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

Abstract

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 RÉSUMÉ Un arbuste de la famille des Éricacées, la gaulthérie shallon (Gaultheria shallon Pursch) est associé aux problèmes de régénération forestière sur différents types de station de la côte ouest de l'Amérique du Nord. Sur les stations sèches, la gaulthérie shallon est un féroce compétiteur pour l'eau, sur les stations humides (thuya-gaulthérie), on considère que celle-ci perturbe la disponibilité en éléments nutritifs des arbres par compétition, et interfère au niveau des mycorhizes et « court-circuite » le cycle de l'azote par la production de composés phénoliques. Des essais à court terme sur le terrain ainsi que des études en laboratoire et sous serre ont permis de mettre en évidence chacun de ces effets. Toutefois, les résultats à long terme d'une série de travaux en sylviculture et d'études associées en écologie ont démontré que la gaulthérie shallon ne constitue pas un problème fondamental de régénération des conifères sur les stations de type thuyagaulthérie. La fertilisation des stations de type thuya-gaulthérie a entraîné une réaction importante et durable de la croissance des arbres sans égard à la présence de la gaulthér...

A multi-resolution satellite imagery approach for large area mapping of ericaceous shrubs in Northern Quebec, Canada

“…Overall, our results are encouraging to the point that a broader application of the method could be applied to other regions in Canada where ericaceous shrub invasion is observed, like Northcentral and Northwestern Quebec, Newfoundland, and British Columbia (Prescott and Sajedi, 2008;Titus et al, 1995;Thiffault and Grondin, 2003). With the general purpose of supporting forest management, the future scope of our project will combine a historical assessment of the spatial distribution of ericaceous shrubs with spatial modeling, at the landscape level, of the conditions favorable to, or refraining from, ericaceous shrub invasion.…”

The Influence of Condensed Tannin Structure on Rate of Microbial Mineralization and Reactivity to Chemical Assays

“…Sarg.) forests of Vancouver Island tannin-rich salal was not a primary cause of poor tree growth, but rather an indicator of poor nutrient availability, especially N limitation (Prescott and Sajedi, 2008). In addition to ericaceous shrubs, CT from other species such as Populus impact nutrient cycling (Schweitzer et al, 2008).…”

Silviculture and planted species interact to influence reforestation success on a Kalmia-dominated site – a 15-year study

“…In particular, the presence of some ericaceous species can slow forest succession to a point where ecosystem retrogression is induced (Nilsson and Wardle 2005). Such shifts from onceproductive forest stands to ericaceous-dominated ecosystems have been documented in various ecosystems in Europe (e.g., Vaccinium myrtillus L., Mallik and Pellissier 2000;Calluna vulgaris L. (Hull), Read and Jalal 1980;Empetrum hermaphroditum Hagerup, Zackrisson et al 1997) and North America (e.g., Rhododendron maximum L., Nilsen et al 1999; Gaultheria shallon Pursh, Prescott and Sajedi 2008). On some sites in eastern Canada, rapid encroachment and site domination by Kalmia angustifolia L. constitutes another well-documented example of this phenomenon (Mallik 2003).…”