Using Epiphytic Macrolichen Communities for Biomonitoring Ammonia in Forests of the Greater Sierra Nevada, California

Abstract

Chronic, excessive nitrogen deposition is potentially an important ecological threat to forests of the greater Sierra Nevada in California. We developed a model for ammonia bioindication, a major nitrogen pollutant in the region, using epiphytic macrolichens. We used non-metric multidimensional scaling to extract gradients in lichen community composition from surveys at 115 forested sites. A strong ammonia deposition gradient was detected, as evidenced by a high linear correlation with an index of ammonia indicator species conventionally known as "nitrophytes" (r = 0.93). This gradient, however, was confounded by elevation (r = −0.54). We evaluated three statistical techniques for controlling the influence of elevation on nitrophytes: simple linear regression, nonlinear regression, and nonparametric regression. We used the unstandardized residuals from nonlinear regression to estimate relative ammonia deposition at each plot, primarily because this model had the best fit (r 2 = 0.33), desirable asymptotic properties, and it is easy to apply to new data. Other possible sources of noise in the nitrophyte-ammonia relationship, such as substrate pH and acidic deposition, are discussed. Lichen communities indicated relatively high deposition to forests of the southern Sierra Nevada, the Modoc Plateau, as well as in stands near urban areas. Evidence of elevated ammonia was also detected for popular recreation areas such as Sequoia and Yosemite National Parks. Lichen communities from forests in the Tahoe basin, northern Sierra Nevada, southern Cascades, and eastern Klamath Range appeared considerably less impacted. This model will be used for continual assessment of eutrophication risks to forest health in the region.

Lichen-based indices to quantify responses to climate and air pollution across northeastern U.S.A

“…43 and 44). Extra steps were needed to ensure that the greater Sierra Nevada model isolates air quality effects from the strong influence elevation naturally exerts on lichen communities (Jovan and McCune 2006). The problem arises because air quality and elevation are at least somewhat correlated with each other in the study area (Fenn et al 2003c).…”

“…42) since there are fewer local emission sources and forests are farther from the Central Valley with its high density of N sources (Jovan and McCune 2006).…”

“…Nitrophytes are most frequently linked to ammonia (NH 3 ), but it is unclear to what degree species are responding to the N versus the increase in bark pH that NH 3 causes (see chapter 3 sections "Direct and Indirect Nitrogen Effects on Lichens" and "Nitrophytes"). To isolate the lichen response to air quality, elevation was regressed on the PNA using nonlinear regression with a generalized sigmoid curve (Jovan and McCune 2006; see sidebar 11). The unstandardized residuals from the nonlinear regression serve as the air quality scores for the greater Sierra Nevada.…”

Lichen community change in response to succession in aspen forests of the southern Rocky Mountains

“…In addition to their use by wildlife for food and nesting (Rosentreter, 1995), fruticose lichens are among the most sensitive to air pollution regionally (Neitlich et al, 2003). In contrast, genera common on aspen substrates, like Physcia and Xanthomendoza, appear to react favorably to nitrogen-based pollutants and air-borne dust particles (Rosentreter, 1990;Jovan and McCune, 2006). The presence of both pollution intolerant and tolerant species in aspen forests suggests linkages to local air quality patterns.…”

Aspen Indicator Species in Lichen Communities in the Bear River Range of Idaho and Utah

“…If local or regional aspen populations are dwindling (or stabilizing) we would expect to see concurrent patterns in lichen associates. Further, if specific pollutants, such as excess nitrogen or ammonia (Jovan and McCune 2006;Rosentreter 1990), are affecting aspen forests lichen communities may provide and early warning of potential forest-wide affects. Additionally, lichen monitoring for these communities may prove to be a cost effective surrogate for total animal and plant enumeration given the high faunal and floral diversity of aspen forests (Mueggler 1988;Shepperd et al 2006).…”