sign in sign up
<<
Home , Castilleja aquariensis, Chuska Mountains, Kaibab Plateau, La Sal Mountains, Mogollon Mountains, Mogollon Plateau

Relationships Between Rare of the White Mountains and the Late Cenozoic Geology of the

JONATHAN W. LONG

Rocky Mountain Research Station, U.S. Forest Service 2500 South Pine Knoll Drive, Flagstaff, AZ 86001

ABSTRACT. A complex geologic history has shaped the distribution of ( Dorn) and the Mogollon paintbrush ( mogollonica Pennell). These subalpine plants do not appear to be strict substrate specialists, but they do seem to favor coarse-textured and well-watered soils. Most of their occupied habitats were shaped by Quaternary glaciations, but are ultimately derived from felsic substrates formed before the Pliocene period. Populations of Arizona willow have been identified in the White Mountains of Arizona, the High of , and in the Southern of and Colorado. Species closely related to the Mogollon paintbrush also occur in the Utah plateaus and the . Genetic dissimilarity among these populations suggest that these taxa likely share an evolutionary history that extends into the Neogene, when tributaries of the ancestral connected young volcanic highlands on the margins of the . This history points to the likelihood of additional populations of Arizona willow in the San Juan Mountains, and it suggests that these plants have survived dramatic changes in their environments. These patterns demonstrate the value of analyzing geology at a detailed level when interpreting habitat preferences and distributions of rare species.

INTRODUCTION The Mogollon paintbrush (Castilleja A few species are endemic to only the mogollonica Pennell) is another rare White Mountains of Arizona, but the list that is endemic to the White has grown shorter in recent years. The Mountains of Arizona, but whose status Arizona willow (Salix arizonica Dorn) as a separate species has been was thought to be a member of this questioned. Pennell first described this select group until Robert Dorn yellow-bracted paintbrush as a separate reidentified a specimen in the Rocky species (Pennell 1951). Holmgren Mountain Herbarium that had been (1973) placed it in the Septentrionales collected in 1913 from southern Utah. group, which includes the yellow- This realization led to the recognition of bracted sulphur Indian paintbrush (C. Arizona willow populations in southern sulphurea Rydb.) as well as several Utah, northern New Mexico, and endemic species of the Southwest (Fig. southern Colorado (Thompson et al. 2). National plant databases (the 2003). The scattered populations in these USDA’s PLANTS National Database four states represent the known and the University of North Carolina’s distribution for the species (Fig. 1). Biota of North America Program) currently hold that C. mogollonica is a synonym for C. sulphurea, which is

59

FIGURE 2: Distribution of members of the FIGURE 1: Distribution of Arizona willow in the Septentrionales group of Castilleja in the Colorado Colorado Plateau region. Plateau region based on Holmgen (1973). distributed widely in the Rocky isolated from other high mountain Mountains. However, a taxonomist ranges during the time in which new currently working with the genus holds species have evolved. that C. mogollonica is a valid species, SIGNIFICANCE OF GEOLOGY TO PLANT and instead C. sulphurea should be DISTRIBUTIONS synonymous with C. septentrionalis (Lindl.) (Egger 2004). Reconstructing the geologic evolution of landscapes helps to explain the With the exception of retaining C. distributions of endemic species. mogollonica, plant nomenclature used Geology not only explains the past throughout this paper conforms to the conditions an organism has withstood, PLANTS database (http://plants.usda.gov). but it also regulates present aspects of Some biologists have even questioned habitat including climate (through the status of the flagbearer of rare orographic effects), hydrology, and soil species in the White Mountains, the chemistry. However, many ecologists trout. Some taxonomists studying rare biota in the White contend that this trout should be Mountains of Arizona have either designated merely as a subspecies (i.e., ignored geologic variation or Oncorhynchus gilae ssp. apache) oversimplified it. For example, in (Behnke 2002). These trends reflect in discussing the biogeography of the part the vicissitudes of . endemic Mogollon paintbrush, However, they also may reveal a Bainbridge and Warren (1992) described growing recognition that the White the region as “basaltic.” Similarly, the Mountains have not been entirely conservation agreement for the Arizona

60 willow asserted that all but one formed from felsic volcanic flows during population of the plant occur on the late Miocene period (Merrill 1974). "basaltic (volcanic) soils" (AWITT Mudflows and lahars down the young 1995). These statements are incorrect, created extensive deposits of and they mislead readers to assume that colluvium that are known as the the White Mountains are monolithic. Crossing Formation (Merrill 1974). The geologic formations underlying During the Quaternary, four distinct populations of Arizona willow and glacial events sculpted the two highest Mogollon paintbrush in Arizona remnant peaks of the volcano, Mount originated from felsic Tertiary Baldy and Mount Ord. The earliest volcanism, which formed several other glaciation carved out five U-shaped montane regions in the Southwest. Some valleys that flowed to the west, north, researchers have considered the and east (Merrill 1974). Within the past importance of variation among these 3000 years, a very small glacier occurred volcanic landforms as well as the on Mount Ord, while periglacial activity influence of glaciation in evaluating the formed talus deposits in northeastern habitat of rare species in the White drainages of the volcano Mountains. Ladyman (1996) reported and also shaped some of its south-facing that the endemic Mogollon Clover slopes (Merrill 1974). (Trifolium neurophyllum Greene) Populations of Arizona willow in appeared “to be positively associated Arizona are concentrated on landforms with basalt soils and negatively derived from the felsic Mount Baldy associated with datil soils” [Datil Group volcanics (Long and Medina, this volcanics are predominantly felsic proceedings, Geologic Associations of pyroclastic rocks containing pumice and the Arizona Willow in the White ash located east of Mount Baldy in New Mountains, Arizona). The four Mexico (McIntosh and Chamberlin populations on glacial deposits are the 1994)]. Other researchers have argued largest and highest density populations that Pleistocene glaciation had been a in Arizona, with estimated populations primary factor controlling the in the hundreds or thousands (AWITT distribution of Arizona willow and other 1995). Nearly half of the subpopulations willow species (Price et al. 1996). Rinne are located on sites mapped as the Sheep (2000) hypothesized that both mineral Crossing Formation, which is a composition and glacial history could sedimentary formation also derived from account for reported differences in trout Mount Baldy volcanics. Most of the productivity between streams derived remaining populations occur within four from rocks close to the Mount Baldy kilometers downstream of outcrops of volcano and those farther away. this formation. The Sheep Crossing Formation is texturally indistinguishable GEOLOGIC ASSOCIATIONS OF ARIZONA from glacial tills in the area, although it WILLOW was deposited millions of years earlier White Mountains, Arizona from debris fans and mudflows from A complex series of volcanic flows Mount Baldy (Merrill 1974). created the White Mountains, but the Comparisons of plant densities to central massif of Mount Baldy was substrates show that alluvium, glacial

