Southern California Mountains Research Articles

Spatial variability of soil metabolic rate along a dryland elevation gradient

A general framework of ecosystem hotspots suggests variation in soil metabolic activity can be understood through the relative distribution and intensity of patches of disproportionately high ecosystem process rates. To better understand the causes of soil metabolic spatial variability and the variation in ecosystem hotspots we quantified soil respiration (R) spatial heterogeneity across a network of seven sites spanning a 2,489 m elevation gradient in the Santa Rosa Mountains of Southern California. At each site, soil samples were collected from 0–5 and 5–15 cm soil depths at 2 m intervals along three 100 m transects. Each soil sample was analyzed for organic matter content (SOM) and was incubated at 40% water holding capacity for 20 days. R was measured at days 5 and 20. Strong contrasts were observed between the relationships of soil physical variables and R at scales of individual landscapes and the whole region. Notably, the relationship between SOM and R was positive within individual landscapes and negative across the entire region. Plant canopy microenvironments were associated with elevated SOM and R relative to the interspaces. This microenvironment effect on R was reduced by elevation, incubation interval, and soil depth. Geostatistical analyses conducted individually for each site identified an increasing range of autocorrelation from 2 to 10 m and a decreasing proportion of variation that was included in this range with elevation. These results suggest hotspots increase in size but decrease in intensity with elevation thereby creating a maximum hotspot effect at middle elevations.

Phymonotus jacintotopos: A new genus and species of shield-backed katydid (Orthoptera: Tettigoniidae: Tettigoniinae: Nedubini) from the San Jacinto Mountains of California, USA

We describe the monotypic shield-backed katydid genus Phymonotus and species jacintotopos from the San Jacinto Mountains of southern California, USA. Phymonotus is unique in having an unusually enlarged dome-like pronotum, a distinctive song, and seven additional distinctive morphological features. We believe that Phymonotus is a Pleistocene relic taxon, now endemic to geographically isolated high elevation conifer forests of the San Jacinto Mountains. Nearest relatives Agalothorax and Neduba taxa occur in lower elevation environments throughout the surrounding region. Phymonotus is a member of the katydid tribe Nedubini which has a Gondwanan distribution with additional taxa in Australia and South America (Chile and Argentina). Western North American Nedubini apparently result from a South American dispersal event. We also describe characters newly used for the description and diagnosis of Phymonotus, the dorsal and ventral lobes of the titillators, and the dorsal sclerites of the titillators. We report evidence that Phymonotus males may produce thoracic glandular secretions that are offered to mating females.

Patterns of pine regeneration following a large, severe wildfire in the mountains of southern California

We examined establishment patterns of pines following a large, severe wildfire in the Peninsular Ranges of southern California, USA. The October 2003 Cedar Fire caused 98% pine mortality. In this study, we asked (i) where did seedlings establish and survive in formerly forested areas of the Cuyamaca Mountains 5 years following the high severity fire and (ii) what factors were associated with the spatial pattern of seedling establishment? Factors analyzed were pre-fire vegetation type, fire severity, post-fire vegetation characteristics, topography (slope, aspect, and elevation), and mapped soil type. We used a unique belt-transect survey method following the existing trail network that resulted in a representative sample of post-fire environments. Almost 1300 100 m × 20 m quadrats were searched in 2008–2009, one third of which supported juvenile pines. Regeneration primarily consisted of Coulter pine ( Pinus coulteri D. Don), a weakly serotinous pine that was establishing at densities of 5–2320/ha on half of the quadrats where it had occurred pre-fire. Pinus coulteri regenerated in areas burned at high severity where pre-fire pine cover was high and its abundance was positively associated with higher elevation and cover of bare soil. In contrast, minimal regeneration of nonserotinous pines occurred patchily in areas that were not severely burned.

