas but the patchiness of higher elevation vegetation. are to fires more burns mainly burning an individual yucca in barren rocky areas, but lightning interior are strikes, where biomass Henrickson sometimes being carried through drainages or at higher elevations the is denser. CDR may Woodland community be and Johnston unique Yucca higher elevations (1986) suggest that the at mono more woody There has been by maintained favoring the semi-succulent cots over species. little fire, DH, should be considered normal. suppression in the so current states effort General Vegetation Description CDR Many For whole, workers have proposed vegetation classification systems relevant to the region. the as a & Henrickson and (Morafka there exist excellent overviews of basic detailed vegetation structure 1977; & Brown (Rogers Johnston 1986, 2004; 1994; Powell Hilsenbeck 1995). Descriptions in several local floras & & Amos 1964; Butterwick Strong 1976; Giles 1992; Hardy 1997) demonstrate the degree of local diver- Beyond tendency towards by possible within hierarchies created the above publications. a large-scale sity DH CDR plant-community homogeneity (Brown 1994), the and larger have basic types that intergrade and change abundance and dominance response complex physiography. Perhaps Whittaker, in the in to Chihuahuan Desert vegetation quoted in Takhtajan has offered the best explanation for general as (1986), warm, no convergence dominant forms can be found in patterns: in semi-arid deserts there clear of as is Warm may canopy be dry support arborescent life-forms or consistent cool semi-deserts. deserts too to However growth supported pockets higher moisture non-arborescent in of availability, cover. a diversity of is and such shrubs maintained by the right combination of aspect, slope, elevation, substrate. Larger plants, as Many and wind shade and Yucca can microclimates. species take advantage of the spp., also create special CDR— low canopy protection that these larger nurse plants provide. This could be considered the of the and discontinuous, but functional. Two some maps, produced through remote sensing and vegetation sampling, generally include vegetation Wood by sampling and ground- inadequate the study area (Plumb 1991, 1992; 1999) but are limited et al. However form an impression the importance of cover types. truthing. they are useful overall of relative to 50.4% on maps, Lechuguilla Scrub covers Based a consolidated version of Plumb's (1991, 1992) vegetation and Opuntia Euphorbia of the study area. This vegetation type includes Agave lechuguilla, spp., antisyphilitica, many species of grasses. Almost equally important in the study area is the High Desert Grassland vegetation and codominant 45.1% coverage, where species like Nolina erumpens, Dasylirion leiophyllum Yucca spp. are at with graminoids. METHODS known The herbaria of institutions that sponsored botanists to collect in the Big Bend, in addition to those when Angelo geographically the study were contacted and possible electronically searched: State close to area, New Garden (NYBG), York Botanical University (SAT), the Botanical Research Institute of Texas (BRIT), the A&M Sam Houston State University (SHST), Sul Ross State University (SRSC), the Texas University Biology A&M's (SWT), Uni- Department herbarium (TAMU), Texas Tracy herbarium (TAES), Texas State University Kansas (KANU), Texas Austin (TEX-LL), the University of Texas El Paso (UTEP), versity of University of at at BGWMA. SRSC and and Bend were conducted Big National Park (BIBE). Sheet-by-sheet searches at