Artist Madelon Galland launched the STUMP project several years to decorate tree stumps on New York City sidewalks as a way to "honor that which had been diminished, and bring it back into relationship with the neighborhood." From her HOWTO at SuperNaturale:
This really began as unauthorized public art, and is not intended as something to have, but rather as a gesture to give. The street stumps are anchored and framed with firm roots and city masonry as they are, and what we do is contribute, care, and dignify that which has been diminished thus giving vitality again to spaces usually below the pedestrian radar. Working in the urban areas is quite easy because these small sidewalk plots, where the tree stumps are found, have an ambiguous jurisdiction and allow for engaged activity without provoking upset, only occasional curiosity. I tend to act spontaneously and from a perspective that where something is obviously blighted, one shouldn’t have to ask permission to care, nor sponsorship to make and exhibit art. So it’s best to work in places that its quite obvious that no one is taking responsibility for the care of the space or tree stump. Engaging to care for something in public space is a radical gesture indeed; it changes our measurement of responsibility into simply, the ability to respond.
Link (via MAKE: Blog)