Farming Magazine - July, 2011


Features: Technology and Trees

Logging, GIS mapping and forest management
By Patrick White

The forest has officially entered the computer age. Or, more accurately, the computer age has entered the forest. Thanks to powerful GIS (geographic information system) mapping technology, forest management plans can now be made more accurate, more comprehensive, more versatile and more understandable for woodlot owners.

GIS mapping can be more accurate, and easier to update, than a traditional paper map. This technology helps foresters in creating management plans, aids loggers during harvests, and benefits landowners who want to better understand and utilize their woodlot.
Image courtesy of Calfee Woodland Management.

"GIS is basically a number of different map layers that you can work with," explains Mike White, a forester with Calfee Woodland Management ( in Dorset, Vt., who has worked extensively with this technology. "You can stack layers of maps - and data layers - on top of each other, and they're all geo-referenced." The map layers can be integrated or viewed separately, depending on what type of information is desired. Basically, that means that, with the click of a button, it's possible to view a map that accurately shows the locations of property boundaries, wetland areas, woods roads or any number of other features. Or, you can view any combination of these features together, along with detailed data about each.

In GIS forestry mapping, aerial photography is generally used as the base map. "If I'm doing any mapping, I start by pulling up the aerial photography. We also use USGS topographic maps and some other imagery available from either the federal or state government," White explains. "Standard aerial photography is black and white, and taken in the spring before the leaves come out. In the last 10 years or so, the federal government has been taking images during the summer as part of the National Agricultural Inventory Program; we call these 'leaf on' images. They're in color, and they're a great resource, as well." He adds that there are also satellite images, but those are used more in large-scale - looking at an entire state or region - analysis rather than at the smaller woodlot scale, where accuracy would suffer.

"We use the aerial photography to aid in our on-the-ground assessment of a woodlot," says White. "For a new property, I start by making a GIS map on the aerial photography base, and another on the topographic map base." These maps may include features such as property boundaries - available electronically from town tax maps or surveys - as well as the locations of streams, town roads, deer yards, wetlands, etc., which are sometimes available from state agencies. The accuracy of all of this information can vary widely and must be checked in the field, he cautions.

"I integrate the GPS [global positioning system] component, as well. In the GIS program [Calfee Woodland Management uses ESRI ArcView GIS software] I make GPS reference points along the property boundary and on the interior of the property for navigation, as well as locating my forest inventory plots, typically arranged as a grid on the property," White explains. After making those reference points on the computer, White uploads the data to a hand-held Garmin GPS unit. He also prints out copies of the maps he's produced on both the aerial and topographic imagery. "Then, when I'm out on the ground, I can keep oriented," he explains. "When I'm out in the field, I can see where I am in relation to the GPS reference points." Before integrating GIS and GPS, field work was completed using a compass and pacing. Technology has sped up field work and increased accuracy, White observes.

While he's in the woodlot, White is writing additional notes, as well as lines, points and polygons indicating streams, woods roads, hiking trails, etc., on the maps. "I take stock of any of these features that didn't show up on the data layers I previously had, and any other feature I want to add or that the woodlot owner might be interested in: cliffs, wetland areas, etc." Although foresters are interested in many features on a woodlot, when forest management is the goal, the most fundamental are the various forest types, or stands, on a property, says White: "A stand is a group of trees of similar species, composition and age. Forest management is typically carried out at a stand level, and GIS makes the delineation of forest stands much easier."

White also usually takes GPS coordinates from at least a couple of different property corners to check the accuracy of the tax map information that was used initially. Calfee Woodland Management also has used GPS and GIS technology to create trails maps for landowners. White says he even takes GPS coordinates of individual specimen trees on occasion. "A little while back I came across a beautiful 23-inch-diameter elm tree - due to Dutch elm disease, we don't have many large elm trees left, so I took a geographic note of that," he explains, with the intent that he will revisit the tree in the future to see if it stays healthy. "When mapping, I always look for things that are out of place, rare or interesting."

Back in the office, White combines any GPS points he's collected in the field, along with the notes he's made on the maps, and adds this information to the GIS file for that property. Each type of data becomes another layer on the overall GIS map. For Calfee Woodland Management, the final product is usually a forest management map - a document that depicts the different forest types and stands on a property, and shows important natural and man-made features such as roads, cliffs, streams, stone walls, fences, cellar holes, landings and so on. "The management map is a document that works to supplement the management plan," he explains. "For example, there may be features in 'Stand 1' that you talk about in the plan, and it is important that these features be depicted on the map so they can be easily considered when executing management activities in the future. For instance, there may be steep areas and wet ground that limit access for logging; you want to be able to see that on the map."

