Santa Catalina Mountains Research Articles

Examining the Impacts of Pre-Fire Forest Conditions on Burn Severity Using Multiple Remote Sensing Platforms

Pre-fire environmental conditions play a critical role in wildfire severity. This study investigated the impact of pre-fire forest conditions on burn severity as a result of the 2020 Bighorn Fire in the Santa Catalina Mountains in Arizona. Using a stepwise regression model and remotely sensed data from Landsat 8 and LiDAR, we analyzed the effects of structural and functional vegetation traits and environmental factors on burn severity. This analysis revealed that the difference normalized burn ratio (dNBR) was a more reliable indicator of burn severity compared to the relative dNBR (RdNBR). Stepwise regression identified pre-fire normalized difference vegetation index (NDVI), canopy cover, and tree density as significant variables across all land cover types that explained burn severity, suggesting that denser areas with higher vegetation greenness experienced more severe burns. Interestingly, residuals between the actual and estimated dNBR were lower in herbaceous zones compared to denser forested areas at similar elevations, suggesting potentially more predictable burn severity in open areas. Spatial analysis using Geary’s C statistics further revealed a strong negative autocorrelation: areas with high burn severity tended to be clustered, with lower severity areas interspersed. Overall, this study demonstrates the potential of readily available remote sensing data to predict potential burn severity values before a fire event, providing valuable information for forest managers to develop strategies for mitigating future wildfire damage.

Draft genome sequences of Arthrobacter sp. AZCC_0090 and Mycobacterium sp. AZCC_0083 isolated from oligotrophic subsurface forest soil in the Santa Catalina mountains of Southern Arizona.

Here, we present the genomes of two soil actinobacteria: Arthrobacter sp. strain AZCC_0090 and Mycobacterium sp. strain AZCC_0083, isolated from oligotrophic subsurface soils in Southern Arizona, USA.

Exploring the identification and use of socially defined indicators to monitor local environmental change in the Santa Catalina Mountains, Arizona

Exploring the identification and use of socially defined indicators to monitor local environmental change in the Santa Catalina Mountains, Arizona

Stanevansite, Mg(C2H3O3)2·2H2O, A New Hydrous Glycolate Mineral, from the Santa Catalina Mountains, Tucson, Arizona, USA

Abstract A new organic mineral species, stanevansite, ideally Mg(C2H3O3)2·2H2O, was discovered from the western end of Pusch Ridge in the Santa Catalina Mountains (32° 21′ 42″ N, 110° 57′ 30″ W, at the elevation of 975 m), north of Tucson, Arizona, USA. It occurs as sprays of bladed crystals (up to 0.40 × 0.07 × 0.03 mm). Associated minerals include lazaraskeite, chrysocolla, malachite, wulfenite, mimetite, phosphohedyphane, cerussite, hematite, calcite, microcline, phlogopite, and quartz. Stanevansite crystals are colorless in transmitted light, transparent with white streak and vitreous luster. They are brittle and have a Mohs hardness of ∼1½; cleavage is perfect on {100}. Twinning is common on (100). The measured and calculated densities are 1.69(5) and 1.682 g/cm3, respectively. Optically, stanevansite is biaxial (+), with α = 1.539(5), β = 1.545(5), γ = 1.558(5), 2Vmeas. = 62(2)°, 2Vcal. = 69°. It is insoluble in water, but slowly dissolves in hydrochloric acid. An electron-microprobe analysis yielded an empirical formula, based on 8 O apfu and Σ(Mg + Zn) = 1 apfu, of (Mg0.95Zn0.05)Σ1.00(C2H3O3)2·2H2O, which can be simplified as (Mg,Zn)(C2H3O3)2·2H2O. Stanevansite is monoclinic with space group P21/c and unit-cell parameters a = 11.4927(2), b = 5.85470(10), c = 12.4711(2) Å, β = 91.1610(10)°, V = 838.96(2) Å3, and Z = 4. It is isostructural with several synthetic glycolate compounds having the general chemical formula M2+(C2H3O3)2·2H2O, where M2+ = Co2+, Mn, Zn, and Mg. The crystal structure of stanevansite is characterized by the mononuclear complex [Mg(C2H3O3)2(H2O)2], with such complexes being connected to one another by hydrogen bonds to form a three-dimensional supramolecular architecture. In a [Mg(C2H3O3)2(H2O)2] complex, Mg is octahedrally coordinated by two chelating glycolate ligands and two H2O molecules. Stanevansite represents the first hydrous glycolate mineral and is believed to have formed through the interaction of fluids containing glycolic acid (C2H4O3) derived from decaying plant materials or bacterial activities with Mg produced by the alteration of primary and secondary minerals. Its discovery, together with other glycolate minerals documented recently, namely lazaraskeite Cu(C2H3O3)2, jimkrieghite Ca(C2H3O3)2, and lianbinite (NH4)(C2H3O3)(C2H4O3), not only implies that more glycolate minerals may be found in nature, but also suggests that glycolate minerals may serve as a potential reservoir for biologically fixed carbon.

