Southern Blue Ridge Mountains Research Articles

Drainage area is not enough: multivariate hydraulic geometry in the Southern Blue Ridge Mountains, U.S.A.

ABSTRACT Regional hydraulic geometry curves, which relate drainage area to channel morphology, are powerful tools for river restoration and watershed management. While there is a strong correlation between channel morphology and drainage area, the importance of watershed slope and relief on channel-forming flow, especially in mountainous regions, cannot be ignored. This research used single variable power functions along with multiple regression to determine which network- and or local-scale variables are influencing channel morphology in the Southern Blue Ridge Mountains. Within this region, watershed topography (i.e. relief and slope) and or local-scale characteristics (e.g. channel slope and sinuosity) are better predictors of channel morphology than drainage area. Additionally, the importance of local-scale characteristics in the multiple regression models provide strong evidence that site-specific conditions can be just as important as watershed characteristics in determining channel morphology. While multiple regression has been used to create hydraulic geometry equations in other regions, this is the first study that determined whether non-drainage area multiple regression models perform better than models that include drainage area. With the increasing ease with which network- and local-scale characteristics can be calculated, this research shows a clear need to incorporate additional network- and or site-specific characteristics into hydraulic geometry equations.

Mowers versus growers: Riparian buffer management in the Southern Blue Ridge Mountains, USA

AbstractDespite long‐standing knowledge of the benefits of riparian buffers for mitigating nonpoint source pollution, many streams are unprotected by buffers. Even landowners who understand ecological values of buffers mow riparian vegetation to the streambank. Do trends in rural riparian conditions reflect the development of riparian forest science? What motivates residential riparian management actions? Using high‐resolution orthoimagery, we quantified riparian conditions and trends between 1998 and 2015 in the rural upper Little Tennessee River basin in Macon County, North Carolina and explored how landowners view riparian zone management and riparian restoration programs. Buffer composition in 2015 was as follows: no buffer (32.5%), narrow (19.3%), forested (26.7%), shrub (7.2%), and intermediate (7.0%). Relative to 1998, the greatest decrease occurred in the no buffer class (−17.7%, 46 km) and the largest increases occurred in the shrub (+72.5%, 20 km) and narrow (12.6%, 14 km) classes. Forested buffer marginally increased. Semi‐structured interview data suggest that landowners prioritize recreational and scenic aspects of riparian buffers over ecological functions such as filtration and bank stabilization. Riparian restoration programs might be made more enticing to non‐adopters if outreach language appealed to landowner priorities, design elements demonstrated intentional management, and program managers highlighted areas where ecological goals and landowner values align.

Systematics of the Ocoee Salamander (Plethodontidae: Desmognathus ocoee), with description of two new species from the southern Blue Ridge Mountains.

The "mountain" dusky is a charismatic ecomorph of Dusky Salamander (Desmognathus): smaller (~20-50mm SVL), more terrestrial and montane woodland species, typically with round tails and extremely variable, often colorful patterns. Originally considered a single species (D. ochrophaeus), populations across the Appalachians are now divided into D. abditus, D. carolinensis, D. ochrophaeus, D. ocoee, and D. orestes, which do not form a clade but are instead scattered across the phylogeny of Desmognathus. A Coastal Plain species with a mountain dusky phenotype (D. apalachicolae) is also nested within a lineage related to D. ocoee. Within the current concept of D. ocoee, there are up to 8 genetically distinct geographic lineages which display significantly different but substantially overlapping morphologies. Recent studies have suggested that as many as six species could reasonably be delimited based on genetic data. We evaluate the strength of that evidence here and find support for five species in the D. apalachicolae + D. ocoee group. The first is D. apalachicolae in essentially its originally described form from the Coastal Plain. The second and third are D. adatsihi sp. nov. and D. balsameus sp. nov., endemic to the Great Smoky/Plott Balsam and Great Balsam Mountains, respectively. The fourth corresponds to the resurrected D. perlapsus for populations from the Alarka and Cowee Mountains in North Carolina, through the Chattahoochee River drainage to the Fall Line in the Piedmont of Georgia and Alabama. The fifth is D. ocoee, here restricted to populations in the Nantahala and Unicoi Mountains and southernmost Blue Ridge escarpment, along with previously recognized populations from the Cumberland Escarpment and Cumberland Plateau of south-central Tennessee and northeastern Alabama. This taxon concept of D. ocoee includes three deeply divergent geographic genetic segments that hybridize across two contact zones, while D. apalachicolae may be nested within some southern Blue Ridge populations of D. ocoee. The resurrected form of D. perlapsus also exhibits some admixture with the newly restricted D. ocoee. While this taxonomic arrangement is robust and stably derived from mitochondrial, morphological, and nuclear data, more sophisticated future analyses sampling additional populations and loci to estimate relationships may reach more subtle conclusions regarding the identity of some lineages within D. ocoee.

