Winter, 1985, Spanish moss on tree (top) Winter, 2004, the same tree, but no moss (bottom)
The breeze stirs the Spanish moss, which is draped gracefully over a sprawling oak tree. Although this is a pretty sight, it has become uncommon in the past few decades. Spanish moss is an important part of the Southern United States' ecosystem—without it, several species could become extinct. It provides a habitat for spiders, bats, snakes and birds, some of which eat insects such as mosquitoes. One species of spider (Pelegrina tillansiae ) and three species of bats live only in Spanish moss (Adams). While looking through old pictures of Houston, I noticed that there was once more Spanish moss in the trees around the Houston area than there is today. One of my neighbors recalled, "There was a lot of Spanish moss on the trees when we moved here in 1971. Now there is no moss left in our neighborhood (Sloan)." Still, small pockets of moss can be seen thriving in certain areas, away from busy roads. What causes these pockets of Spanish moss to thrive when it has declined in other areas of Houston? And if their decline is related to air pollution, which pollutant is doing the most harm? My hypothesis was that Tillandsia usneoides is an indicator species to air pollution, that its decline is directly related to raised levels of air pollution, and that the most acidic pollutants are the most harmful.
The very tip of Spanish moss as seen through a digital
The very tip of Spanish moss as seen through a digital microscope.
Tillandsia usneoides, commonly called Spanish moss, is a relative of the pineapple (order Bromeliales, family Bromeliaceae. genus Tillandsia (air plant), and species usneoides ) (Spanish moss). In fact, it is an epiphyte, a plant that gains all of its moisture and nutrients from the air (Arny). Thus, it is not parasitic and rarely harms trees. Since I was unable to find much information about the anatomy of Tillandsia usneoides. I also used information on Tillandsia recurvata L. (ball moss). These two plants only differ by shape; thus, they were easy to compare. The leaves of Tillandsia usneoides are awl-shaped and pointed. Looking through a Motic Images 2000 digital microscope, I observed that the thin trichomes (scales) that cover the whole plant grow larger towards the base of the leaf, where it merges with the stem. Researching further, I found that these trichomes play an important role in the absorption of moisture and nutrients from the air. The trachomas act as pumps, and draw moisture and dissolved minerals into the plants through the stomata (Arny). This indicates that whatever is present in the air—including pollutants—will be absorbed by the plants. And if the trichomes are harmed, the plant, or a section of the plant, might soon die from lack of nutrients and moisture. The stomata are found just beneath the wings of the trachomas. Perhaps the pollutants that I exposed to the Spanish moss would damage the trichomes. I would find all this out in my experiment.