61 deposits, and Sheep Crossing Formation appears to be the only one in Utah represent the prime habitat for Arizona occurring in a watershed devoid of willow in the White Mountains. Small Tertiary volcanics. However, at least six populations occur on surfaces mapped as other populations have diverse substrates basaltic flows, although these deposits in their watersheds, leading Mead (1996) may be thin enough that underlying to characterize them as being derived in felsic formations yield water and part from sedimentary formations. substrates to the inhabited areas. Southern Rocky Mountains, New High Plateaus, Utah Mexico and Colorado The Utah populations occur in the In northern New Mexico, the Arizona High Plateaus region (Fig. 1) which is willow occurs in at least 21 populations capped by andesitic and dacitic Tertiary in the Sangre de Cristo Mountains and volcanics of the Marysvale volcanic four populations in the field as well as some younger basaltic (Atwood 1996; Atwood 1997; Dorn flows (Stokes 1986; Luedke 1993; 1997). The rocks underlying these areas Rowley et al. 1994). Thus, the petrology are more varied and much older than and age of the High Plateaus of Utah are those in the White Mountains of Arizona similar to the White Mountains volcanic or the High Plateaus of Utah due to the field of Arizona. The populations of tremendous uplift of the Rocky Arizona willow in Utah are scattered Mountains. Substrates for Arizona across the plateaus, with the greatest willow habitat appear to become more concentration on the Markagunt Plateau diverse in these taller mountains. In the around Brian Head, a geologic cousin of Sangre de Cristo Mountains, eight Mount Baldy. Several drainages on the populations in the Pecos drainage are eastern side of this peak were glaciated. found on areas that have been mapped as Nearly 100 kilometers to the northeast Pennsylvanian undifferentiated lie two populations in glacial deposits sedimentary deposits (Miller et al. along Seven Mile Creek on the Fish 1963). Thirteen populations near the Lake Plateau, which is also derived from northern border of New Mexico coincide Tertiary volcanics (Mead 1996). Those with a jumble of upper Oligocene Tertiary lava flows once connected the volcanic rocks and glacial deposits Fish Lake and Markagunt Plateaus, (Green and Jones 1997). Populations in although drainages have since cut down the San Pedro Parks of the Jemez between them. Mountains are underlain by lower An isolated population has been Proterozoic plutonic rocks (Green and reported from the Wasatch Plateau, Jones 1997). A recently discovered representing the currently known population in the southern San Juan northern limit for the species. Another Mountains of Colorado (Colorado small population occurs on the East Fork Natural Heritage Program 2001) is of the on the Paunsaugunt located on Oligocene silicic volcanics Plateau where Tertiary volcanics have (Steven 1975) that were sculpted by been eroded away. This population lies glaciers during the Quaternary. in Quaternary alluvium derived from GEOLOGIC ASSOCIATIONS OF MOGOLLON Wasatch limestone and Kaiparowits PAINTBRUSH AND RELATED Formation (Doelling et al. 1989), and it SEPTENTRIONALES

62 Stream reaches harboring Mogollon parvula Rydb. on the Tushar Plateau, paintbrush were reported by Bainbridge and C. occidentalis Torr. in the La Sal and Warren (1992) and Carl-Eric mountains. The closest relative to both Granfelt (unpublished data). C. aquariensis and C. mogollonica Approximately 12 populations of appears to be the yellow-bracted C. Mogollon paintbrush found in the White sulphurea, which grows throughout the Mountains occur on surfaces derived Rocky Mountains from Alberta to from Mount Baldy volcanics and four southern New Mexico (Holmgren 1973). more are within five kilometers These three species form a group downstream of such outcrops. Four more intermediate in morphology between the populations occur on areas mapped as "occidentalis alliance," which includes younger basalts in drainages of Snake C. revealii and C. parvula, and an Creek that do not flow downstream from alliance of C. kaibabensis and C. Tertiary volcanics. However, the basalt miniata (Dougl. ex Hook.) (Holmgren layers in this area are thin and contain 1973). porous cinder deposits. Consequently, GEOLOGIC FACTORS GOVERNING THE there are likely to be subsurface DISTRIBUTION OF ARIZONA WILLOW AND hydrologic connections to the slopes of MOGOLLON PAINTBRUSH Mount Baldy. Many interrelated factors may Mogollon paintbrush occurs at constrain habitat for the Arizona willow approximately 15 sites with Arizona and Mogollon paintbrush. Factors such willow, with five more sites occurring as high elevation, cold temperatures, and within three kilometers of Arizona increased precipitation are associated not willow populations. This association only with glaciers, but also with the suggests that habitat for the two species volcanic formations that cap most of the are quite similar, although the paintbrush plateaus and mountain peaks of the typically occurs in drier portions of Southwest. These correlations and the meadows. However, the paintbrush has limited fossil evidence of pre-glacial been observed only in north or conditions complicate attempts to infer northeast-trending drainages in areas the role of glaciation in distributing the that were above tree-line during the last modern flora. The effects of glaciation glacial maximum (Merrill 1974). appear to have interacted with the Although C. mogollonica appears to composition of underlying formations to be a distinct species, it has several produce the habitats presently occupied relatives in the Septentrionales group by these plants. that occur in the Intermountain and Glaciation Southern Rocky Mountain regions (Fig. 2). Castilleja aquariensis N. Holmgren Glaciation unquestionably had is a related species that grows in dramatic effects on the habitat currently subalpine sagebrush meadows on the occupied by Arizona willow in Arizona, Aquarius Plateau. Other paintbrushes since most of that area would have been isolated in southern Utah include C. above treeline during the three major revealii N. Holmgren on the glaciations (Merrill 1974). The cooler Paunsaugunt Plateau, C. kaibabensis N. and moister climate during the Pliocene- Holmgren on the , C. Pleistocene glacial periods would have

