Seed Dispersal:  derecho   Lee E. Frelich
  Jun 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 and wind
gusts only peaked at 60-70 mph with 1.5-3 inches of rain. Nevertheless,
there were a few trees down in the neighborhood and over 100,000 houses
were without electricity this morning. I saw it begin to form on the
weather channel radar last night at 9:00 near rapid city South Dakota, and
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 sidewalks are
packed with debris that includes millions of tree seeds of all sorts. These
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 from a
trajectory 60 feet above the ground?   The literature on seed dispersal
only examines dispersal of dry seeds in open fields on days with low

RE: derecho   Robert Leverett
  Jun 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 wonder how
far an acorn or hickory nut might be carried?

RE: derecho   Lee E. Frelich
  Jun 08, 2005 08:32 PDT 

Bob, Scott:

A lot of seeds are mature already (Red maple, the elms, hackberry), since
we have had several weeks of warm, almost tropical weather in southern
MN. For other species of trees whose seeds mature later, yes, we do have
derechos in September.

I have found mature trees 100 feet from where they were rooted after
derechos (and it wasn't a case of rolling down a hill), and have seen tree
branches and furniture flying through the air in derechos. Family picture
albums and wallets belonging to people whose houses were destroyed in
St. Peter, MN, were found on the south side of Minneapolis after a major
supercell thunderstorm, and that is 60 miles away. I would say that a
hickory nut could go anywhere from a few hundred feet to many miles during
a high end derecho.

Seed dispersal
  Jun 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.

RE: derecho   Ernie Ostuno
  Jun 08, 2005 20:47 PDT 


This is a very interesting topic to me as I have done damage surveys for
perhaps two dozen or so derechos over the last 10 years. One thing I
have noticed is that tornadoes are the champs when it comes to carrying
light debris long distances. This is due to the fact that, along with
the horizontal component to the wind in a tornado, there is also a
vertical component that derechos lack. There have been studies on debris
dispersion by tornadoes:

I am not aware of similar studies for derechos, but based on my
surveying experiences, debris lofting/carrying is much less impressive
in a derecho than a tornado. Of course, you can make a convincing
argument that derechos are more important than tornadoes in dispersing
seeds given that derecho winds will typically affect much larger areas
than tornado winds.

RE: derecho   Lee E. Frelich
  Jun 09, 2005 07:29 PDT 


Derechos probably have a bigger cumulative effect on seed dispersal
existing forests than tornadoes, since any given location is hit by many
derechos between tornado episodes, due to both higher frequency and larger
size of derechos. Probably the larger size and greater frequency of
occurrence of derechos overcomes the shorter average distance for
dispersal, at least in terms of the number of seeds moved around the

For a much different case, plants migrating in response to climate change,
it is hard to tell whether tornadoes (which probably have the record for
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 jump
outweighs steady but shorter steps. My guess is that tornadoes help
establish new populations well out in front of the main edge of migrating
species, and the derechos then help those outposts spread around locally,
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 more
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 like white
oak that is now moving north as the climate warms, if a tornado hits
anywhere within the white oak range, and carries a few acorns 100 miles
further north, then that represents an opportunity for the species to start
a population in a new area.

RE: derecho   Miles Lowry
  Jun 09, 2005 07:47 PDT 

Interesting stuff...has there been any thinking about the general
direction of major wind events and the effects these directions have on
the dispersal patterns, that is tornadoes from the SW to NE?
Miles Lowry
RE: derecho   Lee E. Frelich
  Jun 09, 2005 10:41 PDT 


There has been a little thought about such things, but I haven't seen
anything in print that addresses seed dispersal by large-scale wind events.
I suspect you would be shocked at how little we know about a lot of
important ecological topics.

derecho discussion   Robert R. Bloye
  Jun 09, 2005 11:28 PDT 

Hello to all:
         The ultra-long-distance dispersal question first came to my
attention via Dr. Rollin Baker, formerly director of the Michigan State
University natural history museum. He collected storm-tossed fragments from
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.
         Good minds always find good questions. It is the finding of time
to chase them all that is the continuing problem.

                                                 Robert Bloye

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(no subject)   Ernie Ostuno
  Jun 09, 2005 14:16 PDT 


I would definitely agree with your points below.

The great majority of tornadoes are weak and short-lived but according
to the tornado debris study, the long-track, strong tornadoes could
probably (along with the updrafts of their parent thunderstorm) carry
light debris a hundred miles or more from its point of origin. However,
the south to north displacement may be only half that distance given
that most of the tornadoes are moving from southwest to northeast, as
illustrated by this map that shows the paths of tornadoes across
northern Indiana:

This covers the last 170 years, but the period up through 1950 only
includes "significant" tornadoes, usually those with wind speeds over
100 mph. The period since 1950 includes all documented tornadoes, and
the vast majority are those with wind speeds less than 100 mph and path
lengths less than a couple miles. This shows how rare the long track
tornadoes are even in the Midwest. Of course, it would only take one
such tornado striking at the right time of year to do the acorn dipersal
job you refer to.

RE: derecho discussion   Ernie Ostuno
  Jun 09, 2005 14:28 PDT 

Here's an interesting story on "Hurricane birds":

I suppose a few of these involuntary migrants might bring some seeds
along with them?