Ponderosa pines are adapted to survive low-severity fires, with thick bark, few lower limbs for flames to climb, and deep roots to tap moisture and nutrients below scorched soil. While ponderosa pine can survive low severity fires, they are wiped out by high severity fires, leaving large areas without any mature trees to provide seeds to regrow forests. In the Cameron Peak Fire, ponderosa pine had relatively low probabilities of coming back on its own compared to other tree species throughout the burn area. We target ponderosa pine for tree planting efforts because these forests need active intervention to recover, can grow in hot and dry conditions and can be successfully planted by people.

Lodgepole pines are adapted to fire; some contain serotinous cones that do not open until they are exposed to heat. This makes them more likely to recover after fires. Douglas-fir grows best in the shade, and may be able to return naturally in many areas once there is an overstory of ponderosa pines. Douglas-fir have lightweight, winged seeds, allowing the wind to carry them to more distant locations. Engelmann spruce and subalpine fir occur at higher elevations than our current focus, and may be an area to explore for future collaborative work.

The Cameron Peak Reforestation Group worked with the Larimer County Office of Emergency Management and received a list of landowners who were impacted by the Cameron Peak fire and interested in reforestation. Criteria for selecting sites included whether: there was a suitable seed source available, the area burned at high severity with few surviving trees, and the area is projected to be suitable for forests in a future with hotter and drier temperatures. Not every site meets these criteria, as partnerships with landowners are one of the most important factors in making this work possible.

While many Front Range forest types are adapted to fire, their ability to recover varies. Hotter, drier conditions fueled by climate change are contributing to more frequent, more intense wildfires than what some forests can survive. Where burns are severe, some forests cannot regenerate on their own, as wind and natural forces cannot carry seeds over the vast treeless expanses left behind.

Different types of forests respond in unique ways to fire. Some species have fire-adaptive traits, like serotiny in lodgepole pine, or resprouting in aspen, allowing them to rapidly recover from fire. However, other forest types, including ponderosa pine and fir, need seed dispersal from live trees to successfully recover. In areas with no surviving trees, post-fire recovery is limited to anywhere from 300 to 650 feet from a live tree that survived fire.

The history of pre-fire tree mortality further influences the forests’ ability to respond. Forest recovery is more challenging in places that have been impacted by insects, such as bark beetles. Insects preferentially kill large, seed-bearing trees. Therefore, forests that burn after beetle outbreaks have even fewer seed sources. This particularly affects forests made up of subalpine fir and Engelmann spruce trees. (Other species, such as lodgepole pine, show few effects of bark beetle impacts on post-fire recovery, and ponderosa pine and Douglas-fir have had few bark beetle outbreaks.)

Forest recovery is also slowed when forests burn twice in rapid succession. Some areas that burned in the High Park Fire (2012) burned again in the Cameron Peak Fire (2020). Young trees that had begun to grow back were wiped out by the second fire, making it much more difficult for natural recovery to happen again.

In places that suffered high-severity burns, forests are unlikely to grow back on their own and will instead convert to grasslands or shrublands. By planting trees, we can give forests a chance to grow back. Trees grow slowly, but over time they help ecosystems to recover, providing shade for other species to establish. Trees also remove carbon from the atmosphere, so planting trees is a potential climate benefit.

Forests are critically important to our water, wildlife and way of life. They protect watersheds and headwaters for rivers across the West, preventing erosion and filtering water for cities and towns downstream. Our forests provide habitat for species like the Abert’s squirrel, birds like the pygmy nuthatch and Northern goshawk, and mammals like elk, deer, and black bear.

For trees planted in climatically suitable niches and with locally-adapted seeds, we have measured a 48-100% survival rate after one year (average 84%). Post-planting survival varies across Colorado and in the southwestern U.S., ranging from 0-70% with an average of 25%. Many factors influence seedling survival, including weather patterns, temperatures, and whether the seeds were from a local source. Surface temperatures in a burn scar can be particularly hot, with little of the shade or moisture normally provided by vegetation.

To minimize the impacts of hot and dry conditions on seedlings, our group aims to plant trees on the north to northeast side of small shrubs or fallen trees, providing shade during the hottest part of the day. Tree planting sites are prioritized on northern slopes or near valley bottoms, where cooler temperatures can be found.

Monitoring seedling survival and growth is one way that the Cameron Peak Reforestation Group seeks to learn what is working in our region and how to improve our techniques.

We aim to plant 100-150 seedling ponderosa pine trees per acre on north and east facing slopes, mimicking forest densities that historically occurred when fire was present as a key ecosystem process. In addition, we plant trees in clusters with open ground in between, emulating historically fire-maintained forest structures. Over time, these tree islands may fill in the gaps by producing seeds, mimicking natural regeneration. These clumps may help prevent future wildfires from spreading, as the open areas between clumps act as natural fire breaks.