63 created more favorable conditions at low All populations in New Mexico and elevations, while proglacial erosion Colorado are found well above 3000 m would have deposited favorable in areas that were shaped by glaciers substrates far downstream in the three throughout much of the Plio-Pleistocene. major glaciated river valleys where Frost action has greatly affected these Arizona willow occurs (Black River, high altitude areas, since the southern , and ). part of the Sangre de Cristo Mountains Periglacial activity also shaped non- has the highest incidence of freezing and glaciated drainages, including Becker thawing of any area in North America Creek, which has prominent talus (Miller et al. 1963). deposits (Merrill 1974). Becker Creek The retreat of glaciers appears to have also has some of the densest populations created optimal habitat for the Arizona of Arizona willow and Mogollon willow; however, many smaller paintbrush in Arizona. Price et al. (1996) populations of Arizona willow are found noted that heavy snows and rock slides in unglaciated areas shaped by help to rejuvenate willow stands. These periglacial activity such as nivation, responses suggest that periglacial frost action and talus formation. Rock activity could stimulate expansion of slides, exposure of mineral soil, and willow populations. stream braiding are mechanisms that In Utah, glaciation affected many of would have created willow habitat. the locations harboring Arizona willow. Glacial and periglacial activity alone do Mead (1996) classified seven sites, not explain the distribution of Arizona including the largest and healthiest willow, since the plant has not been stands, as being partially derived from reported from many other glaciated glaciated materials. Two of them, Sidney mountains in the region (e.g., San Valley and Castle Valley, have extensive Francisco Peaks, La Sal Mountains, and accumulations of glacial till (Gregory Tushar Mountains) and since its 1950). The Fish Lake and Wasatch distribution is narrow even within areas plateaus, where isolated populations of affected by glacial activity. Therefore, Arizona willow occur, were also other factors such as mineralogy and glaciated (Stokes 1986). The hydrologic connections should be Paunsaugunt Plateau, a third area considered to explain the biogeography harboring Arizona willow, was not of this species. glaciated, although many slopes show Volcanics effects of nivation in past and present Analysis of distributions suggests that (Gregory 1950). Moreover, deposits of the Arizona willow presently has a Quaternary unconsolidated debris are strong affinity for substrates derived found at the top of the drainage where from Tertiary felsic volcanics. The the Arizona willow occurs (Doelling et Tertiary volcanics of Mount Baldy in al. 1989). Frost action has fractured lava Arizona and the High Plateaus of Utah rocks on Brian Head and sandstone are dominated by andesitic to dacitic blocks on the Markagunt Plateau, rocks with silica contents ranging from forming talus piles at the base of slopes 54 to 70% (Nealey 1989; Luedke 1993). that supply substrates to the alluvial Tertiary volcanics in the Sangre de systems (Gregory 1950). Cristo Mountains where Arizona willow

64 occurs include a mixture of rhyolitic- where less permeable basalts force the pyroclastic rocks, andesites and basaltic water to the surface (Merrill 1974). andesites with local felsic flows, and Arizona willow and other felsic flows and pyroclastic rocks (Green congregate at these seeps and springs at and Jones 1997). The area containing the the base of the mountain. lone identified population in Southern Non-volcanic-derived Sedimentary Colorado appears on a small-scale map Formations (Luedke 1993) to be underlain by Tertiary dacite (62-70% silica). Although Arizona willow appears to Throughout its range, Arizona willow favor volcanic substrates in Arizona and seems to be rarely associated with in Utah, it does occur in soils derived basaltic rocks, which have less than 50% entirely from sedimentary substrates, silica content. including the Claron Formation and Kaiparowits Formation (Mead 1996). Many factors that vary between the However, these substrates appear to different mineralogies influence plant share the coarse textures found in the distributions, including age of formation, volcanics. Many of the sedimentary topography, soil texture, hydrology, pH, formations of southern Utah weather to and nutrient levels. As silica-rich fairly coarse cobbles and gravels volcanics weather, they form relatively (Doelling et al. 1989). Limestone gravels deep, acidic soils with low clay content derived from the Claron Formation resist and low organic matter content abrasion and deterioration (Doelling et (Freeman and Dick-Peddie 1970). al. 1989). The Kaiparowits Formation is Flatter-lying basaltic landforms, on the predominantly sandstone, with other hand, tend to form fine-textured occasional conglomeratic beds appearing soils. At several of the sites in Arizona in the western exposures where Arizona where Arizona willow does occur on willow occurs (Doelling et al. 1989). basalt, the rocks are highly fractured Thus, this formation has potential to (pers. observation). Such fractured weather into coarse, silica-rich substrates may allow greater aeration substrates as well. In New Mexico's than is typical of most meadows formed Sangre de Cristo Mountains, from basalts. sedimentary formations bearing Arizona Volcanic-derived Sedimentary willow include undifferentiated Formations Pennsylvanian formations. The stratigraphy of these formations is Because felsic volcanics tend to form complex and hard to discern due to steep domes (Stokes 1986), erosion of extensive vegetative cover, but they are these landscapes may accumulate coarse generally comprised of quartzite-rich substrates in alluvial and colluvial sandstones and limestones of widely valleys. In the White Mountains, these varying ages (Miller et al. 1963). deposits include glacial tills and the Sheep Crossing Formation, which are Edaphic Characteristics texturally indistinguishable (Merrill and Many of the geologic formations Péwé 1971). These “gravelly sands” where Arizona willow grows produce promote hydraulic conductivity and coarse-textured mineral soils. Good serve as shallow aquifers by conducting hydraulic conductivity and aerobic flow from Mount Baldy to contact areas