Alternative Demographic Models for Two Populations of the Seal Salamander, Desmognathus monticola

Variation among desmognathan salamanders in the timing of the female reproductive cycle is poorly understood. Although nesting tends to be seasonal, in the warmer months, females may not reproduce on a strictly annual cycle, but on a biennial or irregular schedule. In the present report, I examine the ramifications of annual and biennial female reproductive schedules on demography in two populations of Desmognathus monticola in the southern Blue Ridge Mountains of southwestern North Carolina. Provisional demographic models for each are developed based on published data on age structure, growth and developmental rates, and fecundity in the populations in question. The models indicate that biennial reproduction would require higher first-year survival than annual reproduction, at levels that appear tenable given our understanding of the ecology of nesting females and larvae of this species.

Immediate Effects of Prescribed Fire on Sub-Surface Water Quality in a Managed Yellow Pine Forest

Although prescribed fire is a forest management tool annually applied to nearly one million hectares across the southeastern United States, little is known about how prescribed fire influences soil water quality in the region. Sub-surface pools of nitrogen (N) and phosphorous (P) are important indicators of ecosystem response to disturbance and are likely modified, at least temporarily, by fire. We undertook a five-month study to examine sub-surface nutrient concentrations and pH in a managed yellow pine (Pinus sp.) forest before and after a low-severity dormant season prescribed fire in the Southern Blue Ridge Mountains of South Carolina. Between February and July 2019, soil solution was collected weekly from a 30 cm porous cup suction lysimeters and analyzed for ammonium (NH4+), nitrate (NO3-), and orthophosphate (PO43-), as well as pH. We compared the five-month mean and maximum nutrient concentrations and pH to quantify the immediate effects of prescribed fire. The prescribed fire caused significant pH buffering towards neutrality in burned transects relative to the control. There was no change in soil solution NO3-. The prescribed fire caused a significant increase in maximum NH4+ (18.0 mg/L) and PO43- (6.6 mg/L) concentrations. Post-fire NH4+ concentrations reached a maximum of 18.0 mg/L before declining three weeks post-fire. PO43- concentrations in burned stands reached a maximum of 6.6 mg/L and remained elevated for four weeks post-fire. Nutrient leaching was minimal due to complexion to soil cations and ground water uptake from regenerating vegetation at the onset of the growing season. The PO43- and NH4+ pulses in this study are likely influenced by fire-induced changes to soil chemistry and future studies should examine the homogeneity of pH buffering and nutrient pulses across the burned landscape.

Watershed- to continental-scale influences on winter stormflow in the Southern Blue Ridge Mountains

