Does steep terrain influence tree stability? A field investigation

2005 ◽  
Vol 35 (10) ◽  
pp. 2360-2367 ◽  
Author(s):  
Bruce C Nicoll ◽  
Alexis Achim ◽  
Shaun Mochan ◽  
Barry A Gardiner
Keyword(s):  
Mineral Soil ◽  
Field Investigation ◽  
Picea Sitchensis ◽  
Risk Modelling ◽  
Tree Stability ◽  
Wind Speeds ◽  
Hinge Point ◽  
Downslope Winds ◽  
Downslope Wind ◽  
Steep Terrain

The anchorage of 40-year-old Sitka spruce (Picea sitchensis (Bong.) Carr.) trees grown in a plantation on a steep (ca. 30°) slope was compared with that of trees grown on an adjacent horizontal area. There was similar gleyed mineral soil on the sloping and horizontal areas. Trees were mechanically overturned using a winch, and anchorage was quantified by measuring load, stem angle, and tree dimensions. Trees on the slope were overturned upslope, downslope, or across-slope. Critical turning moments were calculated around the tree base and the actual hinge point. Critical wind speeds required to uproot or snap trees in this stand were modelled to compare the vulnerability of trees to upslope and downslope winds. No overall difference in anchorage was found between trees grown on the horizontal and sloping parts of the site. However, for trees on the slope, those pulled upslope showed significantly more resistance to overturning for a given stem mass than those pulled downslope. Critical turning moments calculated at the hinge point were smaller than those calculated at the stem base, but differences were small and had no effect on the comparison between treatments. Critical wind speeds for uprooting were estimated to be 28 m·s–1 for an upslope wind and 24 m·s–1 for a downslope wind on this site. The implications of these results are discussed in relation to windthrow-risk modelling and forest soil conservation.

scholarly journals Initial-Condition Sensitivities and the Predictability of Downslope Winds

2009 ◽  
Vol 66 (11) ◽  
pp. 3401-3418 ◽  
Author(s):  
Patrick A. Reinecke ◽  
Dale R. Durran
Keyword(s):  
Wave Breaking ◽  
Initial Conditions ◽  
Static Stability ◽  
Synoptic Scale ◽  
Wind Speeds ◽  
Downslope Winds ◽  
First Case ◽  
Downslope Wind ◽  
The Difference ◽  
Strong Winds

Abstract The sensitivity of downslope wind forecasts to small changes in initial conditions is explored by using 70-member ensemble simulations of two prototypical windstorms observed during the Terrain-Induced Rotor Experiment (T-REX). The 10 weakest and 10 strongest ensemble members are composited and compared for each event. In the first case, the 6-h ensemble-mean forecast shows a large-amplitude breaking mountain wave and severe downslope winds. Nevertheless, the forecasts are very sensitive to the initial conditions because the difference in the downslope wind speeds predicted by the strong- and weak-member composites grows to larger than 28 m s−1 over the 6-h forecast. The structure of the synoptic-scale flow one hour prior to the windstorm and during the windstorm is very similar in both the weak- and strong-member composites. Wave breaking is not a significant factor in the second case, in which the strong winds are generated by a layer of high static stability flowing beneath a layer of weaker mid- and upper-tropospheric stability. In this case, the sensitivity to initial conditions is weaker but still significant. The difference in downslope wind speeds between the weak- and strong-member composites grows to 22 m s−1 over 12 h. During and one hour before the windstorm, the synoptic-scale flow exhibits appreciable differences between the strong- and weak-member composites. Although this case appears to be more predictable than the wave-breaking event, neither case suggests that much confidence should be placed in the intensity of downslope winds forecast 12 or more hours in advance.

scholarly journals Evaluating the Experimental High-Resolution Rapid Refresh–Alaska Modeling System Using USArray Pressure Observations

2018 ◽  
Vol 33 (4) ◽  
pp. 933-953 ◽  
Author(s):  
Taylor A. McCorkle ◽  
John D. Horel ◽  
Alexander A. Jacques ◽  
Trevor Alcott
Keyword(s):  
High Resolution ◽  
Surface Pressure ◽  
Weather Conditions ◽  
Horizontal Resolution ◽  
Production Cycle ◽  
Downslope Winds ◽  
Downslope Wind ◽  
Wind Events ◽  
Environmental Prediction ◽  
Mean Square Errors

