Case Study Aspen.docx

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20 Nov 2012
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Case Study: The Glorious, Golden, and Gigantic Quaking Aspen
Populus Tremuloides aspen most recognized, beautiful, admired of all tree specices
o Besides in north America, its distrivuted in European and Asian countries
Can be found from Alaska Mexico and Vancouver Maine
o In northern-central continent, trees grow at any elevation, but in southern parts, it only grows at higher
elevations
Similar pattern for aspen in Europe and Asia
Bark is living tissue and carries photosynthesis
Drops leaves in winter, but remains alive and thus requires metabolic activity
Soft tan-greenish hues on bark mark an important photosynthetic capability provided by 3 different levels of
chloroplasts
Stem photosynthesis contributes to aspen’s winter survival ( disadvantage is that its low fire resistance, attractive
source of food for elk and numerous insects/fungi)
Form individual patches comprised of numerous stems, called ramets each with its own trunk, branches, leaves
and a shared root system
o All these arise from a single aspen seed often in distant past
o compromise a single clone
o If root system b/w patches is severed then patches form physiologically separate entities but generally still
considered part of the same clone
Boundaries of clones seen in early spring when flowering/leafing occurs
Aspen occur as males and female separately (dioecious) support both male and female reproductive parts on
each individual (monoecious or hermaphroditic)
The catkins of an aspen produces genetically different aspens (sexual reproduction), whereas shared root is for
cloning (asexual reproduction)
In early spring, an aspen clone will produce small strings of catkins are either male and produce pollen or are
female and produce eggs
o Huge number of viable, tiny seeds mature and float off the female on cotton-like seed hairs that catch air
currents sometimes traveling long distance
After shedding pollen/seeds cones produce leaves
Color patches of leaves in fall season don’t mark clonal boundaries cuz chemical process that produce the colors are
very sensitive to local micro-climate conditions such as aspect (whether north or south facing), soil moisture, etc.
o Single clone may exhibit many colors at once
Asexual reproduction benefits: spreading via roots which then send up shoots
o One part of clone may be near source of water thus it can share it with other clones, while those in drier
area may have greater access to vital soil nutrient (phosphorus), which can also be distributed among clone
Quaking aspen is a disturbed species lives near avalanches, mudslides, fires
o Clonal reproduction allows aspen to initially establish or to re-establish into an area after disturbances
occur
Pando covers 107 acres with 47,000 individual ramets most massive clone (weighs 6600 tons)
o In order for this single genotype to occupy this much space for a long time environment must have right
balance of disturbance and stability
If it doesn’t experience fires/avalanche clone can’t establish itself – shade-tolerant conifers tend to
establish and shade out the high-light-requiring aspen stems
Clone structure also varies due to rainfall and humidity largest clones occur in semi-arid enviros such as
mountains
o U.S clones in smaller areas where climate supports germination
Last attribute is ability to occupy huge ranges from its high level of genetic variability among clones
o Interclonal levels of variability provide raw material for evolutionary change across generations
Large number of seeds produced from genetically variable sources generates potentially successful
genotypes for establishment in newly opened areas at higher rates
Leaves of this species quake, shake and tremble in presence of slightest breeze due to physical structure of leaf
stem (petiole) which traces a flat, oblong, elliptical pattern so it has strength in one dimension and minimal
strength in second dimension
o Minimizes risk of too much sunlight in photosynthetic apparatus (photoinhibition)
o reducing the risk overheating in intense, high elevation sunlight
o improving photosynthetic rates by keeping fresh supply of CO2 near leaf surface
o Stabilized leaves also take more leaf damage from insects than leaves that tremble
This tree species seems to almost have it all: powerful, opportunistic, sexual reproduction, long-distance
seed dispersal, effective vegetative spread, clonal reproduction, regeneration from roots, high levels of genetic
variability, living bark and a potentially enormous life span.