6.13.25

What grows when the forest goes?

Area of the H.J. Andrews Experimental Forest in Oregon, a few years after a fire.

The activities are as follows:

The H.J. Andrews Experimental Forest, or Andrews for short, is a long-term ecological research site in the Cascade Mountains of Oregon. The forest is a temperate old-growth rainforest. It is known for its lush and green understory of flowering plants, ferns, mosses and a towering canopy of Douglas fir, Western hemlock, Red cedar, and other trees. Scientists have spent decades studying how plants, animals, land use, and climate are all connected in this ecosystem.

Matt is a biology teacher who has spent two summers in the field working with scientists at the Andrews. These experiences have been valuable ways to bring real data and research back to his students! When he visits, Matt works closely with Joe and Cole. Joe is a scientist who has spent many years working in the forest studying the impact of disturbances on plants. Cole is in Joe’s lab and has been focusing on fire’s effects on the forest during graduate school.

Historically, large, severe fires have been a part of the ecology of forests in Oregon. They typically occur every 200-500 years. Many of the plants at the Andrews Forest are those that can deal with fire. Fires clear out dead plants, return nutrients to the soil, and promote new growth of understory and canopy plants. With climate change impacting temperature and rainfall across the globe, forests in Oregon are increasingly experiencing longer periods of dry and hot weather. These changes are causing an increase in the frequency and severity of wildfires.  

On Matt’s last day at the Andrews in 2023, a lightning strike started a wildfire in a far corner of the forest. With hundreds of firefighters on the ground and several helicopters in the air, the “Lookout Fire” burned for several months, consuming about 70% of the Andrews forest! 

Plots in 2023 being surveyed for native and invasive plants to calculate the proportion that are invasive after a burn.

When Matt returned in the summer of 2024, it looked nothing like the forest he had left. The fire completely changed the course of his research experience. When he saw the scorched forest, he began to wonder how it would recover. He also observed that the fire had not burned at the same intensity throughout the forest. Some areas of Andrews were burned more, and in some spots, the fire had been less intense.  

Matt thought that some plants may do better after a severe burn, while other species might do worse. Specifically, Matt wanted to see whether native and invasive plants would show differences after a fire. Plants that have historically grown in an area without human interference are called native plants. These plants have a long history of adapting to the specific conditions in an area. When a plant species is moved by humans to a new area and grows outside of its natural range, it is called an invasive plant. Invasives often grow large and fast, taking over habitats, and pushing out native species. Invasive plants tend to be the ones that can grow fast and handle disturbances, so the team expected that invasive species would recover more quickly than native plants after high severity fires.  

It was still too early to re-enter the areas burned by the Lookout Fire, so Matt and Joe chose another recent fire. They used data collected from a section of the forest that had burned in 2020. In 2021, a year after the fire, scientists put out 80 plots that were 1m2 in size to collect data on the understory plants. 

Each section was given a burn severity value based on the amount the canopy trees had burned directly over the plot. Scientists would look up at the tree canopy and see how much was missing, and the more that was gone, they knew the burn severity had been higher. Scientists then identified every species of plant in the plots and counted the number of individual plants of each species. This was repeated every year after 2021 to observe changes over time. Matt and Joe decided to analyze data from 2023, which Matt helped collect with Cole. To answer their question, they calculated the proportion of invasive plants in each plot. 

Featured scientists: Joe LaManna (he/him) and Cole Doolittle (he/him) from Marquette University and
Matt Retterath (he/him) from Fridley Public Schools.

Flesch–Kincaid Reading Grade Level = 8.9

Additional teacher resources related to this Data Nugget:

There are two blog posts written about the Andrews LTER research featured in this activity.

  • https://lternet.edu/stories/fire-brings-new-perspectives-on-disturbance-at-h-j-andrews-experimental-forest/
  • https://lternet.edu/stories/burned-forest-bleached-reef-lter-sites-adapt-to-learn-from-disturbance/

10.24.24

A burning question

Fire crew in a woodland prescribed fire.

The activities are as follows:

Forests in the midwestern U.S. provide many important ecological services. They store carbon dioxide, which helps fight climate change. They also host a variety of plant and animal life. Forests provide spaces for recreation and support local economies through tourism.

Unfortunately, forests face threats. Climate change is causing more severe weather events, such as flooding and droughts. The spread of some parasites and diseases is also increasing as temperatures change. Forest managers are motivated to protect forest health. They can help combat these threats with their knowledge of different management practices.

Ellen and John have studied forest health in Wisconsin for decades. Ellen first became interested in nature while camping and hiking in Minnesota with her family when she was young. John became passionate about nature as a child while walking through the oak-hickory forests on his family farm. They teamed up with foresters from the Wisconsin Department of Natural Resources to examine the impact of prescribed fire as a management tool to increase forest health. A prescribed fire differs from a wildfire in that it is a planned fire that is set on purpose. When the conditions are right, forest managers will assign prescribed fires to specific areas to meet land management objectives. A lot of organization goes into prescribed fires to make sure the fire doesn’t spread or burn too hot.

Fire is part of the natural history of oak forests. They are adapted to recover quickly and they actually can benefit from fire. This is important for land managers who want to encourage the health of oak forests.

Ellen recording plant species diversity in a plot.

Oaks are considered a keystone species. This means they play a major role in maintaining ecosystem functions and the success of other species. There are two main reasons. First, they produce large amounts of acorns, which are food for many types of wildlife. Second, their canopies have more open spaces that allow light to reach the forest floor. Light is an important resource for plants, and smaller plants are limited by the shade of large trees. More light passing through the canopy allows more plants to grow below the oak trees. This increases the variety of species found in oak forests.

Ellen and John wanted to know if there were more plant species in oak forests that had prescribed fires. To answer their question, Ellen and John decided to study a part of the Madison School Forest in southwestern Wisconsin. This oak forest is special because research has been done on the impact of fire for over 75 years. In 1996, the forest was split into 15 units that have been under different management plans. One of the experimental treatments included prescribed fire at different frequencies. For example, the units in the prescribed fire treatment could have been burned every 1 to 4 years. Other units served as a control and were not burned. Comparing the control to plots that had been burned allows managers to see how often oak forests should be burned to increase forest health.

All of the management units were sampled in 1996 when the experiment first began and again in 2002 and 2007. In each sampling year, the number of plant species, or species richness, in the management units was counted. In 2023, Ellen, John, and their team resampled the plots to pick up this experiment where it was left off. This research will guide the best ways to support the health of oak forests and determine how important fire is to maintaining forest biodiversity. If fire is necessary to maintain oak forests, and oaks are a keystone species that support biodiversity, the research team expects to find higher biodiversity in plots where prescribed fire has been used.

Featured scientists: Ellen Damschen (she/her) and John Orrock (he/him) from
University of Wisconsin-Madison. Written by: Amy Workman (she/her)

Flesch–Kincaid Reading Grade Level = 8.8