I've always wondered when driving through desert areas why you sometimes see long continuous lines of grasses along both sides of the road. This thin strip of vegetation that presses close against the hard asphalt or concrete seems almost artificial.
A discussion on this topic once came up on a group thread, and various possibilities were mentioned. Water runoff was one possibility, since the non-porous road surface might concentrate water along the sides, thus providing much needed moisture to the plants. One other possibility is that some chemical runoff from the road itself or from the vehicles using the road provide some nutrient(s) that support the growth of the grasses. Indeed, one study found that nitrogen and phosphorus from vehicle exhaust enhanced the growth of surrounding vegetation (Angold 1997). Finally, the sides of roads may also have some kind of micro-climate that is conducive to colonization by grasses.
There are probably other possibilities, but whatever the real reason, I have to admit that I almost always admire the cool long lines of grasses as I zip along the highways and byways of the more arid areas in the West Coast, USA.
Angold, P.G., 1997. The impact of a road upon adjacent heathland vegetation: effects on plant species composition. Journal of Applied Ecology 34, 409–417.