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Local Forest History: What can lasers tell us about our forests?

A snowy road winds through a mixed conifer and deciduous forest in Itasca County on Oct. 30, 2023.
Lorie Shaull
A snowy road winds through a forest in Itasca County on Oct. 30, 2023.

Dennis Kepler of the Minnesota DNR discusses how forests have changed in 40 years and how LIDAR, a type of remote imaging using lasers, is used to study forests.

The Minnesota Department of Natural Resources uses many technologies to determine the composition and status of the state’s forests. A current effort to use high-density LIDAR imaging, or light detection and ranging, to assess and map the state’s forests is underway.

Dennis Kepler is the resource assessment supervisor for the DNR’s forest management section. He joined the KAXE Morning Show as part of the “Local Forest History” series produced by Mark Jacobs to explain how the process works.

Minnesota Forest Resource Assessment

Creating a forest inventory means systematically collecting information over time to monitor forest resources.

“We collect data like tree species, diameter at breast height — which gives us some volume information and baseline information — height, and other metrics important to assessing their quality and the health of the tree,” Kepler said.

While they focus primarily on forests, they also assess some wetlands and other natural resources.

40-year changes

A map of Minnesota counties shows areas affected by emerald ash borers and quarantined in 2023.
Minnesota DNR Forest Health Team
A map of Minnesota counties shows areas affected by emerald ash borers and quarantined in 2023.

Assessments include remotely sensed data, such as aerial photography, satellite imagery and other data such as LIDAR.

The team performs a variety of assessments, including the Forest Inventory Analysis Program. This is a national program that tracks changes in specific plots over time: the program began in the 1930s and covers the continental United States. The plots are measured every five years.

Over the past 40 years, results from these assessments have shown that Minnesota’s forests are growing by about 1% each year — from 16.5 million acres in the 1970s to over 17 million acres currently. Statewide, the forests are getting older, particularly on private land.

Species are changing as well, due to climate factors and invasive species like the emerald ash borer. Birches are declining, and the species composition and ranges of oak and maple species are changing. However, Kepler is not sure which trends will continue.

“I don’t like to predict, and I don’t really want to predict,” he said. “ ... Given time, everything changes. That’s one factor in our life that’s always constant, right, is change. And the forest is changing as well.”


A key tool in the Forest Resource Assessment team’s arsenal is the use of LIDAR. This tool uses a pulsed laser to send out millions of pulses of light per second and determines how long it takes for the signal to return. When these measurements are combined with the sensor location, a map is created detailing the height and shape of the landscape.

In a forest, LIDAR can provide information on the volume of tree material, what size class of trees are present, and what cover type exists.

In the early 2000s, the team conducted a low-density LIDAR analysis of the state. This process created a low-resolution digital elevation map of the state, with each pulse of light mapping one square meter. The next phase, which will be completed in the next few years, is to generate a higher-resolution map with 30 pulses per meter: this map would provide details not seen before.

Critically, these maps can be overlaid with digital photography, satellite imagery and other geographic information to study things like wildlife habitat or water resources.

Private landowners

The Forest Resource Assessment team is currently recruiting private landowners to participate in forest research. Private lands comprise a large portion of Minnesota’s forests, but these forests are underrepresented in forest assessments. The DNR is partnering with local soil and water conservation districts and the Minnesota Forestry Association on the project to designate plots on private land to improve forest modeling for all landowners.

For more phenology, subscribe to our Season Watch Newsletter or visit the Season Watch Facebook page.

Funding for this project was provided by the Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources (LCCMR).

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Charlie Mitchell (she/they) joined the KAXE team in February of 2022. Charlie creates the Season Watch Newsletter, writes segment summaries for the website, and coordinates our Engaging Minnesotans with Phenology project. With a background in wildlife biology, she enjoys learning a little bit about everything, whether it's plants, mushrooms, aquatic invertebrates, or the short-tailed shrew (did you know they can echolocate?).