Answers to questions for teacher lead discussion
1. Is there any desert near your house?
Even though we live in the city and are surrounded by many man made structures, there are still patches of desert nearby. Some of these areas have never been cleared and still have what might be considered their "original vegetation". Others support "second growth" vegetation as a result of being cleared, scraped, grazed or leveled. Some desert plots may only be the size of a residential parcel while others cover a square mile or more. Each patch is unique place with its own plants and animals.
2. What are some attributes of the desert in Tucson?
Tucson is in the Sonoran Desert. Anyone who has lived here any length know that our summer temperatures are hot (sometimes over 110°F) while our coldest winter temperatures can be below freezing. Deserts commonly have large temperature ranges between day and night also. Tucson often has temperature ranges of thirty to forty degrees in one day.
Deserts are characteristically dry. Our part of the Sonoran Desert gets about 11 inches of rainfall a year. Many people have come to live in Tucson because of the dry desert air. About half our rain comes in thunder storms in July and August, while the other half occurs in October to March. Often the summer rains produce torrential downpours that cause flash floods. The winter rains are usually gentle and soak into the ground.
The Sonoran Desert is in the Basin and Range Geologic Province of the Southwestern United States. This geologic area extends into much of Mexico's northern state of Sonora. The term "Basin and Range" refers to a topography of mountain ranges with broad alluvium filled valleys between. Tucson is in the Santa Cruz Valley and is surrounded by the Catalina Mountains on the north, the Rincon Mountains on the east, the Santa Rita Mountains on the south and Tucson mountains on the west. The Tucson Mountains are of volcanic origin while the other mountain ranges are granitic.
The soils in the Tucson Basin are a reflection of their origins. Some soils are rocky, sandy, or gravely: others are combinations of sand, clay and silt. there are enough differences in the soils around Tucson to cause differences in plant distribution. There are plants growing in the Catalina Foothills that do not grow in the Tucson Mountains.
Some Sonoran Desert ecologists distinguish between the habitats of the "lower", "middle" and "upper" desert taking soil, slope, aspect (compass direction of the slope) and elevation into account. There are typical vegetation zones in each of these regions. the plants of the "lower desert" are typically Mesquite and Creosote. The "middle desert" has Saguaros and Palo Verde's. Typical plants of the "upper desert" are Yucca, Bear Grass and sometimes Saguaros.
Temperature, rainfall, slope, elevation, aspect and soil all combine to make each desert study site a unique place.
3. Are desert sites in an urban setting different from those "out in the desert?"
By their very nature urban areas are highly impacted by human activity. Desert areas in the city are no different. Many desert plants are very fragile and do not hold up well to human disturbance. Other desert plants are very particular about the composition of the soil they grow in. As a result, there is less diversity of an urban site than there is "out in the desert". Desert plants that do well in the city are often "opportunists". They invade areas where the soil has been disturbed or where more water might collect. Mesquite, Mexican Palo Verde and Desert Broom are examples of opportunistic desert plants that are very successful in urban areas.
4. If we set out to learn about a desert site, what are some things we could want to know?
Learning the names of the plants and animals on the site is a good place to start. The location of plants and animals on the study site can reveal much about soil composition, moisture, conditions, drainage, etc. transects can also show soil/plant relationships.
Students will have many ideas depending on the type of activity they think they might be engaged in. The frequency of visits to the wash, the observations that will be made, and the data that will be collected will depend on the focus of the student's study. Emphasis needs to be placed on what students want to know and what kind of data will help then answer their questions.