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Tackling Challenges in Forest Regeneration

Engineering Plants to Respond to Drought and Wildfires

Article by Kelsey Evans, CNR Editor


Seedling mortality in reforested areas following fires, harvesting or disturbances is posing a challenge to reforestation researchers.

“We’re seeing increases in intensity and duration of droughts across the West, and it’s connected to climate change and wildfires,” said Andrew Nelson, director of Center for Forest Nursery and Seedling Research (CFNSR) and Franklin H. Pitkin Forest Nursery, and the Tom Alberg and Judith Beck Endowed Chair of Native Plant Regeneration.

In response, the Pitkin Nursery is conducting research and building new greenhouses to optimize growing environments for reforestation seedlings. They are increasing the quality of seedlings produced and training students on modern greenhouse technologies.

We’re seeing a transition away from the traditional Styrofoam block containers, which often end up in landfills, towards Earthpots. Andrew Nelson, director of Center for Forest Nursery and Seedling Research

 “Reforestation efforts are futile if seedlings die along the way,” Nelson said.

One of U of I’s research tactics is nursery drought preconditioning, which challenges seedlings in the nursery with drought conditions by reducing irrigation at various times of their growth. This alters the physiology and morphology of the plants.

“We’re training and engineering the plants to recognize and better withstand drought in the forest. We can optimize nursery conditions to match the environmental conditions,” Nelson said.

Vovener de Verlands Edmond, a second-year doctoral student, said his background working with vanilla plants while obtaining his master’s in horticulture sciences at the University of Florida informs his research on horticulture practices at U of I. Edmond received his bachelor’s in natural resources from the State University of Haiti.

At U of I, Edmond has done experiments exposing different seed sources of plants to various watering regimes.

“Drought exacerbated by climate change can have a fatal effect on seedlings, often close to 80%, because of the lack of moisture, high temperature, etc. By understanding how seedlings respond to drought, and how to optimize conditions in the nursery, we can provide information and instruction to nursery managers to help widescale forest regeneration,” Edmond said.

At U of I, the focus is on native Idaho conifers including Douglas fir and western larch. Results are promising thus far. For the western larch, changes in plant physiology, including growth rates and the ability of the plant to transport water, have been significant.

“When we challenge the seedlings with severe drought conditions in the nursery, afterwards, when they are planted in the field, they allocate more resources to producing roots underground, which is a strategy for reaching deeper pools of water in the soil,” Nelson said.

This is a form of “drought memory” in which seedlings remember their early environment.

Reforestation is a global endeavor. Schools in other regions are working on different species, which often respond differently to various intensities and timings of the drought exposure — whether it happens at the beginning or end of a growth cycle.

“Current collaborations are with Purdue University, Oregon State University and the Rocky Mountain Research Station, to name a few. We’re branching out to a large network to find commonalities and differences for species. We need to develop species-specific propagation protocols,” Nelson said.

Black Walnut research at Purdue University, for example, produces no response to drought preconditioning, unlike the western larch here in the Pacific Northwest.

“And then in the Douglas fir, we see more production above ground, as opposed to underground in the western larch,” Nelson said. “Drought memory research, however, is just the beginning for new work at the nursery. We’re always performing many research projects, from testing different fertilizer and irrigation regimes, and different container types, to modifying the greenhouse climate. At the end of the day, it’s always about how we can improve seedling quality.”

Andrew Nelson, Ph.D.

Director of Franklin H. Pitkin Forest Nursery, Tom A. Alberg and Judith Beck Endowed Chair of Native Plant Regeneration, Associate Professor

CNR 102C


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Department of Forest, Rangeland and Fire Sciences

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A man waves a hand with a forest in the background.
Associate Professor Rob Keefe assessing forest conditions on the U of I Experimental Forest. Credit: University of Idaho Visual Production.

 U of I is also testing more sustainable container technologies that can enhance rooting development in seedlings.

“We’re seeing a transition away from the traditional Styrofoam block containers, which often end up in landfills, towards Earthpots,” Nelson said.

Earthpots are placed into reusable trays and are configured to the rooting environment, leading to changes in root system architecture in the nursery and following planting. This may further increase drought resistance.

Meanwhile, the U of I Center for Forest Nursery and Seedling Research (CFNS) Seedling Quality Lab, for one, is dedicated solely to refining operational seedling testing protocols and operationally testing seed lots, which helps understand potential seedling success in the field.

“We’re the only place in the Western U.S. that offers quality testing for third-party seedlings, which are seedlings that landowners are going to plant. We serve as an unbiased source of information,” Nelson said.

Fire crawls across the floor of a conifer forest.
The 2014 prescribed burn at UIEF. Credit: Aaron Sparks.

“Now, We Let Them Burn”

Beyond the nursery, recent wildfire related projects include “dose-response” experiments, where trees are subjected to increasing doses of fire intensity to see how they respond in terms of mortality, growth and physiological changes after the fire. Different sensors are taken out to the forest to quantify energy release from the fire and its subsequent effects on the trees.

“This information is useful for prescribed fires. It can tell us what intensity level may be required for landowners to thin or maintain the trees they have. It also informs replanting needs required after a fire,” said Aaron Sparks, a CNR research faculty member who focuses on fire ecology and digital forestry.

