Physical properties of snowpack

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Physical properties of snowpack

• Birute Vaitelyte, Marta Martínez,
• Lui Yuen Shan

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Aims of the study

• Study thermal insulation capacity of the snow and
  how plants and insects are affected
• How the snow density changes according to the
  temperature gradients between snow surface
  temperature and ground temperature

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Snow Density
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• When snow fall at the beginning, it is usually in
  hexagonal shape.
• Once it landed, it start to metamorphose
• Metamorphism means to change or transform into
  other shape and state

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Three types of metamorphism

• Destructive metamorphism
• Constructive metamorphism
• Melt metamorphism

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Destructive metamorphism

• Edge of the crystal is rounded, snow crystals
  deteriorate and become round ice grain
• Causes Weight of snow, wind, temperature
• Result Surface area to volume of the ice ?
• The density and strength of snow ?

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Constructive metamorphism

• Snow crystals edge is sharpened
• Causes Temperature gradient within the
  snowpack.
• Result Structural strength of the snowpack ?
• Density is usually kept constant

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Melt metamorphism

• Contributes most to the change in density of snow
  
• Causes Melt-freeze cycles (melt during day
  freezing at night )
• Result Snow density and strength ?

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Results and Conclusion

• Density of snow is the highest in the middle
  layer (30-40cm)
• Lowest density in the top most layer ( 50-70cm)
• The lowest layer of snow pack usually has the
  moderate density due to the constructive
  metamorphism caused by the ground heat.

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• Result is not obvious because
• The depth of snow is not deep enough ?
• Not heavy enough to give pressure (weight) on
  the snow in lower layer for obvious destructive
  metamorphism to increase the snow density in the
  middle layer.
• There is some flora or grass on the ground that
  affect sampling of pure snow.

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Temperature

• Once snow falls to the ground it begins to change
  in a process called metamorphism
• The form of the crystals and the texture of the
  sedimentary layer of snow change over time

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• Snow pack temperature affects the availability of
  snow pack to buffer extreme melt events.
• Snow temperature of a layer helps to determine
  the rate of metamorphism
• If snow is warm process occurs faster

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Results and conclusionsGround temperature may
affect snow temperature?
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(No Transcript)
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• Observations
• Correlation between distance from the ground and
  temperature of the snow
• Each day we see that the closer in the ground,
  the higher temperature we have.
• Same pattern every day but pine forest
  temperature is lower than bog forest temperature
• Air temperature fluctuates a lot between days but
  ground and snow temperature remains without big
  changes
• Near ground, temperature is constantly near 0 C

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Insulative Quality of snow

• Snow serves as an effective thermal insulation
  layer. An accumulation of snow provides
  protection from wind serving as a "roof" over the
  subnivean spaces occupied by many plants, small
  mammals.
• Snow is also an effective insulator, especially
  when newly fallen, because it forms an emulsion
  of crystals and air. It traps dead air that
  increases the insulative efficiency.
• The formula used to calculate insulative quality
  is
• It ? (z/G)I
• Where z is the thickness (cm), G is the density
  (g/cm3) of each layer i ( Marchand 1996)

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The InvertebratesSupranivean and Intranivean
Fauna

• Marten Seidel
• Renata Süß
• Esther Jiménez Casanueva
• Laima Laukaityte

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Content

• Introduction
• Supranivean Fauna
• Intranivean Fauna
• Methods
• Results
• Conclusion

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1. Introduction

• Invertebrate is a term to describe any animal
  without a spinal column
• Seasonal snow cover is an atmospheric sediment of
  short duration
• Life can continue above, in and under snow
• Fauna which lives on and above the snow cover is
  called supranivean fauna
• Fauna which lives in or below the snow cover is
  called intranivean fauna

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1. Introduction

• Wintertime is a passive time for flora and fauna
• Low temperature, thick snow cover and less
  incoming light
• set limits for metabolic cell functions
• reduce energy availability

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1. Introduction

• Fauna and flora developed special adaptations to
  cope with this stress factors
• Five different strategies
• migration
• dormancy
• communal behavior
• winter activity
• physiological escape.

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2. Supranivean Faunaon snow cover

• During sampling period no supranivean
  invertebrates were observed on snow
• Species appear only on or above snow cover when
  climatic conditions fit to their requirements
• Low temperatures might be one explanation for the
  absence of these invertebrates

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2. Supranivean Faunaabove snow cover

• There are groups of invertebrates which
  overwinter above the snow cover
• Samples from passive overwintering invertebrates
  were collected
• Traces of these animals are mostly galls

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2. Supranivean Faunaabove snow cover - examples

• Galls of Rhabdophaga rosaria were collected on
  Salix phylicifolia
• Characteristic rose-like excrescences (gallnuts)
  located at the peaks of willow branches

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2. Supranivean Faunaabove snow cover - examples

• - Each rosette contains a single larva which
  pupates inside the gall

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2. Supranivean Faunaabove snow cover - examples

• Galerucella lineola (brown willow beetle) on
  leaves of Salix phylicifolia
• light reddish brown beetle, about 5-7 mm
• feeds on leaves of willows, poplars
• eggs laid on the lower and upper side of leaves
• beetles feed only single cell layers away
• they do not create holes

