Agriculture

Land within the four suburban counties (Bucks, Chester, Delaware, and Montgomery) was evaluated for agricultural use. Philadelphia was not evaluated for agricultural purposes, owing to the absence of large-scale agriculture within the City limits. Only 300 acres of land within the entire City are in agricultural use.

Using the available agricultural data universal to all four counties, GIS maps defining the most important agricultural areas were created. Development of the maps and weighting of the data were done with the assistance of an advisory group, with representation from agriculture, land conservation, GIS, and land use professionals. Consensus was developed in numerous areas, ranging from the definition of important agricultural lands in this region to the determination of specific agricultural prioritization weights.

Layers

To prioritize land in the region for its agricultural value, a cell-based (raster) modeling technique was used, in which an invisible mesh of cells was overlaid on each of five unique GIS data layers. Each data layer consisted of a grid of 30-square-meter cells. Each cell in each data layer received a score and then the five data layers were weighted and combined to create a final cumulative score for each cell. The five data layers that make up the agricultural component of the report include the following: (weighting was determined through consensus of the advisory group.)

• The presence of prime farmland and soils of statewide importance, as defined by the Natural Resources Conservation Service (NRCS) and the State. This layer determined 35% of each cell's total value.
• Land in agricultural use, as defined by DVRPC's 2000 Land Use Data. This layer determined 24% of each cell's total value.
• The size of contiguous agricultural soils. This layer determined 18% of each cell's total value.
• The proximity to existing protected lands (conservation easements, agricultural easements, parklands, and fee-owned protected lands). This layer determined 15% of each cell's total value.
• The percent area of each township within Agricultural Security Areas (ASAs). This layer determined 8% of each cell's total value.

Once the value of each cell within each data layer was defined, each cell value was multiplied by its overall layer weight and divided by the highest cell value to determine the final cell score (as shown in the tables below). The five weighted data layers were then added together in GIS, with a perfect cell score totaling 100 points. For example, a cell could receive 35 points because it had federally designated prime soils, 24 points because it was in use as farmland, 18 points because it was near other areas of prime soils, 15 points for being near protected lands, and 8 points because a large portion of the township was located in an ASA, for a perfect cell score of 100 points.

Detailed Layer Descriptions

The following is a description of the five data layers, the method used to develop cell scores for each data layer, and layer weights. Maps were created for each layer, although the individual layer maps are not displayed within this report.

Layer 1: Prime Farmland and Soils of Statewide Importance

Prime and statewide important soils are the most critical criteria used to identify priority agricultural lands. The prime agricultural soils were obtained from the United States Department of Agriculture/NRCS "Soils Survey Geographic (SSURGO) Database." Also within those data were soils defined by the Pennsylvania Commonwealth as having statewide importance. The database defines prime farmland and soils of statewide importance based on individual soil types. Cells containing prime farmland were given a score of 2 and cells containing soils of statewide importance were given a value of 1. Lands with a value of 0 indicate no significant soil types.

Layer 2: Agricultural Land Use

DVRPC created the agricultural land use GIS layer by analyzing aerial photographs that were taken in March through April of 2000. Agricultural lands were defined by DVRPC as:

"... land devoted to crops, pastures, orchards, tree farms, or other agricultural uses. The farmstead and associated buildings are also agricultural. Single- or double-lot splitoffs with house are included in the agricultural classification."

These lands are important because they are currently being used for agricultural purposes. Land within areas of agricultural use received a value of 1, and land outside areas of agricultural use received a value of 0.

Layer 3: Contiguous Prime Agricultural Soils

It is necessary for farmers to have contiguous masses of farmland. Large areas of farmland make it economically feasible for nearby businesses that support agriculture (such as seed, fertilizer, and machine shops, etc.) to be sustained. Accordingly, the next important step was to define and identify contiguous masses of farmland. This was done in GIS using two processes. First, a command called "RegionGroup" was performed in GIS to identify each contiguous patch of farmland. Second, a function called "ZonalArea" was performed to calculate the area of each contiguous space. The output is in square meters and is converted to acres by dividing the layer (grid) by 4,042. The final values range from 0 to 6, based on the acreage.

Layer 4: Proximity to Protected Lands

Keeping in line with the idea of maintaining unfragmented landscapes, points were awarded to agricultural lands that abut existing land trust owned and eased lands, preserved farmland, and publicly owned lands. To create this layer, PEC provided land trust owned and eased land data, and DVRPC provided preserved farmland and public land data sets. The data sets were combined to form one layer. This new layer was converted to a grid and a straight-line distance measure was applied to determine the distance of each non-protected land cell to the nearest protected land cell. Final scores ranged from 1 to 5, based on distance to protected land as described in the following table.

Layer 5: Percent of Township within an Agricultural Security Area

Landowners in many townships have the opportunity to join a local Agricultural Security Area (ASA). By being part of an ASA, the landowner adds a layer of protection from litigation caused by sight, sound, and smell issues associated with farming operations. Farms selling their development rights through their county agricultural preservation program must be in an ASA. Therefore, it was determined that higher priority should be given to lands in municipalities that have a high percentage of their land area In an ASA. Scores were assigned to each cell within a municipality according to the following table.

Putting It All Together

All five base layers were weighted as above and added together. The total cell scores were then reclassed into ten quantiles (i.e. ten groups of the same number of cells) and the cells within each quantile were reassigned a value from 1 to 10 to create a composite map that prioritizes all land for agriculture within the four-county region. In other words, one tenth of all land in the four-county region scored a 10, one tenth scored a 9, one tenth scored an 8, etc. After the data was reclassed, developed land, protected land, and areas of open water were removed and these cells were assigned a value of "no data". The resulting map shows areas that scored higher than the median (6-10 points). The higher the score, the deeper the shade.

The following highlights emerge from the analysis:

• Of all lands in the four-county area, 350,000 acres are rated as high value (8, 9, or 10 in the ranking process). This figure includes lands that are already protected or developed.
• Removing developed lands leaves 283,000 high value acres.
• Of the total four-county acreage (1,318,000), 361,000 acres are in agricultural use.
• Of the 361,000 acres in agricultural use, 240,000 acres, or 66%, are high value.

High-value agricultural lands are found across the region. See Map 2: Agricultural Open Space Priorities. In central Bucks County, high-value lands are found primarily in Upper Makefield, Wrightstown, Buckingham, Solebury, Plumstead, Bedminster, and Hilltown townships. In the extreme northern reaches of the county, a sizable area of very high-value lands lies in Durham and Springfield townships. Montgomery County's high-value lands are scattered throughout the upper third of the county. By far the region's largest concentration of high-value agricultural lands is located in southwestern Chester County, primarily in East and West Marlborough, Upper and Lower Oxford, London Grove, Penn, Londonderry, and West Fallowfield townships. Additional high-value lands are scattered throughout the upper third of the county. A small concentration of high-value lands can be found on the Delaware/Chester county border In Newtown, Edgmont and Willistown townships.

While all this is good news, much valuable farmland is in the path of development, and accordingly, its survival as farmland is threatened. Because contiguity to other agricultural lands is important for farming, protection efforts should focus on preserving the larger concentrations of high-resource-value agricultural land.

Notes and Comments

• Agriculture on a small scale, such as vacant lots, backyards, and small cooperative ventures, was not evaluated and in most cases does not show on the grid, yet is recognized to have value.
• Tax parcel data would have been useful. However, these data were not available across the region.
• NRCS soil coverage in some counties may be updated shortly, and when that occurs, the revised data should be used.
• There is good potential for prioritization modeling at the county level to assist agricultural preservation efforts for local land trusts and County preservation programs.