The power of plants

 We found plants growing through the asphalt on the cycle track at Allonby.

I was wondering what force a plant would have to apply to puncture the asphalt and whether it is easier to do from above or from below. Experimental data would be helpful but in the absence of that, here's an idea that will probably lead to a wildly wrong answer. I looked up the compressive strength of asphalt as being between 20 and 35 MPa. Now Pascals are a measure of pressure. Take the lower figure and equate with force/area. Estimate the area as 2cm x 2cm. That gives a force of 10kN or 1 tonne mass, half of a car. It seems unlikely that this small plant can deliver that and a flaw is that for compressive strength there is usually equal push inwards from top AND bottom surfaces. Thus there is no chance of bending so the figure will be lower here where the upper surface has distorted and cracks made it weaker. Even so, the plant must be delivering quite a force.