The article proposes three explanations to illustrates some reasons for declining of yellow cedar trees in Northwestern of the North America. However, the lecturer challenges these theories and avers that none of those are adequate, also he mentions that it is better to confess that we don't know the real reason of this disappearnce of yellow cedars.
First, the professor states that although the insect parasites could damage the trees, the healthy yellow cedar are resistant to insects because of a poison in its leaves and barks. This hazardous chemical is in a high enough concentration which can kill the parasites. In addition, parasites can only harm the weak and sick trees. In account of this parasites could not be the root cause of this yellow cedar decline. This counter argument clearly rebuts the author first proposal.
Second, the lecturer points out even the bear has some negative effects on the yellow cedar tree, but it is not the main factore in this tree's decrease. The spokesman asserts that this decrease in number of trees has happened not only in the main land of Northwestern of the U. S. but also it has happened in the islands far from the shore, where bears do not leave. If the bear cause this problem for the tree how we can justify trees' decline in islands without bears. Thus, this theory about bears does not hold water.
Third, the lecturer explains that many more trees has died in the lower altitude, where the weather is warmer than the upper hight. He reopudiates the author's idea that climate change and seasonal and diel temperature fluctuation can be the reason for yellow cedar dieing out. He emphasize on this contrast that if the roots of yellow trees are sensitive to cold climate, the trees in the higher altitude should be damaged more than lower hight, but it has not been seen. Consequently, we cannot attribute this decline to the cold temperature, he says
The article proposes three explanations to illustrates
some
reasons for declining of yellow
cedar
trees
in Northwestern of the North America.
However
, the lecturer challenges these theories and avers that none of those are adequate,
also
he mentions that it is better to confess that we don't know the real reason of this
disappearnce
of yellow cedars.
First
, the professor states that although the insect parasites could damage the
trees
, the healthy yellow
cedar
are resistant to insects
because
of a poison in its
leaves
and barks. This hazardous chemical is in a high
enough
concentration which can kill the parasites.
In addition
, parasites can
only
harm the weak and sick
trees
. In account of
this
parasites could not be the root cause of this yellow
cedar
decline. This counter argument
clearly
rebuts the author
first
proposal.
Second, the lecturer points out even the
bear
has
some
negative
effects on the yellow
cedar
tree
,
but
it is not the main
factore
in this tree's decrease. The spokesman asserts that this decrease in number of
trees
has happened not
only
in the main land of Northwestern of the U. S.
but
also
it has happened in the islands far from the shore, where
bears
do not
leave
. If the
bear
cause this problem for the
tree
how we can justify trees' decline in islands without
bears
.
Thus
, this theory about
bears
does not hold water.
Third, the lecturer
explains
that
many
more
trees
has
died
in the lower altitude, where the weather is warmer than the upper
hight
. He
reopudiates
the author's
idea
that climate
change
and seasonal and
diel
temperature fluctuation can be the reason for yellow
cedar
dieing
out. He
emphasize
on this contrast that if the roots of yellow
trees
are sensitive to
cold
climate, the
trees
in the higher altitude should
be damaged
more than lower
hight
,
but
it has not been
seen
.
Consequently
, we cannot attribute this decline to the
cold
temperature, he says