The most charismatic are probably the dominant riparian trees. Riparian means "on the edge of a body of water" so these trees, if planted in the yard, tend to struggle to get established without abundant water. They may also do more harm than good to nearby plants, as their cooling shade might not be enough to counteract the fact that they suck all of the moisture out of the soil. They also tend to have very aggressive roots that can damage utility lines, sidewalks, etc. Here are some examples:
Plains Cottonwood (Populus deltoides)
Peachleaf Willow (Salix amygdaloides)
There are also some secondary riparian trees that still need water, but generally less than the cottonwoods and willows because they tend to be smaller and more shade tolerant. They're less well known, but probably better behaved. While some of these trees might have existed as far east as Harvey Park, they would have been more common slightly upriver. They include:
Box Elder (Acer negundo)
Thinleaf Alder (Alnus tenuifolia)
Rocky Mountain Birch (Betula fontinalis aka occidentalis)
Further away from the water, particularly on the north-facing slopes south of 285, there might have been some slow-growing, drought-tolerant plants that are somewhere between large shrubs and small trees. They were located in what's known as piñon-juniper woodland. As the name implies, it would have included:
Piñon Pine (Pinus edulis)
Oneseed Juniper (Juniperus monosperma)
Scrub Oak (Quercus gambelii)
And that's about it. There are quite a few more native pines, spruces, and firs up in the foothill and montane zones, not to mention the trembling aspen. However, most of those trees aren't entirely happy at this low an elevation.
There are also a plethora of non-native eastern hardwoods like oaks, maples, ashes, beech, tulip tree, sweet gum, etc. that will do fine in Denver, assuming they're supplied with plenty of water. They're also not likely to "escape" into the wild, so you can plant them without worrying too much about introducing toxic invaders.
Fruiting trees and shrubs also do well here, and there are actually native plums, raspberries, currants, and strawberries which grow wild in the foothills and montane zones. Though they'll again need more water to get established, they can be a good choice for a semi-native garden.
Would you tell me more about scrub oak? How tall does it get? How fast/slow does it grow? Is it drought tolerant? Any additional information I should know?
ReplyDeleteSure thing! In areas where scrub oak (aka Gambel's oak) is highly stressed due to extremely low water and heavy wildlife browsing, it may only get to be about 1m (3ft) tall. Under good conditions it is usually 3-6m (9-20ft) tall. However, in wet circumstances, it has been known to grow up to 23m (75ft) tall. Essentially, the more water it gets, the bigger and faster it grows.
ReplyDeleteIt is, however, still extremely drought tolerant. It has what's known as a lignotuber, which is an underground storage organ, like a giant woody potato. This tuber makes Gambel's oak nearly impossible to kill (even with herbicides!), which has its plusses and minuses.
The plant sends up vegetative shoots that are "rapid and extensive" if the tree is cut down or damaged. This oak would rather grow as a thicket than as a single tree, somewhat like an aspen, so if you want a real tree, you need to keep the shoots in check. On the other hand, it doesn't seed very successfully, so you don't have to worry about true seedlings.
As far as other positives, it provides food and habitat for wildlife, like deer, songbirds, and even owls and raptors. It's leaves also have some of the best fall color for Colorado natives. They can be anywhere from a vibrant yellow to sharp orange to deep purple, before eventually turning brown and persisting on the plant for some time into winter. The acorns (as with all oaks) are technically edible, but very high in tannins, and so they must be processed or else the are very bitter and mildly toxic.
In short, if you're thinking about planting one, you probably should place it in full sun away from utility lines, NEVER water it (after it's established), and be sure to keep it well trimmed.