Generating ecological insights from historical data

Generating ecological insights from historical data

Structure, chronology, kinematics, and geodynamics of tectonic extension in the greater Catalina metamorphic core complex, southeastern Arizona, USA

Abstract Oligocene and early Miocene displacement on the Catalina–San Pedro detachment fault and its northern correlatives uncovered mylonitic fabrics that form the greater Catalina metamorphic core complex in southeastern Arizona, USA. Gently to moderately dipping mylonitic foliations in the complex are strongly lineated, with a lineation-azimuth average of 064–244° and dominantly top-southwest shear sense over the entire 115-km-long mylonite belt. Reconstruction of detachment fault displacement based on a variety of features indicates 40–60 km of displacement, with greater displacement in more southern areas. Widespread 26–28 Ma volcanism during early extensional basin genesis was followed by 24–26 Ma granitoid magmatism. Cooling of footwall mylonites continued until 22–24 Ma, as indicated by 40Ar/39Ar mica dates. Lower temperature thermochronometers suggest that footwall exhumation was still underway at ca. 20 Ma. Tectonic reconstruction places a variety of unmetamorphosed supracrustal units in the Tucson and Silver Bell Mountains above equivalent units that were metamorphosed and penetratively deformed in the Tortolita and Santa Catalina Mountains. This restored juxtaposition is interpreted as a consequence of older Laramide thrust burial of the deformed units, with northeast-directed thrusting occurring along the Wildhorse Mountain thrust in the Rincon Mountains and related but largely concealed thrusts to the northwest. Effective extensional exhumation of lower plate rocks resulted from a general lack of internal extension of the upper plate wedge. This is attributed to a stable sliding regime during the entire period of extension, with metamorphic core complex inflation by deep crustal flow leading to maintenance of wedge surface slope and detachment fault dip that favored stable sliding rather than internal wedge extension.

Tandem Use of Multiple Tracers and Metrics to Identify Dynamic and Slow Hydrological Flowpaths

Current understanding of the dynamic and slow flow paths that support streamflow in mountain headwater catchments is inhibited by the lack of long-term hydrogeochemical data and the frequent use of short residence time age tracers. To address this, the current study combined the traditional mean transit time and the state-of-the-art fraction of young water (Fyw) metrics with stable water isotopes and tritium tracers to characterize the dynamic and slow flow paths at Marshall Gulch, a sub-humid headwater catchment in the Santa Catalina Mountains, Arizona, USA. The results show that Fyw varied significantly with period when using sinusoidal curve fitting methods (e.g., iteratively re-weighted least squares or IRLS), but not when using the transit time distribution (TTD)-based method. Therefore, Fyw estimates from TTD-based methods may be particularly useful for intercomparison of dynamic flow behavior between catchments. However, the utility of 3H to determine Fyw in deeper groundwater was limited due to both data quality and inconsistent seasonal cyclicity of the precipitation 3H time series data. Although a Gamma-type TTD was appropriate to characterize deep groundwater, there were large uncertainties in the estimated Gamma TTD shape parameter arising from the short record length of 3H in deep groundwater. This work demonstrates how co-application of multiple metrics and tracers can yield a more complete understanding of the dynamic and slow flow paths and observable deep groundwater storage volumes that contribute to streamflow in mountain headwater catchments.