Spatial and temporal influences on the winter (December-March) stormflow characteristics of fifteen United States Geological Survey (USGS)-gaged watersheds in the Southern Blue Ridge Mountains are identified: (1) watershed-scale differences in geomorphology; (2) continental-scale teleconnections during periods of wetness/dryness (based on the relative amount of winter precipitation over a consistent 20 year dataset); and (3) land cover in the context of soil parent material (e.g., development on alluvium/colluvium). Multiple regression was used to determine how much variance could be explained in five hydrologic variables describing the flashiness of peak flow (three original metrics), total seasonal flashiness (Richards Baker flashiness index), and the ratio of total winter stormflow to total discharge (the stormflow index). Models were constrained to three uncorrelated (|0.65|) variables to prevent overfitting to the dataset. Average-, dry-, and wet-years were subset using the z-scores for winter precipitation derived from the 4 km monthly PRISM (Parameter-elevation Relationships on Independent Slopes Model) dataset, for the period of 1986–2006. Relief, slope, and landscape connectivity explain the majority of explained variance in all five of the hydrologic variables during all time periods. During dry-, average-, and wet-years, atmospheric circulation patterns (i.e., North Atlantic Oscillation and Pacific/North American Pattern) explain more variance than total seasonal precipitation (PRISM), which is not true in the majority of the all-years models. Land cover explains only a small portion of the variance in regional stormflow and only when sub-divided based on soil parent material. Results provide a framework for connecting watershed-scale characteristics to regional- and continental-scale processes.

Early Clonal Survival and Growth of Poplars Grown on North Carolina Piedmont and Mountain Marginal Lands

The western half of North Carolina has abundant marginal pasturelands that vary greatly in altitude. Studies have demonstrated high Populus productivity on coastal plains and eastern Piedmont regions. Our objective was to identify best-performing Populus clones on marginal pasturelands representing upper Piedmont (Salisbury, 215 m above sea level, m.a.s.l.), northern Blue Ridge Mountains (Laurel Springs, 975 m.a.s.l.), and southern Blue Ridge Mountains (Mills River, 630 m.a.s.l.). At Salisbury, height and basal diameter (BD) were significantly related to clones (p < 0.0001), and some clones were affected by clone-spacing interaction while spacing affected aboveground wood volume significantly (p < 0.0001). At Mills River, clonal survival (p < 0.0011), height, and volume (p < 0.0051) varied with contrasting significance of some clonal differences between spacings. At Laurel Springs, survival varied among clones in 1 m × 1 m spacing (p = 0.003) but not 2 m × 2 m spacing while heights and volumes differed in both spacings (p < 0.0058). Clone 185 was consistently in the top 10 % for height, BD, and survival at all sites and spacings while other clones performed variably. Height-BD regressions were affected by clones, spacing, and sites. Volume had no clear correlations with precipitation, photosynthetically active radiation, temperature, and altitude across sites while height correlated with precipitation. Our results compared favorably with published results in other US regions, and show short rotation poplars have efficacy in Piedmont and mountain regions if the right clones in terms of growth/productivity, survival, and disease resistance are selected. Larger clonal performance variations are expected as competition increases, and highlight importance of experimentally determining suitable clones for specific sites.

Historical erosion and sedimentation in two small watersheds of the southern Blue Ridge Mountains, North Carolina, USA

Sediment bodies produced during historical periods of human land use, sometimes referred to as legacy sediment, may be found in various locations within drainage basins, and potentially remobilized by hydrogeomorphic processes accompanying land use change. The amounts and locations of stored legacy sediment can be significant factors in modern drainage basin function and should be accounted for when possible. In this study, late nineteenth-century erosion and sediment storage were investigated and used to construct approximate sediment budgets for two small Blue Ridge Mountain drainage basins in North Carolina (USA). Erosion was quantified using a distributed implementation of the Universal Soil Loss Equation (USLE), and calibrated on the separate bases of soil profile truncation data and recent published rates for long-term erosion in the region. Sediment yield information was reconstructed from pond sediments trapped behind a mill dam. Alluvial sediment storage was quantified using field studies of streambank and floodplain sediment profiles and digital elevation data. Colluvial storage was calculated as a residual in the sediment budget, and further evaluated using soil profile studies of footslope deposits, and soil survey maps. The proportions of erosion accounted for by the different budget terms in the most reliable budget are: 28% sediment yield (i.e., a sediment delivery ratio of 0.28), 69% colluvial storage, and 3% alluvial storage. Blue Ridge basins with low levels of ground disturbance erode like Piedmont basins at high levels of ground disturbance, primarily due to higher slope angles. Sediment delivery ratio is high relative to those given for much larger basins in the adjacent and more frequently studied Piedmont province, and generally in accordance with published sediment delivery curves that reflect higher hydrogeomorphic connectivities within smaller basins. Low values for alluvial storage in Blue Ridge basins may be explained by high sediment transport within steep channels. Colluvial storage values have high uncertainties because of the well known problem of error accumulation in residual budget terms. Field data on colluvial deposits reported here are not sufficient to correct for this problem, and in general, the acquisition of accurate field data on historical colluviation remains an important methodological issue in historical sediment budgeting.

