An initial comparison of growth rates in the rare grass Achnatherum hendersonii and its common associate Poa secunda

The rare grass, Achnatherum hendersonii (Vasey) Barkworth, and the more widely distributed Poa secunda J. S. Presl grow together on shallow soils derived from basaltic rock that are subject to cryogenic disturbance. It has been proposed that the solifluction allows A. hendersonii to persist by inhibiting the competitive ability of P. secunda . A correlate of this proposal is that P. secunda will have a superior growth rate in undisturbed soils. This idea was tested by growing both species in potting soil, both singly and in combination. Under these conditions, P. secunda grew faster and attained a larger above‐ground size than A. hendersonii . Thus, one factor allowing the survival of the rare A. hendersonii seems to be its occurrence on sites where the competitive ability of a wide‐ranging species is restricted. The survival of A. hendersonii on disturbed sites may also be partly explained by its roots that are apparently adapted to growing where solifluction occurs.