Bromeliads are called air-plants because they don't need soil, just rain and run off from above.  

**Photo 3/** That is a plant with big cotyledon leaves which comes from a big seed with lots of energy resources. As the seed sprouts it transforms ambient water into a radicle (embryonic root) of 10-20-30cm that is biologically designed to survive challenging conditions, grow straight down and find soil. Wet rotten wood is a perfect medium for propagation of radicles, it has a PH of 4-6 after a few years, which is similar to the humic acid rich leaf humus of the forest, and is easy for the taproot to travel down 20-30cm at a rate of 1-2 cm every day, to find regular water. 

**Photo 2/** A growing root cell's turgor pressure can be up to 0.6 MPa, which is over three times that of a car tire. Roots can search their environment using micron-thin rootlets the width of individual cells that propagate forwards and under patches of wet leaves or moss where they sprout in the spring time. A tree just has to find a hairline crack through the tarmac to establish a lifeline to the soil. Once it is there, the cells can use chemistry to pump water like a hydraulic jack and push new cells upwards through tarmac. Redwood bark cells have 115m of water pressure, equivalent to a hose that ascends a 35 story building. 20m of water pressure in a hose is very difficult to stop manually. 

**Photo 1/** That roof collects a lot of water when it does rain, which can collect in pools, under cracked asphat roof linings, and can create pools and cool damp zones in the abandoned building interstices which last for some weeks in summer. They are as big as their access to soil permits. 

Those trees require a lot of water for the summer and are sized relative to their resources, they are northern plants like birch who's white trunk is white flexible bark which protects from cold and fast temperature changes due to frost and sun, it also reflects summer sun so that the tree stays cooler in arid times. 

Trees also meter their growth by available soil and water and make natural bonsais. There are trees in [cliffs][1] with a thousand years of narrow growth rings that are just 1-2 meters tall. Bonsai cliff trees are often prized for dendrochronology. 

  [1]: https://stonelantern.com/blogs/bonsai-bark/cliff-collecting