| Seed
Dispersal: derecho |
Lee
E. Frelich |
| Jun
08, 2005 06:22 PDT |
ENTS:
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
windspeeds.
Lee |
| RE:
derecho |
Robert
Leverett |
| Jun
08, 2005 08:06 PDT |
Lee:
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?
Bob
|
| 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.
Lee
|
| Seed
dispersal |
abi-@u.washington.edu |
| Jun
08, 2005 12:13 PDT |
All,
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.
Cheers,
- BVP |
| RE:
derecho |
Ernie
Ostuno |
| Jun
08, 2005 20:47 PDT |
Lee,
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:
http://geosciences.ou.edu/~jsnow/Research/Debris/
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.
Ernie
|
| RE:
derecho |
Lee
E. Frelich |
| Jun
09, 2005 07:29 PDT |
Ernie:
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
landscape.
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.
Lee
|
| RE:
derecho |
Miles
Lowry |
| Jun
09, 2005 07:47 PDT |
Friends,
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 |
Miles:
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.
Lee
|
| 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
/\ /\ /\
//\\ //\\ //\\ Michigan
State Univ. Forestry Dep't
///\\\ ///\\\//\\\ 126
Natural Resources Building
////\\\////\\\\/\\\\ East
Lansing, MI 48824-1222
|| || || office
phone 517 353 9630
|| || || fax
517 432 1143
|
| (no
subject) |
Ernie
Ostuno |
| Jun
09, 2005 14:16 PDT |
Lee,
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:
http://www.crh.noaa.gov/iwx/climate/cli/tornadomaps/main.shtml
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.
Ernie |
| RE:
derecho discussion |
Ernie
Ostuno |
| Jun
09, 2005 14:28 PDT |
|