Relationships between climate, vegetation, and energy exchange across a montane gradient

We measured the evaporative fraction (EF) across a semiarid elevation gradient in the San Jacinto and Santa Rosa Mountains of southern California using the Regional Evaporative Fraction Energy Balance platform and four eddy covariance towers. We compared our measurements to precipitation estimates and satellite observations of vegetation indices to assess the seasonal and interannual controls of precipitation and vegetation on surface energy exchanges. Precipitation amount and timing had the largest effect on evaporative fraction, with vegetation having a relatively greater importance at higher elevations than lower elevations. Vegetation cover was linearly related to mean annual EF, but did not predict seasonal variation in EF in most of the study area's ecosystems. Multiyear vegetation observations show that vegetation density increases in a stepwise pattern with precipitation, probably due to shifts in dominant plant communities. Precipitation is a more important factor in controlling EF than temperature. Possible future climate change, including decreases in precipitation amount and increases in variability, could decrease vegetation cover, thus reducing EF and increasing albedo.

Rainfall intensity–duration thresholds for postfire debris-flow emergency-response planning

Following wildfires, emergency-response and public-safety agencies can be faced with evacuation and resource-deployment decisions well in advance of coming winter storms and during storms themselves. Information critical to these decisions is provided for recently burned areas in the San Gabriel Mountains of southern California. A compilation of information on the hydrologic response to winter storms from recently burned areas in southern California steeplands is used to develop a system for classifying magnitudes of hydrologic response. The four-class system describes combinations of reported volumes of individual debris flows, consequences of debris flows and floods in an urban setting, and spatial extents of the hydrologic response. The range of rainfall conditions associated with different magnitude classes is defined by integrating local rainfall data with the response magnitude information. Magnitude I events can be expected when within-storm rainfall accumulations (A) of given durations (D) fall above the threshold A = 0.4D0.5 and below A = 0.5D0.6 for durations greater than 1 h. Magnitude II events will be generated in response to rainfall accumulations and durations between A = 0.4D0.5 and A = 0.9D0.5 for durations less than 1 h, and between A = 0.5D0.6 and A = 0.9D0.5 or durations greater than 1 h. Magnitude III events can be expected in response to rainfall conditions above the threshold A = 0.9D0.5. Rainfall threshold-magnitude relations are linked with potential emergency-response actions as an emergency-response decision chart, which leads a user through steps to determine potential event magnitudes and identify possible evacuation and resource-deployment levels. Use of this information in planning and response decision-making process could result in increased safety for both the public and emergency responders.

Acorn Dispersal of California Black Oak after a Stand-Replacing Fire

We investigated California black oak (Quercus kelloggii Newberry) acorn dispersal by rodents and birds in the months after a stand-replacing fire in a mixed conifer forest in the San Bernardino Mountains of southern California, USA. The objective of this study was to compare scatter-hoarding in a high-severity burn to that in an unburned forest. In the fall of 2007, we placed 600 magnet-bearing acorns under trees in the unburned area. Of the 600, we recovered 77 (13%). Dispersers moved acorns an average distance of 5 m and buried them to an average depth of 30 mm. By spring of 2008, 90% of the cached acorns were missing. In the high-severity burn, we recovered 59 (9.8%) of the 600 acorns placed under top-killed oaks; these had been scatter-hoarded an average of 5.27 m from the source plots and buried an average of 22 mm. By spring of 2008, 55% these acorns were missing, and many of those that we relocated had been re-cached in new locations. Our results suggest that scatter-hoarding of acorns may be a common phenomenon after fire, and likely plays an important role in seedling recruitment.

Granular disintegration of marble in nature: A thermal-mechanical origin for a grus and corestone landscape

