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> Life sucks up there. For you, for me, for trees, and just about everything else except peregrine falcons. It’s hot, cold, windy, the rain lashes at you, and t

> Life sucks up there. For you, for me, for trees, and just about everything else except peregrine falcons. It’s hot, cold, windy, the rain lashes at you, and the snow and sleet pelt you at high velocity. Life for city trees is hard enough on the ground. I can’t imagine what it’s like at 500 feet, where nearly every climate variable is more extreme than at street level. How is being located on top of a tall building much different from being located on top of a tall hill or mountain? Wouldn't the only factors involved be the type of soil and species chosen?

alberich 14y ago
I guess he addressed this point. There are plants well adapted to life on top of a tall mountain... though it's not the beautiful tall trees depicted on the mockups. I'm guessing those plants probably are short shrubs with dark green leafs and contorted trunks.
rhplus 14y ago
My guess is that the raw exposure is a big deal. Trees on hillsides or mountainsides only have one side fully exposed, so there's a dominant direction they could brace against. They would also benefit from having other trees (and a mountain) next to them to help dissipate the energy from the wind and rain.
DanBC 14y ago
Attrition rate for saplings is pretty high. So in nature when you see a bunch of trees on a hill there are many more trees that didn't survive. But in a building you don't get to have any attrition; you want all trees to survive. And city buildings can generate surprisingly strong winds. "The wind loading on a skyscraper is also considerable. In fact, the lateral wind load imposed on super-tall structures is generally the governing factor in the structural design. Wind pressure increases with height, so for very tall buildings, the loads associated with wind are larger than dead or live loads." (https://en.wikipedia.org/wiki/Tall_buildings#Design_and_construction https://en.wikipedia.org/wiki/Tall_buildings#Design_and_cons...)
apendleton 14y ago
Friction with the ground slows air down near ground level, so air 500 feet above the ground will, on average, be faster-moving than ground-level air, regardless of elevation. See http://en.wikipedia.org/wiki/Wind_gradient http://en.wikipedia.org/wiki/Wind_gradient
jcmontalbano 14y ago
Oh man what an interesting question! The short answer is that a tall hill or mountain represents a broad elevation change that's contiguous with the surrounding landscape. Difference in air quality from sea level is not a simple function of elevation, but of air flow and direction. You actually have to treat the air near the surface as a flow. Check out this extremely kickass old film: http://youtu.be/7SkWxEUXIoM?t=29s http://youtu.be/7SkWxEUXIoM?t=29s The drag near the solid surface greatly slows down, and introduces turbulence to, an otherwise laminar flow. This means that the air near the surface of the earth is doing a lot more interacting with the earth than the other air, and is getting and keeping a lot more heat and dissolved gases. Above that turbulent layer, you just have cold dry air. It loses heat, water condenses, gases fall out. What can you use as an indicator for the height of the wet air layer? The height of the local trees! Their tops are about at the top of the survivable boundary layer in the air. Desert plants are short, rainforest plants are tall. Interestingly, this might lead you to wonder where the tallest trees in the world are. Probably in some place where there's an ocean wind that blows into a blind valley, right? Because that thick boundary layer would just pile up and up, right? Here's an elevation map of California: http://www.netstate.com/states/geography/mapcom/images/ca_h.gif http://www.netstate.com/states/geography/mapcom/images/ca_h.... And here's where the Giant Sequoia redwoods are: http://www.yosemite.ca.us/library/sequoias_of_yosemite/distribution.html http://www.yosemite.ca.us/library/sequoias_of_yosemite/distr... So being on top of a tall building is like being on a spike up above the livable atmosphere for trees. Unless your city is built in a place that already had giant trees, it won't have much success growing them at heights above their native height. Unless you choose very specific trees.

alberich 14y ago

I guess he addressed this point. There are plants well adapted to life on top of a tall mountain... though it's not the beautiful tall trees depicted on the mockups. I'm guessing those plants probably are short shrubs with dark green leafs and contorted trunks.

rhplus 14y ago

My guess is that the raw exposure is a big deal. Trees on hillsides or mountainsides only have one side fully exposed, so there's a dominant direction they could brace against. They would also benefit from having other trees (and a mountain) next to them to help dissipate the energy from the wind and rain.

DanBC 14y ago

Attrition rate for saplings is pretty high. So in nature when you see a bunch of trees on a hill there are many more trees that didn't survive. But in a building you don't get to have any attrition; you want all trees to survive. And city buildings can generate surprisingly strong winds. "The wind loading on a skyscraper is also considerable. In fact, the lateral wind load imposed on super-tall structures is generally the governing factor in the structural design. Wind pressure increases with height, so for very tall buildings, the loads associated with wind are larger than dead or live loads." (https://en.wikipedia.org/wiki/Tall_buildings#Design_and_construction https://en.wikipedia.org/wiki/Tall_buildings#Design_and_cons...)

apendleton 14y ago

Friction with the ground slows air down near ground level, so air 500 feet above the ground will, on average, be faster-moving than ground-level air, regardless of elevation. See http://en.wikipedia.org/wiki/Wind_gradient http://en.wikipedia.org/wiki/Wind_gradient

jcmontalbano 14y ago

Oh man what an interesting question! The short answer is that a tall hill or mountain represents a broad elevation change that's contiguous with the surrounding landscape. Difference in air quality from sea level is not a simple function of elevation, but of air flow and direction. You actually have to treat the air near the surface as a flow. Check out this extremely kickass old film: http://youtu.be/7SkWxEUXIoM?t=29s http://youtu.be/7SkWxEUXIoM?t=29s The drag near the solid surface greatly slows down, and introduces turbulence to, an otherwise laminar flow. This means that the air near the surface of the earth is doing a lot more interacting with the earth than the other air, and is getting and keeping a lot more heat and dissolved gases. Above that turbulent layer, you just have cold dry air. It loses heat, water condenses, gases fall out. What can you use as an indicator for the height of the wet air layer? The height of the local trees! Their tops are about at the top of the survivable boundary layer in the air. Desert plants are short, rainforest plants are tall. Interestingly, this might lead you to wonder where the tallest trees in the world are. Probably in some place where there's an ocean wind that blows into a blind valley, right? Because that thick boundary layer would just pile up and up, right? Here's an elevation map of California: http://www.netstate.com/states/geography/mapcom/images/ca_h.gif http://www.netstate.com/states/geography/mapcom/images/ca_h.... And here's where the Giant Sequoia redwoods are: http://www.yosemite.ca.us/library/sequoias_of_yosemite/distribution.html http://www.yosemite.ca.us/library/sequoias_of_yosemite/distr... So being on top of a tall building is like being on a spike up above the livable atmosphere for trees. Unless your city is built in a place that already had giant trees, it won't have much success growing them at heights above their native height. Unless you choose very specific trees.