Grassification and Fast-Evolving Fire Connectivity and Risk in the Sonoran Desert, United States

In the southwestern United States, non-native grass invasions have increased wildfire occurrence in deserts and the likelihood of fire spread to and from other biomes with disparate fire regimes. The elevational transition between desertscrub and montane grasslands, woodlands, and forests generally occurs at ∼1,200 masl and has experienced fast suburbanization and an expanding wildland-urban interface (WUI). In summer 2020, the Bighorn Fire in the Santa Catalina Mountains burned 486 km2and prompted alerts and evacuations along a 40-km stretch of WUI below 1,200 masl on the outskirts of Tucson, Arizona, a metropolitan area of >1M people. To better understand the changing nature of the WUI here and elsewhere in the region, we took a multidimensional and timely approach to assess fire dynamics along the Desertscrub-Semi-desert Grassland ecotone in the Catalina foothills, which is in various stages of non-native grass invasion. The Bighorn Fire was principally a forest fire driven by a long-history of fire suppression, accumulation of fine fuels following a wet winter and spring, and two decades of hotter droughts, culminating in the hottest and second driest summer in the 125-yr Tucson weather record. Saguaro (Carnegia gigantea), a giant columnar cactus, experienced high mortality. Resprouting by several desert shrub species may confer some post-fire resiliency in desertscrub. Buffelgrass and other non-native species played a minor role in carrying the fire due to the patchiness of infestation at the upper edge of the Desertscrub biome. Coupled state-and-transition fire-spread simulation models suggest a marked increase in both burned area and fire frequency if buffelgrass patches continue to expand and coalesce at the Desertscrub/Semi-desert Grassland interface. A survey of area residents six months after the fire showed awareness of buffelgrass was significantly higher among residents that were evacuated or lost recreation access, with higher awareness of fire risk, saguaro loss and declining property values, in that order. Sustained and timely efforts to document and assess fast-evolving fire connectivity due to grass invasions, and social awareness and perceptions, are needed to understand and motivate mitigation of an increasingly fire-prone future in the region.

HYDRAULICS OF PINUS (SUBSECTION PONDEROSAE) POPULATIONS ACROSS AN ELEVATION GRADIENT IN THE SANTA CATALINA MOUNTAINS OF SOUTHERN ARIZONA

The ability of plants to tolerate and recover from periodic water stress affects their competitive ability, survival, and distribution, leading to shifts in plant communities as environmental conditions change. We investigated the hydraulic traits of two closely related Pinus taxa to assess population and taxonomic variability in plant hydraulic traits. We hypothesized that traits would vary with elevation but exhibit similar traits where taxa co-occurred. We measured predawn and midday leaf pressure potential (Ψp) across three seasons, xylem specific hydraulic conductivity (Ks), and vulnerability to xylem embolism (P50). These were measured on Pinus ponderosa var. brachyptera (Engelm.) Lemmon that occurred at a high elevation site (2770 m), P. arizonica Engelm. at a low elevation site (2135 m), and both species where they co-occurred at the mid-elevation site (2475 m) in the Santa Catalina Mountains of southern Arizona. Plants from the high elevation site had the least negative Ψp and the highest Ks. The two taxa differed from one another when compared between the high and low elevation sites, but they were not different where they co-occurred. The two Pinus taxa show plasticity in their hydraulic traits across sites. Conditions across the elevational gradient appear to lead to a convergent solution in hydraulic traits for these taxa where their ranges overlap but differences in traits where they do not overlap. Increasing aridity in the region could lead to shifts in suitable habitat, reduced water transport ability at range margins, and shifts in population distributions.

