I look out on a surface was re-laid around 12 years ago, all black rubber and tar seams. It was pristine, replacing the mess that had bushes growing out of the surface. Over the years, though, things are bound to change. A reverie unfolds.
From somewhere comes gravel. First, just a pebble here and there. Then, larger accumulations collect near the drains. I suppose rain washes them into piles, but where do they come from in the first place?
My theory is that high winds pick them up off of fields and riverbeds, watersheds etc. Particularly tornadic-speed winds, which can throw a semitrailer like a toy. These must be carried aloft, and then eventually fall down with rain to collect on rooftops.
Anyway, the pebbles slowly accumulate. Pigeons make this particular roof their way-station and meeting-place – I'm sure they do with most other downtown roofs as well. So their droppings sprinkle the roof surface along with the pebbles. Sometimes there are larger droppings, since the crows like to roost there every winter. It would seem to me that all of these materials, along with a bit of silt carried in from the wind, could easily create topsoil on the roof surface, eventually. (If no maintenance were done, and if water was perhaps allowed to accumulate a bit more instead of being drained off.)
Do not know if roof maintenance includes spraying off bird droppings and gravel. But in any case, there is a substantial accumulation of debris on even a high roof over time. The birds pay a visit, the gravel and raindrops patter away, and the roof slowly wears over time. On this particular roof, the company has satellite dishes located, and such things. So undoubtedly there is some kind of cleaning routine that goes on. Despite the birds best efforts, the roof gets maintained, and any nests located too close to some kind of critical infrastructure get unceremoniously dumped.
But I like to play out a fantasy in my mind. The building, and the downtown area, gets vacated, by some major event. No more human occupation, it is left to nature. The 10-story building interior has no more air movement or ventilation of any kind. After a decade or two, the interior walls are covered in mildew and mold. Insects run amok in the basements. Perhaps some mice have made it inside. And the roof surfaces begin to get more coated with bird droppings, silt and eventually, seeds in the droppings. Some grass seeds sprout in the “topsoil” and grow. Soon, the roofs have a sparse carpet. More birds make their home – crows in the winter, perhaps sparrows, pidgeons and songbirds in the summer. Windows that were once tightly sealed develop tiny chinks as the building settles over time. Moisture that penetrates the building, along with any animal droppings and windblown silt, provide the new 'carpeting' on which more flora grow.
The basement and interior floors might be populated by forests of fungi several feet tall, on the walls and floors. Bugs and rodents would make their way around in here. As our imaginary clock moves forward, to say over a hundred years, to two hundred, more windows get cracked by storms, or chinks develop. Minor building damage that would have been repaired is left to the wind and elements. More cracks and holes develop, and many more creatures get in.
Small trees on the roof send their roots deep into crumbling masonry, speeding the process. Floors become caves full of detritus. Small critters battle it out, and some become food for larger prey. Birds populate the roof greenery, and the ground floors are crawling with rodents. Every few years, with enough wind and weather events, the building settles or crumples a bit further.
At the 500-year mark, the building is hardly recognizable as a building any more. It is a tall mound of greenery. Interior spaces are largely populated with decomposed materials, soil, roots and the like. Where the roof once sat exposed to the elements, now there is a foot of topsoil with many growing plants on top.
At the 1,000 year mark, the building is a large mound, with very few intact elements.
Some of the plastics may survive in a browned-degraded state. Otherwise it is all streaked, discolored dirt and clay. And future civilizations returning to the area can only speculate and wonder what function this barely hinted-at structure performed. If they even detected that a structure existed.
Then I shake my head, awakening from this daydream. There is work to be done here, while I am around and alive and the building is intact! Onward, ho.