Tenderfoot Creek Experimental Forest Research Articles

Lodgepole Pine Bole Wood Density and Decay Rate 1, 11, and 22 Years After Felling in Central Montana, United States

Estimates of dead and down woody material (DWM) biomass are important for nutrient cycling, wildlife habitat assessment, fire effects and climate change science. Most methods used to sample woody material initially assess volume then estimates of wood density are used to convert volume to biomass. To assess initial wood density and decomposition rate, this study examined in situ wood density of lodgepole pine logs at the Tenderfoot Creek Experimental Forest (TCEF), central Montana, United States, 1, 11, and 22 years after felling. Mean wood density decreased from 0.39 to 0.27 g cm–3 over 22 years and the single exponential decay rate was k = 0.012 yr–1 1 and 11-years post-felling and 0.022 yr–1 11 and 22 years post-felling. A common 5-category decay classification system was evaluated for estimating wood density by decay class, which identified significant difference in three of four observed classes.

Landscape analysis of soil methane flux across complex terrain

Abstract. Relationships between methane (CH4) fluxes and environmental conditions have been extensively explored in saturated soils, while research has been less prevalent in aerated soils because of the relatively small magnitudes of CH4 fluxes that occur in dry soils. Our study builds on previous carbon cycle research at Tenderfoot Creek Experimental Forest, Montana, to identify how environmental conditions reflected by topographic metrics can be leveraged to estimate watershed scale CH4 fluxes from point scale measurements. Here, we measured soil CH4 concentrations and fluxes across a range of landscape positions (7 riparian, 25 upland), utilizing topographic and seasonal (29 May–12 September) gradients to examine the relationships between environmental variables, hydrologic dynamics, and CH4 emission and uptake. Riparian areas emitted small fluxes of CH4 throughout the study (median: 0.186 µg CH4–C m−2 h−1) and uplands increased in sink strength with dry-down of the watershed (median: −22.9 µg CH4–C m−2 h−1). Locations with volumetric water content (VWC) below 38 % were methane sinks, and uptake increased with decreasing VWC. Above 43 % VWC, net CH4 efflux occurred, and at intermediate VWC net fluxes were near zero. Riparian sites had near-neutral cumulative seasonal flux, and cumulative uptake of CH4 in the uplands was significantly related to topographic indices. These relationships were used to model the net seasonal CH4 flux of the upper Stringer Creek watershed (−1.75 kg CH4–C ha−1). This spatially distributed estimate was 111 % larger than that obtained by simply extrapolating the mean CH4 flux to the entire watershed area. Our results highlight the importance of quantifying the space–time variability of net CH4 fluxes as predicted by the frequency distribution of landscape positions when assessing watershed scale greenhouse gas balances.

Diagnostic calibration and cross‐catchment transferability of a simple process‐consistent hydrologic model

AbstractThe transferability of hydrologic models is of ever increasing importance for making improved hydrologic predictions and testing hypothesized hydrologic drivers. Here, we present an investigation into the variability and transferability of the recently introduced catchment connectivity model (Smith et al., ). The catchment connectivity model was developed following extensive experimental observations identifying the key drivers of streamflow in the Tenderfoot Creek Experimental Forest (Jencso et al., ; Jencso et al., ), with the goal of creating a simple model consistent with internal observations of catchment hydrologic connectivity patterns. The model was applied across seven catchments located within Tenderfoot Creek Experimental Forest to investigate spatial variability and transferability of model performance and parameterization. The results demonstrated that the model resulted in historically good fits (based on previous studies at the sites) to both the hydrograph and internal water table dynamics (corroborated with experimental observations). The impact of a priori parameter limits was also examined. It was observed that enforcing field‐based limits on model parameters resulted in slight reductions to streamflow hydrograph fits, but significant improvements to model process fidelity (as hydrologic connectivity), as well as moderate improvement in the transferability of model parameterizations from one catchment to the next. Copyright © 2016 John Wiley & Sons, Ltd.