65 conditions provide favorable habitat, up through shales and sandstones particularly for the tallest and most (Stokes 1986; Betancourt 1990). productive willow plants (Long and Ecologists have reported many Medina, this proceedings, Geologic examples of glacial-pluvial flora whose Associations of the Arizona Willow in distributions are governed by differences the White Mountains, Arizona). in substrates. Several willow species However, other soil factors, including may reach their southern limits in the soil chemistry, may govern the igneous White Mountains of New physiologic factors that lead to this Mexico because the coarse-textured association. geology maintains adequate soil water No studies have described soil (Freeman and Dick-Peddie 1970). preferences of Mogollon paintbrush, but Several conifer species extend their one should expect correspondence to lower elevation limits in sandstone- those of Arizona willow given their derived soils (Betancourt 1990). On the close association. Other members of the other hand, shale and limestone Septentrionales group also inhabit substrates may impose higher elevation coarse-textured soils. C. revealii inhabits limits, where only specially-adapted "limestone gravelly soil," and C. species may survive (Betancourt 1990). aquariensis grows in "rocky soil" Bristlecone pine (Pinus longaeva D.K. (Holmgren 1973), although neither Bailey) enjoys a competitive advantage occurs in wetlands. C. septentrionalis on dolomite in the Sierra Nevada due to inhabits “damp, rocky soil” (Pennell its tolerance for low water and nutrient 1935). Given their relatively narrow conditions (Wright and Mooney 1965). distributions, some members of the These examples reveal the importance of Septentrionales group appear to be more geology in determining suitable refugia edaphically constrained than Arizona for subalpine plants in the Southwest. willow. EVOLUTIONARY HISTORY OF THE While Arizona willow and members ARIZONA WILLOW AND MOGOLLON of the Septentrionales group do not PAINTBRUSH appear to be strict substrate specialists, The distributions of the Arizona they both show affinity for coarse- willow and the Mogollon paintbrush textured soils. The sands and gravels could yield insights into the broader may be derived from a variety of parent landscape evolution of the Colorado materials, including extrusive volcanic Plateau. If the presence of these plants and sedimentary deposits from the were tightly linked to the Pleistocene Precambrian, Paleozoic, and Cenozoic glaciations, then continued warming eras. However, populations are small or might portend rapid doom for these absent from fine-textured soils derived species. On the other hand, if the plants from Pliocene or Pleistocene basalts. had dispersed across the Colorado The La Sal, Henry, and Abajo Plateau far earlier, then they would have Mountains represent a very different demonstrated resilience to the dramatic landscape type because they are climatic swings of the Pleistocene. relatively steep, laccolithic mountains composed of igneous rocks penetrating Opportunities for a Quaternary Dispersal

66 During the Pleistocene, the range of White Mountains, including the Arizona willow may have been larger Mogollon clover, the Goodding onion and more contiguous (Price et al. 1996). ( Ownbey), and the A cooler and moister climate during the Gila groundsel (Packera quaerens Pleistocene would have created more (Greene) W.A. Weber & A. Löve), favorable conditions at low elevations. extend into the of Increased rainfall, glacial and periglacial New Mexico. However, because those processes would have accelerated plants occur in lower elevation, drier erosion, invigorating populations of the microsites on mafic soils, they are less willow and exposing new areas for likely to share the evolutionary history colonization on gravel-rich fan deposits. of the Arizona willow and Mogollon Frost action and erosion may have paintbrush. broken up thin basalt deposits at the Populations of Arizona willow in edges of the volcanic outcrops, exposing Utah remain hydrologically connected new microsites. Headwater stream through the drainages of the Sevier captures also may have provided yet River, which flow into Sevier Lake, a another avenue for dispersal into vestigial Pleistocene pluvial lake. This unoccupied habitats. distribution suggests that Arizona Biogeographers have contended that willow may have been more widely the mountains of Central Arizona and distributed throughout the Sevier the High Plateaus of Utah were watershed, perhaps extending to the ecologically connected to the Southern shores of the Pleistocene Lake Rocky Mountains of Colorado and New Bonneville along with other subalpine Mexico during the last glacial maximum flora (Betancourt 1990). A colder and (Moore 1965; Betancourt 1984). Bailey wetter Pleistocene climate would have (1970) posited that Pinus aristata promoted contiguity among the (Engelm.) descended the Sangre de populations in Utah. Cristo Mountains, crossed the Rio Arguments for a Tertiary Dispersal Grande, traveled the high mountains of west-central New Mexico to the White An earlier dispersal of the species Mountains of Arizona, and then spread may be favored by the fact that across the to Flagstaff populations of Arizona willow in during the Pleistocene. This hypothesis Arizona and Utah are separated by vast is supported by pollen samples from Hay expanses of basalt flows and Lake in the White Mountains that reveal sedimentary deposits across the the presence of bristlecone pine during Colorado Plateau, in addition to the the Middle Wisconsin (Jacobs 1985). A chasm of the Grand . This nearly continuous range of mountains separation has allowed bristlecone pine leads from the White Mountains of populations in the two states to form Arizona to the Sangre de Cristo separate species, perhaps indicating Mountains of New Mexico, and these isolation since the mid-Tertiary (Bailey are dominated by Oligocene andesitic to 1970). Many theories concerning the basaltic-andesitic volcanics that might origin of willows and other Arcto- have provided suitable habitat for the Tertiary flora propose that Arizona willow. Endemic plants of the diversification occurred during the Neogene (Wolfe 1997). Holmgren

67 (1971) suggested that various endemic the climate then cooled (Wolfe 1997). species of Castilleja in the Southwest The climate of the Southern Rocky became isolated during the Pliocene. Mountains then became more favorable The volcanism that formed Mount to dispersal of subalpine plants. Baldy and Brian Head had ended by the Formation of volcanic peaks and start of the Pliocene (Fig. 3). Extensive regional uplift promoted cooling and erosion occurred as the Plateaus were increased precipitation at high elevated (Stokes 1986), and as Mount elevations. Even without changes in Baldy was reduced by 600 m from its climate, peaks such as the White peak elevation (Merrill 1974). Massive Mountains of Arizona would have been debris slides in the valleys below these cooler than at present due to their higher mountains could have yielded ideal elevation (Merrill 1974). The ancestral substrates for the willow to colonize. Rio Grande dates to the upper Pliocene, Similar geomorphic evolution transpired following rapid uplift and block-faulting in New Mexico and Colorado at an of the Sangre de Cristo Range (Axelrod earlier date. Extensive volcanism formed and Bailey 1976). Subalpine plants the San Juan mountains during the could have spread overland or along Oligocene (24-38 M yr) (Fig. 3). During shifting rivers in the Rockies to occupy the Miocene period, 14-15 M yr, the the uplifting Sangre de Cristo region appeared to have a mild winter mountains. climate (Axelrod and Bailey 1976), but Hydrologic Connections Hydrologic connections between

FIGURE 3: Timetable of evolution of the landscapes of the Colorado Plateau and of selected taxa of willows and Septentrionales paintbrushes.

