Download 第九集 檜木森林的共生現象 大片頭30”Forest Story of Taiwan Within

第九集 檜木森林的共生現象
大片頭 30”Forest Story of Taiwan
Within the forest
it is actually not as quiet as the naked eye sees it
Organisms both depend on and compete with one another for survival
This is Yuanyang Lake Nature Reserve // situated on 110 Forest Road off the
Northern Horizontal Highway
As the towering cypress trees strive to survive
at the same time
many organisms are also quietly and passively // marking their own territories within
the forest
小 片 頭 ： 片 名 字 幕 ： Symbiosis Within the Cypress Forest
Situated at 1670 metres above sea level
being influenced by its topography and the north-easterly monsoon
Yuanyang Lake has a high level of precipitation and humidity
It also possesses a vast area of natural and structurally complete // yellow cypress (扁
柏) forest
As rain falls
rainwater will pass through the cypress’ canopy leaves and branches
and finally penetrate into the soil
As rainfall stops
the bottom layer of the forest begins to stir
Turning over a piece of fallen leaf
a snail is slowly moving around
The forest’s humid and dim environment // is a favourite habitat for snails
Within the forest
plants which cannot survive on their own will live off other trees
The humid environment of the cypress forest // has provided a suitable habitat for the
growth of many invertebrates
It has also nurtured many epiphytes // as they live on other trees to obtain nutrients
Many fern and orchidaceae plants are common examples of plants
which live on tree trunks and branches for survival and growth
To be defined as an epiphyte
firstly the plant has to be one which lives on a tree // and does not touch the ground
and secondly is that it does not extract nutrients from its host
On the other hand
parasitic plants are different in that // they will extract nutrients from their hosts
Therefore while epiphytes need to evolve // so that they can produce their own
nutrients for growth
this is not necessary in the case of parasitic plants
because some of them will grow roots deep into the bark // of their host trees to draw
and absorb nutrients
This is the biggest difference between the two
On a global scale
epiphytic plants are mainly distributed in tropical and subtropical rainforests
as well as fog forests (霧林) in mountain regions
Since their habitat is a foggy and rainy environment
they can easily obtain sufficient amounts of water and nutrients
Because of Taiwan’s relatively high level of humidity
their growth is most lush at altitudes between 700 or 800 metres // and 2000 metres
above sea level
Anywhere above 2000 meters above sea level is too cold
Because the roots of epiphytes are exposed in the air
therefore they cannot withstand coldness
The region where they are more lush // is what we call the fog forest zone (霧林帶)
which is situated at an altitude // where fog builds up every afternoon
This increases the level of humidity in the air
thereby providing epiphytes with water vapour
The level of competition within a forest environment // is actually fiercer than what
we would expect it to be
Plants fight for their own space for survival
as well as other factors that they need for growth
such as nutrients water space and sunlight
They fight for all these things because those are what plants need // for their survival
and growth
So imagine an area of one square metre
within which more than ten species of land plants are growing
Originally epiphytes could have also been a land plant
But because it could not compete against other land plants // within that area
it eventually chose the tree as its place for growth
Within the forest
epiphytes often establish many unique symbiotic relationships // with other animals
and plants
For terrestrial molluscs such as snails
because their skin do not have stratum corneum (角質層) // to prevent water
transpiration
the acquisition of water is very important to them
Some snails will choose to stay in areas with a build up // of water by epiphytes in
order to replenish water
Bryophyte is also a common type of non-vascular epiphyte // found in the cypress
forest
and is the food for snails
The very tiny and green bryophyte is a type of green plant // which enjoys humid
environments
Its most distinctive difference from fern plants and other vascular plants
is that since it is quite small and does not grow very tall
it can still flourish as long as such micro-habitats // exist within the forest
Bryophytes are further classified into mosses and liverworts
They are mainly small in size // and like to grow in humid environments
It is actually quite easy to differentiate // between mosses and liverworts
If you look at their leaves
the leaves of mosses do not split apart
It is a whole piece of leaf // and does not split into two segments
With liverworts
their leaves will split into two or three segments
This is a very distinctive difference between the two
As we enter Yuanyang Lake Nature Reserve
we can see a vast spread of bryophytes // creating a pleasant green scene
It appears that every giant tree // has put on a green velvety jacket
Mr Chang
after we enter the fog forest (雲霧森林)
we can see traces of bryophytes everywhere
Within a tropical fog forest zone (霧林帶) in a mountain region
bryophytes are very typical plants
Because it is very humid
therefore you can virtually see their traces on many places // such as rocks and tree
trunks
Sometimes we would call such places a “moss forest” (苔林)
Bazzania (鞭蘚) is a type of liverwort // commonly seen within the cypress forest
It is a creeper plant which looks like highways // supported by concrete columns
below
Therefore
this creepy Bazzania (鞭蘚) can wiggle its way around the cypress forest
while carrying out the process of photosynthesis above // and being kept
well-ventilated below
錦苔 is another unique type of bryophyte // found in the cypress forest
because it grows vertically and can hang upside down
It can still live when it is hung upside down on this branch
When it comes to peat mosses (泥炭苔)
those that grow randomly in swamps are so adaptive
