Are oak and pine trees regenerating after fires in the park?

Each year, your support of the Trust allows us to provide a research grant to help your park better understand the resources it protects. In 2017, that research grant went to Ellen Frondorf, a graduate student from Bemidji State University, who spent the summer examining oak and pine tree re-growth after fires in Shenandoah National Park.

Have you ever hiked through a forest after a fire? It’s a unique experience. The charred earth and trees can be a stark contrast to the usual green leaves you’re used to. But we know that fire is healthy for forests, what we didn’t know was are oak and pines trees specifically regenerating in Shenandoah National Park after a fire?

It seems like a simple question, and it is one that I spent all last summer investigating. The answer is yes…and no.

Let me back up and take you on my journey that brought me to this conclusion.

Measuring tree diameter as increased sunlight makes it to the forest floor of the Rocky Mount Fire of 2016.

During the summers of 2014-2016, I worked as a Fire Effects Monitor in Shenandoah National Park. My primary role was to take measurements of vegetation and fuels (think downed trees and branches that could burn) before and after prescribed burns. An objective that the National Park Service stated in 2008 is that parks should maintain and restore fire-adapted vegetation, so the data I collected would help determine if the use of fire as a management tool was effective in the park. In Shenandoah, this includes a large number of oak and pine species.

Oak and pine trees have many qualities that make them fire-adapted. Oaks re-sprout vigorously from their roots after a fire, and have thick bark that protects them from damaging heat. Pines require thinner soil layers for germination and the heat releases their seeds from closed cones. Both oaks and pines are shade-intolerant and benefit from the increased sunlight following fire, due to the canopy being more open.

As I learned more about the role of fire in forest health, questions started to populate my headspace:

What is the current status of oak and pine regeneration (oak and pine seedling establishment) in Shenandoah?

What conditions produce the most oak and pine regeneration?

How much of an effect does fire have on oak and pine regeneration?

8 sites examined – Prescribed burns or wildfires have occurred on 6 sites since 2002 (orange). 2 sites haven’t been burned since at least 1935 (green).

Shenandoah is constantly monitoring its landscape for species diversity, invasive species, air quality, and all sorts of other parameters. Managers in the park are also currently monitoring oak and pine regeneration through its fire effects program. However, this is a more recent effort and since there has not been a large number of prescribed burns, limited data is available to help them make decisions.

Knowing all of this, I decided to focus my graduate research on the current condition of oak and pine regeneration within Shenandoah National Park. Receiving the Shenandoah National Park Trust Research Grant allowed me to examine six previous fire sites (both prescribed burns and wildfires), dating from 2002 to 2016, as well as two places in the park that hadn’t been burned since at least 1935, when the park fire records roughly started. These two sites acted as my controls, allowing comparison to the more recently burned sites.

My assistant and I worked June through August 2017 to collect data from 12 to 14 plots at each site. We counted oak and pine seedlings and recorded data on factors thought to influence regeneration like shading, seed source availability (oak and pine trees close by that could populate an area with seeds), and soil layer thickness.

The good news is, there is obviously regeneration for both oak and pine overall in Shenandoah. However, even though all sites had living oak and pine trees, pine seedlings were sparse, and only sites with recent fires (2002 or later) had any pine seedlings counted. Pine regeneration did not occur in any plots we sampled at sites that hadn’t had a fire since at least 1935.

Soil layers were measured for thickness.

So what conditions produced the most regeneration? Statistical models were tested with the variables thought to affect regeneration: sunlight, seed source availability, and site were all important in determining the most regeneration for both oak and pine trees. These factors were decisive in determining oak regeneration. Pine regeneration had multiple relatively equally supported models. All pine models though included sunlight as a condition for increased pine regeneration.

Shenandoah National Park has specific goals for regeneration of oak and pine trees to keep the forests healthy and thriving. Currently, from this data, most sites are not meeting those regeneration requirements. However, fire has shown to have a positive effect on increasing the number of seedlings. While oak and pine regeneration in SNP has numerous variables that affect it, this study helps to inform the park on the current status so they can make plans to achieve their forest health goals.

Over the course of the summer, my assistant and I saw rattlesnakes, black bears, turtles, and tested the quality of numerous blueberries (we can assure you they were delicious). Shenandoah National Park is a beautiful landscape, with many different vegetation communities, that overtime have the potential to change – with and without fire.

The next time you are out hiking, see if you can spot the next generation of oak and pine seedlings emerging!

If you’re interested in reading Ellen’s full report, please contact Jess Green at JGreen@SNPTrust.org. You can support projects like Ellen’s research here.