68 Arizona’s White Mountains and Utah’s High Plateaus apparently existed during the mid-late Neogene (Fig. 4). In Arizona, the ancestral Little Colorado River from Mount Baldy toward the Colorado River. Along the way, the system was dammed in places to form the lacustrine/playa deposits of the Bidahochi Formation, or Lake, in northeastern Arizona (Fig. 4) (Scarborough 1989; Gross et al. 2001). The source drainages of this formation remain uncertain, but they included the ancestral Little Colorado River and may have at times included tributaries of the ancestral Colorado River from the Rocky Mountains (Dallegge et al. 2003). Fossil records of beaver and an ancestral pikeminnow (Ptychocheilus) in the formation indicate abundant wetland habitat, although the climate FIGURE 4: Hydrologic connections among features of may have been relatively warm on the Colorado Plateau and Southern Rocky Mountains average (Repenning and Irwin 1954; during the Neogene. Scarborough 1989). Geologic evidence deeper as the area uplifted; suggests that an arrangement of simultaneously, the plateaus of southern mountains and drainages similar to the Utah also rose (Doelling et al. 1989). present-day was in place within the The orogeny coincided with a change to region by the Mid-Miocene, except that a drier climate that may have been the ancestral Colorado River had not yet similar to the present (Scarborough breached the Kaibab Plateau (Gross et 1989). During the late Pliocene and al. 2001). Instead, the river may have Pleistocene, the Springerville volcanic flowed north along the present-day field reached its peak activity (Condit course of Kanab Creek (Lucchita 1990). and Connor 1996). These relatively flat This course leads directly to the plateaus basalt flows overlaid parts of the of Utah, coinciding with drainages of the Bidahochi formation and may have Sevier River where Arizona willow disrupted stream flow along the Little occurs (Fig. 4). Consequently, during the Colorado River from Mount Baldy. Neogene, this drainage system may have These formations may have restricted linked the Rockies to the volcanic peaks the Arizona willow to the areas close to of Mount Baldy and southern Utah. the older and steeper slopes of Mount Around 5 to 6 million years ago, the Baldy. Colorado River changed its course to Arizona willow is well-distributed follow its present path to the Gulf of throughout the glacial tills and exposed California, forming the Sheep Crossing Formation except on the (Scarborough 1989). The Canyon cut western slopes of Mount Baldy and

69 Mount Ord. This asymmetrical connected during the Pliocene to all the distribution suggests that hydrologic areas where Arizona willow occurs in connections played an important control New Mexico, Utah and Arizona (Fig. 4). on its dispersal. The imposing massif of The Peaks and Mount Mount Ord and the deeply incised Taylor are prominent peaks in the canyon of Big Bonito Creek appear to Southwest within the range of Arizona have blocked its spread to westerly- willow. The composition of these flowing drainages. The concentration of volcanoes range from basalt to dacite. subpopulations along the Little Colorado However, the species has not been River strongly suggests that this reported from those peaks. This absence drainage first brought the plant to the could be explained by the fact that these White Mountains of Arizona. Headwater volcanoes formed during the Pliocene stream transfers and low drainage and Pleistocene, possibly after Arizona divides could have permitted extension willow had dispersed. to the White and Black River watersheds. Behnke (1979) presumed The Mogollon Mountains of New that headwater transfers during the Mexico are older volcanoes of Quaternary glaciations were important intermediate to felsic composition that mechanisms in distributing fish species include Sierra Blanca, which was the in the White Mountains. southernmost glaciated peak in North America during the Pleistocene. In Utah, most populations of Arizona Arizona willow and Mogollon willow occur on tributaries of the Sevier paintbrush have not been reported from River, which lies in the transition those mountains, although it is unlikely between the Great Basin and Colorado that systematic surveys have been made Plateau. Populations on the Fish Lake of the region. A predominantly water- and Wasatch plateaus flow into based journey from this region to the tributaries of the Colorado, although other Arizona willow populations would these populations are located close to the require a rather long path through either divide with the Sevier watershed. The the relatively low, warm valley of the population on the East Fork of the Sevier Rio Grande to the Sangre de Cristo River on the Paunsaugunt Plateau is Mountains or across mostly mafic found less than three kilometers from the plateaus via the San Francisco River. drainage divide with Kanab Creek, indicating potential dispersal from the Genetic Evidence Colorado drainage. The time frame for the dispersal of Populations of Arizona willow in Arizona willow and its closest relatives New Mexico extend across several across the Southwest is a subject for major watersheds and occur on all debate. Arizona willow is similar in aspects. This distribution supports the appearance and in genetics to Booth’s idea that the species might have willow ( Dorn) (Thompson dispersed through the southern Rockies et al. 2003). Mead (1996) claimed that via a shifting network of high-elevation Argus, a taxonomic expert on willows, drainages. Straddling the basins of the thought that Arizona willow may have Colorado and Rio Grande, the San Juan diverged from S. boothii during Mountains were hydrologically Pleistocene glaciations. However, Argus