Abstract The High-Resolution Rapid Refresh–Alaska (HRRR-AK) modeling system provides 3-km horizontal resolution and 0–36-h forecast guidance for weather conditions over Alaska. This study evaluated the experimental version of the HRRR-AK system available from December 2016 to June 2017, prior to its operational deployment by the National Centers for Environmental Prediction in July 2018. Surface pressure observations from 158 National Weather Service (NWS) stations assimilated during the model’s production cycle and pressure observations from 101 USArray Transportable Array (TA) stations that were not assimilated were used to evaluate 265 complete 0–36-h forecasts of the altimeter setting (surface pressure reduced to sea level). The TA network is the largest recent expansion of Alaskan weather observations and provides an independent evaluation of the model’s performance during this period. Throughout the study period, systematic differences in altimeter setting between the HRRR-AK 0-h forecasts were larger relative to the unassimilated TA observations than relative to the assimilated NWS observations. Upon removal of these initial biases from each of the subsequent 1–36-h altimeter setting forecasts, the model’s 36-h forecast root-mean-square errors at the NWS and TA locations were comparable. The model’s treatment of rapid warming and downslope winds that developed in the lee of the Alaska Range during 12–15 February is examined. The HRRR-AK 0-h forecasts were used to diagnose the synoptic and mesoscale conditions during this period. The model forecasts underestimated the abrupt increases in the temperature and intensity of the downslope winds with smaller errors as the downslope wind events evolved.

Downslope Flows on a Low-Angle Slope and Their Interactions with Valley Inversions. Part II: Numerical Modeling

2008 ◽  
Vol 47 (7) ◽  
pp. 2039-2057 ◽  
Author(s):  
Shiyuan Zhong ◽  
C. David Whiteman
Keyword(s):  
Wind Speed ◽  
Pressure Gradient ◽  
Buoyancy Force ◽  
Atmospheric Modeling ◽  
Gradient Force ◽  
Ambient Atmosphere ◽  
Pressure Gradient Force ◽  
Small Contribution ◽  
Downslope Winds ◽  
Downslope Wind

Abstract The characteristics of well-developed downslope winds observed by tethered balloon soundings at multiple locations over a low-angle slope in the Salt Lake Valley are studied using the Regional Atmospheric Modeling System (RAMS). The model successfully simulated the key properties of the observed wind and temperature structure and evolution and provided insight into the forcing mechanisms. The results show that, although the slope angle is only 1.6°, the buoyancy force associated with the local temperature perturbation caused by nocturnal cooling of the slope surface is capable of producing the unusually strong and deep downslope winds observed by the tethersondes. The hypothesis that the flow is produced locally by the temperature deficit is further confirmed by analysis of the momentum budget that indicates a very small contribution from advection to the downslope mass flux. The analysis also reveals the importance of the along-slope pressure gradient force, which has been neglected by some previous investigators. On an isolated slope, the pressure gradient force, which develops as the downslope-flow layer deepens with downslope distance, is important mostly in the upper part of the downslope wind layer where it counterbalances the buoyancy force. On a slope in a valley, the pressure gradient force interacts with the valley inversion to produce intermittency in the downslope jet and may also significantly slow the flow as the inversion strengthens during the night. The simulations for two different observational nights indicate that the maximum downslope wind speed is sensitive to ambient stability, with near-neutral ambient stability yielding a stronger downslope jet than does a more stable ambient atmosphere. Sensitivity studies suggest that an increase in down-valley winds leads to a decrease in the maximum downslope wind speed and an increase in the thickness of the downslope wind layer. An increase in slope roughness, on the other hand, increases the height of the downslope jet but has little effect on other properties. The downslope wind is stronger over a gentle 1.6° slope than over a much steeper slope of 11°, mainly because of the combination of the stronger buoyancy and weaker pressure gradient over the gentle slope.