that they can grow just as well wherever you dump them
Therefore the cypress forest is like a kaleidoscope // with a large variety of lives
In terms of its evolution
bryophytes are considered to be quite an early plant
Originally they did not have a vascular structure
and were the first group of plants // that got washed up onto land from the ocean
They then gradually evolved to become a vascular plant
Bryophytes were the earliest pioneer plants // that settled on land after being washed
up from the ocean
With plants such as ferns
gymnosperms whose seeds are exposed externally
as well as angiosperms which are also called flowering plants
they all have vascular structures // arranged as tubes gathered in bundles
which assist in the transporting of water and other substances
However since the simple structure of bryophytes lacks vascular bundles
they have a lower ability to transport water // and will therefore lose water more easily
This is also a factor which limits the size and height of their growth
The moss forest (苔林) is a very humid environment
In such an environment
the level of humidity is very high
Because it is an epiphyte that lives on the tree trunk
when the humidity level in the air is very high
it can absorb water vapour from the air for survival
Since other organisms cannot obtain water in such a way
they will not be able to survive in such an environment
So bryophytes actually have quite strong life endurance
We also have another saying that they are a type of organism // that can become wet
by themselves
In other words
within an environment where changes in the level of humidity // fluctuate quite
rapidly
they are still able to survive
They are different from ordinary plants
and are very unique in that their leaves // do not have a waxy type of component
Their simple double-layered cells means that // they can directly absorb water from
the air
But what happens when it does not rain
They will wither when the environment gets too dry
but they will not die
When the presence of water vapour returns
they can rapidly become alive again
During times of drought
organisms have their own different ways to conserve water
For snails which eat bryophytes as food
since the thick slime secreted from their skin is high in density
the rate at which water is lost from their body can be reduced
Apart from obtaining water via food that they eat
snails can also directly absorb water as they press the skin // of their abdominal foot
flatly onto humid surfaces
The abundance of water vapour brought by rain and fog belts (雲霧帶) // provide
bryophytes with a suitable habitat
As bryophytes live on the towering cypress trees
their chances of absorbing nutrients are thereby increased
They also intercept a large amount of water // for this cypress forest
Mr Chang
so bryophytes actually play quite an important role // within the forest, right
See how this bryophyte lives on the branch
As we mentioned earlier
it can absorb water from the air
and can also intercept fog water droplets
So if we consider the whole forest as a system
bryophytes can help absorb water from the air like sponges
So in terms of a forest ecosystem
they would perform the function of helping to bring water in
So because it lives on its host tree
the tree can actually absorb the water that it brings in
thereby forming a mutually beneficial relationship
Yes
if we look at it from such a perspective
it is certainly mutually beneficial
In the case of Cilan mountain
a bryophyte with a dry weight of one gram can intercept // and hold 0.63 gram of
water in an hour’s time
This is more than half its own weight
and is one and a half times more than // the yellow cypress’ (扁柏) ability to intercept
and hold water
The absorption power of bryophytes is even being // used for medical purposes
The peat moss (泥炭苔) that is commonly seen at Yuanyang Lake
was once used as a replacement for absorbent cotton // for the bandaging of wounds
Because there are numerous amounts of transparent dead cells // within dried peat
moss
these are able to rapidly absorb large amounts of water
thereby promoting the healing process of wounds
Apart from the interception of water
bryophytes also have another function within the forest
Some bryophytes have a nitrogen-fixing ability
A nitrogen-fixing ability means that // it can directly take nitrogen from the
atmosphere
and transform it into a form of nitrogen // that can be consumed by plants
So if it has this ability
then it can directly transform what used to be nitrogen // that could not be previously
consumed
into nitrogen that can now be consumed by the ecosystem
So for both itself and the ecosystem
this provides a channel for the input of nutrients
Bryophytes can grow on rocks
rotten wood
as well as fallen woods and branches
It will gradually grow to form a carpet-like “mat” // on which it will stabilise water
and nutrients
This often becomes the substrate on which other vascular plants grow
Can you see this
This is the seedling of a yellow cypress (扁柏)
See how it is growing on top of the bryophyte
This is a very interesting phenomenon // that we can see in a fog forest zone (霧林帶)
Often it is very difficult to see such cypress seedlings // on the ground
But we can easily spot them on top of bryophytes
We would think that because bryophytes // are able to help such seedlings obtain
water and nutrients
so this place is sort of like a safe haven // for them to sprout and grow
If they can gradually grow and extend their roots // deep into the soil
they might be able to grow into a huge tree
Therefore we are able to see a very important role // which bryophytes play in this
place
When seeds land on top of bryophytes
their opportunities for growth are opened
Some bryophytes can even provide insects and invertebrates // with a habitat and
place for laying eggs
For example
the majority of snails lay eggs on top of bryophytes
so as to avoid getting dried up or to reduce // the chances of getting preyed on by
enemies
Because of its ability to directly absorb water vapour // from the air