70 has said that there is not sufficient Saliceae family in general has a slow evidence to draw conclusions about the evolutionary rate (Leskinen and timing or direction of evolution of these Alstrom-Rapaport 1999) lends some species (Argus 1999). Dorn (1976) support to the hypothesis that the asserted that nearly all American species diaspora of Arizona willow may indeed originated “before or during glaciation.” be ancient. Yet, despite being one of the Glaciation influenced the regional oldest genera of angiosperms, Salix itself distribution of some willow species, as dates only to the Eocene (55-65 M yr, Dorn (1975) suggested that S. boothii Fig. 3) (Leskinen and Alstrom-Rapaport and S. myrtillifolia Anderss. may have 1999). Furthermore, researchers believe been separated during the Wisconsin that diversification of most species glaciation and then converged in the occurred after the Oligocene (post 38 M Northern Rocky Mountains of the yr, Fig. 3) (Axelrod 1987; Leskinen and . Because S. arizonica Alstrom-Rapaport 1999). The limited overlaps with S. boothii over such a genetic evidence does not seem to large area, it seems unlikely that it could support either a very recent dispersal of have evolved as a separate species in Arizona willow or a far more ancient such a relatively short time. Based on one. flavenoid analyses (which are admittedly Palynological Evidence more primitive than DNA testing), Arizona willow appears chemically Unfortunately, pollen samples “very different” from S. boothii and provide little insight into the timing of instead appears more similar to the low- the radiation of Arizona willow. Willow growing blueberry willow, S. pollen is rarely identified to the species myrtillifolia (Dorn 1975). Both S. level, and it is not even reported from boothii and S. myrtillifolia are identified the handful of pollen records from the as synonyms for S. pseudomyrsinites White Mountains of Arizona (e.g., P.S. (Dorn 1975), the name originally applied Martin and R. Hevly unpublished data in to the 1913 collection of Arizona willow (Whiteside 1965), (Merrill and Péwé from Utah (AWITT 1995). These three 1977)). Salix pollen is also absent in species may share a complex reports from Hay Lake (Jacobs 1985) evolutionary history, but DNA and from Dead Man Lake in the Chuska comparisons of Arizona willow Mountains (Wright et al. 1973). This populations (Thompson et al. 2003) did absence may be the result of low pollen not include any S. myrtillifolia. production, insufficient identification, absence of willow in the sampled Those DNA tests did reveal that the depressions, or the tendency of willow populations of Arizona willow in Utah pollen to clump (Faegri and Iversen and Arizona were highly divergent 1964). Regardless of these problems, (Thompson et al. 2003). Based on this the short time frame of most pollen finding, Thompson et al. (2003) records could not resolve whether the hypothesized that the species was plant was present in the White panmictic only as late as the Eocene (ca Mountains of Arizona before the last 50 M yr), when vast lakes connected the glacial period. White Mountains of Arizona to the High Plateaus of Utah. The fact that the Mechanisms of Dispersal

71 Arizona willow and various Pleistocene landscape. However, the paintbrush species may have distributed unusually warm and dry climate along paths different from those of experienced in the White Mountains in upland species such as bristlecone pine. recent years (Lynch 2004) combined Members of the Saliceae have the with increased ungulate abundance and potential to disperse long distances due more continuous grazing may have to their light seeds with long tails that created novel habitat conditions. catch the wind (Wells 1983). Moreover, Herbivory by ungulates, particularly elk, suitable climatic conditions may have has been linked to reduce plant vigor of been lowered by 1000 meters or more in Arizona willow (Maschinski 2001) and canyon bottoms on the Colorado Plateau has been a contributing factor in the loss during the last glacial maximum of individual plants (Granfelt 2004). (Betancourt 1990). However, willow Aided by construction of watering tanks, seeds are short-lived and usually must reduction of predator populations, and land in a sustained moist environment introductions of both domestic livestock within days to germinate (Densmore and and the Rocky Mountain subspecies of Zasada 1983). Thompson et al. (2003) elk (Cervus elaphus ssp. nelsoni), argued that prevailing winds do not ungulate behavior has changed in support seed flow between populations seasonality and extent from the in Utah and Arizona. A Pleistocene conditions under which subalpine flora dispersal across unfavorable habitat have evolved (Axelrod 1987; Burkhardt between Arizona and Utah appears less 1996). likely than a Pliocene voyage along IMPLICATIONS FOR CONSERVATION AND favorable drainages. However, FUTURE RESEARCH connections across the Arizona-New Mexico Mountains may have permitted This interpretation of the dispersal into Arizona from the southern biogeography of Arizona willow has Rocky Mountains. Without a more several implications. Conservation of the detailed fossil record or DNA studies, species should recognize that the glacial the timing of the arrival of Arizona and Tertiary volcanic formations yield willow to the White Mountains will substrates that promote the highest remain speculative. densities of these plants and serve as natural refugia. Populations on basalt Implications for Environmental and other fine-textured formations may Tolerance experience greater stress associated with Understanding how long Arizona warming and drying. Although different willow has lived in its present regions species may have dispersed at different may help resolve its environmental times, similarities among the subalpine tolerances. Regardless of whether the flora of the White Mountains of Arizona, species existed in Arizona and Utah High Plateaus of Utah, Southern Rocky before the last glacial maximum or after, Mountains of New Mexico, and San it would have withstood the dramatic Juan Mountains of Southern Colorado climatic change of the Altithermal point to parallel geologic origins and warming period (about 8000-4000 year past linkages during both the Neogene ago) as well as grazing by the large- and Pleistocene. Surveys in the San Juan bodied mammals that dominated the