scholarly journals Diurnal Variation of Downslope Winds in Owens Valley during the Sierra Rotor Experiment

2008 ◽  
Vol 136 (10) ◽  
pp. 3760-3780 ◽  
Author(s):  
Qingfang Jiang ◽  
James D. Doyle
Keyword(s):  
Diurnal Variation ◽  
Numerical Simulations ◽  
Western Slope ◽  
Owens Valley ◽  
Mountain Waves ◽  
Downslope Winds ◽  
Wind Event ◽  
Downslope Wind ◽  
Rotor Experiment ◽  
The Impact

The impact of diurnal forcing on a downslope wind event that occurred in Owens Valley in California during the Sierra Rotors Project (SRP) in the spring of 2004 has been examined based on observational analysis and diagnosis of numerical simulations. The observations indicate that while the upstream flow was characterized by persistent westerlies at and above the mountaintop level the cross-valley winds in Owens Valley exhibited strong diurnal variation. The numerical simulations using the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) capture many of the observed salient features and indicate that the in-valley flow evolved among three states during a diurnal cycle. Before sunrise, moderate downslope winds were confined to the western slope of Owens Valley (shallow penetration state). Surface heating after sunrise weakened the downslope winds and mountain waves and eventually led to the decoupling of the well-mixed valley air from the westerlies aloft around local noon (decoupled state). The westerlies plunged into the valley in the afternoon and propagated across the valley floor (in-valley westerly state). After sunset, the westerlies within the valley retreated toward the western slope, where the downslope winds persisted throughout the night.

scholarly journals Sequence Analysis of Several Ancient River Blocking Events in the Suwalong Reach of the Upper Jinsha River Based on Multidisciplinary Approaches, SE Tibetan Plateau

2021 ◽  
Author(s):  
Yiwei Zhang ◽  
Jianping Chen ◽  
Qing Wang ◽  
Chun Tan ◽  
Yongchao Li ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Mass Movement ◽  
Field Investigation ◽  
Tibet Plateau ◽  
Tectonic Activity ◽  
The Tibetan Plateau ◽  
Jinsha River ◽  
Steep Terrain ◽  
Sbas Insar ◽  
Blocking Event

Abstract The temporary or permanent river blocking event caused by mass movement usually occurs on steep terrain. With the increase of mountain population and land use pressure and the construction of water conservancy and hydropower projects, river blocking event has gradually attracted people’s attention and understanding. The study area (Wangdalong-Gangda reach) is located in the upper reaches of the Jinsha River and the southeast edge of the Qinghai-Tibet Plateau. Affected by strong tectonic activity in the Jinsha River suture zone and the rapid uplift of the Tibetan Plateau, in the past 6000 years, there have been at least five obvious river blocking events in the reach of about 30 km in the study area. The number and density are very rare. Combined with the field investigation, indoor interpretation, laboratory tests, optically stimulated luminescence (OSL) dating, SBAS-InSAR and previous studies, multidisciplinary approaches are used to systematically summarize the analysis methods and further the understanding of one river blocking event and multiple river blocking events from difference perspectives. Especially in multiple river blocking events, we could get the wrong results, even the opposite conclusion if interaction is not considered. Through this study, the general method of analyzing the river blocking event and the problems that should be paid attention to in sampling are given, and relatively reliable historical results of river blocking events are obtained. This method has extensive applicability to the identification and analysis of river blocking events in other areas.

Anchorage of coniferous trees in relation to species, soil type, and rooting depth

2006 ◽  
Vol 36 (7) ◽  
pp. 1871-1883 ◽  
Author(s):  
Bruce C Nicoll ◽  
Barry A Gardiner ◽  
Bill Rayner ◽  
Andrew J Peace
Keyword(s):  
Pinus Contorta ◽  
Mineral Soil ◽  
Sitka Spruce ◽  
Pinus Nigra ◽  
Picea Sitchensis ◽  
Rooting Depth ◽  
Root Depth ◽  
Equivalent Mass ◽  
Mineral Soils ◽  
Soil Groups

