We need more trees in Downtown Denver. To explain, I’m going to quote myself from a blog I did in September 2007 about Portland, Oregon’s Downtown treescape:
“Trees. They are such a critical element in a downtown streetscape, given all the concrete, asphalt, brick, and other hard and heat-radiating surfaces found in urban centers. In Denver, our Downtown treescape is in poor shape. The trees along 16th Street are generally in good condition and have grown over the past 25 years to create a relatively nice canopy along the Mall. But venture down just about any other Downtown Denver street, and you’ll find plenty of frail specimens looking all battered and abused, jagged stumps poking up from the sidewalk like broken-off toothpicks, and empty tree grates harboring weeds. Given the ubiquitous sunshine in Denver and our increasingly scorching summers, we need all the Downtown trees we can get.”
We also need to take better care of our Downtown trees. It’s very discouraging to see trees that are dead or severely stressed, but still sitting in their tree grate on the sidewalk. That would be like leaving the carcass of a dead animal on the sidewalk until its body decomposes. We would never allow that, yet we allow dead or dying trees to remain in place for years. Except for the trees on the 16th Street Mall and in parks and a few other places, the maintenance of Downtown trees are the responsibility of the owner in front of whose property the tree sits. So the next time you’re Downtown and you spot a dead tree or an empty tree grate, look at the building you’re standing in front of, and you’ll know who to blame.
How many trees are there Downtown and how do we know it’s not enough, you might ask? John D. at the Downtown Denver Partnership did a partial tree survey this past summer, and he was kind enough to share the data with me. The survey focused on just the named streets, from Cleveland Place to Larimer Street, and the blocks between 14th and 18th Streets (the 1400, 1500, 1600, and 1700 blocks). Also, two assumptions: 8 is the desired minimum number of trees per block face (or 16 trees per block), and the named streets run north-south. Using his raw data, I’ve created the following table:
What does this information tell us? Here are some key conclusions:
- Based on the minimum standard of 8 trees per block face, the survey area in total has only about 56% of the street trees that it should have.
- Collectively, the 1700 blocks are the best off, with about 73% of the trees they should have, followed by the 1500 blocks with 58%, the 1400 blocks with 50%, and the 1600 blocks with only 43%.
- Curtis Street is the best off, with about 84% of the trees it should have, followed by California (76%), Larimer (72%), Arapahoe (62%), Stout (58%), Lawrence (55%) and Cleveland (50%). Having less than half the desired number of trees is Welton (44%), Tremont (41%), Court (39%), Champa (36%), and finally Glenarm, with only 30% of the minimum number of street trees.
- Of the 88 total block faces in the study group, 27 of them (31%) were at or greater than the desired minimum. Of the remaining 61 block faces with some kind of shortfall (anywhere from 1 to 8 trees) about one-third (22) had a shortfall of 1 to 4 trees, and about two-thirds (39) had a shortfall of 5 to 8 trees.
- A total of 26 block faces (30% of the entire survey group) don’t have a single street tree!
Keep in mind that this survey did not take into consideration the quality (i.e. health) of a tree, only if a tree was present. In fact, a few of the trees counted were noted as being dead, but were counted nevertheless.
Planting more trees is one goal, keeping every tree in a vibrant state of health is another. Our current system of relying on property owners to maintain the street trees in front of their property is obviously not working very well. We need to either vigorously enforce the current requirements, or make the maintenance of all trees in the Central Business District the responsibility of some entity that can ensure the trees are irrigated, pruned, and cared for on a regular basis. One way or another, we need a Downtown treescape that provides ample shade, shelter, and aesthetics for the pedestrian.
This is my favorite topic, since I love trees and I think trees do 90% of the work in making any urban environment look good and feel healty.
But there are serious issues to face putting trees downtown. Since tree roots spread 2-5 times as far as the height of the tree under normal conditions and twice as far in an urban environment where there's hardly any surface soil, a construction site that seems quite far from a tree can still kill it. Its no wonder you find so many downtown trees are dead.
For that reason, I think it might be better to wait till a block is developed and all the parking lots are replaced to plant a row of trees, since building there would likely cause them to die anyway. Unless you want to accept that the trees are temporary and only to hold the space until the parking lot is replaced (like the trees around the light rail stop in front of the to-be-rebuilt area around Union Station).
Tree roots need contact with oxygen and live in the top 12 inches of soil. There is hardly any such soil downtown since its mostly paved. Also, I guessing that most of the good soil is scraped off and the soil under the pavement Downtown consists of gravel and clay, and is full of salts and pollutants.
A problem that creates is that if you plant too many trees on the same block, they may seem to be really far apart, but their roots are all competing madly with each other for the few remaining cracks in the pavement with surface contact – and planting too many may effect the health of the trees.
I think the answer is to maybe pack the trees in whereever you have open soil, making a bunch of miniature urban forests. That means planting lots of trees along the South Platte River and Cherry Creek, and have a few other planned green strips here and there with no pavement, which gives the trees you do plant a chance to actually get big.
One thing I really want to see is the utilization of native trees – not necessarily plains natives, which the city already uses, but some foothills natives as well. I'd hope to see groves of ponderosas in some areas, since they are not only drought-tolerant but are also really good at surviving in soil litered with rocks and obstacles (like in the mountains).
