Critical Loads - Monitoring Strategy - Section 2c

Monitoring Acidification Effects - Forested Ecosystems

The CLs of acidity for forested ecosystems in the national database are not considered reliable enough to serve as the basis for land management decisions.   These CLs were modeled with a simple mass balance equation using spatially extrapolated data.  Several of the input parameters are soil-based, and the values are from modeled, rather than measured information.  In addition, the scale of the soil data used in the nationwide calculations is too coarse to capture all situations, potentially missing the areas with most sensitive soils because soil type and chemistry varies widely across the landscape.  This is particularly a concern in complex, mountainous terrain, where soils vary widely over short distances.  While these CLs have value for regional assessments and identifying areas of risk, they lack the site specificity needed when making land management decisions at the scale of the national forest.

At the forest level, finer scale soil and soil chemistry information can help improve the CLs of acidity estimates for forested ecosystem.  Only a few forests, however, all with well-documented acidification problems for surface waters, have undertaken soil monitoring programs to improve their critical load estimates.  Before embarking on a soil monitoring program, investigate whether surface waters are affected by acidification.  Surface water monitoring should be conducted on the forest prior to considering a soil monitoring program.  Forests with known acidification problems in surface waters could use the existing terrestrial CLs of acidity for forested ecosystems, in conjunction with surface water data, to identify vulnerable or high-risk areas to target for additional monitoring to refine CLs.  Review the information provided in the previous section (Monitoring Acidification Effects - Aquatic Ecosystems) for assistance with surface water monitoring.

Soil monitoring programs can be expensive; forests may want to reserve soil monitoring funds for areas where surface water samples suggest acidification, and 1) the forest is considering active management, or 2) Class 1 or Wilderness Area protection status suggest the need for proactively mitigating damage or initiating restoration for ecological protection.  Soil chemistry may also be required before performing dynamic modeling for target load calculation.  Consult with a research scientist familiar with critical loads in your region before developing a monitoring plan to improve CLs of acidity for terrestrial ecosystems.  The document, Approaches for Estimating Critical Loads of N and S Deposition for Forest Ecosystems on U.S. Federal Lands (Pardo 2010) should also be consulted for alternative methods of calculating CLs.  You will need to consider the requirements of the method you intend to use to calculate or refine the CLs; let these requirements guide the selection of parameters measured in the environment.  Each method requires varying levels of data intensity.