08, 2005 06:22 PDT
A bow echo derecho crashed through Minneapolis last night at
4:00 am. This
was not a high end event, the storm was only moving at 40 mph
gusts only peaked at 60-70 mph with 1.5-3 inches of rain.
there were a few trees down in the neighborhood and over 100,000
were without electricity this morning. I saw it begin to form on
weather channel radar last night at 9:00 near rapid city South
made a note to myself to wake up at 4:00 am, and sure enough
that is just
when it arrived.
It is amazing how much stuff these storms bring down. The
packed with debris that includes millions of tree seeds of all
storms must play a big role in seed dispersal of trees. I wonder
how far a
rain soaked elm or maple seed will go in a 60 mph wind, starting
trajectory 60 feet above the ground? The
literature on seed dispersal
only examines dispersal of dry seeds in open fields on days with
08, 2005 08:06 PDT
You've opened my eyes to yet another method by
which seeds might end
up far from their origins. Given the power of a derecho, I
far an acorn or hickory nut might be carried?
08, 2005 08:32 PDT
A lot of seeds are mature already (Red maple, the elms,
we have had several weeks of warm, almost tropical weather in
MN. For other species of trees whose seeds mature later, yes, we
derechos in September.
I have found mature trees 100 feet from where they were rooted
derechos (and it wasn't a case of rolling down a hill), and have
branches and furniture flying through the air in derechos.
albums and wallets belonging to people whose houses were
St. Peter, MN, were found on the south side of Minneapolis after
supercell thunderstorm, and that is 60 miles away. I would say
hickory nut could go anywhere from a few hundred feet to many
a high end derecho.
08, 2005 12:13 PDT
I enjoyed reading Lee's comments an unusual seed dispersal.
Here in the PNW, were learned some cool lessons in that regard
at Mt St Helens. After the eruption, there were vast areas with
nothing but ash and studies were set up to track recolonization.
I have worked there during some of this research and it was
learned that long-distance dispersal is fairly common in winter.
Small Abies procera trees were visible a few years after
the eruption up to eight kilometers away from the nearest live
tree. This is a tree with very large seeds (sometimes as large
as a peanut). During the winter, hard crusts often form on the
surface of snowpacks, and even mild winds can transport items
great distances along this very smooth surface. The presence of
a plant in this landscape will quickly trap bits of debris
(organic matter and seeds) which will grow to form islands.
Ultimately, these islands will coalesce to form new forests.
08, 2005 20:47 PDT
This is a very interesting topic to me as I have done damage
perhaps two dozen or so derechos over the last 10 years. One
have noticed is that tornadoes are the champs when it comes to
light debris long distances. This is due to the fact that, along
the horizontal component to the wind in a tornado, there is also
vertical component that derechos lack. There have been studies
dispersion by tornadoes:
I am not aware of similar studies for derechos, but based on my
surveying experiences, debris lofting/carrying is much less
in a derecho than a tornado. Of course, you can make a
argument that derechos are more important than tornadoes in
seeds given that derecho winds will typically affect much larger
than tornado winds.
09, 2005 07:29 PDT
Derechos probably have a bigger cumulative effect on seed
existing forests than tornadoes, since any given location is hit
derechos between tornado episodes, due to both higher frequency
size of derechos. Probably the larger size and greater frequency
occurrence of derechos overcomes the shorter average distance
dispersal, at least in terms of the number of seeds moved around
For a much different case, plants migrating in response to
it is hard to tell whether tornadoes (which probably have the
distance traveled by seeds) or derechos would help more a
species occupy a
new range faster. We really don't know whether an occasional big
outweighs steady but shorter steps. My guess is that tornadoes
establish new populations well out in front of the main edge of
species, and the derechos then help those outposts spread around
so the two phenomena work together.
Still another way to look at seed dispersal by high wind events
is from the
individual tree versus the species. An individual tree is surely
likely to have its seeds dispersed by derechos than by a
tornado, since all
trees in the Midwest endure numerous derechos during their life,
but may or
may nor get hit by a tornado. On the other hand, a for species
oak that is now moving north as the climate warms, if a tornado
anywhere within the white oak range, and carries a few acorns
further north, then that represents an opportunity for the
species to start
a population in a new area.
09, 2005 07:47 PDT
Interesting stuff...has there been any thinking about the
direction of major wind events and the effects these directions
the dispersal patterns, that is tornadoes from the SW to NE?
09, 2005 10:41 PDT
There has been a little thought about such things, but I haven't
anything in print that addresses seed dispersal by large-scale
I suspect you would be shocked at how little we know about a lot
important ecological topics.
09, 2005 11:28 PDT
Hello to all:
ultra-long-distance dispersal question first came to my
attention via Dr. Rollin Baker, formerly director of the
University natural history museum. He collected storm-tossed
Pacific islands during World War II.
It came up
again via another veteran of World War II...Dr. Warren
Wagner of the University of Michigan.
Every time his carrier passed through a hurricane or major
storm, he would
rush out onto the main flight deck to collect seeds and leaves.
always find good questions. It is the finding of time
to chase them all that is the continuing problem.
/\ /\ /\
//\\ //\\ //\\ Michigan
State Univ. Forestry Dep't
///\\\ ///\\\//\\\ 126
Natural Resources Building
Lansing, MI 48824-1222
|| || || office
phone 517 353 9630
|| || || fax
517 432 1143
09, 2005 14:16 PDT
I would definitely agree with your points below.
The great majority of tornadoes are weak and short-lived but
to the tornado debris study, the long-track, strong tornadoes
probably (along with the updrafts of their parent thunderstorm)
light debris a hundred miles or more from its point of origin.
the south to north displacement may be only half that distance
that most of the tornadoes are moving from southwest to
illustrated by this map that shows the paths of tornadoes across
This covers the last 170 years, but the period up through 1950
includes "significant" tornadoes, usually those with
wind speeds over
100 mph. The period since 1950 includes all documented
the vast majority are those with wind speeds less than 100 mph
lengths less than a couple miles. This shows how rare the long
tornadoes are even in the Midwest. Of course, it would only take
such tornado striking at the right time of year to do the acorn
job you refer to.
09, 2005 14:28 PDT