Ecosystems After Fire

Fire is an important agent of change in many of Denali’s ecosystems. It is a naturally occurring disturbance to many plant communities. Fire breathes new life and vigor into aging ecosystems and processes.

How often fire returns to a landscape is unique to each ecosystem. In Denali, there are three types of fire-adapted ecosystems, each with their own relationship with fire.

In tussock-shrub tundra, mosses, lichens, grass-like plants, and dwarf-shrubs dominate the landscape. Here, wildfire occurs every 200 – 10,000 years. Wildfires are usually wind driven and spread at a high rate of speed, consuming just recent years of accumulated tussock grass. However, when fire returns to the landscape more frequently, organic matter built up over decades may be consumed, with potential to instigate major change in these systems.

In boreal forest dominated by Black and White Spruce, wildfires generally occur every 60-100 years. The type and arrangement of vegetation in these forests causes them to burn with high intensity. Fire effects in these forests are often severe, sometimes killing most of the overstory trees in a process known as "stand-replacement fires". The short-and long-term effects of such fires can be dramatic.

In mixed spruce and deciduous boreal forests, species like birch and poplar mix with spruce, and fire occurs less frequently, every 100-300 years. Deciduous trees may slow down the spread of wildfires, or moderate their severity, thanks to their broad, moist leaves.

Just as these fires are quick to change the landscape, being fire-adapted, these ecosystems are quick to recover. Fire adaptations come in many forms. For example, black and white spruce are adapted to reseed themselves efficiently after fire. Both species have semi-serotinous cones that release seeds when a fire passes through. Many plants can resprout from their burned stems. For species like willow, this means a flush of new and nutritious leafy growth will occur after fire. Wildlife, like moose, can benefit from the improved habitat and food source wildfire provides. Additionally, downed and dead woody material turned to ash feed the next crop of growth by depositing valuable nutrients. The duff layer, composed of built-up organic matter, may also be consumed in fire, releasing even more nutrients into the soil.

Changes in fire frequency, severity, or fire behavior may have consequences to Denali’s fire adapted ecosystems. An increase in fire frequency could lead to a shift in vegetation composition and changes to biodiversity. Fires that burn too intensely, or again too frequently, could lead to the degradation of permafrost or the destruction of ancient organic matter layers, both of which are crucial for maintaining soil stability and storing carbon. Changes to soil conditions due to fire can have cascading effects on lake chemistry and aquatic systems.

Deep Dive: A Look at Fire Effects

Fire is a natural part of the cycle of Alaska's ecosystems. It provides renewal and change to the species that call these biomes home. Below are photos that highlight successional changes after fire and show the natural cycle of ecosystem.

This photo set shows how dramatic a fire can alter a spruce boreal forest. In the photo series above, the photo on the left shows a spruce boreal forest plot in 2005. By chance, a few weeks later this plot burned in the 2005 Highpower Fire. The photo in the center shows the same plot 1 year post fire. The photo on the right, taken in 2011, shows the same area 6 years after the Highpower fire. Note the new spruce trees already starting to regrow.