A database was constructed of tree-anchorage measurements from almost 2000 trees from 12 conifer species that were mechanically overturned on 34 sites in the United Kingdom between 1960 and 2000. Anchorage was compared among species, soil groups (freely-draining mineral, gleyed mineral, peaty mineral, and deep peat) and root depth classes (shallow, <40 cm; medium, 40–80 cm; and deep, >80 cm) using regressions of critical turning moment against stem mass. Sitka spruce (Picea sitchensis (Bong.) Carr.) was used as a benchmark because it formed the largest part of the database and was the only species with all soil-group and depth-class combinations. Anchorage of Sitka spruce was strongest on peat and poorest on gleyed mineral soils. Deep rooting increased critical turning moments by 10%–15% compared with trees of equivalent mass with shallower roots. Significantly better anchorage than Sitka spruce was found for grand fir (Abies grandis (Dougl. ex D. Don) Lindl.), with various rooting depths on freely draining and gleyed mineral soils and for Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) on medium-depth mineral soil. Lodgepole pine (Pinus contorta Dougl. ex Loud.) had poorer anchorage than Sitka spruce over a range of soil groups and root depth classes. Norway spruce (Picea abies (L.) Karst.) on shallow gleyed mineral soil, and Corsican pine (Pinus nigra subsp. laricio (Poir.) Maire) on medium depth mineral soil, also had poorer anchorage. Other combinations had similar anchorage to the equivalent Sitka spruce. These results are discussed with respect to the development of forest wind-risk models.

Effects of Inversion Height and Surface Heat Flux on Downslope Windstorms

2011 ◽  
Vol 139 (12) ◽  
pp. 3750-3764 ◽  
Author(s):  
Craig M. Smith ◽  
Eric D. Skyllingstad
Keyword(s):  
Vertical Displacement ◽  
Falkland Islands ◽  
Similar Response ◽  
Surface Cooling ◽  
Low Level ◽  
Jet Length ◽  
Downslope Winds ◽  
Downslope Wind ◽  
Downslope Windstorms ◽  
Level Inversion

Abstract Simulations are presented focusing on the role of temperature inversions in controlling the formation and strength of downslope wind storms. Three mechanisms are examined depending on the relative height of the inversion with respect to the mountain and the stability of vertically propagating mountain waves. For low-level inversions, flows are generated that closely resemble a reduced gravity shallow water hydraulic response with a large vertical displacement of the inversion on the lee side of the mountain. For higher-level inversion cases, simulated flows more closely followed a stratified hydraulic behavior with the inversion acting as a rigid reflective lid. In the third mechanism, downslope winds were forced by a self-induced critical layer located below the inversion height. The presence of the inversion in this case had little effect on the resulting downslope winds. Observations made on the Falkland Islands show that downslope windstorms may preferentially occur in early morning even without synoptic-scale changes in atmospheric structure. Most windstorms on the Falkland Islands generally have a short jet length; rare, longer jet length storms typically occur in conjunction with a strong low-level inversion. Idealized numerical experiments tend to produce a similar response depending on the presence of strong low-level inversion and surface cooling. Results suggest that surface heating can have significant control on the flow response by reducing the low-level inversion strength, or by changing the stratification and wind velocity below the inversion, thereby preventing a strong downslope windstorm.

Ectomycorrhizal Inoculation Fails to Improve Performance of Sitka Spruce Seedlings on Clearcuts in Southeastern Alaska

1988 ◽  
Vol 3 (4) ◽  
pp. 110-112 ◽  
Author(s):  
Elaine M. Loopstra ◽  
Charles G. Shaw ◽  
Roy C. Sidle
Keyword(s):  
Seedling Survival ◽  
Mineral Soil ◽  
Sitka Spruce ◽  
Picea Sitchensis ◽  
Cenococcum Geophilum ◽  
Fungal Treatment ◽  
Improve Performance ◽  
Growing Seasons ◽  
Rotten Wood ◽  
High Fertilization

