A hidden forest future

February 3, 2025

How fire, canopy gaps, and deer reshape the soil’s secret seed bank

 

Smoke from a prescribed burn in a forest.
Smoke from a prescribed burn in a forest.

What if the future of a forest was determined not by the trees we see, but by the seeds hidden beneath our feet? A groundbreaking study, recently published in the Journal of Ecology, reveals how prescribed burning (which mimics historic fire cycles in ecosystems that depend on fire to thrive, reducing fuel buildup that could lead to large, destructive wildfires), tree canopy gaps, and deer activity — three of the most common disturbances in temperate forests — combine to dramatically alter the seed bank, the collection of viable seeds stored in the soil.

While scientists have long studied these disturbances individually, no one has examined their combined effects belowground — until now. “Forests are dynamic ecosystems, and disturbances rarely happen in isolation,” explains lead author Samuel Reed, PhD, Institute on the Environment and Department of Forest Resources in the University of Minnesota’s College of Food, Agricultural and Natural Resource Sciences (CFANS). “By studying fire, canopy gaps, and deer together, we’re getting a much more realistic picture of how forests regenerate and change over time.”

 

A thousand-fold change below the surface 

One of the study’s most striking findings is how different combinations of disturbances created unique shifts in the seed bank’s composition. For example, when fire was followed by canopy gaps and deer were excluded from an area, shrub seed abundance skyrocketed by 1,000 percent. Some of these shrub species, such as Rubus, produce seeds that can remain dormant in the soil for over a century, waiting for the right conditions to sprout.

Samuel Reed, PhD.
Samuel Reed, PhD

Meanwhile, other disturbance combinations had different effects. In areas where fire and treefall gaps occurred but deer were allowed to browse freely, there was a big increase in seed biodiversity. Normally, we see that deer overconsume plants and reduce biodiversity on the landscape, but the region’s relatively low deer populations were shown to actually favor seed biodiversity. This highlights how combined prescribed burning, canopy gaps, and healthy deer populations can actually be beneficial for the forest’s biodiversity in moderation. “The changes we found in the seed bank have big implications for forest ecology and management because these seeds represent the plants that will eventually grow and can determine 21st and 22nd century forest biodiversity,” said Reed.

The role of climate change in future forests 

Smoke from a prescribed burn in a forest.
A prescribed burn taking place in a forest.

The findings are particularly urgent given that each of these disturbances — fire, tree canopy gaps, and deer population shifts — are expected to become more frequent and intense due to changes in forest management and climate change.

Reed notes that the fires being studied are relatively low intensity fires, and the reason these will become more frequent is because we need more prescribed burns to reduce fuel and avoid future wildfire scenarios. “We don’t really understand yet how prescribed burning interacts with the other disturbances, many of which are increasing and changing with climate change,” he said. “It is possible that wildfires would have similar effects as these prescribed burns, but I think that is unlikely, as wildfires can burn off the top layer of soil and reset the clock on the forest’s development.”

Rising temperatures and prolonged droughts increase the likelihood of wildfires, while more frequent extreme weather events, such as storms and hurricanes, create additional treefall gaps. At the same time, changing predator populations, warmer winters, and human land use patterns are causing fluctuations in deer numbers, which could further shape seed banks in unpredictable ways.

Understanding these disturbance interactions is essential for forest conservation. If land managers and ecologists can predict how different disturbance patterns shape future forests, they can make more informed decisions about reforestation, controlled burns, and deer population management to promote biodiversity and resilience.

A new way to think about forest restoration

This research challenges traditional forest management strategies, which often focus on aboveground vegetation and only manipulate a single disturbance at a time without considering the hidden seed bank’s role in long-term ecosystem dynamics. By demonstrating how different disturbance interactions lead to varied ecological outcomes, Reed and his colleagues provide a crucial roadmap for preserving forest biodiversity in the face of climate change.

Forests are constantly evolving, shaped by disturbances both large and small. With this research, we now have a clearer understanding of how the seeds lying dormant in the soil today may shape the landscapes of tomorrow.