Lazaraskeite, Cu(C2H3O3)2, the first organic mineral containing glycolate, from the Santa Catalina Mountains, Tucson, Arizona, U.S.A.

Abstract A new organic mineral species, lazaraskeite, ideally Cu(C2H3O3)2 with two polytypes M1 and M2, was discovered in the high elevation of the Santa Catalina Mountains, north of Tucson, Arizona, U.S.A. Both lazaraskeite-M1 and -M2 occur as euhedral individual crystals (up to 0.20 × 0.20 × 0.80 mm) or aggregates, with the former being more equant crystals and the latter bladed crystals elongated along the c axis. Associated minerals include chrysocolla, malachite, wulfenite, mimetite, hydroxylpyromorphite, hematite, microcline, muscovite, and quartz. Both polytypes are greenish-blue in transmitted light, transparent with white streak, and a vitreous luster. They are brittle and have a Mohs hardness of ~2; cleavage is perfect on {101}. No parting or twinning was observed. The measured and calculated densities are 2.12(2) and 2.138 g/cm3, respectively, for lazaraskeite-M1 and 2.10(2) and 2.086 g/cm3 for lazaraskeite-M2. Optically, lazaraskeite-M1 is biaxial (−), with α = 1.595(3), β = 1.629(8), γ = 1.645(5), 2Vmeas = 69(2)°, 2Vcal = 67°. Lazaraskeite-M2 is also biaxial (−), with α = 1.520(5), β = 1.578(6), γ = 1.610(5), 2Vmeas = 73(2)°, 2Vcal = 70°. Lazaraskeite is insoluble in water or acetone. An electron microprobe analysis for Cu and an Elemental Combustion System equipped with mass spectrometry for C yielded an empirical formula, based on 6 O apfu, Cu1.01(C1.99H2.99O3)2 for lazaraskeite-M1 and Cu1.01(C1.98H3.00O3)2 for lazaraskeite-M2. The measured δ13C ‰ values are –37.7(1) and –37.8(1) for lazaraskeite-M1 and -M2, respectively. Both lazaraskeite-M1 and -M2 are monoclinic with the same space group P21/n. The unit-cell parameters are a = 5.1049(2), b = 8.6742(4), c = 7.7566(3) Å, β = 106.834(2)°, V = 328.75(2) Å3 for M1 and a = 5.1977(3), b = 7.4338(4), c = 8.8091(4) Å, β = 101.418(2)°, V = 333.64(3) Å3 for M2. Lazaraskeite-M1 is the natural analog of synthetic bis(glycolato)copper(II), Cu(C2H3O3)2. Its crystal structure is characterized by layers made of octahedrally coordinated Cu2+ cations and glycolate (C2H3O3)– anionic groups. These layers, parallel to (101), are linked together by the strong hydrogen bonds (O-H···O = 2.58 Å). The CuO6 octahedron is highly distorted, with four equatorial Cu-O bonds between 1.92 and 1.94 Å and two axial bonds at 2.54 Å. Lazaraskeite-M2 has the same topology as lazaraskeite-M1 and possesses all structural features of the low-temperature phase transformed from lazaraskeite-M1 at 220 K (Yoneyama et al. 2013). The major differences between the two polytypes of lazaraskeite include: (1) M1 has b > c, with β = 106.8°, whereas M2 has b < c, with β = 101.4°; (2) the CuO6 octahedron in M1 is more elongated and distorted than in M2; and (3) there is a relative change in the molecular orientation between the two structures. Lazaraskeite represents the first organic mineral that contains glycolate. Not only does its discovery imply that more glycolate minerals may be found, but also suggests that glycolate minerals may serve as a potential storage for biologically fixed carbon.