Here we document for the first time in detail a natural landscape dominated by granular disintegration of marble and the associated production of marble grus sediment and corestones. We provide several lines of evidence for a thermal-mechanical origin for the observed granular disintegration and resulting corestones. In the San Bernardino Mountains of southern California, calcite marble outcrops whose average grain diameter is greater than approximately 0.5mm are weathering into grus sediment and exhibit a corestone morphology. Minimal soil development in thick grus colluvium combined with results from a simple erosion experiment indicates that grus production and erosion is rapid. Our data indicate that unlike granite, marble granular disintegration and corestone development is a uniquely sub-aerial process. Environmental Scanning Electron Microscope (ESEM) and micro-probe analyses of rock samples collected in recent quarry exposures indicate that detachment of grain boundaries occurs primarily within the upper 2–20cm of the outcrop surface. There is minimal evidence of secondary calcite dissolution or precipitation at grain boundaries below the upper-most few centimeters of the rock surface, despite widespread intergranular fracturing. At depths greater than 20cm below the natural ground surface, granular disintegration and corestone weathering are not evident, and dissolution and precipitation of secondary calcite is only observed within a few centimeters of joint planes. Corestone morphology appears to form through the erosion of loosened grus debris at sharp edges of subaerially exposed joints. The resulting form represents a morphologic equifinality to that of granite corestones and results from different processes than those which have been proposed for granite. An 8-month, once-per-three minute temperature record from a thermocouple embedded into a marble corestone indicates that the upper 2.5cm of the corestone regularly achieves temperatures greater than 40°C, the temperature which is thought to be sufficient to produce permanent strain in calcite. All of these results are consistent with theoretical and experimental studies that indicate that marble is susceptible to mechanical weathering by thermal processes. Overall, this study provides new documentation that solar heating and cooling can be an important driver of physical weathering in natural systems of the Earth's surface.

Vegetation dynamics and exotic plant invasion following high severity crown fire in a southern California conifer forest

Early post-fire vegetation dynamics following large, severe forest fires are largely unknown for the southern California mountains owing to historic fire suppression. Vegetation in 38 forest stands was surveyed (2004, 2005, and 2007) following the 2003 Cedar Fire in the Cuyamaca Mountains, Peninsular Ranges, San Diego County, California, USA. Each stand was sampled using four 10-m radius plots for the tree stratum, and 20 1-m2 quadrats for shrub and herb strata. Changes in canopy cover by species, origin (native and exotic) and life form were analyzed. 2007 data were subjected to clustering to examine the divergence in species composition of the stands with time. Shrub cover increased from 3 to 31%, and exotic herbaceous cover increased from 3 to 40%. Cover of native annuals had increased from 2004 (17%) to 2005 (33%), but then dropped to 15% in 2007. Forty percent of the stands were dominated by the shrub species Ceanothus palmeri, and associated with higher pre-fire conifer cover and fire severity. More than 50% of the stands were dominated by exotic annuals and associated with lower fire severity and less steep slopes. The remaining stands (<10%) were dominated by chaparral shrubs and occurred on lower elevation, steep west-facing slopes. Species traits predict their dynamics following disturbance, as environmental conditions change. Establishment and increasing abundance of species dependent on dispersal to reach a site, including exotic and native herbaceous species, occurred in years 2–4. Differences among stands in species composition 4 years post-fire were associated with topographic and fire severity gradients.

The 2007 Southern California Wildfires: Lessons in Complexity

Abstract The 2007 wildfire season in southern California burned over 1,000,000 ac (∼400,000 ha) and included several megafires. We use the 2007 fires as a case study to draw three major lessons about wildfires and wildfire complexity in southern California. First, the great majority of large fires in southern California occur in the autumn under the influence of Santa Ana windstorms. These fires also cost the most to contain and cause the most damage to life and property, and the October 2007 fires were no exception because thousands of homes were lost and seven people were killed. Being pushed by wind gusts over 100 kph, young fuels presented little barrier to their spread as the 2007 fires reburned considerable portions of the area burned in the historic 2003 fire season. Adding to the size of these fires was the historic 2006-2007 drought that contributed to high dead fuel loads and long distance spotting. As in 2003, young chaparral stands and fuel treatments were not reliable barriers to fire in October 2007. Second, the Zaca Fire in July and August 2007 showed that other factors besides high winds can sometimes combine to create conditions for large fires in southern California. Spring and summer fires in southern California chaparral are usually easily contained because of higher fuel moisture and the general lack of high winds. However, the Zaca Fire burned in a remote wilderness area of rugged terrain that made access difficult. In addition, because of its remoteness, anthropogenic ignitions have been low and stand age and fuel loads were high. Coupled with this was severe drought that year that generated fuel moisture levels considerably below normal for early summer. A third lesson comes from 2007 conifer forest fires in the southern California mountains. In contrast to lower elevation chaparral, fire suppression has led to major increases in conifer forest fuels that can lead to unnaturally severe fires when ignitions escape control. The Slide and Grass Valley Fires of October 2007 occurred in forests that had been subject to extensive fuel treatment, but fire control was complicated by a patchwork of untreated private properties and mountain homes built of highly flammable materials. In a fashion reminiscent of other recent destructive conifer fires in California, burning homes themselves were a major source of fire spread. These lessons suggest that the most important advances in fire safety in this region are to come from advances in fire prevention, fire preparedness, and land-use planning that includes fire hazard patterns.