In fact, some of the information that makes up the forest management plan can be incorporated directly into the GIS map itself. "One of the other main tenants of GIS is that each feature depicted on the map has (or can have)<0x202F>attribute data associated with<0x202F>it," says White. "It can be simple, such as identifying a forest stand, stream or road with a name or size,<0x202F>or it can be a<0x202F>bit more complex. For example, including forest statistics, such as basal area, mean stand diameter, species composition, timber volume, date of last harvest, etc., for a given forest stand." These data are stored in attribute tables that open as spreadsheets in the map, or the data can be pulled up by clicking on a specific feature on the map. The data can be searched, ordered and processed, allowing for analysis.

"Another function the GIS data allows me to do is accurately calculate acreage of the overall property, or of different stands and features. It also provides the ability to measure distances or the lengths of features, which is a very powerful tool," White explains. "Much of what is done in forestry involves knowing the size, length or distance of different features, and GIS makes these measurements very easy."

White says his goal is simply to use the technology to create maps with the degree of accuracy and data analysis required in forest management. "Field foresters only scratch the surface of the capabilities of GIS," he explains. Others, such as research foresters and policy foresters, tap in to more of the analytic power of the software. As more foresters use GIS, the forestry-specific capabilities and features of the software will undoubtedly increase. Some people in forestry probably use it to a much greater extent than we do, but in general the work in our field is pretty basic in relation to what is possible with GIS," he explains. With all the power and precision of GIS technology, it can be tempting to try to do more with it than is needed for basic forest management applications, he adds.

While much of the information on the GIS map is collected and analyzed by and for foresters as a management tool, a number of other parties also benefit from this data. For example, many of the maps prepared by Calfee Woodland Management are done to satisfy requirements of the state's use appraisal (current use) program. Maps also are provided to loggers in the event of a harvest. "We would make a more specific map for a harvest," says White. "The overall property might be 120 acres, but we can zoom in and create a map of a 50-acre harvest area to provide more details on the map. We would include certain layers showing wet or steep areas that should be avoided during harvest, for example. I think they appreciate the map because it helps them to navigate through the stand."

One thing the GIS map does not do is substitute for a survey or for marking the unit boundaries on the ground for a timber harvest, especially if it's a property line, White stresses. "The GIS map is not a survey, and all the maps we produce state that clearly on the map. You can't assume that the map is completely accurate, and you can't assume that the user will interpret it accurately." The accuracy of the map is dependent on the accuracy of the initial data used, as well as the accuracy of the additional data collected in the field during the process, he states.

Of course, the GIS maps are also available to the woodlot owners. Even if they aren't experienced at reading maps, woodlot owners appreciate the easy-to-visualize nature of the GIS maps. "I think the landowner values the map as much, if not more, than they do the management plan. It's easier for them to interpret," says White. "We can even make a map for the landowner that includes the aerial photo base, and they really like that. They can see their house and where fields and forests are." In fact, he points out, there is a free software tool called ArcExplorer available from the same company (ESRI) that provides the ArcView software used to create the map. This limited-function software allows interested woodlot owners to view and change the appearance of the GIS maps on their own computer, if they so desire.

Perhaps the most lasting benefit of utilizing GIS technology in forest management is the fact that the data remains, and can easily be accessed and updated, well into the future. "In addition to being generally more accurate than a paper map, GIS maps can be edited much easier. If the landowner acquires more land or sells land, or something on the property changes, those changes can be made very easily to a GIS map," White points out. "Once the data is in the computer from creating the forest management map, it's possible to make subsequent maps, such as harvest maps or a trail map or enlargements of select areas, fairly quickly and easily. It's much harder to update and make new paper maps."

Creating a GIS map is not a one-time act; it's the beginning of a process that can aid in forest management for years to come. "A key component to forest management is a management map. So you need a map," says White. "It's a good investment to go with a computer-based map, because it can be more accurate, and you can more easily make changes and additional maps that might be useful down the road."

Patrick White is a freelance writer based in Middlesex, Vt. Over the past 10 years, he has covered a wide range of agricultural operations around the Northeast. He is always on the lookout for unusual stories and cutting-edge installations. Comment or question? Visit and join in the discussions.