Species diversity in relation to soil disturbance in an alpine fellfield vegetation in Alaska (after Fox, 1981)
 

Disturbance was estimated as the proportion of a line transect covered by recently frost-churned soil.
Species diversity was estimated as 1/(Sum(p_i²)), where p_i is the proportion of total vascular plant cover contributed by species i.

The fellfields from which the data of the figure are taken occur on windswept ridges and slopes and are characterized by patches of wind erosion and frost scars. The vegetation is dominated by creeping perennials (mainly Dryas octopetala, Diapensia lapponica and Salix phlebophylla) and fruticose lichens. In heavily frost-disturbed areas, herbs (of the genera Arenaria, Oxytropis, Campanula and Antennaria), which are unimportant elsewhere, are frequent.