Epiphytes: Pictured Rocks National Lakeshore, MI   Edward Frank
  Sep 02, 2005 20:29 PDT 

On August 07, 2005 I visited Pictured Rocks National Lakeshore in Michigan.
The place is gorgeous. I visited Sable Falls and the Sable Dunes on the
seventh. On the eighth I hiked around the Grand Point and saw some of the
spectacular arches eroded into the cliffs along the lakeshore.

What I wanted to mention were the Jack Pines in the Sable Dunes area. The
Grand Sable Dunes Trail runs a half mile from the parking lot, through a
Jack Pine forest, to grassy dunes, to the Lake Superior shore. One sign
reads, "At this point the jack pine forest meets the Grand Sable Dunes. The
dunes are a dynamic and unsettled environment compared to the serene
forest. As you ascend you will notice marked changes in light intensity,
wind velocity, temperature, and soil composition. Here in this narrow
transitional zone, pine saplings are encroaching on the dunes, while sand
sometimes spills into the woods."

At this point are numerous Jack Pine trees 15 to 30 feet high. What was of
particular interest were the large numbers of epiphytic lichens on the Jack
Pine branches (see attached photo) The branches on the lower part of the
trees were often completely covered. The amounts may have caused the death
of some of these branches in these trees. The upper branches tended to be
much greener than the lower branches, although green needles were present
on many of the branches covered with the Epiphytes.

aug07-256a.jpg (55074 bytes)

I have more pictures if anyone is interested. Other trees in the forest
were completely devoid of the Epiphytes or had only minimal amounts of
them. They seemed to selectively inhabit the Jack Pines. In most cases
the number and diversity of Epiphytes is related to the amount of rainfall
in an area. The moss covered trees at Olympic National Park are one
example. There are significant numbers in the Great Smokies as well:


Other examples from the Smokies are also on the website. Both locations
have significantly more annual rainfall than does the upper peninsula of
Michigan. Other areas of the northeast with lower rainfall have minimal
numbers of Epiphytes growing in the tree canopy.

I am proposing that these Epiphytes are growing so well because of aerosol
spray blown from Lake Superior, and fog from lake Superior collecting in
the branches of these first trees on the edge of the dune fields. I still
find it curious that they have preferentially infested the Jack Pines,
suggesting that the Jack Pines are in some way a better host than other
species in the forest.

I am looking for input or comment from people more familiar with the
process than myself.

Ed Frank

RE: Epiphytes: Pictured Rocks National Lakeshore, MI   Robyn Darbyshire
  Sep 05, 2005 01:21 PDT 

My relatives often wonder about the heavy epiphyte loads on deciduous
trees in Oregon (especially on oaks and ash) when they visit in the
winter time when the leaves are off - they think that the epiphytes must
be killing the trees, but I have never found that to be the case. In
conifer forests in western Oregon and Washington, certain epiphytes are
more characteristic of open, young stands vs. intermediate-aged stands
vs. old-growth stands, probably reflecting differences in light and/or
microclimate or possibly changes in bark characteristics. Air pollution
levels can also have a marked influence. The red alder "bark" that most
of us know is actually a lichen community on the smooth-barked red
alder. Red alder growing near air pollution sources (and growing near
well-travelled roads) has greatly reduced and/or absent bark lichens,
and the "bare" alder bark looks very different than what one would see
in the woods. Many lichens growing in trees are good air pollution

How this applies to the situation you observed at Pictured Rocks is hard
to say from here.....

RE: Epiphytes: Pictured Rocks National Lakeshore, MI   Edward Frank
  Sep 05, 2005 13:16 PDT 


Thanks for the comments. I am not sure if the epiphytes are causing
die-off of the Jack Pine branches, or whther they are simply taking
advantage of exisitng dead and dying limbs. On branches with both green
needles and plentiful epiphytes, the epiphytes seem to overwhelming the
needles. But there are no dead trees in the stand that I saw,
suggesting that even if individual branches may be being harmed by
epiphytes, trees as a whole are not being killed. I don't know how to
disentangle cause and effect in the case of these dead branches, without
long term observations.

Re: Epiphytes: Pictured Rocks National Lakeshore, MI   Lee Frelich
  Sep 05, 2005 17:29 PDT 


Epiphytes become numerous in climates with cool damp summers with little
air pollution, and Pictured Rocks definitely qualifies on all
counts. There is a lot of fog, and the lake effect keeps temperatures
during summer quite cool, possibly cool enough to make the climate
effectively just as wet as areas further south with much more rainfall,
because there is so little evaporation. Surface temperatures of Lake
Superior stay around 55-60 degrees all summer, making summers very cool.

Many trees in the boundary waters in northern MN have almost literally tons
of arboreal lichens. In this case they get moisture from dew, which is very
heavy (almost like a light rainfall every night).

Many species of of arboreal lichens grow on certain species of trees
because the bark has the right texture to catch propagules and allow them a
firm attachment, and the chemistry of the bark may play a role as well, as
does the leaf area index of the crown of the tree--lichens need sunlight
and may be more abundant on trees that allow light through. Jack pine
certainly has a low leaf area index.


RE: Epiphytes: Pictured Rocks National Lakeshore, MI   Willard Fell
  Sep 06, 2005 05:23 PDT 

Here in southeast GA we have a series of "prehistoric" dunes known as
the Ohoopee Dunes. The trees are very stunted and sparse because of the
arid conditions, but they are covered with lichens looking very much
like those you show in the jack pines. There is little ground cover,
mostly bare sand, but there are patches where the sand is carpeted in
lichens. Other than the sandy droughty soil, the area is 50 miles inland
from the ocean and the climate I would imagine is worlds apart.