Transcript
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The ecology of tree regeneration in Bhutan
Georg Gratzer
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Forest management - what to consider in terms ofecology?
1. How does the environment change after felling of trees?
2. What are the pools for tree regeneration?
3. How to manage competition?
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How does the environment change after felling?
1. Radiation
Felling trees
meansmanaging sunlight
It is in your hand
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How does the environment change after felling?
21.3
21.12.
21.6.
36.4 m
15.3 m
1.8 m
Length of shades thrown by a 30 m high stand edge at different times of a year,Time: 12: 00 Bhutan (Latitude: 27N)
Lengths of shades in anopening
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How does the environment change after felling?
32.7m
Bhutan (Latitude of 27N),slope angle 35,
1st of April, at 12: 00
On a northernexposed slope,slope angle 35
Lengths of shades in anopening
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How does the environment change after felling?
1.4.
6.7m
Length of shades at 12:00, 1st of April, thrown by a30 m high stand edge, in Bhutan (latitude of 27N)
On a southernexposed slope,slope angle 35
Lengths of shades in anopening
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How does the environment change after felling?
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0.2
0.22
0.24
The radiation in a gap the region with the highest percentage of openarea radiation is north of the gap in the forest
Gap
area
Extended gaparea
Percentage of above
canopy light
Johannserkogel, Austria
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How does the environment change after felling?
Large openings have
a clearcut climate
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How does the environment change after felling?
Temperature extremes are more
pronounced in canopy gaps than in theadjacent forest
MORE FROST AND MORE HEAT
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How does the environment change after felling?
MORE FROST
A clearcut in Montana, USA had24 frostfree days per year
The uncut control had
113 frostfree days per year(Farnden, C. 1994)
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How does the environment change after felling?
MORE HEAT
Overheating of seedbeds of more than 60C
The west side of a gap receives sun in the morning when you have colder
temperatures, dew etc. whereas the east side is warmer because itreceives sun in the evening when dew already dried and temperaturesare higher
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Windspeed in gaps is increaseswith increasing size of the gap
4 haDiameter 225 m 0.4 haDiameter 72 m 0.12 haDiameter 40 m 0.04 haDiameter 22 m
100% 41%
28% 20%
(Mitscherlich, 1971)
Percentage of open area windspeed
How does the environment change after felling?
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How does the environment change after felling?
More frequent winds and
stronger winds speedsremove the insolating airaround the plant and causemore overheating.
It increases the evaporationlosses and stomata have tobe closed earlier the plant
grows less
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How does the environment change after felling?
Trees are like a water pump.
Removing trees on wet soils islike removing the water pump
This can cause the water tableto rise to the surface and
create marshy conditions.
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How does the environment change after felling?
Changing the forest cover in a
landscape changes the wholewater regime in the watershed.
This has consequences alsofor the runoff characteristics inlandscapes and the productionof electricity by water power
plants
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How does the environment change after felling?
1.4.
6.7m
Southern exposed slope, slope angle 35
More than 60Calso in smallergaps on southernslopes this is
too much formost treeseedlings
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Overheating of seedbeds isa severe regenerationobstacle for shade toleranttrees like Tsuga dumosa
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Tsuga dumosaseeds are very small they dryout easily.
They need moss for germination.
The moss needs shade and dries out in theopen.
Toomuch
sun
Mosses dryout
Hemlockseeds dry
out
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How does the environment change after felling?
Felling not onlychanges themicroclimate but
strongly changes thevegetation in thelogged over area
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How does the environment change after felling?
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How does the environment change after felling?
The increased light on the ground triggers thegermination of seeds which were resting in the soil.
It also allows for quick regeneration of species which canoutcompete tree regeneration (from seeds andvegetatively)
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How does the environment change after felling?
REGULATING LIGHT ISREGULATING
COMPETITION
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How do trees and other plants respond to felling?
But before you fell trees you have tomake sure that there will be enough
tree regeneration
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How do trees and other plants respond to felling?
What are the pools for tree regeneration?
Reproductiveplant (age)
Seedling andsapling bank
Soil seed bank
Soil surface
Crown seedbank
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How do trees and other plants respond to felling?
What are the processes to look at?
The best is, if theregeneration is
there already
Do not kill it while
felling directionalfelling!
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How do trees and other plants respond to felling?
Seed production
When?
Where?
Viable?
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How do trees and other plants respond to felling?
What are the processes to look at?
Seed dispersal
How far?
Who does it Wind or animals?
Will there be enough seeds inthe logged over area?
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How do trees and other plants respond to felling?
Who eats the seeds?
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