Strong slope‐aspect control of regolith thickness by bedrock foliation

AbstractThe porous near‐surface layer of the Earth's crust – the critical zone – constitutes a vital reservoir of water for ecosystems, provides baseflow to streams, guides recharge to deep aquifers, filters contaminants from groundwater, and regulates the long‐term evolution of landscapes. Recent work suggests that the controls on regolith thickness include climate, tectonics, lithology, and vegetation. However, the relative paucity of observations of regolith structure and properties at landscape scales means that theoretical models of critical zone structure are incompletely tested. Here we present seismic refraction and electrical resistivity surveys that thoroughly characterize subsurface structure in a small catchment in the Santa Catalina Mountains, Arizona, USA, where slope‐aspect effects on regolith structure are expected based on differences in vegetation. Our results show a stark contrast in physical properties and inferred regolith thickness on opposing slopes, but in the opposite sense of that expected from environmental models and observed vegetation patterns. Although vegetation (as expressed by normalized difference vegetation index [NDVI]) is denser on the north‐facing slope, regolith on the south‐facing slope is four times thicker (as indicated by lower seismic velocities and resistivities). This contrast cannot be explained by variations in topographic stress or conventional hillslope morphology models. Instead, regolith thickness appears to be controlled by metamorphic foliation: regolith is thicker where foliation dips into the topography, and thinner where foliation is nearly parallel to the surface. We hypothesize that, in this catchment, hydraulic conductivity and infiltration capacity control weathering: infiltration is hindered and regolith is thin where foliation is parallel to the surface topography, whereas water infiltrates deeper and regolith is thicker where foliation intersects topography at a substantial angle. These results suggest that bedrock foliation, and perhaps by extension sedimentary layering, can control regolith thickness and must be accounted for in models of critical zone development. © 2020 John Wiley & Sons, Ltd.

Variation in selective regimes drives intraspecific variation in life‐history traits and migratory behaviour along an elevational gradient

Comparative studies, across and within taxa, have made important contributions to our understanding of the evolutionary processes that promote phenotypic diversity. Trait variation along geographic gradients provides a convenient heuristic for understanding what drives and maintains diversity. Intraspecific trait variation along latitudinal gradients is well-known, but elevational variation in the same traits is rarely documented. Trait variation along continuous elevational gradients, however, provides compelling evidence that individuals within a breeding population may experience different selective pressures. Our objectives were to quantify variation in a suite of traits along a continuous elevational gradient, evaluate whether individuals in the population experience different selective pressures along that gradient and quantify variation in migratory tendency along that gradient. We examined variation in a suite of 14 life-history, morphological and behavioural traits, including migratory tendency, of yellow-eyed juncos along a continuous 1000-m elevational gradient in the Santa Catalina Mountains of Arizona. Many traits we examined varied along the elevational gradient. Nest survival and nestling growth rates increased, while breeding season length, renesting propensity and adult survival declined, with increasing elevation. We documented the migratory phenotype of juncos (partial altitudinal migrants) and show that individual migratory tendency is higher among females than males and increases with breeding elevation. Our data support the paradigm that variation in breeding season length is a major selective pressure driving life-history variation along elevational gradients and that individuals breeding at high elevation pursue strategies that favour offspring quality over offspring quantity. Furthermore, a negative association between adult survival and breeding elevation and a positive association between nest survival and breeding elevation help explain both the downslope and reciprocal upslope seasonal migratory movements that characterize altitudinal migration in many birds. Our results demonstrate how detailed studies of intraspecific variation in suites of traits along environmental gradients can lend new insights into the evolutionary processes that promote diversification and speciation, the causes of migratory behaviour, and how animal populations will likely respond to climate change.