Spatiotemporal processes that contribute to hydrologic exchange between hillslopes, valley bottoms, and streams

AbstractQuantifying how watershed structure influences the exchanges of water among component parts of a watershed, particularly the connection between uplands, valley bottoms, and in‐stream hydrologic exchange, remains a challenge. However, this understanding is critical for ascertaining the source areas and temporal contributions of water and associated biogeochemical constituents in streams. We used dilution gauging, mass recovery, and recording discharge stations to characterize streamflow dynamics across 52 reaches, from peak snowmelt to base flow, in the Tenderfoot Creek Experimental forest, Montana, USA. We found that watershed‐contributing area was only a significant predictor of net changes in streamflow at high moisture states and larger spatial scales. However, at the scale of individual stream reaches, the lateral contributing area in conjunction with underlying lithology and vegetation densities were significant predictors of gross hydrologic gains to the stream. Reach lateral contributing areas underlain by more permeable sandstone yielded less water across flow states relative to those with granite gneiss. Additionally, increases in the frequency of steps across each stream reach contributed to greater hydrologic gross losses. Together, gross gains and losses of water along individual reaches resulted in net changes of discharge that cumulatively scale to the observed outlet discharge dynamics. Our results provide a framework for understanding how hillslope topography, geology, vegetation, and valley bottom structure contribute to the exchange of water and cumulative increases of stream flow across watersheds of increasing size.

Landscape position influences microbial composition and function via redistribution of soil water across a watershed.

Subalpine forest ecosystems influence global carbon cycling. However, little is known about the compositions of their soil microbial communities and how these may vary with soil environmental conditions. The goal of this study was to characterize the soil microbial communities in a subalpine forest watershed in central Montana (Stringer Creek Watershed within the Tenderfoot Creek Experimental Forest) and to investigate their relationships with environmental conditions and soil carbonaceous gases. As assessed by tagged Illumina sequencing of the 16S rRNA gene, community composition and structure differed significantly among three landscape positions: high upland zones (HUZ), low upland zones (LUZ), and riparian zones (RZ). Soil depth effects on phylogenetic diversity and β-diversity varied across landscape positions, being more evident in RZ than in HUZ. Mantel tests revealed significant correlations between microbial community assembly patterns and the soil environmental factors tested (water content, temperature, oxygen, and pH) and soil carbonaceous gases (carbon dioxide concentration and efflux and methane concentration). With one exception, methanogens were detected only in RZ soils. In contrast, methanotrophs were detected in all three landscape positions. Type I methanotrophs dominated RZ soils, while type II methanotrophs dominated LUZ and HUZ soils. The relative abundances of methanotroph populations correlated positively with soil water content (R = 0.72, P < 0.001) and negatively with soil oxygen (R = -0.53, P = 0.008). Our results suggest the coherence of soil microbial communities within and differences in communities between landscape positions in a subalpine forested watershed that reflect historical and contemporary environmental conditions.

The impacts of mountain pine beetle disturbance on the energy balance of snow during the melt period

AbstractMountain snowpacks provide most of the annual discharge of western US rivers, but the future of water resources in the western USA is tenuous, as climatic changes have resulted in earlier spring melts that have exacerbated summer droughts. Compounding changes to the physical environment are biotic disturbances including that of the mountain pine beetle (MPB), which has decimated millions of acres of western North American forests. At the watershed scale, MPB disturbance increases the peak hydrograph, and at the stand scale, the ‘grey’ phase of MPB canopy disturbance decreases canopy snow interception, increases snow albedo, increases net shortwave radiation, and decreases net longwave radiation versus the ‘red’ phase. Fewer studies have been conducted on the red phase of MPB disturbance and in the mixed coniferous stands that may follow MPB‐damaged forests. We measured the energy balance of four snowpacks representing different stages of MPB damage, management, and recovery: a lodgepole pine stand, an MPB‐infested stand in the red phase, a mixed coniferous stand (representing one successional trajectory), and a clear‐cut (representing reactive management) in the Tenderfoot Creek Experimental Forest in Montana, USA. Net longwave radiation was lower in the MPB‐infested stand despite higher basal area and plant area index of the other forests, suggesting that the desiccated needles serve as a less effective thermal buffer against longwave radiative losses. Eddy covariance observations of sensible and latent heat flux indicate that they are of similar but opposite magnitude, on the order of 20 MJ m−2 during the melt period. Further analyses reveal that net turbulent energy fluxes were near zero because of the temperature and atmospheric vapour pressure encountered during the melt period. Future research should place snow science in the context of forest succession and management and address important uncertainties regarding the timing and magnitude of needlefall events. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Model-based analysis of the influence of catchment properties on hydrologic partitioning across five mountain headwater subcatchments.

