Eastern Temperate Forests

Human activity in the last century has led to a substantial increase in nitrogen (N) emissions and deposition. This N deposition has reached a level that has caused or is likely to cause alterations to the structure and function of many ecosystems across the United States. One approach for quantifying the level of pollution that would be harmful to ecosystems is the critical loads approach. The critical load is dei ned as the level of a pollutant below which no detrimental ecological effect occurs over the long term according to present knowledge. The objective of this project was to synthesize current research relating atmospheric N deposition to effects on terrestrial and aquatic ecosystems in the United States and to identify empirical critical loads for atmospheric N deposition. The receptors that we evaluated included freshwater diatoms, mycorrhizal fungi and other soil microbes, lichens, herbaceous plants, shrubs, and trees. The main responses reported fell into two categories: (1) biogeochemical, and (2) individual species, population, and community responses. The range of critical loads for nutrient N reported for U.S. ecoregions, inland surface waters, and freshwater wetlands is 1 to 39 kg N ha-1 y-1. This broad range spans the range of N deposition observed over most of the country. The empirical critical loads for N tend to increase in the following sequence for different life forms: diatoms, lichens and bryophytes, mycorrhizal fungi, herbaceous plants and shrubs, trees. The critical loads approach is an ecosystem assessment tool with great potential to simplify complex scientii c information and effectively communicate with the policy community and the public. This synthesis represents the i rst comprehensive assessment of empirical critical loads of N for ecoregions across the United States

Illustration list for Macrolichens of the Pacific Northwest, 3rd edition (2023)

We give references for illustrations in the third edition of Macrolichens of the Pacific Northwest. For each illustration, we list the photographer or illustrator, the specimen photographed, where the specimen was from, collector, collection number, and herbarium

Species Changes in Macrolichens of the Pacific Northwest, 2nd edition (2009)

We list additions, deletions, and other changes in species included in Macrolichens of the Pacific Northwest, 2nd edition, as compared to the 1st edition. The changes resulted from discoveries of range extensions into the Pacific Northwest, descriptions of new species, taxonomic revisions, and nomenclatural revisions

Illustration List for Macrolichens of the Pacific Northwest, 2nd edition (2009)

References are given for illustrations in the second edition of Macrolichens of the Pacific Northwest. For each illustration, we list the photographer or illustrator, the specimen photographed, where the specimen was from, collector, collection number, and herbarium

On-road emissions of ammonia: An underappreciated source of atmospheric nitrogen deposition

We provide updated spatial distribution and inventory data for on-road NH3 emissions for the continental United States (U.S.) On-road NH3 emissions were determined from on-road CO2 emissions data and empirical NH3:CO2 vehicle emissions ratios. Emissions of NH3 from on-road sources in urbanized regions are typically 0.1– 1.3 t km−2 yr−1 while NH3 emissions in agricultural regions generally range from 0.4–5.5 t km−2 yr−1, with a few hot spots as high as 5.5–11.2 t km−2 yr−1. Counties with higher vehicle NH3 emissions than from agriculture include 40% of the U.S. population. The amount of wet inorganic N deposition as NH4+ from the National Atmospheric Deposition Program (NADP) network ranged from 37 to 83% with a mean of 58.7%. Only 4% of the NADP sites across the U.S. had \u3c45% of the N deposition as NH4+ based on data from 2014 to 2016, illustrating the near-universal elevated proportions of NH4+ in deposition across the U.S. Case studies of on-road NH3 emissions in relation to N deposition include four urban sites in Oregon and Washington where the average NH4- N:NO3-N ratio in bulk deposition was 2.3. At urban sites in the greater Los Angeles Basin, bulk deposition of NH4-N and NO3-N were equivalent, while NH4-N:NO3-N in throughfall under shrubs ranged from 0.6 to 1.7. The NH4-N:NO3-N ratio at 7–10 sites in the Lake Tahoe Basin averaged 1.4 and 1.6 in bulk deposition and throughfall, and deposition of NH4-N was strongly correlated with summertime NH3 concentrations. On-road emissions of NH3 should not be ignored as an important source of atmospheric NH3, as a major contributor to particulate air pollution, and as a driver of N deposition in urban and urban-affected regions

Nitrogen-induced terrestrial eutrophication: cascading effects and impacts on ecosystem services

Human activity has significantly increased the deposition of nitrogen (N) on terrestrial ecosystems over pre-industrial levels leading to a multitude of effects including losses of biodiversity, changes in ecosystem functioning, and impacts on human well-being. It is challenging to explicitly link the level of deposition on an ecosystem to the cascade of ecological effects triggered and ecosystem services affected, because of the multitude of possible pathways in the N cascade. To address this challenge, we report on the activities of an expert workshop to synthesize information on N-induced terrestrial eutrophication from the published literature and to link critical load exceedances with human beneficiaries by using the STressor–Ecological Production function–final ecosystem Services Framework and the Final Ecosystem Goods and Services Classification System (FEGS-CS). We found 21 N critical loads were triggered by N deposition (ranging from 2 to 39 kg N·ha−1·yr−1), which cascaded to distinct beneficiary types through 582 individual pathways in the five ecoregions examined (Eastern Temperate Forests, Marine West Coast Forests, Northwestern Forested Mountains, North American Deserts, Mediterranean California). These exceedances ultimately affected 66 FEGS across a range of final ecosystem service categories (21 categories, e.g., changes in timber production, fire regimes, and native plant and animal communities) and 198 regional human beneficiaries of different types. Several different biological indicators were triggered in different ecosystems, including grasses and/or forbs (33% of all pathways), mycorrhizal communities (22%), tree species (21%), and lichen biodiversity (11%). Ecoregions with higher deposition rates for longer periods tended to have more numerous and varied ecological impacts (e.g., Eastern Temperate Forests, eight biological indicators) as opposed to other ecoregions (e.g., North American Deserts and Marine West Coast Forests each with one biological indicator). Nonetheless, although ecoregions differed by ecological effects from terrestrial eutrophication, the number of FEGS and beneficiaries impacted was similar across ecoregions. We found that terrestrial eutrophication affected all ecosystems examined, demonstrating the widespread nature of terrestrial eutrophication nationally. These results highlight which people and ecosystems are most affected according to present knowledge, and identify key uncertainties and knowledge gaps to be filled by future research

