Summer in Tucson
During my summer vacations from a Tucson, Arizona
high school, close to high noon I go outside to the Sonoran Desert and
map and photograph soil crusts. My brother tells me this is why I am so,
you know, dippy. Even though its very hot outside then, the light is good
for seeing the crusts. If you can't understand the logic behind anything
in these lessons, just remember its source. Sometimes I take a painful
approach to get to some ephemeral point. "The light is better."
This is a guide for the teaching of ecology in a high
school classroom. It is designed after research I have done on the ecology
of soil lichen in the Tucson Basin area during the summers of 1997 and
1998. Its purpose is to guide students into adopting the problem solving
thinking of ecologists.
Little things matter
The overriding focus is on the tiny unobtrusive organisms that so often
exist in the middle of a place's ecology. Really, the main objective is
for you and your charges to give credit to the little things. We all know
it is the little things that matter.
The lesson could be considered the entire ecology unit: it encompasses
all the concepts of interactions between organisms and their environment.
If you aren't lucky enough to live in the Sonoran Desert, just spend a
little time looking very closely at the ground or on rocks or trees. You
will find the organisms that are just beyond the tunnel vision of society,
yet of panoramic proportions in ecology.
There is "my" logic behind the order of the activities.
One activity develops the skills of ecologists; students will construct
their own knowledge of an area. This will be used for the next lesson.
Making maps of plants becomes a focus for a couple day lesson. These maps
will then be digitized and analyzed using NIH Image on the Macintosh computers.
This assists the students in turning observations into a numerical format
that can be quantified and analyzed.
The end of the lesson could be an extended inquiry into
succession of communities. This could be done by comparing the organisms
from different replicates of a given area. Identifying invasive, transition
and climax communities would be the main objective.
Without a passing knowledge of the diversity of an area, ecology is meaningless.
Dick Barber's Field Book is a great
template. The ability to identify the perennials of the area, Acacia,
Larrea tridentata, Ambrosia deltoides, Prosopis ssp., Opuntia ssp.,
and Cercidium would be essential. Also being able to identify
the differences between perennials and annuals would be helpful because
of the nature of nutrient recycling. A plant identification book could
be made by bringing in clippings of native plants and have the students
paste them into their own little booklet along with a brief comment as
to its importance in the desert ecology. Completion of the booklet as
well as the comments could be the assessment.
Once these organisms are identified, then a closer observation
of the way they congregate becomes apparent. For example, foothills paloverde
thrives in very coarse soil with large boulders, while blue paloverde
is usually found in deep sandy soils. Creosote grow poorly around caliche
and heavy clay soils. These trees above ground tell what is below ground.
Very few things grow under the canopy of the mesquite tree because of
its thick litter.
Analyzing the soil taken from plots is a fun activity that incorporates
movement, mud, measuring, and (ugh!) mathematics. Sometimes it is possible
to discern a difference between soils with crust on them and soils without
crust on them using the sieve method. This uses a stack of four sieves
with different sized grating and the weights of each grate's particles
is weighted and divided into the total, giving a percentage of the total.
Completion of this activity would be the assessment.
If the class hasn't totally burned out, then the Bouyoucous method of
soil analysis could be taught which gives an extremely accurate percentage
of gravel, silt and clay. It is for a class that is interested in actually
doing research. But this method takes a full 120 minutes and has much
down time between readings.
The last lesson would be to go back to our concept maps and transects
and to see if there is a relationship between the plants above ground
and the lichen on the ground. Typically, there are few lichen colonies
where the land is disturbed. Also, there are several bush species (Burroweed,
burrow bush) that indicate the land has been disturbed within the past
six years. Ambroisia deltoides is a bush that is very long lived,
as indicated by retaking old photographs. It has been shown that the same
bush can live fifty years or more. This, along with creosote, which has
been estimated to live for 11,000 years, are typically associated with
soil lichen, whereas Burroweed is not.
With the original small groups, ask them to think of what
would influence the growth of soil lichen. Make a master list from all
unique ideas and have the groups create a concept map. Assess the concept
map on the number of concepts, the cross connections, coherence of ideas
and the logic of the hierarchy.
Rubric for Concept Maps