Air Photos and GIS


Air photos provide useful information about land undergoing restoration. In our area of Wisconsin we are fortunate in having a large array of air photos, both historical and current.

The first air photos of Dane County, Wisconsin were taken by the U.S. Soil Conservation Service in 1937, as part of major efforts in soil erosion arising from the "dust bowl" period of the 1930s. Subsequently, air photos were taken in 1940, 1949, 1955, 1962, and with increasing frequency thereafter. At present high quality air photos are available from many sources.

Georectified air photos of Wisconsin counties are available free of charge from Wisconsinview.org. Downloads of all available 1937 air photos are available gratis from the State Cartography Office.

Geographic Information Systems (GIS)

GIS is a broad term that deals with high-level mapping of spatial or geographical information. Pleasant Valley Conservancy uses industry-standard software from ESRI (Environmental Systems Research Institute) to display our air photos, maps, and field data.

 

What does the 1937 air photo tell us?

The photo below, taken in 1937, shows the property that is now Pleasant Valley Conservancy. At that time it was part of the Lockwood farm, which was a relatively low-impact farming operation. The outlines that I have drawn on the air photo provide interpretation of the site. This photo should be compared with the management map.

The area outlined in blue is the steep south-facing slope. At that time this area was only lightly grazed or not grazed at all. The area outlined in red represents oak savanna, evident from the scattered trees. Many of the trees shown on this photo are still present on the Conservancy, but considerably larger.Characteristic patterns of trees today are very similar to those seen on this photo. However, when restoration began, all of these large trees were completely hidden by the massive amount of invasive brush and weed trees such as elm and black walnut.

Much of the oak woods on the north-facing slope remains intact today, although there are spots where logging had obviously taken place. At the time of the 1937 photo, the land along County Highway F was not part of the Lockwood farm, but was owned by farmers north of County F.

The cultivated fields are easy to see on this air photo. Although these fields are smaller today (trees have encroached), they still retain similar outlines to what they were then. All formerly cultivated fields have now been planted to prairie and have highly diverse flora.

 

The 1990 air photo: changes wrought by time and neglect

The air photograph shown below, taken by the Dane County Regional Planning Commission in 1990, provides a stark contrast to the 1937 photo.The original photo has been cropped so that only the prairie remnants and oak savannas are seen, to emphasize the differences.

In 1990 the south-facing slope was almost completely wooded, except for a few small areas of prairie remnants.

 

After Restoration: A 2007 Air Photo

The final photo in this sequence, taken September 1, 2007, shows what restoration can do. Using the 1937 air photo as a guide, we have returned Pleasant Valley Conservancy to a semblance of its original state. Of course, we have not been able to bring back "all" of the ecosystem. Many species of plants are difficult to establish, and may require many years of work. But most of the trees seen in the 1937 photo are still present today. Thus, in the 11 years of restoration work, dramatic changes have taken place. This should provide encouragement for others who might be interested in oak savanna restoration.

 

Air photos and GIS permit extensive analysis of various restoration processes. As an example:

The photo below shows the area (outlined in red) that actually burned in the North Woods burn of 10-30-2008. It was created by ArcGIS 9.3, an earlier version of the ESRI software. The red outline is a track created by walking the whole burn unit with a Garmin GPS unit. The track was then turned into an ESRI shape file.

The white outline shows an area in the woods where in the spring there is a very large patch of Trillium grandiflora. The gray line that overlaps the red outline is the mowed fire break we maintain just at the top of the ridge. It was from this fire break that we backburned to control the upper end of the burn unit. The orange line just below that is the woods road that also serves as the hiking trail for visitors.

The air photo is a larger portion of the same air photo shown just above here.