Ungauged headwater basins are an abundant part of the river network, but dominant influences on headwater hydrologic response remain difficult to predict. To address this gap, we investigated the ability of a physically based watershed model (the Distributed Hydrology‐Soil‐Vegetation Model) to represent controls on metrics of hydrologic partitioning across five adjacent headwater subcatchments. The five study subcatchments, located in Tenderfoot Creek Experimental Forest in central Montana, have similar climate but variable topography and vegetation distribution. This facilitated a comparative hydrology approach to interpret how parameters that influence partitioning, detected via global sensitivity analysis, differ across catchments. Model parameters were constrained a priori using existing regional information and expert knowledge. Influential parameters were compared to perceptions of catchment functioning and its variability across subcatchments. Despite between‐catchment differences in topography and vegetation, hydrologic partitioning across all metrics and all subcatchments was sensitive to a similar subset of snow, vegetation, and soil parameters. Results also highlighted one subcatchment with low certainty in parameter sensitivity, indicating that the model poorly represented some complexities in this subcatchment likely because an important process is missing or poorly characterized in the mechanistic model. For use in other basins, this method can assess parameter sensitivities as a function of the specific ungauged system to which it is applied. Overall, this approach can be employed to identify dominant modeled controls on catchment response and their agreement with system understanding.

Land–atmosphere carbon and water flux relationships to vapor pressure deficit, soil moisture, and stream flow

Climatic change is exerting considerable influence on the hydrologic and biogeochemical cycles of snow- dominated montane forest ecosystems. Growing season drought stress is a common occurrence after snowmelt-derived soil water content (WC) and stream flow (Q) have declined, leading to an increase in atmospheric water demand (i.e., vapor pressure deficit, VPD). Here, we analyzed a 6-year record (2006–2011) of H2O and CO2 fluxes from the Tenderfoot Creek Experimental Forest, a montane forest in the northern Rocky Mountains to examine (1) how growing season evapotranspiration (ET), net ecosystem production (NEP), and water-use efficiency (WUE, NEP/ET) respond to changing WC and VPD, (2) how stream flow (Q), an integrated measure of catchment-level water availability, relates to NEP, and (3) how annual NEP is related to annual precipitation and the temperature-defined growing season length (GSL). Growing season NEP exhibited a linear relationship with WC and a log-linear relationship with Q, indicative of persistent water limitations when streamflow and soil moisture reach their annual minima late in the growing season. Nevertheless, years with long GSLs had relatively higher NEP, with a small net carbon sink maintained even at low levels of WC and Q, suggesting that trees are able to obtain water from deeper portions of the soil profile (>30cm) during droughts. However, the warmer, drier climate projected for this region could bring this system closer to a critical threshold of GSL, WC, and VPD, introducing vegetation water stress that could alter the current relationship between GSL and annual NEP.