A continental analysis of ecosystem vulnerability to atmospheric nitrogen deposition

Atmospheric nitrogen (N) deposition has been shown to decrease plant species richness along regional deposition gradients in Europe and in experimental manipulations. However, the general response of species richness to N deposition across different vegetation types, soil conditions, and climates remains largely unknown even though responses may be contingent on these environmental factors. We assessed the effect of N deposition on herbaceous richness for15,136 forest, woodland, shrubland, and grassland sites across the continental United States, to address how edaphic and climatic conditions altered vulnerability to this stressor. In our dataset, with N deposition ranging from 1 to 19 kg N·ha−1·y−1, we found a unimodal relationship; richness increased at low deposition levels and decreased above 8.7 and 13.4 kg N·ha−1·y−1 in open and closed-canopy vegetation, respectively. N deposition exceeded critical loads for loss of plant species richness in 24% of 15,136 sites examined nationwide. There were negative relationships between species richness and N deposition in 36% of 44 community gradients. Vulnerability to N deposition was consistently higher in more acidic soils whereas the moderating roles of temperature and precipitation varied across scales. We demonstrate here that negative relationships between N deposition and species richness are common, albeit not universal, and that fine-scale processes can moderate vegetation responses to N deposition. Our results highlight the importance of contingent factors when estimating ecosystem vulnerability to N deposition and suggest that N deposition is affecting species richness in forested and nonforested systems across much of the continental United States

Synthesis

Human activity in the last century has led to a substantial increase in nitrogen (N) emissions and deposition. This N deposition has reached a level that has caused or is likely to cause alterations to the structure and function of many ecosystems across the United States. One approach for quantifying the level of pollution that would be harmful to ecosystems is the critical loads approach. The critical load is dei ned as the level of a pollutant below which no detrimental ecological effect occurs over the long term according to present knowledge. The objective of this project was to synthesize current research relating atmospheric N deposition to effects on terrestrial and aquatic ecosystems in the United States and to identify empirical critical loads for atmospheric N deposition. The receptors that we evaluated included freshwater diatoms, mycorrhizal fungi and other soil microbes, lichens, herbaceous plants, shrubs, and trees. The main responses reported fell into two categories: (1) biogeochemical, and (2) individual species, population, and community responses. This report synthesizes current research relating atmospheric nitrogen (N) deposition to effects on terrestrial and aquatic ecosystems in the United States and to identify empirical critical loads for atmospheric N deposition. The report evaluates the following receptors: freshwater diatoms, mycorrhizal fungi and other soil microbes, lichens, herbaceous plants, shrubs, and trees. The main responses reported fell into two categories: (1) biogeochemical; and (2) individual species, population, and community responses. The range of critical loads for nutrient N reported for U.S. ecoregions, inland surface waters, and freshwater wetlands is 1 to 39 kg N ha-1 y-1. This range spans the range of N deposition observed over most of the country. The empirical critical loads for N tend to increase in the following sequence for different life forms: diatoms, lichens and bryophytes, mycorrhizal fungi, herbaceous plants and shrubs, trees

Synthesis

Human activity in the last century has led to a substantial increase in nitrogen (N) emissions and deposition. This N deposition has reached a level that has caused or is likely to cause alterations to the structure and function of many ecosystems across the United States. One approach for quantifying the level of pollution that would be harmful to ecosystems is the critical loads approach. The critical load is dei ned as the level of a pollutant below which no detrimental ecological effect occurs over the long term according to present knowledge. The objective of this project was to synthesize current research relating atmospheric N deposition to effects on terrestrial and aquatic ecosystems in the United States and to identify empirical critical loads for atmospheric N deposition. The receptors that we evaluated included freshwater diatoms, mycorrhizal fungi and other soil microbes, lichens, herbaceous plants, shrubs, and trees. The main responses reported fell into two categories: (1) biogeochemical, and (2) individual species, population, and community responses. This report synthesizes current research relating atmospheric nitrogen (N) deposition to effects on terrestrial and aquatic ecosystems in the United States and to identify empirical critical loads for atmospheric N deposition. The report evaluates the following receptors: freshwater diatoms, mycorrhizal fungi and other soil microbes, lichens, herbaceous plants, shrubs, and trees. The main responses reported fell into two categories: (1) biogeochemical; and (2) individual species, population, and community responses. The range of critical loads for nutrient N reported for U.S. ecoregions, inland surface waters, and freshwater wetlands is 1 to 39 kg N ha-1 y-1. This range spans the range of N deposition observed over most of the country. The empirical critical loads for N tend to increase in the following sequence for different life forms: diatoms, lichens and bryophytes, mycorrhizal fungi, herbaceous plants and shrubs, trees