Anthropic signatures in alluvium of the Upper Little Tennessee River valley, Southern Blue Ridge Mountains, USA

Abstract Human activities have become important influences on the fluvial systems of eastern North America since post-colonial settlement. This research identifies post-settlement anthropic signatures in alluvial sediments in the Upper Little Tennessee River, USA. Agricultural and mining activities were scattered and discontinuous in this relatively remote region of the Southern Blue Ridge Mountains. We compared physical and chemical characteristics of sediments in post-settlement and pre-settlement stratigraphic units at three separate sites. Chronologies were calculated using non-linear power functions based on radiocarbon and optically stimulated luminescence ages, as well as dates from 137 Cs and historical records. These chronologies suggest that sedimentation rates increased with time during the post-settlement period but decreased with time during the pre-settlement period. In addition, long-term average sedimentation rates are one order-of-magnitude higher in the post-settlement time than in the pre-settlement time. Sediment becomes finer upward through the pre-settlement unit but coarsens-upward in the post-settlement unit. Statistical analyses on adsorbed elemental concentrations suggest that three elements (Ca, Hg, Pb) clearly differentiate sediments between pre-settlement and post-settlement periods. The identified anthropic signatures thus include higher sedimentation rates, coarser sediment texture, and higher concentrations of the three elements in the post-settlement units. These characteristics likely reflect human activities such as commercial timber harvest and scattered gold mining in the late 19th and early 20th century, modern agricultural practices, and urbanization since the 1970s. Findings of this study demonstrate significant impact on fluvial systems in regions with very limited history of intense human activities. This history stands in stark contrast to other parts of the world, like Europe and Asia, that record thousands of years of anthropic impact.

Nineteenth-century sediment yields from the Southern Blue Ridge Mountains

Land-use change can dramatically alter soil erosion and sediment yield in watersheds. This paper describes late 19th-century sediment yield reconstructed for two small, low-order catchments in the Southern Blue Ridge Mountains of North Carolina at a time when each catchment had been partially cleared for agricultural activities and/or timber harvest. Historical sediment yield values are compared and contrasted to modern values obtained for the adjoining and better-known Piedmont province, and to modern values recorded in both provinces. The results indicate that had Blue Ridge land clearance equaled that of the Piedmont, historical sediment yield values would have been substantially higher than those recorded for the Piedmont. Secondly, despite differences in geology, physiography, and land-use intensity, sediment yield values trend similarly in both Blue Ridge and Piedmont regions where 19th-century agriculture and logging were replaced by 20th-century reforestation. Although early slope stabilization resulted in lower sediment yield, there was a time lag between slope stabilization and a return to pre-disturbance sediment yield in small catchments in both physiographic provinces. The remobilization of anthropogenic sediment stored in small catchments has been as influential in the Blue Ridge as in the Piedmont in terms of 20th-century fluvial sediment dynamics.

Modeling stream-bank erosion in the Southern Blue Ridge Mountains

Deforestation, followed by soil erosion and subsequent deposition of alluvium in valleys, played a critical role in the formation of historical terraces in much of the Southern Blue Ridge Mountains. Such terraces add a significant amount of sediment to the tributaries of the region as streams laterally erode the terrace banks. This study examined the contribution of total sediment yield derived solely from eroded stream banks in small watersheds (<20 km²), using floodplain widths as proxies for long-term lateral erosion rates. The raw data were derived from watersheds with different land covers (Coweeta Creek and Skeenah Creek watersheds in the Upper Little Tennessee River basin). Bank-derived sediment yield estimates were modeled in a Geographic Information System, using linear regression to relate floodplain widths and erodible terrace bank heights. We found total stream length to be a good predictor of both lateral erosion rates and erodible bank heights. Land cover, basin/network morphometrics, and reach-scale stream conditions were not good predictors. Modeled lateral migration and sediment yield results compare favorably to empirical measurements from five independent watersheds in the region. Modeled estimates fall within ±50% or better of the observed values, at 16.33 to 25.02 t km−2 yr−1.