Variable-Retention Harvesting as a Silvicultural Option for Lodgepole Pine

Bark beetle-induced mortality in forested landscapes of structurally uniform, even-aged lodgepole pine stands has inspired a growing interest in the potential of silvicultural treatments to enhance resilience by increasing spatial and vertical complexity. Silvicultural treatments can simulate mixed-severity disturbances that create multiaged lodgepole pine stands, which, along with heterogeneous forest landscapes, can play a role in mitigating susceptibility to primary disturbance agents (bark beetles and wildfire). With this article, we review multiaged lodgepole pine stand dynamics and discuss variable-retention harvesting as a silvicultural option for lodgepole pine. We describe the establishment and initial outcomes of an experimental variable-retention harvesting project established at the Tenderfoot Creek Experimental Forest (Montana) in 1999‐2003 and the objectives of a collaborative multiagency effort that is presently revisiting and analyzing that experiment.

Using field data to inform and evaluate a new model of catchment hydrologic connectivity

[1] We present a new hydrologic model based on the frequency distribution of hillslope landscape elements along the stream network as a basis for simulating landscape-scale hydrologic connectivity and catchment runoff. Hydrologic connectivity describes shallow water table continuity between upland and stream elements of the catchment and is important for the movement of water and solutes to streams. This concept has gained traction in physical hydrology but has received less attention in rainfall-runoff modeling. Our model is based on the empirical studies of Jencso et al. (2009, 2010), who found a strong correlation between the duration of shallow groundwater connectivity across hillslope, riparian, and stream zones and upslope accumulated area. We explored the relationship between catchment form and function by testing the extent to which streamflow generation could be predicted by a model based on the topographic form (distribution of landscape elements) of the catchment. We applied the model to the Stringer Creek catchment of the Tenderfoot Creek Experimental Forest, located in Montana, USA. Detailed field observations collected by Jencso et al. (2009) were used to inform the underpinnings of the model and to corroborate internal consistency of the model simulations. The model demonstrated good agreement between the observed and predicted streamflow and connectivity duration curves. The ability of this model to simulate internal dynamics without conditioning the parameters on these data suggests that it has the potential to be more confidently extrapolated to other shallow, topographically driven catchments than hydrologic models that fail to consistently reproduce internal variables.

Lodgepole Pine Bole Wood Density 1 and 11 Years after Felling in Central Montana

Estimates of large dead and down woody material biomass are used for evaluating ecological processes and making ecological assessments, such as for nutrient cycling, wildlife habitat, fire effects, and climate change science. Many methods are used to assess the abundance (volume) of woody material, which ultimately require an estimate of wood density to convert volume to biomass. To assess wood density and decomposition rate, this study examined in situ wood density of lodgepole pine logs at the Tenderfoot Creek Experimental Forest, central Montana, 1 and 11 years after felling. Wood density decreased from 0.39 g cm−3 to 0.35 g cm−3 over 10 years and the single exponential decay rate was 0.0085 yr−1. A common 5-category decay classification system was evaluated for estimating wood density by decay class; however, the relationship was only partially significant.

Ecohydrology of an outbreak: mountain pine beetle impacts trees in drier landscape positions first

ABSTRACTVegetation pattern and landscape structure intersect to exert strong control over ecohydrological dynamics at the watershed scale. The hydrologic implications of vegetation disturbance (e.g. fire, disease) depend on the spatial pattern and form of environmental change. Here, we investigate this intersection at Tenderfoot Creek Experimental Forest (TCEF), Montana, with a focus on the mountain pine beetle (Dendroctonus ponderosae) epidemic currently affecting the Rocky Mountains. We calibrated QuickBird remote sensing imagery with a leaf‐level spectral library of local vegetation. We used this spectral library to determine diagnostic vegetation indices for differentiating stages of beetle infestation within the 37 km2 TCEF watershed. These indices formed the basis of a three‐component mixing model to establish the extent and magnitude of beetle infestation across the TCEF watershed. We compared disturbance patterns with spatially distributed topography and vegetation variables derived from a light detection and ranging‐based digital elevation model of TCEF. We determined that certain landscape characteristics (low vegetation density, south‐facing slopes, steep slopes, locations with small contributing areas and locations with lower values of the topographic wetness index) were significantly more likely to exhibit the effects of beetle infestation. Our efforts to monitor vegetation mortality across space and time provide a context for assessing landscape susceptibility to initial mountain pine beetle infestation and how outbreak (i.e. landscape scale infestation) patterns may affect watershed ecohydrology via altered water and biogeochemical cycles. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Landscape structure and climate influences on hydrologic response