bryophytes are not threatened // by the lack of water within the soil
Therefore they can be distributed in places // where seed plants cannot survive
Bryophytes often are the pioneers in opening up places // such as alpine rocks and
land surfaces that are exposed
We often say that bryophytes are pioneer plants
For example
as this island first emerges
there were no organisms at all
Volcanic eruption has washed it clean // and left it in a sterile condition
As this island begins to grow
the very first arrivals may be lichens followed by bryophytes
Either way
such lichens and bryophytes have a naturally exploitative characteristic
which is their ability to decompose rocks
They way by which they do this is to use a chemical substance
acid
to slowly decompose them
Then other micro invertebrates will excrete matters // that slowly break down the
particles on the rock surface
thereby loosening up the rocks into a form // similar to that of soil
As seeds of higher-level ferns or the spores of angiosperms // are scattered onto this
surface
it is easier for them to embed and sprout
The bryophyte layer has also provided activity space // for many soil organisms
thereby creating a higher level of organism diversity // within the cypress forest
ecosystem
So what sorts of organisms actually live in the bryophyte layer
Dr Hou and her students are currently conducting a research // into soil organisms at
Yuanyang Lake
They will bake the bryophyte sample collected // to observe the organisms within
Previously when we collected samples of soil organisms
we directly dug up the soil which we then baked // in order to get the organisms to
come out
When we arrived at Yuanyang Lake
although we wanted to dig up the soil
but it was not possible because it was completely covered // by a thick layer of
bryophytes
The soil layer was only extremely thin // and was fully covered by bryophytes
So we decided that we would dig up the bryophytes // together with the soil beneath
Then we actually discovered that there were large quantities // of soil organisms
within the bryophyte layer
The most abundant springtails and mites play the role of // what we usually call
engineers of the ecosystem
Springtails mainly eat fungus
while apart from predatory mites
species such as the oribatid mite (甲螨) // will directly graze on fallen matters
So either way they will release nutrients // that were previously fixed within fungus
and fallen matters
and allow them to return into the soil
which will in turn get absorbed by plants
There is no one to fertilise a natural forest
It simply relies on its internal circulation of nutrients
For example
snails eat plants to survive and scrape on rocks to absorb // calcium carbonate for the
formation of their own shells
At the same time
such an action will increase the rate // at which rocks are decomposed
which in turn releases minerals // back into the land for absorption by plants
This is similar to the endless cycle
where micro-organisms decompose fallen leaves and branches // within the bryophyte
layer resulting in the release of nutrients
As leaves and branches fall onto the forest floor every year
the process of decomposition needs to depend // on the function of micro-organisms
such as bacteria and fungus
to transform them into nutrients // which can be absorbed and consumed by plants
However during such a process
micro-organisms also want to take these nutrients // for their own consumption
Therefore a slightly competitive relationship for nutrients // will exist between plants
and micro-organisms
This is when animals within the soil // come in to adjust micro-organisms
by feeding on them to achieve the result of // the adjustment of microbial biomass
This way
micro-organisms will not be able to take away all the nutrients
as their numbers are being adjusted by soil animals
After micro-organisms get eaten
such nutrients will be excreted in the form of animal faeces
which will then be absorbed and consumed by plants again
Within fog forests (雲霧森林) that have extremely high precipitation // and therefore
severe washouts
the outstanding ability of bryophytes to conserve water and nutrients // becomes even
more important
We believe that the bryophyte layer plays a vital role
because under normal conditions // where the layer of soil is so thin
organisms within the soil virtually // do not have any space to survive
However the bryophyte layer acts like // an extra layer of carpet-like space
So in fact
soil organisms are not directly living within the soil layer
They actually live within the bryophyte layer
Above the bryophyte layer are live bryophytes while underneath it // lie dead
bryophytes and other fallen matters
Therefore soil animals can act in between these two layers
So on a physical level
bryophytes have provided an extra topsoil-like layer // for the soil beneath
In fact it has created an even better environment // than that of topsoil
As we walk into a forest and see how well organisms big and small // flourish
delightfully under the sun
you will discover and feel the hustle and bustle // of the world within the forest
But if you also have a scientific sense
you will find that things are ever moving and developing // within that world
Bryophytes have shown us a micro-world
which we cannot usually see with our naked eye // to which we should place special
value
As we can see
the forest is filled with organisms // which usually get underestimated and neglected
These are in fact major contributors in balancing // the entire forest ecology
thereby adding vitality to the forest vitality
Within the forest
not one single matter is at a standstill
Everyday
old trees wither and die
new seedlings spring up from the ground
and organisms strive between one another for survival
Within the forest
organisms are closely linked to one another for survival
and we are no exceptions
as we are also living on the same piece of land // on which forests live
We must constantly remind ourselves
to treat every single life on this land // with a more humble heart