Perhaps it's time to convene a group of those interested in Downtown Denver trees – this group could: advocate for more trees (the Mayor has an interest – witness the Million Tree program), the City Forester has an interest, as do propoerty owners, residents and those who work and play downtown. This group could also put together a small working group who would remove and replace dead trees on behalf of the owner – assuring quick replacement, if the building owner couldn't/didn't want to (CHUN has a tree committee, and DEnver Dig Trees does a wonderful volunteer effort).
One other reason certain streets have littel to no tress (17th Street), is that the volume of utilies under our streets are so numerous that the area under the sidewlaks are being used – and trees can't be planted.
The other big issue for downtown street trees is that the species of street trees is often forgotten in favor of their aesthetic qualities when healthy. Not just anything can be planted–there's a reason why most of the 16th Street Mall is filled with honey locusts. I know they're not everyone's favorite, but they're ideal for urban environments because they tolerate pollution better than most deciduous trees.
As for Matt's idea for ponderosas–I love them too, but my understanding, gleaned from a UCD class in environmental science about a decade ago (a professor named Annie someone or other), is that conifers with their evergreen needles are actually a poor choice for urban environments because the particulates in the air simply stay on the needles year after year, and after several years the trees "suffocate." This is what happened to the ponderosa pines between the North Classroom building and Speer. Deciduous trees get to start over with fresh leaves every spring, so the pollutants don't get a chance to build up. On the other hand, conifers are great for urban parks, as long as they're not planted too close to a busy roadway and not too close together (which could lead to crime or personal comfort issues).
Are London plane trees available here? Would they grow?
–historymystery
I'd like to see more shade trees. The honey locust, esp the skyline variety is soooo over used in many cities, including our downtown. The reason of course is they are easy to maintain and perfectly suited to denver's sunny weather. Uniformity is nice and good, but overuse is dreadful.
Hopefully tree's will have maintenance if they are planted, other wise whats the use.
To be honest, I care less about the tree's being planted downtown than say central denver. Mostly because getting accountability from landlords and businesses is weak, and tree's end up looking bad, also because an urban landscape can do without. Central Denver has made tremendous headway in the last 10 years. The block I live on for example has 30 new tree's since I moved to the block in 8 years. Highlites too, how much work needs to be done all over.
What about the cottonwood tree? They are a deciduous tree. Or do they need more moisture such as riverbeds etc.? Maybe they'd be useful around plaza fountains or places with waterfalls that could spare a little of the water…Then there's the russian olive tree which smell great in the late spring. Also how about some man-made art sculpture type canopies for shade?
CSU has a nice handout with recommended trees for the Front Range:
http://csfs.colostate.edu/pdfs/trees_for_frontrange.pdf
Conifers in general don't perform well as street trees, like Anon 8:32 said. Cottonwoods (and some of the other native trees) have a very weak structure and are probably too messy for a dense urban area. One heavy snow storm and there will be branches lying everywhere. As for Russian Olives, they're actually highly invasive and there are efforts in many Colorado communities to eradicate them. They're also very messy when they drop their fruit.
Denver uses mag chloride and salt on our streets. If you've ever been behind one of the sprayer trucks, they often overspray onto the sidewalks and areas where the trees are planted and this overspray kills our trees. This occurs when a big healthy tree goes into fall but is totally dead by spring. Remember the fifty trees along Auraria Parkway? Why do you think the new curbs were poured so high after all the trees had been removed?
Before one more tree is planted
Denver needs to decide how to deal with snow/ice issues that will do no harm to our trees. At least the dogs aren't getting the blame anymore, thank goodness!
The selection of certain species of trees is a particular problem since many trees can grow but the reflective heat build up from the asphalt/concrete makes it really tough for certain types of trees. Unfortunately, the City has chosen to often use the Linden whose leaves sorch so badly that the trees actually appear dead by July but pop out again the following spring. Sadly, these need to be removed.
Two species which seem to thrive well downtown are the Red Oak (they hang onto their leaves over winter and turn a chocolate brown in the fall) and the Locust which we might have problems with if the borer shows up again someday. Similar to the Elm, the Locust has the Locust Tree Borer but we've been able to dodge this bullet for quite a long time.
Frankly, businesses forget the needs of their trees so the City needs to commit itself to controlling the chloride, replace the Lindens and provide water where there is no irrigation. Just finding out which trees are not serviced by a drip system will be a project and leaning on the businesses that do have irrigation systems will be critical. As for pruning, well this makes for not only pretty trees but will ultimately protect the low hanging branches from pedestrian damage.
When Hick got the trees, I winced.
This City doesn't have the slightest clue as what to do with them other than torture those of us who know its only a matter of time before they die.
Anon@9:00pm:
Cottonwoods are bad in urban environments becasue when they're under stress they die back in huge chunks, and even when healthy they'll shed evertyhing ranching from twigs to massive branches.
They're a great native tree in a field but they're too "dirty" and haphazard for the urban environment, they wouldn't keep their shape, and the mess left after every windstorm or late snow would start to get bothersome.
I also just wanna say I love the number of people commenting here who actually know a lot about trees, some with savant-like insider knowledge or interest.
The intersectionality between those who are amazed by big trees and those who are excited by tall buildings means either 1) we all have Asperger's syndrome or 2) we're afraid of wide open spaces, so like to have one thing or another looming over us at all times.