Jess:
I had thought about mentioning it before, but when you say that the
growth rate of a pine tree is influenced by its current height, you
bring up an important consideration. Strictly speaking it is better
to say that growth rate is influenced by age, and it is this
relationship that the growth curves are representing.
But the growth rate/height relationship is something that is too
often ignored. Years ago I read a report of a provenance trial of
white oine, that said that the best way to measure results is not the
height of the trees after some set period of time, but to measure
their growth rate at various specific heights. The idea behind this,
if I remember rightly, is that different sites, including microsites
(my term) influence the early growth of the seedlings differently, but
this influence is minimized in the data if the growth rates of trees
are compared when they are at the same heights (comparably
established, comparably developed). And this kind of measurement would
best predict the trees’ overall growth potential over time.
Now the data that prompted me to open the white pine growth topic
showed that the growth rate of white pine on the better sites declines
more rapidly than that of white pine growing on the poorer sites, so
much so that after age 55, the growth rates are the same—one foot per
year. I thought this had some application in the discussion of
whether or not white pines could, or did grow to 250 feet. Thus if
the fastest growing pines maintain their relatively fast growth rate
for only 55 years, then the best growing white pines would not grow as
much taller than white pines with more ordinary growth rates as we
might have thought. White pines 100 feet tall in 50 years is good,
but “ordinary.” Growth of 120 feet is excellent, but after gaining 20
feet over the more ordinary trees in 50 years, and maybe a foot or two
in the next five, no further advantage will be gained. All that made
me think 250 foot white pines, if view of the fact that none exist
today, less likely than I might have thought.
Sorry—I said all that before. But I wanted to re-establish the context.
Now to the height/growth rate relationship: lost is the above data
may be the fact that the trees with the most outstanding growth will,
in spite of any decline in growth rates down to the level of other
white pine trees after age 55, still be growing faster at any specific
height.
Of course as Will and others have pointed out, there is the risk of
storm damage. I would add to that the damage from large bird perch.
The bird perch issue is not recognized by all foresters, but I have
observed it first hand many, many times. The tallest trees in my pine
and spruce stands are the ones usually hit. The new growth is often
completely mashed down. If this happens early enough in the growing
season, especially with the Norway spruce, a leader can be
re-established. I can imagine that slower growing very tall old trees
would have some difficulty doing that, and the damage could
accumulate. This would be a significant influence on the ability of
older, very tall trees to make good further progress upward.
This relates to the ability of second growth stands to exceed the
growth of trees in the virgin forest. I will take this up in my next
response. Enough for one post here already.
--Gaines
