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Conference by Linda Geiser (US Forest Service, Pacific Northwest Air Resource Management Program, USA) on 15 December 2010 at FCUL, Lisbon.

Part I: “Evidence of climate related shifts in epiphytic lichen communities of the Pacific Northwest”

Within the US Pacific Northwest, some of the many anticipated effects of climate change include shifts in species distributions and diversity, including extirpation. The US Forest Service Forest Health Monitoring lichen indicator is designed to track climate-related changes in epiphytic macrolichen communities, a type of forest vegetation that is diverse, ecologically integral, and particularly sensitive to climate.  From 1993-1999 epiphytic lichen communities in coniferous forests were surveyed at 350 sites across five national forests in the Coast Range, Columbia River valley, and Cascade Ranges of western Oregon and Washington. Repeat surveys were made in 2003-2009. Gradient analysis was used to relate lichen community patterns relate to PRISM (Parameter-Elevation Regressions on Individual Slopes Model) climate estimates for the survey sites.  A non-metric multidimensional scaling (NMS) ordination of sites in species-space resolved two perpendicular gradients (axes 1 and 2), together explaining 84% of the variability in lichen communities.  Lichen community scores along axis 2 reflected community-level responses to climate and correlated well with mean minimum December temperatures (r2 = 0.72), elevation (r2 = 0.63), continentality (r2= 0.54), mean % relative humidity (RH; r2= 0.36) and mean temperature (r2=0.34), but not precipitation (r2= 0.012).  Axis 1 was correlated with air quality, primarily N deposition.  Changes in climate scores between Round 1 and Round 2 and twenty year simple linear regressions of PRISM climate variables indicated that lichen communities in the Coast Ranges are shifting towards cooler climate species, associated with greater moisture in the air from increased % RH, possibly a result of greater winter storm energy along the coast. No change was detected in communities of low elevation valleys. Shifts in species composition towards warmer-climate communities and higher biodiversity (species richness increases >25%) were widespread further inland along the Oregon Cascade Ranges, especially at mid to high elevations where the greatest winter temperature warming (2-4o C) occurred.  These data demonstrate that lichen communities are highly sensitive to and provide an excellent ecological response indicator of short term (10-20 year) trends in climate.  They are also some of the first evidence of shifts in species distribution and diversity in the US Pacific Northwest that can be directly related to climate trends.  Regarding the broader plant community, these results imply that managers can expect variable responses and response rates to climate change across the landscape with greatest potential changes at high elevation sites where the most rapid warming is occurring.

Part II: “Predicting Nitrogen Deposition to Forests in the Los Angeles Basin using Lichen Communities”

Forests in the Los Angeles Basin receive the highest known levels of nitrogen (N) deposition in the United States.  Excess N is implicated in a wide variety of detrimental ecological impacts to both terrestrial and aquatic systems, leading to shifts in vegetation communities that favor invasive species, elevated nitrate (NO3-) runoff, soil acidification, decreased frost-hardiness in trees, and so on.  In 2008, we surveyed the epiphytic lichen communities of Quercus kelloggii forests at 23 sites across the San Bernardino Mountains, the Palomar Mountain area and the Sawmill Mountains.  We employed gradient analysis to determine how lichen community patterns relate to N measurements collected at our survey sites; these include throughfall N (kg ha-1 y-1), seasonal averages of NH3, NO2, and HNO3 from Ogawa passive monitors (μg m-3), modeled site N deposition (kg ha-1 y-1) from the Community Multi-scale Air Quality model (CMAQ), and assays of NO3- accumulated on twig surfaces (μg cm-2).  With non-metric multidimensional scaling ordination (NMS) we resolved a gradient explaining almost half the variability in lichen communities (r2 = 0.48), which clearly reflected a community-level response to N.  Lichen community scores along the gradient correlated exceptionally well with throughfall N (r2 = 0.94) , an N measure that captures the hydrologic flux of ammonium (NH4+) and NO3- ions from the tree canopy to the forest floor.  We then used simple linear regression (SLR) on community scores to predict throughfall N at all sampled sites. The two-phase model combining NMS and SLR yielded N predictions sufficiently accurate (error: + 4.6 kg N ha-1 y-1) for use in the Basin where throughfall N spans 6.1 to 71.1 kg ha-1 y-1.  The ability to make reasonably accurate N predictions based solely on lichen community information marks a significant utilitarian advancement in the lichen-bioindication field.  In the highly N-compromised Basin, land managers and air quality regulators may use lichen estimates as a surrogate or justification for implementing more costly campaigns that measure N directly. 

The Environment & Functional Ecology is a research group within CBA, Centre for Environmental Biology