Climate variability and catchment structure (topography, geology, vegetation) have a significant influence on the timing and quantity of water discharged from mountainous catchments. How these factors combine to influence runoff dynamics is poorly understood. In this study we linked differences in hydrologic response across catchments and across years to metrics of landscape structure and climate using a simple transfer function rainfall‐runoff modeling approach. A transfer function represents the internal catchment properties that convert a measured input (rainfall/snowmelt) into an output (streamflow). We examined modeled mean response time, defined as the average time that it takes for a water input to leave the catchment outlet from the moment it reaches the ground surface. We combined 12 years of precipitation and streamflow data from seven catchments in the Tenderfoot Creek Experimental Forest (Little Belt Mountains, southwestern Montana) with landscape analyses to quantify the first‐order controls on mean response times. Differences between responses across the seven catchments were related to the spatial variability in catchment structure (e.g., slope, flowpath lengths, tree height). Annual variability was largely a function of maximum snow water equivalent. Catchment averaged runoff ratios exhibited strong correlations with mean response time while annually averaged runoff ratios were not related to climatic metrics. These results suggest that runoff ratios in snowmelt dominated systems are mainly controlled by topography and not by climatic variability. This approach provides a simple tool for assessing differences in hydrologic response across diverse watersheds and climate conditions.

Hierarchical controls on runoff generation: Topographically driven hydrologic connectivity, geology, and vegetation

Understanding the relative influence of catchment structure (topography and topology), underlying geology, and vegetation on runoff response is key to interpreting catchment hydrology. Hillslope‐riparian‐stream (HRS) water table connectivity serves as the hydrologic linkage between a catchment's uplands and the channel network and facilitates the transmission of water and solutes to streams. While there has been tremendous interest in the concept of hydrological connectivity to characterize catchments, few studies have quantified hydrologic connectivity at the stream network and catchment scales with observational data. Here we examine how catchment topography, vegetation, and geology influenced patterns of stream network HRS connectivity and runoff dynamics across 11 nested headwater catchments in the Tenderfoot Creek Experimental Forest (TCEF), MT. This study builds on the empirical findings ofJencso et al.(2009) who found a strong linear relationship (r2= 0.91) between the upslope accumulated area (UAA) and the annual duration of shallow groundwater table connectivity observed across 24 HRS transects (146 groundwater recording wells). We applied this relationship to the entire stream network across 11 nested catchments to quantify the frequency distribution of stream network connectivity through time, and quantify its relationship to catchment‐scale runoff dynamics. Each catchment's hydrologic connectivity duration curve (CDC) was highly related to its flow duration curve (FDC) and the slope of the relationship varied across catchments. The slope represents the streamflow yield per unit connectivity (Conyield). We analyzed the slope of each catchment's CDC‐FDC relationship or Conyield(annual, peak, transition, and base flow periods) in multiple linear regression models with common terrain, land cover vegetation, and geology explanatory variables. Significant predictors (p&lt; 0.05) across 11 catchments included the ratio of flow path distances and gradients to the creek (DFC/GTC), geology, and a vegetation index. The order and strength of these predictors changed seasonally and highlight the hierarchical controls on headwater catchment runoff generation. Our results highlight direct and quantifiable linkages between catchment topography, vegetation, geology, their topology, and hydrologic dynamics.

