Three new hosts for Phytophthora ramorum confirmed in Washington State: Salal, Oregon grape, and red huckleberry

Salal (Gaultheria shallon), Oregon grape (Berberis aquifolium), and red huckleberry (Vaccinium parvifolium) are common shrubs in the understory of northwestern forests and are ecologically, culturally and economically important to the region. They are also sold in nurseries for use in ornamental landscapes and ecological restoration. These plant species were symptomatic for Phytophthora in nursery surveys in Washington State between 2011-2015. Symptoms observed on these three hosts resembled those of foliar Phytophthora infection on other woody broadleaf plants. The nursery plants were positive for P. ramorum and Koch’s postulates were completed on potted plants of the three host species, illustrating their potential as a pathway of spread from nurseries to wildlands. We recommend these three hosts be added to the USDA-APHIS regulated host list, which will aid in the effort to prevent movement of P. ramorum into new areas.

Colonization and decomposition of salal (Gaultheria shallon) leaf litter by saprobic fungi in successional forests on coastal British Columbia

The colonization of leaf litter by saprobic fungi was studied in old-growth and post-harvest successional Douglas-fir forests on southeast Vancouver Island, British Columbia. This study focused on leaf litter of salal ( Gaultheria shallon Pursh.), a dominant understory shrub in all stands. Salal litter is characterized by the occurrence of bleached portions attributable to fungal colonization of the litter and to the variable decomposition of recalcitrant compounds, such as lignin. Analyses of proximate chemical fractions, fungal assemblages on the bleached leaf area, and pure culture decomposition assays indicated that Marasmius sp. and Coccomyces sp. were responsible for rapid decomposition and bleaching of salal leaf litter. The bleached area accounted for 17%–22% of total area of salal leaf litter collected in immature (40–60 years old), mature (85–105 years old), and old-growth (more than 290 years old) stands, but for only 2% in regeneration (5–15 years old) stands. The reduction of bleached leaf area occupied by Marasmius sp. and Coccomyces sp. in regeneration stands could be due to the changes in microenvironmental conditions on the forest floor, in litter quality, or in food-web structure in soils. The decrease of fungi able to decay recalcitrant compounds may lead to a reduction of salal decomposition rates in clear-cut sites that would persist until canopy closure occurs.

The role of salal in forest regeneration problems in coastal British Columbia: problem or symptom?

The ericaceous shrub, salal (Gaultheria shallon Pursch) is associated with forest regeneration problems on a variety of site types along the west coast of North America. On dry sites, salal is a serious competitor for water; on wet (cedar-salal) sites, salal is thought to limit nutrient availability to trees by competing, interfering with mycorrhizae and "short-circuiting" the nitrogen cycle through production of phenolic compounds. Short-term field experiments and laboratory and greenhouse studies provided some evidence of each of these effects. However, long-term results from a suite of silvicultural trials and associated ecological studies indicated that salal is not the fundamental problem for regenerating conifers on cedar-salal sites. Fertilization of cedar-salal sites caused a large and sustained response in tree growth regardless of the presence of salal, and growth responses to salal removal were much smaller than fertilization responses. Greenhouse experiments indicated that salal does not have allelopathic effects on germination or growth of conifer seedlings. In laboratory studies, salal did not demonstrate a greater capacity to take up organic N forms than the conifers, and molecular studies uncovered a vast diversity of mycorrhizal fungi associated with salal and hemlock roots. Together these findings indicate that the nutrient "short-circuiting" hypothesis, based on assumptions about ericoid versus non-ericoid mycorrhizal plants does not adequately describe the nutrition of plants in these ecosystems. We conclude that salal should be viewed as a symptom of the underlying problem of poor nutrient supply on cedar-salal sites, and that fertilization, rather than salal control, is the optimal solution for improving forest regeneration on these sites. Key words: ericaceous shrubs, fertilization, scarification, allelopathy,mycorrhizae, Gaultheria shallon, nitrogen