Lichen refugia within sub-boreal spruce forests: The role of riparian alder swales.

Wetland swales, corridors of willows and alders adjacent to streams and seepage areas, may play a role as refugia for lichen biodiversity because likely escape stand replacement disturbance such as fire more often than adjacent upland forest, especially moist to drier sub-boreal and boreal landscapes, and are also not disturbed by forest harvesting. Macrolichen communities in 75 alder-dominated wetland swales along an east (wet) to west (dry) gradient in the Sub-Boreal Spruce biogeoclimatic zone of central interior British Columbia were examined. Spatial analysis of wetland swales indicated an average size of 20.5 m wide by 854 m long (following patch contours). A total of 43 macrolichen species (and six other macrolichen genera) were found in the alder dominated sites, with a maximum of 30 taxa present in the richest site. The macrolichen diversity of alder swales included the old-growth associated lichens Lobaria scrobiculata, L. retigera, Nephroma isidiosum, and Sticta limbata. Canonical Correspondence Analysis identified mean annual temperature and abundance of large stems (dbh > 10 cm) as significant explanatory variables for chlorolichens and mean annual precipitation and age of adjacent conifer forest as significant explanatory variables for the majority of the cyanolichens. Regional precipitation gradients explained the exclusion of many lichen species from both the most westerly and most easterly swales, with drier summer conditions and heavy winter snowpack, respectively, being major limiting factors. Within sites, lichens preferentially occupied large leaning stems, which provided greater precipitation interception and long-lived substrates for many old-growth associated lichen species. Physiological analyses of six common cyanolichens indicated low contributions of cyanolichens to the nitrogen budgets of alder swales. However, adaptations and niches of each of the cyanolichens were revealed. Nephroma parile was the best adapted to the widest range of conditions, followed by Lobaria pulmonaria. Pseud