RiverWatch November 2017!
by Tom Davis
As Fall progresses, the air chills a little bit more each night. This causes tree sap to slowly revert back to the roots of trees, taking the life of the leaves with it. The leaves become dessicated, turn color, and drop to the ground. One of the most common, and perhaps largest trees found in riparian areas are Cottonwoods (Populus sp.).
The variety found most often in southwestern watercourses is Populus fremonteii, or Fremont Cottonwood. Cottonwoods were once far more common along southwestern watercourses than they are today. In fact, the entire southern Colorado River riverbed from around Utah to Baja California was once classified as Cottonwood/Willow habitat. This began changing in the early 1900's, when steamboats plied the river from the Gulf of Mexico to as far north as Coalville, Utah. The steamboats ran on wood fuel, and had a range of about 30 miles a day. Refueling stations cropped up along the river, and Native Americans chopped down the cottonwoods and sold them to the riverboat captains. The trees slowly disappeared, and were replaced by non-native exotics like bamboo and tamarisk. Today, vast stretches of the river are inhabited by these invasive exotics.
Luckily, there are dozens of conservation efforts along the river and other watercourses, like the San Diego River, to eliminate these exotics and re-introduce the native species. That effort continues today right here at Lakeside's River Park. Cottonwoods, Sycamores, and Willows are being planted and nurtured, while removing the exotics is an ongoing struggle.
As you walk along the River Park trail, you will see some of these trees gaining stature every year. Eventually, they will be nearly as tall as the eucalyptus trees nearby. This is all part of a grand conservation plan.
Although non-native, the eucalyptus trees are used by birds and raptors. The raptors build "aeries" (nests) high up in the trees to raise their young. As part of this long-term plan, the eucalyptus will remain until the native trees have reached a status where they can support this wildlife. At that time, the eucalyptus will be removed.
As the days get cooler, you will be able to recognize the Cottonwood trees by their leaves turning a bright yellow, in beautiful contrast with a blue sky. The next time you are out hiking the River Park trail, take note of the progression of this grand conservation plan.
Help make science matter to more students!
#GivingTuesday is November 28, 2017
#GivingTuesday is just a few weeks away! It is the Tuesday after Thanksgiving.
Please consider a donation on our National Day of Giving so that we can build the first ever San Diego River Science Field Station and give students a taste of environmental science in all of its muddy, weedy, frog-filled glory.
FREE Mystery Hike
December 15th, 8:30 AM
Register by: December 12th