Nobody
likes disaster. I strongly dislike even the smallest inconvenience. But they
happen, and they have happened throughout the evolutionary history of life. And
all organisms have inherited adaptations to cope with many of them, to a
certain extent.
One
such disaster (or, in ecological parlance, a disturbance) is fire. To all of us
who watched Bambi, a forest fire is a
disaster. But even in the Bambi
movie, the dead forest had green grass growing after the fire. Disturbance is
followed by renewal. This renewal occurs in stages (in ecological parlance,
succession). There is no way to prevent all fires. Biomass burns. But most
organisms have ways of dealing with fire—perhaps not as individuals, but at
least as populations. Even alders, which grow out in the water, have to deal
with it, because the flames can spread from the adjacent forest and burn their
crowns.
A
fire burned a large area of Cross Timbers forest near the Blue River in Johnson
County, Oklahoma, in the summer of 2011. Despite its severe beauty, the
fire was pretty grim for the plants and animals that experienced it.
There were
burned turtle skeletons everywhere.
Yes, even the alders out in the
middle of the river burned. But the next spring, in 2012, there was a luxurious
growth of wildflowers and grasses, making use of the flush of nutrients
released by the ashes of the fire. Many of the trees resprouted from the
ground. By the summer of 2013, the growth was so exuberant that I could not
even walk through it when doing field work with a visiting scholar from France.
But
not all of the wildflowers, at least in 2012, were the same species that one
normally finds in the spring. Two species in particular grew abundantly after
the fire, but are rare the rest of the time. One is the mustard Selenia aurea.
The
other is a member of the Hydrophyllaceae family, Phacelia strictiflora.
This
wildflower is a relative of Phacelia
grandiflora, which grows abundantly after chaparral fires in California.
Now here is where it gets strange. It is no surprise that grasses and
wildflowers grow abundantly after fires. What is strange is that a few species,
such as Phacelia strictiflora, seldom
grow except after large fires. That is, there is something about the fire that
makes the seeds germinate. The flowers do not grow just because the ashes have
released nutrients or because there is more sunlight as a result of the trees
being burned. Many plant species that live in habitats with a fire cycle (such
as the chaparral) require exposure to
smoke chemicals in order to germinate. Phacelia
grandiflora is one of them.
Oklahoma
does not have any habitats with fire cycles. It therefore came as a surprise to
us that the germination of the Oklahoma wildflower Phacelia strictiflora is greatly enhanced by exposure to smoke
chemicals. The results of our research have just been published in the 2013
volume of the Oklahoma Native Plant Record.
We demonstrated that very few Phacelia
strictiflora seeds germinated—whether scarified or not; whether in light or
in dark—unless exposed to a water suspension of smoke chemicals.
It
was a fun experiment to do. How does one produce a smoke suspension, without
having access to a budget for scientific equipment? You have probably already
guessed the answer. Remember, this is Oklahoma. My student, Sonya Ross, who
conducted the experiments, had access to a hookah pipe. We burned oak wood in
the bowl and drew the smoke through the water. Usually hookah aficionados want
the smoke, but we wanted the water, which after a few hours had turned amber
and had a smoke scent.
This allowed me to produce a
particularly interesting Darwin video. This
was a low-budget experiment, but it yielded important results. This may be the
first report of a plant species from a habitat that does not have a fire cycle
but whose germination is so strongly enhanced by smoke. Many seeds germinate
more upon exposure to smoke, but not this much.
There
are a lot of interesting experiments just waiting to be done and which do not
require a lot of equipment or a budget. Please check out the article. And I
have to say, good work, Sonya.
Oh,
and by the way, oak smoke is not very enjoyable, even after it has been through
a hookah pipe.