Pink sand-verbena (Abronia umbellata) COSEWIC assessment and status report: chapter 8
Limiting Factors and Threats
Invasive species – Ammophila arenaria and A. breviligulata
The greatest threat to the persistence of populations of Abronia umbellata is the potential invasion and subsequent stabilization of upper beach and foredune systems by Ammophila arenaria and A. breviligulata. At Wickaninnish Beach, Pacific Rim National Park, one of the most extensive beaches on the British Columbia outer coast, Ammophila invasion has greatly reduced the potential habitat for Abronia umbellata.
Ammophila arenaria spreads primarily by rhizomes, although viable seeds are produced. Long distance dispersal is usually by marine transport of rhizomes, which can withstand submersion for long periods (Pickart and Sawyer 1998). Once established it develops vigourous root and rhizome systems. It also has the ability to withstand more sand burial (up to one m) than Leymus mollis. Without fresh sand burial Ammophila arenaria declines in vigour (Pickart and Sawyer 1998). Although A. breviligulata has the same vigorous rhizome system as A. arenaria, it is even more aggressive but has less ability to trap sand, probably due to its lower stem density and less persistent winter leaves (Seabloom and Wiedemann 1994).
The eradication of A. arenaria, because of its extensive underground rhizome network, has proven to be a difficult and challenging problem for land managers. It is now so widespread on the United States coast that its eradication, except in local situations, is not presently practical. To date, the main eradication techniques have included chemical, manual and mechanical techniques. All of these have met with variable success (Pickart 1997). In some areas, however, the use of herbicides, D8 caterpillars, and intensive manual follow-up has resulted in upper beaches and foredunes being returned to a nearly natural state (Pickart 1997).
Winter storms
The sand beach habitats of Abronia umbellata are usually scoured by high tides and winter storms thus few plants in this zone ever persist over winter. These storms also alter beach and sand dune morphology. The annual phenomena of winter storms, although natural, must be considered for management purposes, especially if reintroduction is considered.
Recreation
A minor threat to populations of A. umbellata is the potential of trampling by hikers. There are often numerous hikers in areas of potential A. umbellata habitat on the coast of British Columbia and if plant numbers are small fencing of these areas would be desirable.
Page details
- Date modified: