Overview
This tool is designed to synthesize information about nitrogen deposition, species sensitivity, site and current climate conditions into an easy-to-use, web-based geospatial tool (N-CLAS) to facilitate effective resource management across the northern forest region.
The N-CLAS tool allows land managers to determine critical loads (CL), quantify exceedance, and set targets for the purposes of land management and restoration. N-CLAS can be used to address questions about selected areas such as:
The interactive web interface provides maximum flexibility for the user to assess heterogeneous landscapes for specific areas and species of interest. Outputs include downloadable maps, tables and figures summarizing critical loads and exceedance based on a range of customizable options, including output products that reflect the minimum CL value, range of CL values, or percent of the target area protected.
You can also download base layer maps of N deposition, climate, soil, and topographic parameters.
How it Works
Nitrogen Critical Load Assessment by Site (N-CLAS) is a GIS-based tool designed for resource managers and policy makers to assess the effects of nitrogen deposition and climate change on forest ecosystems in the Northeastern United States. N-CLAS uses geospatial data layers for key topographic, climactic, soil abiotic factors, and nitrogen deposition levels to predict whether growth at a site will be optimal or suboptimal for each of 23 significant tree species. N-CLAS can then be used to assess critical loads and exceedance for individual species or summarized for all species combined for user selected areas.
Customize your output by setting your preferences for area unit (acres or hectares), and tree species name (Latin or common).
Step 1: Select your target Area
N-CLAS includes data aggregation by state, ecoregion, National Forest, National Park, and wilderness area classes. You can select one, or multiple areas for comparison within each class.
Step 2: Select your Species of interest
A total of 23 tree species are included in the N-CLAS assessment. You may select a single species of interest, any combination of key species, or all species to better understand the forest as a whole.
Step 3: Select your preferred Output
Three levels of detail are provided for output maps, figures, and tables:
Step 4: View your generated Results
The results window allows users to explore a variety of graphs, tables, and figures generated according to their customized settings.
Outputs
The tool's output includes downloadable summary tables and figures as well as spatially explicit maps of CL and exceedance values across the landscape of interest. Some outputs are designed to specifically address common questions (see overview above), while others are designed to provide detailed comparisons across sites or species.
Various types of map products, data aggregation and summary statistics include:
N-CLAS Overview
N-CLAS is a GIS-based tool designed for resource managers to assess the effects of nitrogen deposition and determine critical loads and exceedance for forest ecosystems in the Northeastern United States.
N-CLAS can be used to determine critical loads and exceedance for individual tree species or all tree species present for user selected areas, including national forests and parks, wilderness areas, and ecoregions (areas with similar ecosystem structure and function as defined by the Commission for Environmental Cooperation (CEC)).
N-CLAS uses geospatial data of abiotic modifying factors (topographic, climatic, and soil parameters) to predict whether growth in each 30 m x 30 m pixel is likely to be optimal or sub-optimal for a given species. Sub-optimal growth conditions are expected to increase sensitivity to N deposition, whereas optimal growth conditions are expected to result in increased N demand and higher tolerance of N deposition.
N-CLAS combines the effect of the abiotic modifying factors on growth to determine if the critical load for a species will be in the bottom half or upper half of the species' documented critical load range.
N-CLAS includes 23 species of management concern, of commercial interest and dominant species in the northern forest.
N-CLAS can be used to determine critical loads and exceedance for individual tree species or all tree species present at user-selected areas, including national forests and parks, wilderness areas, and ecoregions (areas with similar ecosystem structure and function as defined by the Commission for Environmental Cooperation (CEC)).
N-CLAS uses geospatial data for topographic, climatic, and soil parameters to assess whether growth is likely to be optimal or sub-optimal for each species at a given location. N-CLAS then modifies the critical load for each species based on these factors.
N-CLAS Approach
N-CLAS uses a 5-step process to calculate critical loads.
PDF containing detailed methodologyN-CLAS critical loads can be reported for individual species or aggregated for all tree species present.
