Sapling that has engulfed a fence.
One advantage to working with living material is the capacity it has for growth, adaptation and self repair. Not only do living things heal, but they can even incorporate inanimate foreign objects into their structure. One example many are familiar with is is what happens as trees grow up along a fence line as pictured above. The living tissue flows around and engulfs the wire. The tree binds to the wire rather than distorting it, a connection that becomes stronger over time. Structures built with prefabricated cement and steel on the other hand are unchanging, except that they slowly degenerate from the day they are put in place. The main advantage that those materials have is that a post or wall made of either could be replaced with an identical one instantly, regardless of time of year, and with little advanced planning.
___Tree trying to engulf sign_____Tree straightening self after slope failure
The process of plants incorporating foreign objects into themselves is part of a phenomenon called edaphoecotropism. Gray (2003) describes how it can be turned into an advantage producing strong structures such as walls. It is essentially stress avoidance as the plant grows in directions that avoid deficits of moisture or light, temperature extremes, going around mechanical obstructions, and areas of low porosity. Plant tissue can flow around, engulf and bind to foreign objects, with an end result that is quite strong. Trees on unstable slopes can even curve in order to continue growing straight and optimize access to sunlight (as in the photo above, right).
The wrong species in the wrong place can damage human built structures by forcing them aside, rather than moving around them. The tree with the sign in the picture above will probably break the sign before it successfully engulfs it. The tree below is too close to the sidewalk, and by growing under it, has broken and shifted the concrete creating a hazard that can trip people, and complicate snow removal.
__ _____Tree growing under sidewalk forcing it aside
The process of recovery from wounds is not all that different, as can be seen in the series of photos at right. The photograph below shows a tree next to a driveway that has presumably been injured by turning vehicles, probably on more than one occasion. The exposed heartwood is essenially dead wood that the tree is engulfing. Unfortunately, given the recurring nature of the injury, this wound is large enough that it is unlikely to heal over before the tree gets hit badly again. However one can see by the thickness and soft rounding of the edges of the callus that significant time has passed since the worst impact. Given the amount of healing that has occurred the tree seems to be reasonably healthy despite the wound. That could change if the tree gets attacked by insects or fungus entering through the wound.
_____________Tree next to driveway injured by turning vehicles