Size-Mediated Tradeoffs in Life-History Traits in Dusky Salamanders

Among salamanders of the genus Desmognathus, the larger species tend to be more aquatic and the smaller more terrestrial. I studied life histories in assemblages of Desmognathus in the southern Blue Ridge Mountains of North Carolina at sites in the Cowee and southern Nantahala Mountains. Traits evaluated included mortality/survival, age at first reproduction, fecundity, and body size. The first three are direct fitness traits that enter into the characteristic equation, x = αΣ∞lxmxe−rx = 1.0. One assemblage (Wolf Creek), in the Cowee Mountains, comprises three species, from larger to smaller, D. quadramaculatus, D. monticola, and D. ocoee. A second assemblage (Coweeta Creek), in the Nantahala Mountains, also includes D. quadramaculatus, D. monticola, and D. ocoee, as well as the smaller D. aeneus and D. wrighti. I also studied three species only (D. ocoee, D. aeneus, D. wrighti) in an assemblage of six species (Nantahala River) in the Nantahala Mountains just west of Coweeta Creek. In these assemblages,...

Rates of Biotite Weathering, and Clay Mineral Transformation and Neoformation, Determined from Watershed Geochemical Mass-Balance Methods for the Coweeta Hydrologic Laboratory, Southern Blue Ridge Mountains, North Carolina, USA

Biotite is a common constituent of silicate bedrock. Its weathering releases plant nutrients and consumes atmospheric CO2. Because of its stoichiometric relationship with its transformational weathering product and sensitivity to botanical activity, calculating biotite weathering rates using watershed mass-balance methods has proven challenging. At Coweeta Hydrologic Laboratory the coupling of biotite to its transformational weathering product is only valid if the stoichiometric relationship for the two phases is known; this relationship is unlikely layer-for-layer. Rates of biotite weathering and transformation of its secondary weathering product at the Coweeta Hydrological Laboratory are comparable with other Appalachian watersheds. The magnitude and sign of the difference between field- and laboratory-determined biotite weathering rates are similar to those of other silicate minerals. The influence of major-cation proportions in biomass on the rates of biotite weathering and transformational weathering product is greatest for watersheds with high biomass aggradation rates. The watershed with the lowest bedrock reactivity and highest flushing rate yielded the highest gibbsite formation rate of ~500 mol ha−1 year−1 and lowest kaolin-group mineral formation rates of 4–78 mol ha−1 year−1. The kaolin-group mineral formation rate increases as bedrock reactivity increases and flushing rate decreases to a maximum of ~300 mol ha−1 year−1, with a similar minimum gibbsite formation rate. The relative differences in bedrock reactivity and flux of water through Coweeta Hydrological Laboratory watersheds studied appear to be invariant over geologic timescales.

Predicting Microstegium vimineum invasion in natural plant communities of the southern Blue Ridge Mountains, USA

Shade-tolerant non-native invasive plant species may make deep incursions into natural plant communities, but detecting such species is challenging because occurrences are often sparse. We developed Bayesian models of the distribution of Microstegium vimineum in natural plant communities of the southern Blue Ridge Mountains, USA to address three objectives: (1) to assess local and landscape factors that influence the probability of presence of M. vimineum; (2) to quantify the spatial covariance error structure in occurrence that was not accounted for by the environmental variables; and (3) to synthesize our results with previous findings to make inference on the spatial attributes of the invasion process. Natural plant communities surrounded by areas with high human activity and low forest cover were at highest risk of M. vimineum invasion. The probability of M. vimineum presence also increased with increasing native species richness and soil pH, and decreasing basal area of ericaceous shrubs. After accounting for environmental covariates, evaluation of the spatial covariance error structure revealed that M. vimineum is invading the landscape by a hierarchical process. Infrequent long-distance dispersal events result in new nascent sub-populations that then spread via intermediate- and short-distance dispersal, resulting in 3-km spatial aggregation pattern of sub-populations. Containment or minimisation of its impact on native plant communities will be contingent on understanding how M. vimineum can be prevented from colonizing new suitable habitats. The hierarchical invasion process proposed here provides a framework to organise and focus research and management efforts.