72 Mountains are likely to reveal additional Albuquerque, NM; , populations of Arizona willow. Rocky Mountain Region, Denver, CO; U.S. Fish and Wildfire Service, Mountain-Prairie Future research may help to resolve Region, Salt Lake City, UT; U.S. Fish and questions concerning the evolution of Wildlife Service, Southwest Region, these rare plants. Genetic comparisons Albuquerque, NM. of willow populations in New Mexico Axelrod, D. I. 1987. The late Oligocene Creede and Colorado with those in Utah and Flora, Colorado. University of California Arizona could help to resolve the Publications in Geological Sciences, Volume 130. Berkeley: University of California sequence by which existing populations Press. 235 p. separated. For example, if the Axelrod, D. I. and H. P. Bailey. 1976. Tertiary populations in Arizona are more similar vegetation, climate, and altitude of the Rio to those in New Mexico, then a Grande depression, New Mexico-Colorado. Quaternary dispersal to the White Paleobiology 2: 235-254. Mountains, like that of bristlecone pine, Bailey, D. K. 1970. Phytogeography and would seem plausible. However, if the taxonomy of Pinus subsection balfourianae. Arizona, Utah, and Rocky Mountains Annals of the Missouri Botanical Garden 57: populations are equally dissimilar, then 210-249. an earlier Neogene dispersal would seem Bainbridge, S. J. and P. L. Warren 1992. Status more likely. report, April revision: Castilleja mogollonica (Mogollon paintbrush). Unpublished report ACKNOWLEDGMENTS submitted to U. S. Fish and Wildlife Service, I thank Carl-Eric Granfelt for his Ecological Services, Phoenix, AZ. dedication to understanding the rare Behnke, R. J. 1979. Monograph of the native plants of the White Mountains and for trouts of the genus Salmo of Western North America., Denver, CO: U.S. Department of sharing his thoughts on this manuscript. Agriculture, Forest Service, Rocky Mountain I also thank Steve Overby for his review Region. 163 p. of this manuscript, and Mark Egger for ______. 2002. Trout and salmon of North providing an update on the taxonomy of America. New York, NY: The Free Press. the Mogollon paintbrush. 359 p. REFERENCES Betancourt, J. L. 1984. Late Quaternary plant zonation and climate in southeastern Utah. Argus, George W. 1999. [E-mail to J. W. Long]. The Great Basin Naturalist 44: 1-35. 11-17-1999. ______1990. Late Quaternary biogeography of Atwood, D. 1996. Final report for inventory of the Colorado Plateau. In: Betancourt, J. L., Salix arizonica on the Santa Fe National Devender, T. R. V., and Martin, P. S., eds. Forest. Unpublished report on file at Rocky Packrat middens: The last 40,000 years of Mountain Research Station, Flagstaff, AZ. 5 biotic change. Tucson, AZ: University of p. Arizona Press: 259-293. ______Survey of Arizona on the Carson Burkhardt, J. W. 1996. Herbivory in the National Forest. Unpublished report on file at Intermountain West: An overview of Rocky Mountain Research Station, Flagstaff, evolutionary history, historic cultural impacts AZ. 8 p. and lessons from the past. Station Bulletin AWITT (Arizona Willow Interagency Technical 58. Moscow, ID: Idaho Forest, Wildlife and Team) 1995. Arizona willow conservation Range Experiment Station, College of agreement and strategy. Ogden, UT: U.S. Forestry, Wildlife and Range Sciences, Forest Service, Intermountain Region; U.S. University of Idaho. 20 p. Forest Service, Southwest Region,

73 Colorado Natural Heritage Program. 2001. Plant Granfelt, C. 2004. [Phone conservation with J. species of special concern survey form. W. Long]. 4-19-2004. Unpublished report on file at College of Green, G. N. and Jones, G. E. 1997. The digital Natural Resources, Colorado State geologic map of New Mexico in ARC/INFO University, Fort Collins, CO. 2 p. format. Open-File Report 97-52. Denver: U. Condit, C. D. and C. B. Connor. 1996. S. Geological Survey. Recurrence rates of volcanism in basaltic Gregory, H. E. 1950. Geology of eastern Iron volcanic fields, an example from the County, Utah. Bulletin 37. Salt Lake City: Springerville volcanic field, Arizona. GSA University of Utah Press. 153 p. Bulletin 108(10): 1225-1241. Gross, E. L.; P.J. Patchett,, T. A. Dallegge and J. Dallegge, T. A., M. H. Ort, and W. C. McIntosh. E. Spencer. 2001. The Colorado River 2003. Mio-Pliocene chronostratigraphy, System and Neogene sedimentary formations basin morphology and paleodrainage along its course: Apparent Sr Isotopic relations derived from the Bidahochi connections. Journal of Geology 109(4): Formation, Hopi and nations, 449-461. northeastern Arizona. The Mountain Geologist 40(3): 55-82. Holmgren, N. H. 1971. A taxonomic revision of the Castilleja viscidula group. Memoirs of Densmore, R. and J. Zasada. 1983. Seed the New York Botanical Garden 21(4): 1-63. dispersal and dormancy patterns in northern willows: ecological and evolutionary ______Five new species of Castilleja significance. Canadian Journal of Botany 61: (Scrophulariaceae) from the Intermountain 3207-3216. Region. Bulletin of the Torrey Botanical Club 100(2): 83-93. Doelling, H. H., F. D. Davis, and C. J. Brandt. 1989. The geology of Kane County, Utah, Jacobs, B. F. 1985. A middle Wisconsin pollen geology, mineral resources, geologic hazards. record from Hay Lake, Arizona. Quaternary Bulletin 124. Salt Lake City: Utah Research 24: 121-130. Geological and Mineral Survey. 192 p. Ladyman, J. 1996. Distribution and biology of Dorn, R. D. 1975. A systematic study of Salix Trifolium longipes subsp. neurophyllum section Cordatae in North America. (Greene). In Maschinski, J., H. D. Canadian Journal of Botany 53: 1491-1522. Hammond, and L. Holter, L., (eds.) Southwestern rare and endangered plants, ______1976. A synopsis of American Salix. second conference: proceedings; 9-11-1995; Canadian Journal of Botany 54: 2769-2789. Flagstaff, AZ: 262-269. ______1997. Survey of Arizona willow on the Leskinen, E. and C. Alstrom-Rapaport. 1999. Carson National Forest. Unpublished report Molecular phylogeny of Saliceae and closely to the U.S. Forest Service Region 2, on file at related Flacourtiaceae, evidence from 5.8 S, U.S. Department of Agriculture, Forest ITS 1 and ITS 2 of the rDNA. Plant Service, Rocky Mountain Research Station, Systematics and Evolution 215: 209-227. Flagstaff, AZ. Lucchita, I. 1990. History of the Grand Canyon Egger, J. Mark. 2004. [E-mail to J. W. Long]. 4- and of the Colorado River in Arizona. In: 19-2004. Flagstaff, AZ: Museum of Faegri, Knut and Iversen, Johs. 1964. Textbook Press: 311-332. of pollen analysis. NY: Hafner Publishing Luedke, R. G. 1993. Maps showing distribution, Company. 237 p. composition, and age of early and middle Freeman, C. E. and W. A. Dick-Peddie. 1970. Cenozoic volcanic centers in Colorado and Woody riparian vegetation in the Black and Utah. Miscellaneous Investigations Map I- Sacramento Mountain Ranges, Southern New 2291-B. Mexico. The Southwestern Naturalist 15: Lynch, A. M. 2004. Fate and characteristics of 145-164. Picea damaged by Elatobium abietinum (Walker) (Homoptera: Aphididae) in the