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2. Supranivean Faunaabove snow cover - examples

• Galerucella lineola

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3. Intranivean Fauna

• Invertebrates migrate vertically into the ground
  to prevent freeze damages
• Snow cover is an excellent insulator
• snow layers near soil are usually warmer than air
• animals tend to live in or under the snow, to
  avoid the cold temperature ? can stay active
  during winter

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4. Methods

• Samples from Myrtillus type pine forest and from
  pine bog forest
• Snow profile was dug and snow samples were taken
  in different depths
• Each sample was taken in horizontally direction
  by using plastic sampling containers (Volume one
  liter)
• In the laboratory
• snow was melted in a plankton net
• melting water was filtered and collected in
  plastic test tubes
• melting water samples were examined
• individuals were identified and counted
• amount of individuals per m3
• the vertical distribution of animals was
  estimated

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5. ResultsCollembola
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5. ResultsAcari
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5. Results
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5. ResultsPseudoscorpion
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5. ResultsAraneae
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5. Resultsfor pine bog forest
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5. Resultsfor myrtillus - type pine forest
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5. Resultscomparison between both sites
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5. Resultscomparison between both sites
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6. Conclusion

• Highest individual and species density in the
  snow layer closest to the soil surface
• It is assumed that temperature affect the
  vertical distribution of invertebrates
• During the sampling period temperatures were very
  low (max. -23C) ? possible explanation for the
  high abundance of species and individuals in the
  lowest layer of the snow cover
• Other factors which might influence migration
• food availability, snow density or competition

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6. Conclusion

• high total amount of individuals in the upper
  most snow layers of the pine bog forest
• higher solar radiation
• the snow layers density is relatively low ?
  enables migration

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6. Conclusion

• Pine bog forest hosts high numbers of Collembola
  and Myrtillus-type pine forests host high numbers
  of Acari
• Reasons might be soil properties
• Peatlands have very wet and acidic soils (pHlt
  4.0)
• Myrtillus-type pine forests not so acidic soil pH
  and less moister content
• ? differences in the species composition

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6. Conclusion

• Comparable results were reported in similar
  studies which were done during the last years

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Case study of twig lice egg density and goldcrest
winter demand

• Maria Luisa Castrillo
• Iago Fernandez Perello
• Vincent Viblanc

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Aims of the study

• Density and mortality variations in overwintering
  eggs of two species of twig lice Lachnus pineti
  and Lachnus spp
• Repercussions on the foraging and feeding
  behaviour of the common goldcrest Regulus regulus
  

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Overwintering in Pine aphids

• Lachnus pineti and Lachnus spp increase their
  chances of survival by overwintering in the egg
  stage.
• In the beginning of autumn, females lay their
  eggs on pine needles where the latest remain
  until next thaw.
• From this study we shall see whether or not a
  difference can be observed about oviposition
  site, as we expect the females to prefer young
  annual shoots having higher nutritional value
  than older ones.

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Material and methods

• The eggs of 2 different species were studied
  Lachnus pineti and Lachnus spp.
• The density of twig lice eggs, both total and
  living densities, were estimated via obtaining
  field samples of pine branches and counting the
  total number of eggs found on the needles.
• Dead or living eggs can be easily separated by
  visual determination. Living eggs are smooth and
  shiny whereas dead eggs are rough and dehydrated

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Living and dead eggs of Lachnus pineti and
Lachnus spp.

• Top Live and dead eggs of Lachnus spp
• Bottom Live and dead eggs of Lachnus pineti

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Results
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Results

• The egg density is higher in the first annuals

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Results

• Survival of twig lice eggs decreases through the
  annuals

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Results

• Daily food necessities of the goldcrest 6 g
• Average weight of one egg 0,26 mg
• Around 23,000 eggs are required per bird and day
  !!!
• This means that the goldcrest must find and eat
  an average of 48 eggs per minute in order to
  complete its daily food needs.
• Therefore, the goldcrest does not rely only on
  the availability of aphid eggs but complements
  its daily food intake with other insects found
  amongst pine branches.

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Discussion

• The twig lice prefer to lay their eggs on the
  first annual needles
• Lice prefer to feed on the first annuals, because
  of higher energetic value of the younger shoots.
• The survival of eggs of the first annual is
  higher.
• Goldcrest optimizes its energetic intake by
  foraging on the younger shoots

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References

• Gray, D. M. and D. H. Male, 1981. Handbook of
  Snow Principles, Processes, Management and Use.
  Willowdale, Ontario, Canada, Pergamon Press,
  776p.
• Holopainen, I. J et all, 1994. Northern Winter
  as an Ecological Factor, University of Joensuu,
  Finland, 22p.
• Marchand, P. J., 1996. Life in The Cold,
  University Press of New England.
• McClung, D. and P. Schaerer, 1993. The Avalanche
  Handbook. The Mountaineers, Seattle, WA.
• http//www.blueiceonline.com/howsite/snowpit_about
  .html
• http//www.geotech.org/survey/geotech/Snow20Metam
  orphosis.pdf.