But let's talk specifics. Looking at satellite images of the Hemlock Forest area I noticed that there are some odd looking parallel formations present in one area of the forest. You can just make them out in the image from Google Earth (Image One). What are they? What process created them?
Viewed in Google Earth I couldn't see enough detail to come up with a plausible explanation for what the lines represent or how they were created. But, for locations in New York State, other options exist including the very high resolution orthoimagery available from the New York State GIS Clearinghouse (NYSCG). Orthoimagery is a fancy name for aerial photographs; pictures taken from airplanes using high resolution cameras and techniques that minimize distortion. When you take pictures of the earth from a satellite the distance between the satellite and the ground pretty much ensures that the camera is at a right angle to the ground. So there is little or no distortion of the image. When you take those same pictures from an airplane, if the camera is not perfectly parallel with the ground, the images are distorted.
The imagery available from the New York State GIS Clearinghouse (NYSCG) covers (nearly) all of New York State and is available to the public via the NYSGC website. The catch is that there are thousands of files and they are big files. And, once you find the right images, you need a way to view them. These images are geo-referenced meaning that using the right software you can view the images and they will line up correctly with other map-based data layers. The software you use is commonly referred to as GIS; an acronym for Geographic Information System. Loaded into a GIS these geo-referenced images can be analyzed using a variety of methods. They can also be used to provide a base layer on which you overlay other data. This is much like what you do when you view satellite imagery in Google Earth and then add points or lines or outlines (polygons) on top.
The Hemlock Forest orthoimagery (Images Two and Three) (viewed using Quantum GIS) reveals a lot more detail and those curious lines now take on a distinctly man-made look. Particularly telling is the track that comes in from the left and crosses the formation (Image Three). They look like tire tracks but when taking measurements in the GIS I found that the lines in main set are about 50 yards apart. That made me think that they might be ditches created using a tractor or bulldozer. It is also more apparent from the orthoimages that the formations are filled with water. The dark color seen in the formations is the same as the color of small ponds and streams present in nearby areas.
Still, I had to wonder why someone would create ditches -about 50 yards apart- through the forest at this place. That left only one solution: field trip. From the Hemlock Trail parking area twenty minutes by trail and another half hour winding my way through the swampy forest brought me to the place pictured in Image Four. This, clearly, was one of the ditches seen in the orthoimagery and it was also immediately apparent that these are ditches that someone dug.
The ditches are roughly 50 yards apart and run in straight lines through the forest for two to three hundred yards. What was not apparent from the aerial imagery is that the area where these ditches are found is very flat and very swampy. A few larger and older trees are present but most of the trees are roughly the same size (and age). Based on the size of the trees I estimated that this area was probably in use for some type of farming 50 years ago.
But something was still missing. The surrounding areas were all clearly used for agriculture in the past but this area is very wet and it is surrounded by swamps. My visit took place in late November and it had been generally dry, and even so, every depression in this area is filled with water. During wetter parts of the year this area would likely be flooded. The trees that are present are types that you find in a hardwood swamp or floodplain forest.
However, after poking around a bit more, a possible explanation appeared. One of my interests is in how invasive species compete against native species so I'm always on the lookout for invasive plants and trees. And I noticed the presence of a number of small, stunted, trees interspersed among the common species. Being late November, with the leaves down, I couldn't tell right away what those trees were. Then, one of them gave up its' secret, on a branch I spotted a small apple. The stunted trees are apples trees and now I could see that someone had tried to drain the area to create an orchard.
It appears that that plan did not work out very well. Apple trees prefer well drained soil and perhaps the farmer was unaware that this area is notable for lying over a layer of impermeable clay. Not too far away that clay, combined with the nearly flat topography, has produced a type of wetland known as a "perched" swamp. A perched swamp is a wetland where the water on the surface is not connected to the local water table but where the drainage is so poor that you get a swamp anyway. In most swamps the water level rises and falls along with the local water table but this is a place where the water doesn't drain through the soil and runoff is slow or non-existent. Creating an orchard here was never going to be easy. Which may be why we now have this wonderful little wild area to explore and enjoy.
Resources:
New York State GIS Clearinghouse Orthoimagery