Doctoral student Alex Blanco is examining the effect of varying intensities of fire on younger trees. Blanco is currently working on dose-response experiments for western white pine and Douglas fir, but said that collectively, their current project includes a wider range, with eight species of younger plants aged up to approximately 2 years old.

“We are varying the intensity of the fires and then observing the effects. At the end of the day, we want information from many species and ages to develop robust mathematical models to inform land management,” Blanco said.

Right now, models are limited to adult trees.

“Land managers need a better understanding of how much fuel — as in young growth — they may need to add or clear for a prescribed fire, depending on what they want for the land,” Blanco said.

The main goal is to have models that will predict fire behavior for trees ranging from seedlings to adults to inform land managers, foresters, agriculturalists and anyone who takes a stake in the forest.

For Blanco, however, the research is about more than local fires.

“U of I is having four to six publications every year on different trees and regions,” Blanco said.

Blanco concurs that reforestation is a worldwide effort.

“I’d like to research and study in northern Thailand,” Blanco said. “Because there are a lot of wildfires and pine species there too.”

“We even have high school students working on these reforestation projects. And now they are authors in our publications. It’s not just grunt work — it’s research and environmentalism. We’re connecting the dots,” said Blanco, whose background is in marine science.

For example, “better reforestation practices means there’s less harmful erosion and pollutants going into the rivers and oceans,” Blanco said.

Moscow and Beyond

At the U of I Experimental Forest (UIEF) specifically, one of the biggest experiments involves monitoring growth of a 30-acre area burned in 2014.

“We’re seeing that trees exposed to more intense fires in 2014 are growing slower because they must allocate more resources for repair and maintenance. We’re seeing these results in both field-collected diameter cores from the trees, and in height measurements taken with LiDAR remote sensing,” Sparks said.

In October 2023, Sparks and Rob Keefe, professor and UIEF director, published “Integrating active fire behavior observations and multitemporal airborne laser scanning data to quantify fire impacts on tree growth: A pilot study in mature Pinus ponderosa stands” in Forest Ecology and Management, vol. 545. This lidar-based study measured the growth of individual trees for nine years following the 2014 treatments.

Both Nelson and Sparks say students contribute directly to these research projects and papers like this.

“We’re student focused. We have six different summer interns at the nursery and 25 plus interns during the year — all funded through donations. The end goal is always to increase the flow of skilled people for the industry,” Nelson said.

Meanwhile, in the forest, students take measurements before, during and after burns.

“They plan treatments, do the prescribed burning, they monitor after and then we’ve had several follow-up projects, such as Emily Yurcich’s project," Keefe said.

Yurcich is a doctoral student of Charles Goebel, professor of forest ecosystem restoration and ecology and department head of Forest, Rangeland and Fire Sciences, who is studying how goats graze shrubs, and the effect that has on reforestation growth.

Even though thousands of acres are currently being treated this way in Idaho, “we still don’t know how this affects seedlings,” Keefe said, let alone other ecological and sociological impacts.

Aaron Sparks, Ph.D.

Research Faculty

IRIC 243

Email Aaron Sparks

Department of Forest, Rangeland and Fire Sciences

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Robert Keefe, Ph.D.

Associate Professor and Director, University of Idaho Experimental Forest



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Department of Forest, Rangeland and Fire Sciences

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We’re student focused. We have six different summer interns at the nursery and 25 plus interns during the year — all funded through donations. The end goal is always to increase the flow of skilled people for the industry. Andrew Nelson, director of Center for Forest Nursery and Seedling Research

Dalyna (Lyn) Hannah, a forestry doctoral student, is also working with Keefe and Goebel to test how seedling phenology and soil chemical properties are affected by mastication. Mastication, or mulching, is a fuel-reduction treatment that returns the forest to natural conditions.

At the UIEF in June 2023, “we created eight plots; four were masticated and four were non-masticated. We planted a total of 800 seedlings including white pine, western larch, Douglas fir and western red cedar,” Hannah said.

After planting, seedlings were measured in two rounds for height, DRC (diameter at root collar) and mortality rate. Also collected were five soil samples from each plot to compare the nitrogen levels held within the masticated and non-masticated plots.

Hannah, a National Science Foundation fellow in the Bridge to Doctorate Program and Navajo Nation tribal member, said that they are working on methods to include Indigenous knowledge into their research, with the long-term goal of improving mortality rates for tree species that have cultural significance to the Indigenous community.

Through all reforestation efforts, the forest must be prepped for decades of growth, said Keefe. That means that behind every reforestation endeavor is foundational work including management techniques such as prescribed burns to remove fuels and dangerous plant material before planting and studying seedlings can even begin.

Think of prescribed burns as a primary, real fire that enables future resiliency and more positive burns in the forest. Then, once trees are big enough, “we can burn in the understory, creating the possibility of multiple prescribed burns for generations of plants,” Keefe said.

In this way, the longevity of our forests is a team effort, not just here at U of I and in our Pacific Northwest forests, but around the world. Every individual plant and researcher plays a role in regenerating the forest for generations to come.

Looking into the future, reforestation and restoration needs are only going to increase.

“Our forests and rangelands are facing so many challenges, from increased drought, wildland fire, invasive species, to insects and disease,” Goebel said. “It is exciting that reforestation and restoration efforts provide a unique opportunity to help improve the health of our forests and rangelands, and our students and faculty are leading the way in many of these efforts.”

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