Landscape structure, groundwater dynamics, and soil water content influence soil respiration across riparian–hillslope transitions in the Tenderfoot Creek Experimental Forest, Montana

AbstractVariability in soil respiration at various spatial and temporal scales has been the focus of much research over the last decade aimed to improve our understanding and parameterization of physical and environmental controls on this flux. However, few studies have assessed the control of landscape position and groundwater table dynamics on the spatiotemporal variability of soil respiration. We investigated growing season soil respiration in a ∼393 ha subalpine watershed in Montana across eight riparian–hillslope transitions that differed in slope, upslope accumulated area (UAA), aspect, and groundwater table dynamics. We collected daily‐to‐weekly measurements of soil water content (SWC), soil temperature, soil CO2 concentrations, surface CO2 efflux, and groundwater table depth, as well as soil C and N concentrations at 32 locations from June to August 2005. Instantaneous soil surface CO2 efflux was not significantly different within or among riparian and hillslope zones at monthly timescales. However, cumulative integration of CO2 efflux during the 83‐day growing season showed that efflux in the wetter riparian zones was ∼25% greater than in the adjacent drier hillslopes. Furthermore, greater cumulative growing season efflux occurred in areas with high UAA and gentle slopes, where groundwater tables were higher and more persistent. Our findings reveal the influence of landscape position and groundwater table dynamics on riparian versus hillslope soil CO2 efflux and the importance of time integration for assessment of soil CO2 dynamics, which is critical for landscape‐scale simulation and modelling of soil CO2 efflux in complex landscapes. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Hillslope hydrologic connectivity controls riparian groundwater turnover: Implications of catchment structure for riparian buffering and stream water sources

Hydrologic connectivity between catchment upland and near stream areas is essential for the transmission of water, solutes, and nutrients to streams. However, our current understanding of the role of riparian zones in mediating landscape hydrologic connectivity and the catchment scale export of water and solutes is limited. We tested the relationship between the duration of hillslope‐riparian‐stream (HRS) hydrologic connectivity and the rate and degree of riparian shallow groundwater turnover along four HRS well transects within a set of nested mountain catchments (Tenderfoot Creek Experimental Forest, MT). Transect HRS water table connectivity ranged from 9 to 123 days during the annual snowmelt hydrograph. Hillslope water was always characterized by low specific conductance (∼27 μS cm−1). In transects with transient hillslope water tables, riparian groundwater specific conductance was elevated during base flow conditions (∼127 μS cm−1) but shifted toward hillslope signatures once a HRS groundwater connection was established. The degree of riparian groundwater turnover was proportional to the duration of HRS connectivity and inversely related to the riparian: hillslope area ratios (buffer ratio; r2 = 0.95). We applied this relationship to the stream network in seven subcatchments within the Tenderfoot Creek Experimental Forest and compared their turnover distributions to source water contributions measured at each catchment outlet. The amount of riparian groundwater exiting each of the seven catchments was linearly related (r2 = 0.92) to their median riparian turnover time. Our observations suggest that the size and spatial arrangement of hillslope and riparian zones along a stream network and the timing and duration of groundwater connectivity between them is a first‐order control on the magnitude and timing of water and solutes observed at the catchment outlet.

Hydrologic connectivity between landscapes and streams: Transferring reach‐ and plot‐scale understanding to the catchment scale

The relationship between catchment structure and runoff characteristics is poorly understood. In steep headwater catchments with shallow soils the accumulation of hillslope area (upslope accumulated area (UAA)) is a hypothesized first‐order control on the distribution of soil water and groundwater. Hillslope‐riparian water table connectivity represents the linkage between the dominant catchment landscape elements (hillslopes and riparian zones) and the channel network. Hydrologic connectivity between hillslope‐riparian‐stream (HRS) landscape elements is heterogeneous in space and often temporally transient. We sought to test the relationship between UAA and the existence and longevity of HRS shallow groundwater connectivity. We quantified water table connectivity based on 84 recording wells distributed across 24 HRS transects within the Tenderfoot Creek Experimental Forest (U.S. Forest Service), northern Rocky Mountains, Montana. Correlations were observed between the longevity of HRS water table connectivity and the size of each transect's UAA (r2 = 0.91). We applied this relationship to the entire stream network to quantify landscape‐scale connectivity through time and ascertain its relationship to catchment‐scale runoff dynamics. We found that the shape of the estimated annual landscape connectivity duration curve was highly related to the catchment flow duration curve (r2 = 0.95). This research suggests internal catchment landscape structure (topography and topology) as a first‐order control on runoff source area and whole catchment response characteristics.

