There is a wide variety of trees at Willow Spring Open Space, some native, and some brought in either by being planted or through their seeds on the wind from nearby developments.
Most people in Colorado are used to the idea of a high-elevation timberline around 11,000 feet, where conditions are so severe that trees can’t grow above that level.
What is not so well known is that there is also a low-elevation timberline around 5,600 feet, where conditions are so dry that trees do not get enough moisture to grow below that level. That is why the grasslands of the Great Plains are notable for not having any trees.
At that elevation of 5,600 feet and lower, native trees live near the wetter riparian zones by streams, and a creek can be spotted from far away by the cottonwood trees growing along the creek edge.
Willow Spring Open Space is at about 5,600 feet elevation, so it has trees native to the riparian zone, along with some trees that may have been planted or had seeds escaped from the nearby neighborhood.
Here are some of the trees at Willow Spring Open Space
The Plains Cottonwood is a large, dominant tree found along stream beds where more moisture is available than in the grasslands of the Plains. It requires periodic flooding to survive!
It is the foundation for a plant community known as the cottonwood community, providing shade and shelter for other trees and shrubs to grow and thrive. It is native to this area.
Rocky Mountain Juniper
The Rocky Mountain Juniper is a conifer tree with scale-like leaves that keeps its leaves year-round. Although it is native to Colorado, the tree pictured looks like it was purposefully planted there.
These trees are can be found along creeks in conjunction with mature cottonwood trees, and also in foothills communities and higher with sagebrush, pinyon pine ponderosa pine or oak. An example of a mature Cottonwood-Juniper community occurs just north of the Englewood dam.
The Green Ash tree is a favorite in cities because it grows fast. The female trees produce a large number of winged seeds each summer allowing it to spread to other locations.
Far out in the eastern plains of Colorado, it is a native tree on floodplains of rivers or the margins of lakes, but it is not considered a native in this area. This photo shows the beautiful golden fall leaves.
Russian Olive trees can be recognized by their silver leaves and spines along the branches.
They were introduced as ornamental trees, but escapes have become a serious problem. They are now classified as a Colorado List B noxious weed, meaning local governments are required to develop and implement management plans designed to stop their spread.
- From Grassland to Glacier: The Natural History of Colorado and the Surrounding Region, by Cornelia Fleischer Mutel and John C. Emerick, 1992
- Explore Colorado: A Naturalist’s Notebook, by Frances Alley Kruger and Carron A. Meaney with Photography by John Fielder, 1995
- Flora of Colorado, by Jennifer Ackerfield, 2015