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Analysis of Viticultural Potential along the Niagara Escarpment in Wisconsin

Updated on December 16, 2015
Final result of project is the above map that shows potential for viticulture in East Central Wisconsin.
Final result of project is the above map that shows potential for viticulture in East Central Wisconsin.

Introduction

This project stems from a summer internship in which I looked at viticultural potential in Calumet County,WI. Results of that study indicated that the Niagara Escarpment Area did indeed have the most suitable “terroir” for grape growing in Calumet County. I wanted to extend the analysis along all of the Niagara Escarpment to see if the trend would continue. I have analyzed the area using ArcMap and a list of requirements necessary for establishing terroir. For me, terroir is a combination of all of the factors that go into growing excellent grapes including soils, geology, and climate. In my quest to find potential terroir inWisconsin, I have found many reasons to strengthen Wisconsin’s wine industry.

There is some question about how the upcoming climate change will affect the U.S. wine industry. A paper published by Proceedings of the National Academy of Sciences (2006) stated that by the year 2100, 81% of our premium wine grape areas could decline. Scientists attributed the decline to the increased frequency of extreme hot temperatures. However, this study only looked at premium wine grapes such as Cabernet Sauvignon, Merlot, Chardonnay, and Pinot Noir. There are many small wineries opening all over the United States, and there are quite a few vineyard owners experimenting with new varietals in hopes of finding wine grapes that are ideally suited to their area. There are already successful vineyards located in Wisconsin, and it seems that grape variety is the key to success.

A crop of prime quality grapes can bring in much more income than conventional crops. Farmers all over are losing money and many of them are resorting to selling their land to developers. This practice causes urban sprawl, lowers our potential food productivity, and increases demand for transportation of food. Growing wine grapes is a feasible alternative to “growing houses” because the crop is amenable to using sustainable agricultural practices and offers farmers the opportunity to create a product (bottle of wine) that is very profitable. Another concept that may work in the farmer’s favor is that of agritourism. A vineyard/winery would attract tourists and bring income to the rural area.

Methods

The methodology for my project is designed around another study that I came across. John D. Boyer from Virginia Polytechnic Institute and State University did an analysis of viticultural potential in Virginia. His analysis was initially based on climate and was much more complicated because it included all of the microclimates in Virginia (due to the elevation differences found there). After finding regions that have good climate, he then concentrated on the physical aspects of the land. Similarly, my summer project to do an analysis of viticultural potential for CalumetCountywas first an examination of the climate in the area. I will refer you to Potential for Commercial Viticulture in Calumet County, WI for a complete description of variety choice and climate methodology. The Niagara Escarpment area is part of the same climate region as Calumet County, so I am able to move ahead and analyze land characteristics that offer the best conditions for wine grape growing.

The characteristics I chose, in order of importance, are: land use (only agricultural land was included in the analysis), soil drainage, depth to groundwater, soil composition, depth to bedrock, slope, and slope aspect. Everything that I have read emphasizes the fact that grapevines need good drainage. Also, since grapevines will not last long in standing water and a vineyard represents such a large investment, I added twice as much value to soil drainage and depth to groundwater in the final suitability equation (explained below). Soil composition by particle size indirectly affects the flow of water and the capacity to hold it. It is quite important but was not given weight because grapes are somewhat forgiving to physical soil composition. Also, it seems that with the exception of the Niagara Escarpment outcrop, soil depth to bedrock in Calumet County is consistently greater than 60 inches, sufficient for growing grapes. Slope was included in the analysis because of increased water drainage, air flow, and sun exposure. Slope aspect is not a limiting factor, but in the right direction, it can increase solar radiation enough to ensure ripening of the fruit. The NRCS and USGS websites on the internet supplied data for the project, and ArcGIS software was used to bring it all together.