Shifts in Climate–Growth Relationships of Sky Island Pines

Rising temperatures and changes in precipitation may affect plant responses, and mountainous regions in particular are sensitive to the impacts of climate change. The Santa Catalina Mountains, near Tucson, Arizona, USA, are among the best known Madrean Sky Islands, which are defined by pine-oak forests. We compared the sensitivity and temporal stability of climate–growth relationships to quantify the growth responses of sympatric taxa of ponderosa pine to changing climate. Three taxa (three-needle, mixed-needle, and five-needle types) collected from southern slopes of two contact zones (Mt. Lemmon, Mt. Bigelow) were evaluated. Positive climate–growth correlations in these semiarid high-elevation pine forests indicated a seasonal shift from summer- to spring-dominant precipitation since 1950, which is a critical time for reproduction. Mixed- and five-needle types responded to winter precipitation, and growth was reduced for the five-needle type when spring conditions were dry. Growth trends in response to temperature and specific to site were observed, which indicated the climate signal can be weakened when data are combined into a single chronology. Significant fluctuations in temperature–growth correlations since 1950 occurred for all needle types. These results demonstrated a dramatic shift in sensitivity of annual tree growth to the seasonality of the limiting factor, and a climatic trend that increases local moisture stress may impact the stability of climate–growth relationships. Moreover, output from temperature–growth analyses based on ring-width data (for example from semiarid sites) that does not account for positive and negative growth trends may be adversely affected, potentially impacting climate reconstructions.

Distant neighbors: recent wildfire patterns of the Madrean Sky Islands of southwestern United States and northwestern Mexico

BackgroundInformation about contemporary fire regimes across the Sky Island mountain ranges of the Madrean Archipelago Ecoregion in the southwestern United States and northern Mexico can provide insight into how historical fire management and land use have influenced fire regimes, and can be used to guide fuels management, ecological restoration, and habitat conservation. To contribute to a better understanding of spatial and temporal patterns of fires in the region relative to environmental and anthropogenic influences, we augmented existing fire perimeter data for the US by mapping wildfires that occurred in the Mexican Sky Islands from 1985 to 2011.ResultsA total of 254 fires were identified across the region: 99 fires in Mexico (μ = 3901 ha, σ = 5066 ha) and 155 in the US (μ = 3808 ha, σ = 8368 ha). The Animas, Chiricahua, Huachuca-Patagonia, and Santa Catalina mountains in the US, and El Pinito in Mexico had the highest proportion of total area burned (>50%) relative to Sky Island size. Sky Islands adjacent to the border had the greatest number of fires, and many of these fires were large with complex shapes. Wildfire occurred more often in remote biomes, characterized by evergreen woodlands and conifer forests with cooler, wetter conditions. The five largest fires (>25 000 ha) all occurred during twenty-first century droughts (2002 to 2003 and 2011); four of these were in the US and one in Mexico. Overall, high variation in fire shape and size were observed in both wetter and drier years, contributing to landscape heterogeneity across the region.ConclusionsFuture research on regional fire patterns, including fire severity, will enhance opportunities for collaborative efforts between countries, improve knowledge about ecological patterns and processes in the borderlands, and support long-term planning and restoration efforts.

Hydrologic functioning of the deep critical zone and contributions to streamflow in a high‐elevation catchment: Testing of multiple conceptual models

AbstractHigh‐elevation mountain catchments are often subject to large climatic and topographic gradients. Therefore, high‐density hydrogeochemical observations are needed to understand water sources to streamflow and the temporal and spatial behaviour of flow paths. These sources and flow paths vary seasonally, which dictates short‐term storage and the flux of water in the critical zone (CZ) and affect long‐term CZ evolution. This study utilizes multiyear observations of chemical compositions and water residence times from the Santa Catalina Mountains Critical Zone Observatory, Tucson, Arizona to develop and evaluate competing conceptual models of seasonal streamflow generation. These models were tested using endmember mixing analysis, baseflow recession analysis, and tritium model “ages” of various catchment water sources. A conceptual model involving four endmembers (precipitation, soil water, shallow, and deep groundwater) provided the best match to observations. On average, precipitation contributes 39–69% (55 ± 16%), soil water contributes 25–56% (41 ± 16%), shallow groundwater contributes 1–5% (3 ± 2%), and deep groundwater contributes ~0–3% (1 ± 1%) towards annual streamflow. The mixing space comprised two principal planes formed by (a) precipitation‐soil water‐deep groundwater (dry and summer monsoon season samples) and (b) precipitation‐soil water‐shallow groundwater (winter season samples). Groundwater contribution was most important during the wet winter season. During periods of high dynamic groundwater storage and increased hydrologic connectivity (i.e., spring snowmelt), stream water was more geochemically heterogeneous, that is, geochemical heterogeneity of stream water is storage‐dependent. Endmember mixing analysis and 3H model age results indicate that only 1.4 ± 0.3% of the long‐term annual precipitation becomes deep CZ groundwater flux that influences long‐term deep CZ development through both intercatchment and intracatchment deep groundwater flows.

