To maintain healthy ecosystems, it is increasingly imperative that federal land managers be prepared to monitor and assess levels of atmospheric pollutants and ecological effects in national parks, wildlife refuges, and wilderness areas. Atmospheric deposition of sulfur and/or nitrogen has the potential to damage sensitive terrestrial, and especially aquatic, ecosystems and can affect the survival of in-lake and in-stream biota. Federal land managers have a need to assess, at the individual park or wilderness area level, whether surface water resources are sensitive to air pollution degradation and the extent to which they have been impacted by atmospheric deposition of sulfur or nitrogen or influenced by other complicating factors. The latter can include geologic sources of sulfur, natural organic acidity, and the influence of disturbance and land use on water quality. This paper describes a knowledge-based decision support system (DSS) network for classifying lakewater resources in five acid-sensitive regions of the United States. The DSS allows federal land managers to conduct a preliminary assessment of the status of individual lakes prior to consulting an acid–base chemistry expert. The DSS accurately portrays the decision structure and assessment outcomes of domain experts while capturing interregional differences in acidification sensitivity and historic acid deposition loadings. It is internally consistent and robust with respect to missing water chemistry input data.

Knowledge-based systems are computer models that facilitate reasoning such that human experience and expertise can be represented and made available to non-specialists. In this paper we describe the application of a knowledge-engineering methodology, using the NetWeaver™ software, to the problem of lakewater acid-base chemistry assessment. We present, and document with examples, the structure, arguments, and criteria values of a knowledge-based decision support system for classifying lakes in five acid-sensitive regions of the United States. We also discuss the significance of this software tool for federal land managers in the management of aquatic resources in national parks, national wildlife refuges, and wilderness areas to protect against water quality degradation associated with atmospheric deposition of sulfur and nitrogen. The Lake Chemistry knowledge bases have undergone repeated testing by members of a lake chemistry domain expert panel. There is agreement among the panel that these regional models provide accurate classifications of lakewater chemistries. The graphical and executable rendering of knowledge bases within NetWeaver™ greatly facilitates the knowledge engineering process, as it permits the inclusion of the domain expert(s) in the knowledge representation process and hence encourages greater participation in the design of the final knowledge-based model. In addition, the inclusion of fuzzy arguments, against which data values can be compared, greatly reduces the potential for combinatorial explosion that often occurs in expert systems that rely on categorical data interpretation, while at the same time providing a robust description of complex systems. It is our expectation that adoption of this approach, and others like it, will stimulate further development of knowledge-based systems for agriculture, natural resource management, and other complex decision support arenas.

Foliage was sampled in June and late August-early September in 1988 and 1989 from the outer crowns of codominant red maple (Acer rubrum L.), northern red oak (Quercus rubra L.), and white oak (Q. alba L.) trees in forest stands along an atmospheric deposition gradient in north-central Pennsylvania. Leaf samples from approximately 480 trees were analyzed for concentration of macroelements N, P, K, Ca, Mg, and S, as well as microelements Al, B, Cu, Fe, Mn, Mo, Na, Pb, Si, Sr, V and Zn. Foliar concentrations of Fe, S, and Sr were generally greater in the high deposition portion of the gradient. Concentrations of other foliar elements generally were not related to the spatial pattern of atmospheric input.

Acervuli of Discula campestris were frequently observed on necrotic portions of thrips-injured sugar maple leaves in 1989. Necrosis was present on 82-98% of leaves collected at three sites in May, June, and August 1990 in Potter County, Pennsylvania, but symptoms were not severe. Evaluation of necrotic leaves indicated that 82-91% of the leaves were affected on ≤5% of their surface area. Marginal and interveinal necrosis were most common, while veinal necrosis was rare. The study was expanded to five central Pennsylvania counties in 1991. The median incidence and severity of all forms of necrosis were 0.1-1.0%. Twenty-one of 25 trees were rated positive for D. campestris following incubation of symptomatic or asymptomatic leaves in a moist chamber

Surveys were conducted in Pennsylvania during 1989 and 1990 to determine the distribution and incidence of Cryphonectria parasitica ( = Endothia parasitica) cankers on scarlet oak (Quercus coccinea). Cankered scarlet oak were found throughout the natural range, with incidence levels (15.0%) comparable to those previously reported in North Carolina (13.8%). C. parasitica was recovered from 69.7% of attempted isolations. Macroscopic signs (pycnidia or stroma) of C parasitica were associated with 67% of typical cankers. This represents a significant source of inoculum that may serve to further infect scarlet oaks and also American chestnut sprouts. This is the first report of C parasitica cankers on scarlet oak in Pennsylvania.

Assessment of tree health requires accurate estimates of crown condition and identification of specific biotic and abiotic agents that may affect crowns, stems, or roots. ForestHealth, an expert advisory system written in C language for the Macintosh™ platform, provides a diagnostic module and two training modules. The diagnostic module provides guidance in identifying foliar symptoms and the common insects, diseases, and abiotic disorders found on leaves of: sugar maple (Acersaccharum Marsh.), red maple (Acerrubrum L.), black cherry (Prunusserotina Ehrh.), northern red oak (Quercusrubra L.), and white oak (Quercusalba L.). Graphical user interfaces are central to both training modules. The Foliar Severity routine trains users to categorize injury (percent leaf area) on single leaves using a modified Horsfall–Barratt scale. The Crown Dieback routine displays different types and degrees of crown injury that users must identify and classify. Each crown is unique, generated in "real time" using tree–branch parameters selected by the user. Since the crowns are created on a three-dimensional basis, multiple views are possible. Written output from training sessions or periodic checks provide quantitative information for quality assurance and quality control. ForestHealth provides diagnostic assistance, training, quality assurance and quality control data, and standardization for research or survey projects involving forest health.

A well-defined gradient of wet atmospheric depositions characterized by SO4, NO3, H, and NH4 ions has been described in north-central Pennsylvania. The forests of this region are of the oak/hickory type as they extend across the Allegheny Plateau. Sulfate levels along a 160-km west-east gradient varied from approximately 40 kg/ha to 25 kg/ha in the western and eastern portions, respectively. The objective of this research project was to determine if forest trees along the gradient showed anomalous characteristics that might be related to acidic atmospheric deposition. Trees were relatively healthy across the gradient, as measured by observations of crown transparency, twig dieback, and trunk condition. No general relationship was apparent between overall tree health and deposition patterns. Specific disorders noted at greater frequencies at the high deposition portion of the gradient included the presence of insect borers on white oak trunks and early fall coloration of red maple. Disorders observed at greater frequencies at the low deposition portion of the gradient included twig and branch dieback of red oak, white oak, and red maple; chlorosis of red oak; and thrips injury of red maple. A direct cause-and-effect relationship between the pollution gradient and these disorders has not been established.

The groups were the same or differed among cankers on single trees. On scarlet oak, several different v-c groups were present within small portions of infected butt sections. The number of different v-c groups within single scarlet oaks varied from to five. Distribution patterns of v-c groups were not predictable, even amont trees located close to each other

Research in the oak-hickory forest of northcentral Pennsylvania is being conducted to detect anomalies in forest condition that may be due to atmospheric deposition, with the intent that such anomalies will be further studied to determine the role, if any, of atmospheric deposition. This paper presents the status of research along a 160-km gradient of sulfate/nitrate deposition across northern Pennsylvania begun in 1986 by a multidisciplinary group of researchers at Penn State University and Ohio State University.