Human and Climate influence on Floodplain Sedimentation in the Upper Little Tennessee River Valley, Southern Blue Ridge Mountains, USA

Human and Climate influence on Floodplain Sedimentation in the Upper Little Tennessee River Valley, Southern Blue Ridge Mountains, USA

Late-Holocene paleofloods in the Upper Little Tennessee River valley, Southern Blue Ridge Mountains, USA

We derive a paleoflood chronology for the past 2000 years from three stratigraphic sections of overbank sediments with dates from radiocarbon, luminescence, 137Cs techniques, and historical records. Particle sizes were measured in 6–15 year intervals in post-1870 sediments and in 45–170 year intervals in pre-1870 sediments using an automatic laser analyzer. The sedimentological characteristics of ad 1948–2009 deposits were compared with gaging records, demonstrating that fine sand content and sorting discern time intervals of large floods, but flood magnitudes are not well resolved. This modern analog was applied to pre-1870 sediments and revealed two periods in the last 2000 years with large floods during ad 650–850 and ad 1100–1350, which are times when the regional tree-ring record showed extreme wetness and no severe or extreme droughts. Our findings indicate flood-prone phases of transitional climate at the beginning and end of the ‘Medieval Warm Period’ (MWP), and relatively subdued flooding during the ‘Little Ice Age’ (LIA), possibly correlated with rearrangement of macro-scale atmospheric circulation patterns between the MWP and the LIA.

Terminal Pleistocene through Holocene Evolution of Whiteoak Bottoms, a Southern Blue Ridge Mountains Peatland

Our primary objective was to develop an understanding of the geomorphic evolution of Whiteoak Bottoms (WOB), a peatland along the Nantahala River in the Southern Blue Ridge Mountains (SBRM) of western North Carolina. Radiocarbon dates directly above basal fluvial sediments returned ages of 14,000 to 15,000 cal yr BP. These ages indicate WOB is the oldest dated peatland in the SBRM and that such wetlands have persisted throughout the Holocene. Below the relatively flat surface of the wetland, paleochannels, similar to those of the modern channel, were found; suggesting a persistence of similar channel morphology since the terminal Pleistocene. The wetland’s stratigraphy reveals a consistent pattern with basal fluvial cobbles being overlain by sandy channel-fill grading up into peat. Two different distinct inorganic deposits separate the lower organic deposits from the sapric peat deposits at the surface. Interestingly, we estimate more than 56% of the organic matter preserved by the wetland accumulated during the first 6,000 years of development. Overall, WOB has accumulated approximately 424 Mg/ha of carbon during the past 15,000 years. Maintenance of this wetland initially depended on the Nantahala River; however, today it is ground water and beavers that allows for the persistence of this rare landscape.

Effects of watershed land use and geomorphology on stream low flows during severe drought conditions in the southern Blue Ridge Mountains, Georgia and North Carolina, United States

