Tree blowdowns   Lee E. Frelich
  Apr 03, 2006 11:46 PDT 

Yep, the exciting part of the year is just starting. Millions of trees
will come crashing to the ground in storms between now and August. The
funny thing is, the canopy residence times for our trees don't seem to be
any shorter than elsewhere. My guess is that trees in benign climates like
the Smokies and western MA grow taller and thinner so that a lesser storm
will topple them, and those lesser storms occur at about the same frequency
as very severe storms in the Midwest that topple our relatively short fat

Re: Tree blowdowns   Edward Frank
  Apr 03, 2006 12:31 PDT 


That is a really interesting observation. How would you measure canopy
residence times?

Re: Tree blowdowns   Lee E. Frelich
  Apr 03, 2006 13:35 PDT 


Residence time can be measured from:

1. Tree rings of recently fallen trees. Years from release from
suppression until tree death for shade-tolerant species, or total age at
death for intolerant species that would never have been suppressed tells
you how many years a typical canopy tree was in the canopy.

2. Observing the proportion of area in recent gaps on permanent plots. It
is best to observe gaps over a large area and/or at least a few decades to
get an accurate estimate of annual canopy turnover, which is the reciprocal
of canopy residence time.

3. Transects that examine the proportion of landscape area in gaps. This
requires some sort of time information, such as the average age of a gap,
or the ability to get the age of new saplings entering gaps. Reciprocal of
annual proportion turned over in gaps is the residence time.

4. Reconstruction of disturbance chronologies of a large number of stands
to get the landscape annual disturbance rate, which is the reciprocal of
residence time. For example, you can reconstruct the proportion of trees
entering the canopy per decade for the life of a stand, and get the average
percent for all decades, and then do that for a number of stands across the
landscape, and take the grand mean.

For my Ph.D. Thesis I used methods 1 and 4 for hemlock and maple forests in
the Porcupine Mountains and Sylvania. I had about 40 slabs from recent
windfalls, and 70 plots on which I reconstructed disturbance rate for the
last 120 years. Both methods yielded the same result: residence times were
about 160 years for sugar maple and 175 years for hemlock. IN fact most of
the literature from around the world shows 150-200 year canopy residence
times for late-successional forests.

RE: Tree blowdowns   Robert Leverett
  Apr 03, 2006 13:18 PDT 


   I wonder how far the taller-thinner comparison can be taken. Taller,
for certain, but as to thinner, is that the case? Considering the
circumferences of the trees Will and Jess routinely report on, they are
often quite large. Congaree and the Smokies grow whoppers in all
dimensions. The young southern trees gain significant height more
quickly than their northern counterparts, but then many fill out to
become the true giants of their species. The ratio of height to diameter
may be the key. The visual impact that a 150-foot tall, 10-foot
circumference hemlock is of a rather slender tree. A 100-foot tall,
10-foot circumference hemlock looks fairly stocky.

   However, this saod, the taller and thinner comparison seems to apply
to southern New England relative to the upper Mid-west.

   On a different theme, I was looking at an interesting comparison on

Location        Avg Hgt    Avg Cir

MTSF              135.4        7.2
Monica's Woods    112.1        7.0

   I've come to expect the tallest members of the hardwood species that
we track in southern New England to often be between 6 and 8 feet in
circumference. However, that relationship does not hold for hemlocks and
white pines. The tallest members of those species are usually above 10
feet in circumference. However, the maximum circumferences of the
hardwoods usually exceed their conifer counterparts. More in this theme
RE: Tree blowdowns   Lee Frelich
  Apr 03, 2006 15:57 PDT 


Yes, Thinness is measured as a ratio. Trees that have a higher H-D ratio
are thinner. The fact that the maximum circumference is similar in the east
and south does not mean the trees are not thinner. Thinner trees as
defined by H-D ratio are more susceptible to breakage in wind.

Re: Tree blowdowns   Edward Frank
  Apr 04, 2006 04:59 PDT 


I am wondering how the H-D ratio changes through time as the tree grows.
Once it has approached the maximum height for the species, does it just slow
down height, but con timue to grow fatter? The trees in the north tend to
be shorter and thinner, than the same species in the Smokies - the but the
biggest ones have similar H-D ratios. Do they have he same history of
growth? Were the northern trees always smaller than the southern ones at
all stages of gowth or did they keep up for awhile and then slow down as the
approached the maximum while the southern trees continued to enlarge? Would
there be distinctive patterns found in differnt areas or would they all be
similar? Would there be different patterns apparent if height were compared
to cross-sectional area, or even volume, rather than H-D? How much is
actually know about these patterns, has research been done on the subject,
and how much is supposition?

Re: Tree blowdowns   Lee E. Frelich
  Apr 04, 2006 07:49 PDT 


For some species both height and diameter are smaller in the north than the
south throughout their lives (e.g. hemlock), and for other species the
volume is not much different from north to south throughout the life of a
tree, and the trees in the south are thinner in relative and absolute terms
(e.g. white pine). This is based on my inspection of ENTS data. I don't
think any formal analyses have been done. This is a topic ENTS may be able
to address should they ever assemble a database of sufficient quality for
scientific analysis.