74 White Mountains of Arizona. Western North Pennell, F. W. 1951. A new Indian paint-brush American Naturalist 64(1): 7-17. from the of Arizona (Castilleja: Scrophulariaceae). Notulae Maschinski, J. 2001. Impacts of ungulate Naturae, no. 237. Philadelphia: The herbivores on a rare willow at the southern Academy of Natural Sciences of edge of its range. Biological Conservation Philadelphia. 300 p. 101(1): 119-130. Price, P. W., T. G. Carr and A. M. Ormond. McIntosh, W. C. and R. M. Chamberlin. 1994. 1996. Consequences of land management 40AR/39AR geochronology of middle to late practices on willows and higher trophic Cenozoic ignimbrites, mafic lavas, and levels. In Maschinski, J., H. D. Hammond, volcaniclastic rocks in the Quemado Region, and L. Holter, L., (eds.) Southwestern rare New Mexico. In Chamberlin, R. M.; B. S. and endangered plants, second conference: Kues, S. M. Cather, J. M. Barker, and W. C. proceedings; 9-11-1995; Flagstaff, AZ 219- McIntosh, (eds).9-28-1994; New Mexico 223. Geological Society, Inc.: 165-173. Repenning, C. A. and J. H. Irwin. 1954. Mead, L. L. 1996. Habitat characteristics of Bidahochi formation of Arizona and New Arizona willow in Southwestern Utah. Mexico. American Association of Petroleum Provo, UT: University. Geologists Bulletin 38: 1821-1826. Unpublished master's thesis. Rinne, J. N. 2000. Fish and grazing relationships Merrill, R. K. 1974. The late Cenozoic geology in southwestern National Forests. In: of the White Mountains, Apache County, Jemison, R., and Raish, C., eds. Livestock Arizona. Tempe, AZ: Arizona State management in the American southwest: University. Ph.D. dissertation. ecology, society and economics. The Merrill, R. K. and T. L. Péwé. 1971. Sheep Netherlands: Elsevier Science: 329-371. Crossing formation, a new late Cenozoic Rowley, P. D., H. H. Mehnert, C. W. Naeser, L. epiclastic formation in East-central Arizona. W. Snee, C. G. Cunningham, T. A. Steven, J. Journal of the Arizona Academy of Science J. Anderson, E. G. Sable, and R. E. 6: 226-229. Anderson. 1994. Isotopic ages and ______1977. Late Cenozoic geology of the stratigraphy of Cenozoic rocks of the White Mountains, Arizona. Special Paper Marysvale Volcanic Field and adjacent areas, No. 1. Tucson, AZ: University of Arizona. West-Central Utah. Bulletin 2071. Washington, DC: US Government Printing Miller, J. P., A. Montgomery and P. K. Office. 35 p. Sutherland. 1963. Geology of part of the southern Sangre de Cristo Mountains, New Scarborough, R. 1989. Cenozoic erosion and Mexico. Memoirs M-11. Socorro, New sedimentation in Arizona. In: Jenney, J. P., Mexico: New Mexico Bureau of Geology and Reynolds, S. J., eds. Geologic evolution and Mineral Resources. 106 p. of Arizona. Tucson, AZ: Arizona Geological Society: 515-537. Moore, T. C. 1965. Origin and disjunction of the alpine tundra flora on San Francisco Steven, T. A. 1975. Middle Tertiary volcanic Mountain, Arizona. Ecology 46: 860-864. field in the Southern Rocky Mountains. In: Curtis, B. F., ed. Cenozoic History of the Nealey, L. D. 1989. Geology and petrology of Southern Rocky Mountains, Memoir, the Late Cenozoic Mount Baldy trachytic 144.The Geological Society of America, Inc. volcanic complex, White Mountains volcanic 94 p. field, Apache and Navajo Counties, Arizona. Albuquerque, NM: University of New Stokes, William L. 1986. Geology of Utah. Salt Mexico. Ph.D. dissertation. Lake City, UT: Utah Museum of Natural History, University of Utah and Utah Pennell, F. W. 1935. The Scrophulariaceae of Geological and Mineral Survey Department Eastern temperate North America. of Natural Resources. 280 p. Monograph, 1. Philadelphia: Academy of Natural Sciences of Philadelphia. 650 p. Thompson, J. T.; R. Van Buren and K. T. Harper. 2003. A genetic analysis of the rare

75 species, Salix arizonica () and associated willows in Arizona and Utah. Western North American Naturalist 63(3): 273-282. Wells, P. V. 1983. Paleobiogeography of montane islands in the Great Basin since the last glaciopluvial. Ecological Monographs 53: 341-382. Whiteside, M. C. 1965. Paleoecological studies of Potato Lake and its environs. Ecology 46: 807-816. Wolfe, J. A. 1997. Relations of environmental change to angiosperm evolution during the Late Cretaceous and Tertiary. In: Iwatsuki, K., and P.H. Raven, (eds.) Evolution and diversification of land plants. New York: Springer-Verlag: 269-290. Wright, H. E. Jr., A. M. Bent, B. S. Hansen, and L. J. J. Maher. 1973. Present and past vegetation of the , northwestern New Mexico. Geological Society of America Bulletin 84: 1155-1180. Wright, R. D. and H. A. Mooney. 1965. Substrate-oriented distribution of bristlecone pine in the White Mountains of California. American Midland Naturalist 73: 257-284.

76