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 The Pantano wash Growing up in Tucson, I have always been intrigued by these ecosystems. One wash in Tucson, called the Pantano Wash, flows through my neighborhood. I have always had questions about this wash. How do the many trees and shrubs that live in the bottom of the wash survive the flash floods? How does the water flow through the wash? Does this have anything to do with how the plants survive? I decided to investigate the wash to see if I could answer some of my questions.  Plant biodiversity found in a wash On my expeditions, I was surprised by the amount of diversity inside the wash. I observed many different varieties of grasses, shrubs, and even small trees. Over time I began to notice that the wash was divided into four layers, which I decided to call the Top Level, the Upper Level, the Lower Level, and the Bottom Level, respectively. |
 Soil Sample #1 (Click to see soil samples from the 4 levels) The Top Level is the term I am using for the land surrounding the wash (see picture ). I included this level as a layer because its vegetation is so different from the other layers. From my research I identified some of the trees in this area: the Prosopis (mesquite) tree and the Parkinsonia florida (palo verde) tree. Both of these trees have unique adaptations to survive in the desert. The mesquite tree has extremely tiny leaves—their size makes it harder for the water to be evaporated from the leaves. And the palo verde tree has green bark, which helps it to perform photosynthesis, the process plants use to make food. I took two soil samples from each of the four levels and examined them under a microscope to see if I could find any reasons why these plants grow better in one area than in another.  The upper level  Photo and drawing of Baccharis sarothroides (Click to enlarge) The Upper Level is directly below the Top Level. There are many plants growing at this level. Here, I identified 20 female and 10 male Baccharis sarothroides (desert broom) trees. Desert broom is an unusual plant because the female and male flowers grow on separate trees. In most plants, both male and female flowers grow on the same plant. From my research I discovered that Baccharis sarothroides can grow to be 10 feet tall, but the ones I saw were about six or seven feet tall on average. I also identified mesquite trees and many large shrubs growing in this level. When I took a soil sample from this level, I observed that the soil was very moist compared to the other soil samples I had taken. In a later soil sample I took here, I noticed that the soil was dry but was packed into dirt "clods." From these observations I concluded that the soil had been moist at one time, but then the water had dried out and made the soil form into clods. |
 
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