Distribution of Adult Cerambycidae and Buprestidae (Coleoptera) in a Subalpine Forest under Shelterwood Management

Abstract We examined the distribution of adult Buprestidae and Cerambycidae in the Tenderfoot Creek Experimental Forest in the Little Belt Mountains of central Montana, U.S.A., using pan traps and sweep samples on different species of flowering plants. Using several methods during multi-year (2001–2004), summer-long surveys, we documented the presence of adults of three species of Buprestidae and ten Cerambycidae. Pan traps were placed along transects within meadows, unlogged lodgepole pine forests, and in differentially-logged plots initially logged in 1999–2000 and managed by the U.S. Forest Service. Results from pan trap samples support the conclusion that, compared to unlogged plots and meadows, adult buprestids and cerambycids were more abundant in the shelterwood areas after 2001, perhaps because of the greater abundance of decaying wood in the logged areas. Cerambycids, particularly Cosmosalia chrysocoma (Kirby) and Gnathacmaeops pratensis (Laicharting), were also commonly collected on flowers, and...

Snow accumulation in thinned lodgepole pine stands, Montana, USA

Alternative silvicultural treatments such as thinning can be used to restore forested watersheds and reduce wildfire hazards, but the hydrologic effects of these treatments are not well defined. We evaluated the effect of two shelterwood-with-reserve silvicultural prescriptions, one leaving residual trees evenly distributed (SE) and the second leaving residual trees in groups (SG), both with ∼50% basal area removal, on snow accumulation in lodgepole pine stands at the Tenderfoot Creek Experimental Forest, west-central Montana. The snow water equivalent (SWE) close to the seasonal peak was measured at >250 locations in the SE and SG treatments and a control in 2003, 2004 and 2005. Reduced interception in SE resulted in significant ( P < 0.0001) 7.2 and 5.6 cm increases in SWE relative to the control in 2003 and 2004, respectively, and a 1.7 cm increase in 2005. Predictive models for the mean peak SWE in the control and the SE treatment were based on an inverse-exponential relationship between interception efficiency and mean storm intensity, and the average percent deviation for the two models was 9.4 and 7.6%, respectively. In the SG treatment, increased solar radiation and wind resulted in sublimation losses that offset gains due to reduced interception in the openings between groups. Consequently, SG always accumulated significantly less snow than SE ( P < 0.0001), and the SG treatment and control means were not significantly different. Differences in snow accumulation between groups and openings and between the north and south sides of groups meant that the SWE in SG was up to three times more variable than in either SE or the control. The contrasting responses in the SE and SG treatments demonstrate that thinning can have substantially different effects on snow accumulation depending on the spatial arrangement of tree removal.

VASCULAR FLORA OF THE TENDERFOOT CREEK EXPERIMENTAL FOREST, LITTLE BELT MOUNTAINS, MONTANA

ABSTRACT Tenderfoot Creek Experimental Forest (TCEF) is situated in the Little Belt Mountains of Montana, 120 km east of the Continental Divide. TCEF is composed of 3693 ha at elevations between 1840 and 2420 m and is dominated by lodgepole pine forest, which covers about 3366 ha, with interspersed floristically rich meadows. Our floristic inventory is based on collections and field observations made by Scott Mincemoyer during 1996–1999 and collections by Jennifer Birdsall during 2003–2005. We also include collections made by Earle Layser in 1992 and Jessica Fultz in 2002–2003. The vascular flora of TCEF consists of 312 species, representing 162 genera and 44 families. Twenty-seven exotic species occur in TCEF including Centaurea maculosa, Chrysanthemum leucanthemum, Cirsium arvense, and Tanacetum vulgare which are listed as noxious weeds in Montana. Phlox kelseyi var. missoulensis is found in the experimental forest and is listed as sensitive by the USDA Forest Service Northern Region.