Steps N-CLAS uses to calculate the critical load:
Identify the species present
N-CLAS uses LANDFIRE geospatial data, which provides SAF (Society of American Foresters) forest cover type fore existing vegetation.
Species composition of each forest cover type is derived from Eyre (1980), the USDA Fire Effects Information System, and Little's Little's species range maps. We created a list of species included in each SAF forest cover type used by LANDFIRE.
Evaluate whether abiotic modifying factors are more likely to lead to optimal or sub-optimal conditions for growth
For each tree species, Robin-Abbott and Pardo (2017) identified the optimal range for growth for specified topographic, climatic, and soil abiotic modifying factors.
The optimal range for growth for specified topographic, climatic, and soil abiotic modifying factors is based on importance values and distribution data from the Climate Change Tree Atlas (U.S. Forest Service, n.d.) and information from other sources, including the Forest Service silvics handbook "Silvics of North America" (Burns and Honkala, 1990); the PLANTS database (NRCS 2014); and additional literature sources.
N-CLAS makes calculations for each 30 m x 30 m pixel for each species present at that location.
Weigh the strength of evidence for the response of each abiotic factor
The weight of evidence is a way of quantifying the strength of the scientific evidence currently available for a species' response to an abiotic factor.
The weight of evidence for abiotic modifying factor thresholds is set using FIA-based importance value data from the Climate Change Atlas.
The overall uncertainty rating was determined through the arithmatic mean of three weighting criteria:
The matrix used to assign the weight of evidence for abiotic factors included in the Climate Change Atlas is described in Robin-Abbott and Pardo (2017).
Another matrix was used to assign the weight of evidence for abiotic modifying thresholds set using data from the Forest Service silvics handbook, "Silvics of North America" (Burns and Honkala, 1990), PLANTS database (NRCS 2014), or other literature sources.
Values for the weight of evidence are summed across all factors in the optimal range and then compared to the sum of the weights of evidence for all factors in the sub-optimal range. If the sum of the weight of evidence of sub-optimal factors is higher, overall growth is likely to be sub-optimal. If the sum of the weight of evidence of optimal factors is higher, overall growth is likely to be optimal.
This weighting system is based on the endorsement theory, which is described in detail in Hall and Wadsworth (2010)
Incorporate the relative ecological significance of each abiotic factor
Adjust the critical load value based on the combined effect of all abiotic modifying factors
The critical load is reported as a range to incorporate the variation in response to N deposition across sites and individuals.
If the adjusted critical load is in the bottom half of the CL range, it means that in this area, the species is more sensitive to N deposition. Suboptimal growth conditions are expected to increase sensitivity to N deposition and thus shift the critical load to the bottom half of the species' critical loads range.
If the adjusted critical load is in the upper half of the CL range, it means that in this area, the species is less sensitive to N deposition. Optimal growth conditions are expected to result in increased N demand and thus shift the critical load to the upper half of the critical loads range.
Instructions for Use
This interactive web interface provides maximum flexibility for the user to assess heterogeneous landscapes. To get the most from the outputs of the N-CLAS tool and match user needs, there are several customization steps that must be completed before viewing outputs. This includes selecting your target areas of interest, which of the 23 forest species to include in the analyses, and the type of response variable, data aggregation and summary statistics to be reported in the output. The N-CLAS tool walks users through each of these customization steps:
Step 1: Select your target Area
N-CLAS includes data aggregation by state, ecoregions (levels 2 and 3), National Forest, National Park, and wilderness area classes. You can select one, or multiple areas for comparison within each class.
Step 2: Select your Species of interest
A total of 23 tree species are included in the N-CLAS assessment. You may select a single species of interest, any combination of key species, or all species to better understand the forest as a whole.
Step 3: Select your preferred Output format
Three levels of detail are provided for output maps, figures and tables:
Output products can be previewed to ensure that all required results are included, with the ability to remove unnecessary outputs or select additional outputs.