Variable climate response differentiates the growth of Sky Island Ponderosa Pines

The seasonally cool and moist conditions of spring improved the growth of two co-occurring ponderosa pine species, which displayed different seasonal climatic responses and length of correlations to drought. We examined the climatic sensitivity of two partially sympatric pine species growing at their transition zone in the Santa Catalina Mountains, AZ, USA. Pinus arizonica is found at lower elevations compared to P. ponderosa var. brachyptera. Ring widths were measured in trees at two sites and correlated with precipitation, temperature, and Palmer Drought Severity Index to assess the influence of climate on growth. The two species were analyzed within and between sites, which have similar elevation, aspect, and species composition, although soils at the two sites have different water-holding capacities. Response function analyses of P. arizonica [sampled near its upper (and wetter) elevation limit], and P. ponderosa var. brachyptera [sampled near its lower (and drier) elevation limit] indicated that annual growth correlated positively and strongly with spring precipitation at both study locations. Local site conditions had a major impact on tree growth and variability in site conditions helped resolve the differences in species’ response to climate. For example, at the less dry site, growth of the lower-elevation pine (P. arizonica) responded to early-winter precipitation, while P. ponderosa var. brachyptera did not. Also, correlation analysis indicated that P. arizonica’s growth was more sensitive to drought for longer periods than P. ponderosa var. brachyptera. Finally, partial temperature-growth correlations of P. arizonica and P. ponderosa var. brachyptera indicated growth was limited by increased growing season and winter respiration, respectively. Rising night-time temperatures during spring significantly reduced growth of P. arizonica at Mt. Lemmon. These findings demonstrate subtle yet meaningful interspecies differences in sensitivity to seasonal moisture stress and use of carbon resources.

Fire history and moisture influences on historical forest age structure in the sky islands of southern Arizona,USA

AbstractAimThe purpose of this study was to examine the influence of moisture and fire on historical ponderosa pine (Pinus ponderosaDougl. ex Laws.) age structure patterns.LocationWe used a natural experiment created over time by the unique desert island geography of southern Arizona.MethodsWe sampled tree establishment dates in two sites on Rincon Peak and another site in the Santa Catalina Mountains. The influence of regional moisture patterns was investigated by examining synchrony among tree age peaks and periods of favourable moisture. The influence of fire was investigated by examining the relationship between local fire histories and age peaks.ResultsTree age peaks (recruitment events) were synchronized with periods of reduced fire frequencies, suggesting that periods of reduced fire activity allowed time for young trees to develop fire‐resistant characteristics. For example, two age peaks (1670s–1680s and 1770s–1780s) in the Rincon Peak‐north site coincided with a period of reduced fire frequency. These age peaks were absent in the Rincon Peak‐south site where fires were more frequent during that time. All three sites had age peaks in the early 19th century, coinciding with regional climate variability (i.e. El Niño Southern Oscillation patterns) that reduced fire activity.Main conclusionsHistorically prior to fire suppression, the survivorship, and thus cohort establishment, of ponderosa pine was ultimately determined by local fire history patterns. The importance of fire as a tree establishment regulator highlights the need to use fire at appropriate intervals not just to restore but to maintain healthy forests.

Ground-Dwelling Arthropod Communities of a Sky Island Mountain Range in Southeastern Arizona, USA: Obtaining a Baseline for Assessing the Effects of Climate Change.

