There are also some advantages. Urban trees, being more spread out, sometimes have greater sunlight and therefore grow faster. For some trees age isn't the limiting factor but height. They grow until they risk toppling over.

So the urban tree does die "young", but is the goal to keep trees alive as long as possible? If it is, then there are lots of things that can be done to slow their growth and prolong their lives. Deprive them of nutrients. Shorten their growing season. Keep them cold. Some of the oldest trees live in the most extreme environments. Bonzi trees age very slowly too. Perhaps we should trim our urban trees more aggressively.

https://en.wikipedia.org/wiki/Methuselah_(tree) (5000+ years old, 10,000 feet above sea level)

The canonical paper on this topic is Edmund Schulman's classic "Longevity under Adversity in Conifers" (1954)[1]

When I worked in a tree-ring dating lab, we always sought out the harshest local environments in a region and then at a given site, the harshest micro-environments (typically water limited but fire protected) because that's where you find the most ragged, pathetic, and correlatively oldest trees around with the most climate sensitivity in their ring patterns. This makes the ideal trees to date and build climate chronologies from.

[1]: https://sci-hub.tw/10.2307/1682970

10k above sea level would also put the tree well above major jet streams that carry pollution. A similar pattern occurred with a group in (I think) Norway, that were said to have the "fountain of youth", but it just simply turned out they were out of the way of pollution.

Sorry to nitpick, but I think you might have confused 10k feet vs 10k meters (10kms). The grandparent was using feet. 10k feet is about 3kms, the height of a medium sized mountain. 10kms is about the height of Everest, whose peak does not have trees at all. I don't know at what elevation trees stop appearing, but it would be well under 10kms.

> I don't know at what elevation trees stop appearing

This is known as the "tree line", and varies a lot based on particular location (due to sun exposure, climate, and plant species). Here's a wikipedia article which outlines where the tree line: https://en.wikipedia.org/wiki/Tree_line . Summary is that the treeline is rarely above 12k feet (3500m), though in Bolivia it gets all the way up to 17k feet (5200m)!!

You are probably correct w.r.t. the main flow of the jet stream being far in excess of the highest tree lines in the world. The jet stream's main flow is usually 30k feet (10k meters) or higher.

>but is the goal to keep trees alive as long as possible?

For some trees, being 100year old means that the trees are in their late teens/twenties/thirties (source above book). With that in mind, the answer to above question becomes somewhat difficult.

You are also applying mammalian standards to a plant. Trees may indeed be capable of living a very long while, but that does not mean that such lives are normal. A tree can live a full and productive life, reproducing and spreading many times, centuries before its total lifespan. There is also some speculation that trees may be immortal, that if their growth is artificially managed that they may just never have to die. Plants are different than mammals. They don't all have the same definitive life cycles.

For many cities, the goal is a healthy and sustainable urban canopy. Arboriculture has advanced a lot in the last hundred years, and we've made a lot of mistakes.

Eg, inappropriate species like Big Leaf Maple in inappropriate locations, like under power lines. Bad pruning practices. Planting monocultures (Elm). Boxing in roots.

As sick trees come down, better practices can lead to better trees for the next generation.

For some common species, 100 years is downright old, and reaching the end of their natural life anyways.

> So the urban tree does die "young", but is the goal to keep trees alive as long as possible?

In an urban area, it should be. Not only does it cost money to have to replace a dead tree, but a dead (or even not-quite-yet-dead) tree runs the risk of falling over, which means damaging property, blocking streets/sidewalks, or even injuring/killing animals (including humans).

> is the goal to keep trees alive as long as possible?

climate change and economic reasons would support this goal.

> Perhaps we should trim our urban trees more aggressively.

Killing it much faster

Came here to discuss the same section. It makes sense that urban trees die younger when you think about how heavily the odds are stacked against them:

* No network of fellow of trees to share nutrients and information with via their roots, as mentioned above.

* Dogs constantly pissing on the trunk.

* Smog.

* Planted in a small patch of dirt, surrounded by concrete. The dirt itself is usually extremely compacted so no water gets through to the roots.

* Gardeners and city workers constantly cutting off branches, exposing inner wood to deadly fungi.

Not to mention people constantly ramming vehicles into them. There's not a tree in my town that doesn't have a big scar on the trunk at bumper level.