Step 4: View your generated Results
The results window allows users to explore a variety of graphs, tables, and figures generated according to their customized settings.
These products are nested in the results window on the right side of the map interface. Select and expand various result tabs, hover for additional information on each output product, or click for a zoomed view.
All products are individually downloadable, and (coming soon) can be used to generate a common report for all selected outputs.
Tips for New Users
Tutorials (coming soon)
Frequently Asked Questions
What is the best way to troubleshoot or get more information when using N-CLAS?
How do I clear the selections I have made in the tool to start over?
How are non-forested areas shown?
Which level of detail is appropriate for me for output selection?
How do I alter the assortment of outputs that N-CLAS selects for me?
How do I download figures and tables?
How can I reset my preferences?
Which species are included in the N-CLAS assessment?
How do the tree species critical loads included in N-CLAS differ from other critical loads?
How does N-CLAS differ from other critical load assessment tools?
How are the critical loads set?
How does N-CLAS adjust the critical load by site conditions?
How do the ranges for optimal growth vary by species for each abiotic factor?
What is the weight of evidence?
Where are the abiotic factor data from?
Where do the species ranges come from?
Which critical load value should I use (most or least sensitive)?
What does it mean if my entire site is in exceedance?
What is the best way to troubleshoot or get more information when using N-CLAS?
When in doubt, hover. Hovering will generally open a brief description of the item of interest. Many items in the web app contain an info icon . Hovering over these icons provides a summary of the function of each item.
How do I clear the selections I have made in the tool to start over?
There is a refresh button in the upper right-hand corner of the home page.
If there is white on the CL or EXC map (provided the baselayer is either 'State Outlines' or 'None'), what does this mean?
White on the map indicates that the area is not forested. Non-forested pixels contain no shading and thus expose the current baselayer.
How are non-forested areas shown?
Non-forested areas are not shown on the map making whatever baselayer is present visible in those areas.
Which level of detail is appropriate for me for output selection?
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How do I alter the assortment of outputs that N-CLAS selects for me?
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How do I download figures and tables?
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How do I download maps?
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Can I save my settings?
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How do I undo a selection?
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How can I reset my preferences?
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Why is N-CLAS by site?
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Which species are included in the N-CLAS assessment?
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How do the tree species critical loads included in N-CLAS differ from other critical loads?
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How does N-CLAS differ from other critical load assessment tools?
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How are the critical loads set?
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How does N-CLAS adjust the critical load by site conditions?
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How do the ranges for optimal growth vary by species for each abiotic factor?
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What is the weight of evidence?
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Where are the abiotic factor data from?
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Where do the species ranges come from?
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Which critical load value should I use (most or least sensitive)?
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What does it mean if my entire site is in exceedance?
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What does it mean if none of my area is in exceedance?
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How can I get help interpreting my results?
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Glossary
Abiotic Modifying Factors | Characteristics of the environment in which trees grow. In N-CLAS, these include: Topographic - elevation, slope, aspect |
Aggregated | Aggregated outputs in N-CLAS refer to combining the results of all the tree species present for a given area and reporting them as a group, rather than by individual species. |
Class I Area | Class I federal lands include areas such as national parks, national wilderness areas, and national monuments. These areas are granted special air quality protections under Section 162(a) of the federal Clean Air Act. |
Class II Area | Class II Areas encompass nearly all other areas in the U.S. These areas are only allowed moderate change in the air quality and have stringent standards to meet. |
Competitive Advantage | The ability to outcompete neighboring trees for resources to promote growth. |
