Figure 4. Each point represents a plot, and its ratio of grass on the runway to off the runway, plotted against its ratio of all other herbs (forbs) on the runway to off the runway. The shaded areas indicate where there are more grasses or more other herbs (forbs) off runways than on runways, the unshaded area has fewer grasses AND forbs off runways than on runways. Where the blue and yellow shading overlap and make green, there is more grass on the runways than off, AND more of all other herbs (forbs) on the runways than off: thus there are more herbs of all kinds on the runways than off. Note that the majority of the plots are in the yellow section, in which grass is relatively more abundant on runways and other herbs are relatively less abundant on runways.