Dendrochronology-based fire history of mixed-conifer forests in the San Jacinto Mountains, California

The growing public awareness of the increasing number of large wildfires across forested landscapes, coupled with needs of resource base management has accelerated research into forest reference conditions and the historical role of fire in coniferous ecosystems. This work investigates historical fire regimes of mixed-conifer forests in the San Jacinto Mountains of southern California using fire-scar dendrochronology. As such this is the first reconstruction of fire history in the mixed-conifer forests of southern California using landscape-scale systematic-based fire-scar dendrochronology. The pre-historical fire size, seasonality, and frequency within these forests are reconstructed and demonstrated graphically, employing systematic sampling and Geographical Information System (GIS) reconstruction. A 250 m grid system was overlaid upon a 270 ha sample location, and fire-scar samples were collected from each of the grid intersection points. Fire-scar dendrochronology resulted in a 653 years long chronology, indicating a point mean fire return interval of 5.2 years, and an area wide grand mean fire interval of 32.2 years. The majority of fires occurred within latewood or at the ring boundary. Graphic modelling of fire events indicate three-quarters of all fires sampled were less than 6.25 ha in size, but burned over 50% of the area sampled during the period; only a small portion of fires were larger than 18 ha within the sample area. Use of systematic sampling is an important step in modeling long-term frequency and effects of fire on a landscape level, and is invaluable to the long-term management planning.

Ozone distribution and phytotoxic potential in mixed conifer forests of the San Bernardino Mountains, southern California

In the San Bernardino Mountains of southern California, ozone (O(3)) concentrations have been elevated since the 1950s with peaks reaching 600 ppb and summer seasonal averages >100 ppb in the 1970s. During that period increased mortality of ponderosa and Jeffrey pines occurred. Between the late 1970s and late1990s, O(3) concentrations decreased with peaks approximately 180 ppb and approximately 60 ppb seasonal averages. However, since the late 1990s concentrations have not changed. Monitoring during summers of 2002-2006 showed that O(3) concentrations (2-week averages) for individual years were much higher in western sites (58-69 ppb) than eastern sites (44-50 ppb). Potential O(3) phytotoxicity measured as various exposure indices was very high, reaching SUM00 - 173.5 ppmh, SUM60 - 112.7 ppmh, W126 - 98.3 ppmh, and AOT40 - 75 ppmh, representing the highest values reported for mountain areas in North America and Europe.

Evaluating predictive models of critical live fuel moisture in the Santa Monica Mountains, California

Large wildfires in the Santa Monica Mountains of southern California occur when low levels of live and dead fuel moisture coincide with Santa Ana wind events. Declining live fuel moisture may reach a threshold that increases susceptibility to large wildfires. Live fuel moisture and fire history data for the Santa Monica Mountains from 1984 to 2005 were used to determine a potential critical live fuel moisture threshold, below which large fires become much more likely. The ability of live fuel moisture, remote sensing, and precipitation variables to predict the annual timing of 71 and 77% live fuel moisture thresholds was assessed. Spring precipitation, measured through the months of March, April, and May, was found to be strongly correlated with the annual timing of both live fuel moisture thresholds. Large fires in the Santa Monica Mountains only occurred after the 77% threshold was surpassed, although most large fires occurred after the less conservative 71% threshold. Spring precipitation has fluctuated widely over the past 70 years but does not show evidence of long-term trends. Predictive models of live fuel moisture threshold timing may improve planning for large fires in chaparral ecosystems.

