Graph of the Day: Nitrophytic Lichen Abundance versus Air Quality in Central Valley, California

Scatterplot of the greater Central Valley, California calibration data showing the relationship between air quality score and the proportion of nitrophytic lichen abundance at each plot.
Abstract: Lichens are highly valued ecological indicators known for their sensitivity to a wide variety of environmental stressors like air quality and climate change. This report summarizes baseline results from the U.S. Department of Agriculture, Forest Service, Forest Inventory and Analysis (FIA) Lichen Community Indicator covering the first full cycle of data collection (1998–2001, 2003) for Washington, Oregon, and California. During this period, FIA conducted 972 surveys of epiphytic macrolichen communities for monitoring both spatial and long-term temporal trends in forest health. Major research findings are presented with emphasis on lichen biodiversity as well as bioindication of air quality and climate. Considerable effort is devoted to mapping geographic patterns and defining lichen indicator species suitable for estimating air quality and climate. …Excessive N is a growing problem in many developed nations as documented in many studies (Driscoll et al. 2003, Fenn et al. 1998, Holland et al. 2005, Vitousek et al. 1997). But in the bigger picture, how dire is the status of forest air quality…? A direct comparison to other regions is precluded by the lack of comprehensive instrumented pollutant measurements, which means that we hardly know how much N is actually getting into the system. As reviewed by Fenn et al. (2003a), N deposition patterns are unknown for most of the Western United States, which underscores the importance of lichen-air quality bioindication. … NMS detected an air quality gradient suggesting that one or more N compounds are impacting lichens in the greater Central Valley (Jovan and McCune 2005). Air quality scores determined for plots were linearly related to the proportion of nitrophyte abundance (PNA; r = -0.78), a simple measure of nitrophyte dominance in the community. Nitrophytes are a well-studied group of lichen indicator species known to react positively to N and the alkalinization of substrates. Plot scores were also substantially correlated to NH3 estimates from the emissions model and the land use index (r = -0.51 and -.63, respectively) but less so with NO2 (r = -0.33). In the literature, nitrophytes are often linked specifically to NH3, which is expected to be a major component of total N deposition in the study area owing to the density of agriculture. Altogether these results suggest that plots receiving low (poor) air quality scores are the most impacted, wherein N is relatively high and lichen communities are dominated by weedy nitrophytic species. … 1. As in the west-side Pacific Northwest, the model suggests nitrogen (N) is a major stressor shaping lichen communities in the greater Central Valley. 2. Jovan and McCune (2005) found that air quality scores from the model were correlated with estimates of ammonia (NH3) and the dominance of nitrophytes (e.g., lichen species commonly associated with high NH3 habitats and high bark pH). 3. Lichen species expected to be N intolerant were rare in the greater Central Valley, most especially at plots where the model indicated high N impact. The regional rarity of N-sensitive species, however, may be partly due to the hot and
dry climate. 4. Poor air quality was estimated for most forests in urban and agricultural areas where lichen communities consisted of up to 100 percent nitrophytes. 5. Small hotspots of poor air quality were scattered across the study area, with the largest hotpots detected in the Central Valley and San Francisco Bay area.

Jovan, Sarah, “Lichen bioindication of biodiversity, air quality, and climate: baseline results from monitoring in Washington, Oregon, and California,” 2008. Gen. Tech. Rep. PNW-GTR-737. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 115 p.[pdf] via Wit’s End