Base Maps

In earlier posts I introduced the Hemlock Forest area and I talked about why I want to understand how ecological communities are changed when non-native species become fully established (look back at those previous posts for the details). I've also said that anyone with motivation can acquire and contribute valuable scientific data. What I have not talked about is what data you might get and how you might get it. The what and how will vary based on your interests but the thing I can do is to describe my project in detail. If you extrapolate from there.

As for the "what" you have to start with a question; something that interests you. I want to understand how non-native species alter existing ecological communities and species assemblages. My thinking is that in many cases these aggressive non-native species are not going away. They are here to stay. So, at what point do the invaders alter previously existing communities to an extent that a new community type is present. Most importantly, are those new assemblages of species more or less fit in terms of their capacity to provide ecological services and to resist future disruptions. It's commonly held that the general reason invasive species are so successful is that predators and pathogens that co-evolved with the invader are not present in a new locale. That is certainly part of the story but I wonder if some species are in effect "generalists" able to dominate where ever they are found. Take Japanese Knotweed for example. Once established, you can repeatedly mow a stand of Japanese Knotweed off at the ground for several years running and it will grow back with vigor as soon as you stop. And, if you are not paying attention, it will spread to surrounding un-mowed areas via rhizomes. Eventually you can kill it by depleting the energy reserves present in the roots, but Japanese Knotweed is one tough plant. Human activities have increased the speed at which plants like Japanese Knotweed are dispersed but it seems possible that this plant has evolved strategies that would allow it to spread far and wide on its own. We need to better understand how these aggressive generalist species operate because it seems likely that they will eventually be present globally where ever there is suitable habitat.

Back to the project, the first thing I want to know is which communities are present and where they are located. This is the easy part for me because my interest in this has emerged from working with geographic information systems (GIS). A GIS allows you to place your data into a geographic context. Using a GIS you can visually look for patterns in the distribution of the phenomena of interest. Going further, there are a wide variety of analysis techniques you can use to learn more about the phenomena as represented by your particular set of data. In short, I am starting the project with the creation of a GIS.

The first thing you need are base maps. As a term, "base-maps" doesn't have a distinctly defined meaning. It refers to whatever map layers are needed to put your data into a geographic context. These days we can download a wide variety of base-map layers from the Internet. Believe me, it didn't used to be that easy. And, if you are working outside of the United States, it might still be a major undertaking to get the base-map layers that you need. For my project I'm starting with a raster base-map layer created from a USGS topographic map. The USGS refers to these as digital raster graphics or DRGs. I'll be writing about where you can get map layers of various types in future posts but, for now I'll let the images tell the story.

A digital raster graphic (DRG) base layer showing the hemlock forest. The red line delineates the boundary of the land that is included in the Saratoga Spa State Park. The orange line shows the marked trails coming from the parking area on Crescent street (upper right in the image). Notice that in the lower left portion of the image the red boundary line does not follow the boundary visible in the underlying DRG. The boundary line was digitized from a map of the State Park and there is a slight discrepancy between the two sources. This could be the result of the two sources using different surveys or it could be a cartographic discrepancy coming from differences in the scale and accuracy represented by the two different sources.

I have also acquired aerial imagery of the Hemlock Forest Area; orthoimagery made available for public use by the New York State GIS Clearinghouse (see the Mystery Lines post for more information on this imagery source). The images are geo-registered and line up pretty well with the underlying topographic map layer. My data will be layered on top of the background provided by the DRG and the orthoimagery and I've started by creating a layer containing the park boundary and the state maintained trails present in the forest.

Image Two: The Hemlock Forest aerial image base layer with park boundary (red) and trails (orange) superimposed. Many details emerge from this view of the forest. For one, the old growth hemlocks that provide the area's namesake are easily seen clustered in the area circled by the upper trail loop.   

My interest is in ecological communities so I need to know what communities are present and where they are located. That information is available in a map published along with the Spa State Park Master Plan released in 2009. The ecological communities map is provided as an image in a PDF file. You can't add this PDF to the GIS directly but I was able to take the image and register it with the base maps in my GIS. I'll document the process used to do that in a future post but images three and four show the results A key feature of the GIS software is that it allows you to control the level of transparency used to display each layer.

Image Three: The ecological communities map registered in the GIS. I grabbed the image from the PDF using standard screen capture software. The screen capture was saved to a JPEG format image file. That file was added to the GIS and registered with the base-map layer. As seen here, the ecological communities layer is displayed as a non-transparent layer; you can't see through it but you can see the base layers around the edges. The boundary and trail outlines are visible because that layer is displayed on top of the eco-communities layer. Each colored area represents a different community type and the zones can be interpreted using the legend found in the original document. 

Image Four: The same map with the eco-communities layer set be partially transparency. Now we can see through the eco-communities layer to the underlying imagery. Using the GIS in this way each additional layer provides more information and seen in combination patterns that were not previously visible become apparent.

There's one more layer that I need for may base layer set. That is a layer of just the outlines of the community zones created in a way that will allow a database table row to be linked with each zone. This linkage between map objects and data is what GIS is all about and this capability will provide the basis for future analysis. I created the layer by "hand digitizing" the ecological community image; essentially I traced the outlines of the zones using tools provided in the GIS. The window seen in Image Five shows data associated with the object selected in the map (the blue area in the center). I'm just getting started, so I have only a couple of columns in the database table. But now that the linkage is in place I can add more columns as I need them.

Image Five: The complete base-map set from the GIS. The black outlines are the zonal boundaries for the various ecological communities identified in the Spa State Park master plan. Each outlined object is linked to a row in a database table. This allows the map representation of each ecological community to be associated with whatever data we want to capture.

Reference and Resources:
The Spa State Park Master Plan Eco-communities map