Land use and physiographic variability influence stream low flows, yet their interactions and relative influence remain unresolved. Our objective was to assess the influence of land use and watershed geomorphic characteristics on low‐flow variability in the southern Blue Ridge Mountains of North Carolina and Georgia. Ten minute interval discharge data for 35 streams (in watersheds from 3 to 146 km2) were measured for two late summer low‐flow seasons, coinciding with a severe drought period in the southeastern United States. Three low‐flow metrics were calculated (1 and 7 day minimum flows and 1st percentile flow) for each low‐flow season (5 August to 12 November 2007 and 1 August to 12 November 2008). A comprehensive suite of watershed characteristics, including factors of topography, channel network morphometry, soils, land use, and precipitation were used in multiple regression analysis of low‐flow variability among the 35 watersheds. Additionally, low flows in groups of lower‐ and higher‐forest cover watersheds were compared. Drainage density, areal coverage of colluvium, topographic variability (as slope standard deviation), and percent of the channel network as first order stream emerged as the most important variables for explaining low‐flow variability. Watershed forest cover demonstrated a consistent, significant positive relationship with low flows, despite the higher evapotranspiration rates associated with forest compared with other land covers and despite the relatively small range of disturbance in this study area. This highlights the importance of infiltration and recharge under undisturbed land cover in sustaining low flows, and it bears noteworthy implications for environmental flows and water resource sustainability.

Morphology and Channel Evolution of Small Streams in the Southern Blue Ridge Mountains of Western North Carolina

Los riachuelos son sub-estudiados en las Blue Ridge Mountains del Sur, sin embargo ellos constituyen una gran porción de la red de drenaje y son relevantes en lo que respecta al impacto humano y a los esfuerzos de restauración de paisajes y corrientes. Morfologías de 44 riachuelos (cuencas hidrográficas de 0.01 a 20 km 2 ) del oeste de Carolina del Norte son caracterizadas y formuladas en el contexto de la evolución histórica del canal e impactos humanos. Secciones transversales topográficas y gradientes longitudinales, ancho de los canales y los llanos inundables, y el tamaño de las partículas en el fondo son los datos básicos. Ecuaciones de regresión describen la forma de los canales. Nueva luminiscencia estimulada ópticamente, radiocarbono, y cesio-137 días resuelven la evolución de los canales. Los resultados indican que los canales se comportan de una manera lineal de cambio predecible en respuesta al tamaño en incremento de las cuencas. Sin embargo, los ríos con bosques tienen canales más anchos que los ríos con pastos/pastizales, lo que indica la pérdida de más de 50 por ciento del hábitat dentro de la corriente relacionada en algunos casos con la conversión de bosques de rivera a pastos/pastizales. El ancho de los llanos inundables indican de forma conservadora (escala-siglo) tasas de erosión lateral a largo plazo de aproximadamente 0.5 a 5.0 cm al año. Los insumos coluviales son causantes probables de la forma del canal y tamaño de las partículas más pequeñas en los cauces principales. El actual llano inundable parece haberse constituido en los temprano años de 1900s y todavía está evolucionando.

Proximate Contributions to Adult Body Size in Two Species of Dusky Salamanders (Plethodontidae: Desmognathus)

I used skeletochronological data to evaluate the contributions of propagule size, larval/juvenile growth, and age at first reproduction to differences in adult body size in two species of plethodontid salamanders of the genus Desmognathus. The traits in question were evaluated in populations of the larger D. quadramaculatus and smaller D. monticola in the southern Blue Ridge Mountains of North Carolina, USA. Gompertz and von Bertalanffy functions were fitted to the plots of standard length on skeletochronological age of each complete sample (larvae and/or juveniles, and adults) of earlier data sets; linear functions were fitted to data of immatures (larvae and/or juveniles). In order to examine the relationship of body mass and age, I conducted regressions of body mass on standard length in later samples of both species, calculated estimated body masses of the salamanders in the skeletochronological data sets, and then fitted a modified Gompertz function to each plot of body mass on age. The results showed that age at first reproduction is the principal factor contributing to differences between the species in size at first reproduction and adult size. Larger propagule sizes (i.e., hatching sizes) in D. quadramaculatus versus D. monticola may also be a factor; however, there is no evidence that a difference in larval/juvenile growth rate contributes to the adult size differential. Comparison of two populations of D. monticola suggested that small differences in adult body size result mainly from slight differences in age at first reproduction. Tradeoffs among propagule size, clutch size, growth, and age and size at first reproduction are discussed in the context of selective pressures that may have generated diversification in body size and life history in the genus.