Soils data provided access to soil type polygons. It was possible to look up characteristics of each soil type using Web Soil Survey through the Natural Resources Conservation Service. To determine soil drainage, I used the drainage class listed for each soil type. Finding soil composition was a matter of looking up percent clay and percent sand for each soil type and classifying it into groups labeled excellent, fair, and poor. An excellent soil composition would have close to a 1:1:1 ratio (~30%) of clay:sand:silt. A poor soil would have more than 50% of one component or less than 25% sand, 15% clay, or 5% silt. A good soil would be anything in between 25-30% or 40-50% sand, 10-25% or 36-50% clay, and 10-25% or 36-50% silt. The soil depth information was already categorized. Depth to bedrock was either less than or greater than 60 inches and depth to groundwater was less than 2 feet, 2-6 feet, or greater than 6 feet. Each category received a score between 0-5 that corresponded to the requirements of the grapevine. I created a table in Excel for each county that included the scores for all of the land characteristics. This was the quickest way to join the table data to the existing attribute tables for each county, making it possible to easily categorize the soil polygons for making maps.

Slope and aspect data was provided through topographical data from the USGS. ArcGIS has an extension that allows both types of land information to be converted from Digital Elevation Models (DEMs) of the area. The DEMs were separated by county (some counties had two DEMs), so when it came time to run the suitability analysis, it was important to make sure that each area was classified the same. Percent slope values were scored as follows: 0-2.49% =1, 2.5-4.99%=2, 5-7.49%=3, 7.5-9.99%=4, 10-12.49%=5, 12.5-15%=4, and anything over 15% was given a score of 1. Aspect values were scored accordingly: flat=1, N=1, NE=2, E=3, SE=4, S=5, SW=4, W=3, and NW=2. The weighted sum tool in the spatial analyst extension for ArcMap layered all of these scored characteristics (including the double weight on drainage and depth to groundwater) and put them into an equation that resulted in a map that ranks areas (pixels) as most suitable to least suitable. It was necessary to merge each slope layer as well as each aspect layer for the counties with more than one DEM before proceeding with the analysis.

Results

Each of the land characteristics were mapped separately (see above). Soil depth to bedrock was deep enough for the most part, but in Door County there were very shallow areas with a low score that would not be suitable for grapevines. In other areas, the depth to groundwater was quite shallow (pale green) and those areas were scored accordingly. Overall, many areas in this part of Wisconsin have very good drainage.

It was important to be able to classify all of the counties in the same way. Out of a possible 45 points, the scores ranged from 7 – 45. Anything that scored below 20 was eliminated from consideration and the rest of the ratings were as follows: 21-30 was classified as least suitable, 31-35 was moderately suitable, 36-40 was considered quite suitable, and 40-45 was most suitable.

Conclusion/Discussion

Results for all of the counties did not follow the trend that I expected. The areas around the Escarpment in Fond du Lac, Dodge, and Calumet counties were well-suited to wine grape growing. Also, there were some well-suited areas in Outagamie, Kewaunee, and Sheboygan counties that are not associated with the Niagara Escarpment. The thing that surprised me most was that there were so few well-suited areas in Brown and Door counties. Brown County’s scores ranged from 7 to 42 and the average score was 28 with the majority falling between 30 and 35 (moderately suitable). It seems that low scores in Brown County reflect the depth to groundwater and soil composition scores. Door County scored from 15 to 38 with an average of 29. The majority of the areas scored between 28 and 32, classified as least suitable to moderately suitable. This is mostly due to low soil depth scores. Unfortunately, the few areas that were considered quite suitable for grape growing in Door County were pixel size and it is difficult to see them on the map.

Starting a vineyard is a large investment with no guarantees. Analyzing the suitability of an area before planting can reduce some of that risk. Each potential site must be physically examined and other factors such as soil chemistry should be taken into consideration before planting vines. It is best to site vineyards in an environment in which it will have the proper conditions so that the grower can practice sustainability. However, I do not intend to criticize areas that are not marked as “potential grape growing sites.” After all, amendments can be made to soils that could turn a moderately suitable area into a quite suitable area. Nevertheless, if a grower is considering sustainable agriculture, this type of information would be valuable for any proposed crop.

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