Abstract Hebeloma crustulini-forme (Bull. ex St. Amans) Quel., Laccaria laccata (Scop. ex Fr.) Berk and Br., and Cenococcum geophilum (L. ex Fr.) Pers. ex Hooker were established as ectomycorrhizae on container-grown Sitka spruce (Picea sitchensis [Bong.] Carr.) seedlings that, along with noninoculated controls, were planted in rotten wood, exposed mineral soil, and undisturbed duff on a recently clearcut site in southeastern Alaska. At planting, seedling heights differed significantly among all fungal treatments: the tallest were those inoculated with C. geophilum, the shortest with H. crustuliniforme. High fertilization controls, reared under a standard nursery regime, had significantly greater height and diameter than other treatments at out-planting. Four growing seasons after planting, seedling survival exceeded 99%. Total height and diameter after 4 years, as well as 4-year increments, did not differ significantly among fungal treatments and low fertilization controls. High fertilization controls had greater total heights and diameters than any other treatment; these differences were significant from seedlings inoculated with L. laccata or H. crustiliniforme. Although differences were not significant, seedlings planted in rotten wood, regardless of fungal treatment, had the smallest increase in height after 4 years (136%); those planted in undisturbed duff had the largest (162%). These data support earlier indications that prior colonization by these fungi provides little benefit to out-planted Sitka spruce seedlings on various microsites in southeastern Alaska clearcuttings. West. J. Appl. For. 3(4):110-112, October 1988.

scholarly journals Episode with strong downslope wind in the Southern and Curvature Carpathians in the period 5-6 february 2020

2021 ◽  
Vol 28 (1) ◽  
pp. 79-89
Author(s):  
M.H. HUȘTIU ◽  
A. BOARIU
Keyword(s):  
Wind Direction ◽  
Critical Level ◽  
Thermal Inversion ◽  
Downslope Winds ◽  
Downslope Wind ◽  
Two Factors ◽  
Southern Carpathians ◽  
The Ideal

The phenomenon that occurred during the blizzard from February 5-6 in the mountains and especially on the southern slopes of the Southern Carpathians, is known in the literature as "strong downslope winds". This phenomenon occurred in a typical blizzard configuration, in which the differentiated advection of temperature led to the formation of a very stable air layer, with thermal inversion approximately between the levels of 850 and 700 hPa; and it also contributed in this layer to the change of wind direction to vertical. Thus, the existence in the same air layer of two factors favorable to the formation of a critical level, created the ideal conditions for generating strong downslope winds.

Mycorrhizal chronosequence near Exit Glacier, Alaska

1996 ◽  
Vol 74 (9) ◽  
pp. 1496-1506 ◽  
Author(s):  
D.J. Helm ◽  
E.B. Allen ◽  
J.M. Trappe
Keyword(s):  
Mycorrhizal Fungi ◽  
Woody Plants ◽  
Arbuscular Mycorrhizae ◽  
Mineral Soil ◽  
Picea Sitchensis ◽  
Populus Balsamifera ◽  
Black Cottonwood ◽  
Third Stage ◽  
Successional Stages ◽  
Time Required

Mycorrhizal fungi associated with plant species may change as vegetation develops following disturbance. The objectives of this study were to compare ectomycorrhizae through a chronosequence on deglaciated land from bare mineral soil to mature forest and to determine time required for mycorrhizal formation on natural seedlings. A chronosequence that formed as Exit Glacier retreated enabled us to document changes in mycorrhizae on existing woody plants, including Populus balsamifera ssp. trichocarpa (Torr. & Gray) Hult, (black cottonwood) that dominates the early stages, Alnus sinuata (Regel) Rydb. (Sitka alder) that has few ectomycorrhizal fungal associates, and Picea sitchensis (Bong.) Carr. (Sitka spruce) that typifies late successional stages. Some seedlings of Populus balsamifera became ectomycorrhizal within 3 weeks of germination but most took longer. Although a dark type without clamp connections dominated willows in the second and third stage, it was not a dominant in the first stage and was rare on 1st year seedlings. Ectomycorrhizal types differed among successional stages for Populus balsamifera. Diversity increased from early successional stages to later stages, mostly from an increase in evenness rather than richness. Arbuscular mycorrhizae were not found on any woody plants, although a few herbaceous plants had low infection percentages. Keywords: ectomycorrhizae, chronosequence, Populus, Alnus, Picea, Salix.

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