III. EVALUATION OF HISTORIC LANDSCAPES
Landscapes must be evaluated as carefully as other property types and subjected to equally rigorous examination. They must be significant in American history, architecture, landscape history, engineering, archeology, or culture, and must possess sufficient integrity in order to be eligible for listing in the National Register of Historic Places. A surveyor might feel certain that a landscape is eligible, but careful documentation and a clearly articulated statement of significance based on the historic context will be necessary to justify that conclusion. While more than one property can be eligible within the same historic context, the evaluation should include a comparison with any other properties that may exist within that context. Be aware of any state or local surveys or preservation plans that could include the landscape and that might guide an evaluation. Remember to consult project managers to discuss possible avoidance measures before undertaking lengthy evaluative studies.
1. National Register criteria
An eligible historic landscape must meet one or more of the National Register criteria:
Any of the National Register criteria may apply to historic landscapes, and more than one may apply, such as when a landscape eligible under Criterion C also contains archeological sites that may be eligible under D or buildings important under Criterion A or B. Properties must be over 50 years old, or if under 50, must meet criteria for exceptional significance. Note the integrity considerations in Section B below which must apply to historic landscapes.
2. Eligibility details
If a landscape appears to meet the National Register criteria, then the following details of boundaries, period of significance, level of significance, and contributing and noncontributing features must be specifically identified and listed. Some of these details will have been developed during the identification stage, while others will emerge during the application of National Register criteria.
Historic landscape boundaries should be selected to encompass but not exceed the full extent of contributing elements, including contributing natural features. The boundaries must encompass a concentration or continuity of historic landscape characteristics which should predominate and occur throughout the landscape. Spatial organization, concentration of historic characteristics, and evidence of the historic period of development distinguish a historic landscape from its immediate surroundings. Exclude areas containing a concentration of nonhistoric features. If concentrations of nonhistoric features seriously fragment the property’s overall historic integrity, perhaps the landscape could be divided into smaller individual properties. The setting, a compatible or similar area outside the property’s boundaries, can add greatly to a landscape’s sense of place, but setting is by definition outside the boundaries. If "setting" elements are an essential component of the property, expand the landscape’s boundaries to include them, but do not include buffer zones within the boundaries.
Establishing boundaries can be particularly difficult with vernacular landscapes. A resource’s important qualities may not present distinct edges, or several different boundary determinations may be possible. For mining landscapes or archeological sites, boundaries may need to extend beyond visible surface features to include areas of underground workings or subsurface deposits. Property lines, roads, fences, changes in land use, or natural features such as streams or ridgelines can serve as boundary markers, but they must be logically defensible by use, historical association, or visual characteristics. National Register bulletins provide guidance on establishing boundaries, and Bulletin 30 offers specific direction on defining the edges of a rural landscape.
b. Period of significance
In most cases, a single period of significance should be established for the entire historic landscape. It should encompass the span of time when the property was associated with its important events, activities, persons, groups, or land uses, or when it attained its important physical qualities or characteristics. On occasion, more than one period of significance may be appropriate when a landscape contains resources dating from substantially different periods, such as when resources from an earlier and a later occupation both contribute to a property’s importance.
The period of significance begins with the date of the earliest important land use or activity of which tangible historic characteristics remain today. It ends with the date when the important events, activities, or construction ended. Continuous use or association does not justify extending a period of significance beyond the time when the property made its historically important contributions. If a specific closing date cannot be identified, 50 years ago can be used as the end date for the period of significance. Care should be taken in assigning a period of significance because it becomes the benchmark for measuring whether changes are part of the property’s history or whether they constitute loss of integrity.
c. Level of significance
Indicate whether the landscape is significant at the local, state, or national level of significance. The level of significance can reflect the landscape’s association with local, state, or national history, or it can apply to the geographic area within which the historic context was developed. For example, a landscape associated with the development of the state highway system could be significant at the state level, but if that landscape’s primary significance is its effect on the growth of a local community, the property should be found significant at the local level.
d. Contributing and noncontributing features
Contributing and noncontributing features must be identified and named, but this is not always so easy to do. Since there is more than one right way to look at landscape components, there will often be more than one way to organize, identify, and name contributing and noncontributing features. Whatever approach is used, it is important to select a logical system supported by evidence presented in the evaluation. Refer back to Section II C, above, for an organizational approach to describing landscapes.
Contributing landscape features are associated with a period and area of significance, and they possess an adequate level of integrity. Noncontributing elements were either not present during the historic period, or they were not part of the property’s documented significance, or they have lost integrity and no longer reflect historic character. As with any historic district, a historic landscape must normally contain a high proportion of contributing features, but it is possible than a landscape with a greater number of noncontributing features could be eligible. Not all features in a landscape necessarily carry the same weight. Large-scale elements frequently exert a dominant physical presence, although small-scale elements, such as individual plants, benches, signs, and planters, can have a strong cumulative effect.