The few studies that have addressed past effects of climate change on species distributions have mostly focused on plants due to the rarity of historical faunal baselines. However, hyperdiverse groups like Arthropoda are vital to monitor in order to understand climate change impacts on biodiversity. This is the first investigation of ground-dwelling arthropod (GDA) assemblages along the full elevation gradient of a mountain range in the Madrean Sky Island Region, establishing a baseline for monitoring future changes in GDA biodiversity. To determine how GDA assemblages relate to elevation, season, abiotic variables, and corresponding biomes, GDA were collected for two weeks in both spring (May) and summer (September) 2011 in the Santa Catalina Mountains, Arizona, using pitfall traps at 66 sites in six distinct upland (non-riparian/non-wet canyon) biomes. Four arthropod taxa: (1) beetles (Coleoptera), (2) spiders (Araneae), (3) grasshoppers and crickets (Orthoptera), and (4) millipedes and centipedes (Myriapoda) were assessed together and separately to determine if there are similar patterns across taxonomic groups. We collected 335 species of GDA: 192/3793 (species/specimens) Coleoptera, 102/1329 Araneae, 25/523 Orthoptera, and 16/697 Myriapoda. GDA assemblages differed among all biomes and between seasons. Fifty-three percent (178 species) and 76% (254 species) of all GDA species were found in only one biome and during only one season, respectively. While composition of arthropod assemblages is tied to biome and season, individual groups do not show fully concordant patterns. Seventeen percent of the GDA species occurred only in the two highest-elevation biomes (Pine and Mixed Conifer Forests). Because these high elevation biomes are most threatened by climate change and they harbor a large percentage of unique arthropod species (11–25% depending on taxon), significant loss in arthropod diversity is likely in the Santa Catalina Mountains and other isolated mountain ranges in the Southwestern US.

New analysis of the genus Pseudouroctonus with the description of two new species (Scorpiones: Vaejovidae)

Two new species of Pseudouroctonus are described from southeastern Arizona, USA, Pseudouroctonus santarita, sp. nov. from the Santa Rita Mountains and P. kremani, sp. nov. from the Santa Catalina Mountains. These new species are closely related to P. apacheanus (Gertsch et Soleglad, 1972). A combination of morphological differences in the hemispermatophore, the mating plug, and several morphometric-based characters are identified as diagnostic. New substructures are identified for the mating plug.

Latest Pleistocene–Holocene debris flow activity, Santa Catalina Mountains, Arizona; Implications for modern debris-flow hazards under a changing climate

Hazard mitigation for extreme events such as debris flows requires geologic mapping and chronologic information, particularly for alluvial fans near mountain fronts in the southwestern United States. In July 2006, five consecutive days of monsoonal storms caused hundreds of debris flows in southeastern Arizona, particularly in the southern Santa Catalina Mountains north of Tucson. Before 2006, no historical debris flows from the Santa Catalina Mountains reached the populated mountain front, although abundant evidence of prehistoric debris flows is present on downslope alluvial fans. We used a combination of surficial geologic mapping and 10Be exposure dating to produce a debris-flow history for Pima and Finger Rock Canyons. The largest debris flows, of latest Pleistocene to early Holocene age, covered much of the apices of alluvial fans formed at the mouths of these canyons and extended up to 3km downslope. These debris-flow deposits were inset against higher and older alluvial surfaces with few debris-flow deposits of late Pleistocene age. The 10Be ages in this study have considerable scatter for surfaces believed to be of uniform age, indicating the dual possibilities of inheritance from previous cosmic-ray exposure, as well as the potential for composite deposits derived from numerous debris flows. We then used an empirical inundation model, LAHARZ, to assess probable magnitudes of the older debris flows to evaluate possible initiation mechanisms. In-channel and terrace storage within the canyons is not sufficient to generate volumes likely needed to produce the larger late Pleistocene to early Holocene debris-flow deposits. The abundance of latest Pleistocene and early Holocene deposits suggests that large debris flows were generated during the instability associated with climate and vegetation changes at the Pleistocene–Holocene transition. Under present watershed conditions with limited sediment supplies, modern debris-flow hazards are generally limited to within mountains and near mountain fronts.