Finite study areas and vital rates: sampling effects on estimates of spotted owl survival and population trends

Summary Evaluating the status of endangered wildlife depends upon well‐designed field studies. Finances and logistics often constrain field studies to finite (limited‐sized) areas where inductive inferences are needed to extrapolate results to populations. Although available quantitative techniques for analysing data are robust to many aspects of field investigations, few investigators assess the influence of their study area size on estimators of population parameters and subsequent inferences derived from those estimators. We used mark–recapture to monitor an entire population of spotted owls Strix occidentalis in the San Bernardino Mountains of southern California (2140 km2) for which we knew the approximate true rate of survival. We defined hypothetical study areas of varying size by subsampling the population in increments of five territories; we then estimated apparent survival and emigration for non‐juvenile and juvenile owls within each of these sample study areas to assess the influence of study area size on estimators of survival and population trends. Estimated survival rates of juvenile spotted owls increased approximately fourfold from the smallest sample area to the largest (min = 0·08, SÊ = 0·03; max = 0·33, SÊ = 0·03). In contrast, estimates of apparent survival for non‐juvenile owls did not vary with study area size (range non‐juvenile = 0·80–0·82, SÊ = 0·01–0·03). Juvenile emigration was extremely high in the smallest study area (juvenile = 0·77, SÊ = 0·09) and remained above 10% until &gt; 62% of our study area (approximately 900 km2) was encompassed by a sample study area. Non‐juvenile owls had low annual emigration probabilities from all sample study area sizes (range non‐juvenile = 0·00–0·02). Although estimates of λ (finite population growth rate) increased gradually from 0·828 to 0·903 as the subsample increased from 20 to 143 territories, these estimates were similar to the ‘true’ value. Synthesis and applications. We provide direct estimates of the bias that sampling limited study areas has on emigration and mark–recapture estimators of survival. Our results demonstrate that permanent emigration from limited study areas can lead to underestimates of survival and population growth rates. In addition, our approach illustrates a technique for using multistate models to assess study design and estimator assumptions.

Airborne dust transport to the eastern Pacific Ocean off southern California: Evidence from San Clemente Island

Islands are natural dust traps, and San Clemente Island, California, is a good example. Soils on marine terraces cut into Miocene andesite on this island are clay‐rich Vertisols or Alfisols with vertic properties. These soils are overlain by silt‐rich mantles, 5–20 cm thick, that contrast sharply with the underlying clay‐rich subsoils. The silt mantles have a mineralogy that is distinct from the island bedrock. Silt mantles are rich in quartz, which is rare in the island andesite. The clay fraction of the silt mantles is dominated by mica, also absent from local andesite, and contrasts with the subsoils, dominated by smectite. Ternary plots of immobile trace elements (Sc‐Th‐La and Ta‐Nd‐Cr) show that the island andesite has a composition intermediate between average upper continental crust and average oceanic crust. In contrast, the silt and, to a lesser extent, clay fractions of the silt mantles have compositions closer to average upper continental crust. The silt mantles have particle size distributions similar to loess and Mojave Desert dust, but are coarser than long‐range‐transported Asian dust. We infer from these observations that the silt mantles are derived from airborne dust from the North American mainland, probably river valleys in the coastal mountains of southern California and/or the Mojave Desert. Although average winds are from the northwest in coastal California, easterly winds occur numerous times of the year when “Santa Ana” conditions prevail, caused by a high‐pressure cell centered over the Great Basin. Examination of satellite imagery shows that easterly Santa Ana winds carry abundant dust to the eastern Pacific Ocean and the California Channel Islands. Airborne dust from mainland North America may be an important component of the offshore sediment budget in the easternmost Pacific Ocean, a finding of potential biogeochemical and climatic significance.