Critical Load | A critical load is defined as the level of deposition below which no harmful effects occurs over the long term (UBA 2004). In N-CLAS, this is the amount of N deposition that will negatively impact the tree species present. |
Cumulative Frequency | A figure used to visualize the proportion of observations that lie above (or below) a particular value in a data set. |
Ecoregion | Ecoregions are areas where ecosystems are generally similar. The CEC ecoregion classification system has four levels, of which only the first three are currently included in N-CLAS. "Level I" divides North America into 15 broad ecoregions. "Level 2" subdivides those regions again into 52 smaller ecoregions. "Level 3" subdivides those regions again into 182 ecoregions. |
Exceedance | The amount by which the actual load of deposition is greater than the critical load. |
Forest Cover Type | The name for a specific composition of tree community; for example, red spruce-balsam fir. In N-CLAS, forest cover type, derived from Landfire spatial data products, is used to identify tree species present at a given location. |
Harmful Ecological Effects | Harmful ecological effects include: detrimental responses at the tissue level (nutrient deficiencies, nutrient imbalances), at the plant level (declines in growth, survival, and health), at the community level (decreased species richness, shifts in community composition), and at the ecosystem level (increases in watershed nitrate export). |
Importance Values | A measure of how dominant a species is in a given forest area (the relative importance of a species within a plot). The more dominant a species is, the higher its importance value. |
Negative Consequences of Increased N Deposition | Negative consequences of increased N deposition include: detrimental responses at the tissue level (nutrient deficiencies, nutrient imbalances), at the plant level (declines in growth, survival, and health), at the community level (decreased species richness, shifts in community composition), and at the ecosystem level (increases in watershed nitrate export). |
Nitrogen Deposition | The input of nitrogen from the atmosphere to ecosystems in wet and dry forms (including rain, snow, fog, gas, particles). Nitrogen is a pollutant emitted in fossil fuel combustion and farming. |
Optimal Growth | Based on ecology and plant nutrition, for a given species, there is a range of values for each parameter within which that species grows best. |
Pixel | The smallest unit represented in mapping outputs and summarized in tables and figures. In N-CLAS, each pixel represents a 30x30 meter area on the ground. |
Species Range | The historical distribution of a given species across the landscape, determined by evolutionary tolerances to site, soil, and climate conditions. Species ranges in N-CLAS are delineated using Little's range maps. |
TDep | Maps summing dry and wet deposition of nitrogen (total deposition) are created as part of the National Atmospheric Deposition Program |
Weight of Evidence | A way of quantifying how strong the evidence currently available is for a species' response to an abiotic factor. In N-CLAS, the weight of evidence is used to determine how likely a given factor is to modify the critical load. |
Weight of Influence | The rating of how important a given abiotic factor is in determining the ultimate growth response of a given tree species and its susceptibility to N deposition (since not all factors are equally important). Note that the weight of influence reflects the ecological significance of the factor and is different than the weight of evidence, which addresses the strength of the relationship shown by the data. |
Wilderness Areas | Protected areas of undeveloped federal land retaining its primeval character and influence, without permanent improvements or human habitation; where the earth and community of life are untrammeled by humans. |
Welcome to the N-CLAS tool
N-CLAS facilitates assessment of risk to forest ecosystems for resource managers and policy makers. This tool is designed to calculate critical loads and exceedances for Nitrogen deposition to forests in the northeastern US. It provides high resolution outputs (maps, graphs, and tables) for multiple areas and accounts for the influence of site, climate, and topographic conditions on 23 key tree species in the region.
Getting Started
Step 1: Select your target Area
Step 2: Select your Species of interest
Step 3: Select your preferred Output format
- Basic: Summary figures and tables for most protective critical load of most sensitive species
- Tailored: Set of outputs based on your response to screening questions about your needs
- Comprehensive: All figures and tables
Step 4: View your generated Results
- Explore graph, table, and map outputs
- Download individual outputs
Preferred units for area measurements:
Preferred naming convention for species titles:
Show boundaries of target ecoregions on map:
Simple output maps, summary figures, and tables (most protective critical load: most sensitive of all species present)
Select from a checklist of questions to determine which output materials exactly suit your needs
All relevant figures, tables, and maps
1. Would you like to see only the most protective critical load or critical loads for a range of
levels of protection?
2. Would you like to see outputs for individual species, all species combined, or both?
3. Would you like to compare your site to other ?
Click on an image to view here
Mouseover above figure to zoom in