Not a single one?

It's a town tradition to inaugurate a tree's planting by ramming it with a car.

You got me. I exaggerated. A large number of streetside trees in the downtown area have accident scars on them.

Not even the one in their backyard.

I thought the piss was nutritious for plants?

As with many things, the quantity matters. Too much of a good thing is not beneficial. If you over fertilize, it can "burn" the plant. That is why most dog owners will find dead spots in their grass where the dog prefers to pee.

Not so much on their trunks.

the odds are not stacked against them, plants (and other living creatures) do their best to colonize new places. That's why trees have soooo many seeds. Reproduction is the goal, not longevity.

Do you see a lot of urban trees naturally propagating?

Living in an urban forest, ripping up wild young trees is part of normal yard maintenance. I probably get at least a dozen a year. Two of my full-sized trees in my yard were wild seedlings that I allowed to grow because I like those particular kinds of trees (a catalpa and a sumac), and they were in good locations.

This also includes invasive tree species like buckthorn, which is a villain in our area. Buckthorns pop up constantly.

I guess one could view urban tree dynamics as extreme selection for certain traits. They have to be pretty, and in a location that won't inconvenience humans, and they can't do anything to inconvenience humans, like cause allergies, and they have to be extremely resilient.

And around here, they have to be ok if it hits -20F sometimes in the winter.

I have a magnolia, and it completely boggles me that it survives and thrives this far north.

The "close cousins" thing is interesting for me. I live in a tree-lined streets neighborhood. Historically, they chose species on a street-by-street basis. My street was all linden trees for the curb trees (except for a last remaining elm, we've lost most of them to Dutch Elm disease). A few years back, a severe wind storm took out seven of the curb trees on my block, in a cluster (and smashed a few cars in the process).

Rather than planting more lindens, the city put in a diverse new collection - I think every one is different. Our new tree is a hackberry. Our next door neighbor got a japanese maple, and there's a buckeye across the street, etc.

So now I'm wondering what that means for the long-term health of our scrawny little hackberry. I don't know of any other hackberry trees in the neighborhood - the dominant species are lindens, maples, walnuts, ashes, catalpas, and a few ancient elms. Within our yard, there's a big old ash, a catalpa, a sumac, a magnolia, and a dogwood.

Oh, and I live in an urban forest, apparently.

I don't know about your hackberry in particular. This has been a topic of fascination for me, though.

Trees connect to each other via symbiotic root fungi called "mycorrhizae". Any given species of plant probably has several species of fungus with which it is compatible. The fungus and the plant form a mutually beneficial pair, but the fungus can additionally connect to other nearby plants. Then you have a network, potentially with multiple plant species.

The network can be used for nutrient storage (summer to winter), nutrient transfer (to offspring), or chemical signalling. ("Bugs attacking. Get ready.") Different species are known to support each other, giving nutrients back and forth and different times of year. Of course, the black walnut will use the network to poison its neighbors.

Playing in my flower pots, I have observed that plants growing right next to sweet potatoes or succulents do better when I forget to water them, but I haven't measured that. In my mind, they're leaching water from their neighbors through the network.

So, it's complicated, and there is such a thing as a bad actor on the network, but basically I don't think your tree will be lonely. I'm optimistic.

Roots of the same species can fuse directly. It helps canopy tree species grow up inside of an already closed canopy, and similar to mycorrhizal networks, can spread around sugars and water.

Hackberrys grow very quickly, you can water them and watch it grow like a weed. They also fall down in storms. I removed one from my yard and will be planting an Eastern Persimmon instead.

Mine still looks pretty sad and despondent after a couple of years. I hope it's beautiful someday, but for now it's pretty dull next to its glamorous Japanese maple neighbor.

Well, check on soil quality, maybe add compost, check water supply, maybe add a dripper, check that the soil isn't rock-hard, so the roots can get around. If you want to know exactly what the tree needs, though, research is probably in order.

OK, here's a pretty thorough guide to the hackberry: https://homeguides.sfgate.com/special-care-hackberry-tree-56...

Sounds like you should keep crap off the trunk so it doesn't rot, it needs to be pruned to grow right, and if the soil gets dry it will start dropping leaves about it.