Osmia bees (Hymenoptera: Megachilidae) can detect nectar-rewarding flowers using olfactory cues

Nectar-foraging bees frequently face the choice of which flowers to visit and which to avoid. One possible mechanism by which bees could discriminate between flowers before visiting them is by detecting nectar via its odours. To test this idea, we observed visits by solitary bees in the genus Osmia (Megachilidae) to flowers of Penstemon caesius (Scrophulariaceae) in the San Bernardino Mountains of southern California. We observed that free-foraging Osmia bees visited flowers containing nectar seven times more frequently than they visited nectar-depleted flowers. To test whether bees could detect the presence of nectar via odour cues, we compared floral preferences between trials where we blocked the olfactory capabilities of bees by coating their antennae with nontoxic silicone and where bees foraged with uncovered antennae. We randomly assigned the order of the silicone treatments and attempted to test 32 bees at P. caesius arrays containing nectar-depleted flowers, nectar-depleted flowers with added water and nectar-rewarding control flowers. Bees with uncovered antennae visited more than twice as many control flowers as they did either group of nectar-depleted flowers. In contrast, bees foraging with silicone-covered antennae visited all treatment flowers equally. Bees that completed both trials visited nectar-rewarding control flowers twice as frequently while foraging with uncovered antennae as they did while foraging with silicone-coated antennae. These results are consistent with the idea that solitary Osmia bees are capable of perceiving nectar volatiles to identify nectar-rewarding Penstemon flowers.

Storm rainfall conditions for floods and debris flows from recently burned areas in southwestern Colorado and southern California

Debris flows generated during rain storms on recently burned areas have destroyed lives and property throughout the Western U.S. Field evidence indicate that unlike landslide-triggered debris flows, these events have no identifiable initiation source and can occur with little or no antecedent moisture. Using rain gage and response data from five fires in Colorado and southern California, we document the rainfall conditions that have triggered post-fire debris flows and develop empirical rainfall intensity–duration thresholds for the occurrence of debris flows and floods following wildfires in these settings. This information can provide guidance for warning systems and planning for emergency response in similar settings. Debris flows were produced from 25 recently burned basins in Colorado in response to 13 short-duration, high-intensity convective storms. Debris flows were triggered after as little as six to 10 min of storm rainfall. About 80% of the storms that generated debris flows lasted less than 3 h, with most of the rain falling in less than 1 h. The storms triggering debris flows ranged in average intensity between 1.0 and 32.0 mm/h, and had recurrence intervals of two years or less. Threshold rainfall conditions for floods and debris flows sufficiently large to pose threats to life and property from recently burned areas in south-central, and southwestern, Colorado are defined by: I = 6.5 D − 0.7 and I = 9.5 D − 0.7, respectively, where I = rainfall intensity (in mm/h) and D = duration (in hours). Debris flows were generated from 68 recently burned areas in southern California in response to long-duration frontal storms. The flows occurred after as little as two hours, and up to 16 h, of low-intensity (2–10 mm/h) rainfall. The storms lasted between 5.5 and 33 h, with average intensities between 1.3 and 20.4 mm/h, and had recurrence intervals of two years or less. Threshold rainfall conditions for life- and property-threatening floods and debris flows during the first winter season following fires in Ventura County, and in the San Bernardino, San Gabriel and San Jacinto Mountains of southern California are defined by I = 12.5 D −0.4 , and I = 7.2 D −0.4 , respectively. A threshold defined for flood and debris-flow conditions following a year of vegetative recovery and sediment removal for the San Bernardino, San Gabriel and San Jacinto Mountains of I = 14.0 D −0.5 is approximately 25 mm/h higher than that developed for the first year following fires. The thresholds defined here are significantly lower than most identified for unburned settings, perhaps because of the difference between extremely rapid, runoff-dominated processes acting in burned areas and longer-term, infiltration-dominated processes on unburned hillslopes.

Hydrologic response of upland catchments to wildfires

To which extent do wildfires affect runoff production, soil erosion and sediment transport in upland catchments? This transient effect is investigated here by combining data of long term precipitation, sediment yield and wildfire records with a fine resolution spatially distributed modeling approach to flow generation and surface erosion. The model accounts for changes in the structure and properties of soil and vegetation cover by combining the tube-flux approach to topographic watershed partition with a parsimonious parametrization of hydrologic processes. This model is used to predict hydrologic and sediment fluxes for nine small catchments in Saint Gabriel mountains of southern California under control (pre-fire) and altered (post-fire) conditions. Simulation runs using a 45 years record of hourly precipitation show the passage of fire to significantly modify catchment response to storms with a major effect on erosion and flood flows. The probability of occurrence of major floods in the post-fire season is shown to increase up to an order of magnitude under same precipitation conditions. Also, the expected anomaly of sediment yield can increase dramatically the desertification hazard in upland wildfire prone areas. One should further consider the role of firefloods produced by the combined occurrence of wildfires and storms as a fundamental source of non-stationarity in the assessment of hydrologic hazard.

