Resound wrote:
> "Theo Bekkers" wrote
>> Duracell Bunny wrote:
>>> I have a tree in my garden that has wrapped itself round a steel
>>> post that was used to hold it up when it was a sapling (I presume),
>>> it's now some 15' off the ground, much higher than it was when I
>>> bought the block some 15 years ago.
>>
>> That's very interesting. Most trees grow up from the top, and just
>> get wider at the bottom.
> That doesn't sound right. How do trees wind up with substantial
> amounts (metres in some cases) of straight trunk prior to the first
> branch then?
I don't know what happens to the lower branches. Maybe some trees shed them
and some don't. I know that in a dense forest the lower branches die and
fall off due to lack of sunshine for their leaves. We have about ten Golden
Ambers in our driveway which are now at four to five metres. I started
trimming the lower branches last year, otherwise they would be lying on the
ground. I've noticed that the gums in my backyard have long clear trunks
but the same tree in my front yard with lots of space has branches down to
ground level. See below for explanation of a very common misconception.
http://www.cnr.vt.edu/dendro/forsite/howdoes.htm
Trees grow in height as a result of meristems that are located at
their branch tips. These meristems are called apical meristems. Roots also
expand through the soil by growing at their tips as a result of apical
meristems. All buds that you see on a tree contain apical meristems. Trunk
diameter growth occurs as a result of another meristem already mentioned
called the vascular cambium. The vascular cambium produces new xylem and
phloem each year and as a result the trunk, branches and roots continue to
increase in diameter. Have you ever seen a fence wire or board grown into a
tree?
That is the result of the vascular cambium. The fence wire or board
doesn't rise into the air because height growth doesn't occur out of the
ground, it only occurs from the branch tips.
<picture of fence board in tree left out>
Now for a little demonstration on how a branch grows. Notice that the
buds grow out - the whole twig doesn't extend. This is the reason why a
nail pounded into a tree trunk never changes height. New growth is added to
the tips. The only other way a tree grows is in diameter.
Cheers.
Theo