Concordant molecular and phenotypic data delineate new taxonomy and conservation priorities for the endangered mountain yellow‐legged frog

AbstractThe mountain yellow‐legged frogRana muscosa sensu lato, once abundant in the Sierra Nevada of California and Nevada, and the disjunct Transverse Ranges of southern California, has declined precipitously throughout its range, even though most of its habitat is protected. The species is now extinct in Nevada and reduced to tiny remnants in southern California, where as a distinct population segment, it is classified as Endangered. Introduced predators (trout), air pollution and an infectious disease (chytridiomycosis) threaten remaining populations. A Bayesian analysis of 1901 base pairs of mitochondrial DNA confirms the presence of two deeply divergent clades that come into near contact in the Sierra Nevada. Morphological studies of museum specimens and analysis of acoustic data show that the two major mtDNA clades are readily differentiated phenotypically. Accordingly, we recognize two species,Rana sierrae, in the northern and central Sierra Nevada, andR. muscosa, in the southern Sierra Nevada and southern California. Existing data indicate no range overlap. These results have important implications for the conservation of these two species as they illuminate a profound mismatch between the current delineation of the distinct population segments (southern California vs. Sierra Nevada) and actual species boundaries. For example, our study finds that remnant populations ofR. muscosaexist in both the southern Sierra Nevada and the mountains of southern California, which may broaden options for management. In addition, despite the fact that only the southern California populations are listed as Endangered, surveys conducted since 1995 at 225 historic (1899–1994) localities from museum collections show that 93.3% (n=146) ofR. sierraepopulations and 95.2% (n=79) ofR. muscosapopulations are extinct. Evidence presented here underscores the need for revision of protected population status to include both species throughout their ranges.

Comparison of the performance of flow‐routing algorithms used in GIS‐based hydrologic analysis

AbstractFlow direction and specific catchment area were calculated for different flow‐routing algorithms using TAPES‐G and TauDEM. A fuzzy classification was used along with eight topo–climatic attributes to delineate six landscape classes from a 10‐m USGS DEM. A series of maps and tabular outputs were produced to compare flow‐routing predictions in different parts of the study area in the Santa Monica Mountains of southern California. The matched pair t‐test was used to compare the performance of pairs of specific catchment area grids across six user‐defined fuzzy landscape classes. The results show that (1) the ‘source’ cells predicted with the D∞, DEMON, and FD8 algorithms were confined to hilltops; (2) two single flow‐routing algorithms (Rho8, D8) produced poor results; and (3) the choice of flow‐routing algorithm has potentially important consequences for the calculation of upslope contributing areas, sediment transport capacity, topographic wetness, and several other topographic indices. Copyright © 2007 John Wiley &amp; Sons, Ltd.

Smog Nitrogen and the Rapid Acidification of Forest Soil, San Bernardino Mountains, Southern California

We report the rapid acidification of forest soils in the San Bernardino Mountains of southern California. After 30 years, soil to a depth of 25 cm has decreased from a pH (measured in 0.01 M CaCl2) of 4.8 to 3.1. At the 50-cm depth, it has changed from a pH of 4.8 to 4.2. We attribute this rapid change in soil reactivity to very high rates of anthropogenic atmospheric nitrogen (N) added to the soil surface (72 kg ha–1 year–1) from wet, dry, and fog deposition under a Mediterranean climate. Our research suggests that a soil textural discontinuity, related to a buried ancient landsurface, contributes to this rapid acidification by controlling the spatial and temporal movement of precipitation into the landsurface. As a result, the depth to which dissolved anthropogenic N as nitrate (NO3) is leached early in the winter wet season is limited to within the top ~130 cm of soil where it accumulates and increases soil acidity.