What Is the Effect of Wildfires on Biodiversity?

Biodiversity refers to the variety of life that may be found in a given place. It includes animals, plants, fungi, and even microbes such as bacteria. Because many species rely on specific resources or habitats to survive, changes in the environment like fire, which changes the balance of resources, can impact biodiversity.

With the number of wildfires increasing and forecasted to rise by 50% by 2100, it’s important to assess the effect of wildfires on biodiversity. Wildfires can have both positive and negative effects on biodiversity, depending on the frequency, size, and severity of the fires. This article will explore how wildfires impact biodiversity, including increasing it and decreasing it in certain situations.

Key Takeaways

  • The effect of wildfires on biodiversity depends on how often fires are occurring, how big they are, and how intense they are. Fire’s impacts also depend on the species that exist in the affected area.
  • Wildfires can increase biodiversity by supporting fire-dependent ecosystems and by causing changes in ecosystems that creates “space” for new species to thrive.
  • Wildfires can decrease biodiversity by killing native species directly, or indirectly through habitat destruction and increased advantages for invasive species.

Positive Effects of Wildfires on Biodiversity

The effects of wildfires on biodiversity depend on the ecosystem’s historical fire regime, the pattern of how fire has occurred in the ecosystem over time. Areas that have evolved without frequent fire will likely be significantly damaged by fire. However, some ecosystems are fire-adapted, meaning they can survive fire, while others are fire-dependent, meaning the ecosystem actually requires fire to thrive. For example, some ecosystems, such as tropical or temperate savannas, require fires as often as every 1 to 10 years. In these fire-adapted and fire-dependent ecosystems, fires may not change the amount of biodiversity present, and in some cases, fire can promote biological diversity.

Frequent fires can benefit ecosystems that are adapted to this fire regime. Wildfires can reduce debris buildup (leaving less fuel for fires in the future), increase soil nutrients, and clear plants that are not adapted to fire. This can spur increases in biodiversity, as native plants that are adapted to fire-dependent ecosystems are left with better growing conditions (such as increased resources or decreased competition), and animals are left with more resources as a result. Plants that require fire more frequently, such as many herbaceous plants (plants with a flexible, green stem), will thrive. However, others, such as woody plant species, will likely not be able to survive frequent or high intensity fires.

The best examples of fire-dependent plants are those with fire-activated seeds. For example, the lodgepole pine’s pinecones are sealed with resin, and so the seeds can only be distributed after the resin is melted in a fire. Another example is plants that use chemical signals in smoke as a signal to break their seeds from dormancy. These plants then germinate after the fire and become one of the first species to grow back after the fire (allowing for less competition for resources like nutrients or light). These plants are known as serotinous species.

Video of burning jack pine cones, a species that releases its seeds in response to fire.

Negative Effects of Wildfires on Biodiversity

In recent years, fires have become much more frequent, more severe, and larger in size, leading to severe damage to many ecosystems. A number of factors have contributed to the increased frequency and severity of wildfires. One of the major drivers is human wildfire suppression, which has led to a buildup of natural debris on forest floors that normally would have been burned away in small fires. This debris buildup acts as excess fuel for fires in the future, thus increasing their intensity. Changes in the types of plants growing in the forest as a result of a lack of fires can also make fires more intense when they happen. Climate change and increasing drought have also contributed to making wildfires more frequent and more destructive.

This increase in frequency, severity and size of wildfires contributes to biodiversity loss. First, fires can kill many species directly, especially those that are not adapted to fire. Increased frequency of fires is especially harmful to plants that need a long time to mature or reproduce. If these plants are not given adequate time to reproduce before being killed by fire, then the plant species’ population will decrease over time and eventually die off. This leads to a loss of forest biodiversity.

Long-lasting, large, or extremely frequent fires reduce the ability of the ecosystem to recover adequately. When habitats that are essential for native species are lost, native species’ populations can decrease or go extinct. An ecosystem’s inability to recover after a fire can also reduce native vegetation biodiversity. Additionally, ecosystems are often changed after a fire. In many cases, native species are unable to adapt to these changes while invasive species may be better suited or able to adapt to these new conditions. This increase in invasive species can lead to a decrease in native species, and thus a decrease in local biodiversity.

Even species that are adapted to fire may not survive the unprecedented intensity and frequency of the wildfires we face today. For example, sequoias, a type of redwood tree, are extremely resistant to fire. While young sequoias may be killed by fire, mature trees historically survive fire and are able to continue to reproduce after fires to support the population. However, the frequency of fires has increased in recent years, leading to six major fires between 2015-2021 that killed off large numbers of sequoias in California’s Sierra Nevada mountains. In fact, over 85% of the sequoia groves in the Sierra Nevada have burned in just those six years, with the other 15% or so burned across the entire century before. This case study highlights the fact that even ecosystems that are fire-adapted may be threatened by current and expected increases in fire intensity and frequency.

fires in the sierra - wildfire effect on biodiversity
Six major fires between 2015-2021 have burned more than 85% of the mountain range’s sequoias, killing many trees that are normally fire resistant.
Source: NPS.gov

Finally, forest fires can indirectly worsen climate change, a major driver of biodiversity loss. This is because burning trees releases carbon dioxide stored in them into the atmosphere. For example, a 2020 study found that increased fires in the Amazon rainforest have led to a decrease in the number of trees and a 25% decrease in the amount of carbon stored in the trees. This loss of carbon stores contributes to climate change, which is causing habitat changes that may drive species unable to adapt to extinction. 

Read more about how climate change impacts biodiversity: Threats to Biodiversity

The Effect of Wildfires on Biodiversity: Balance Is Key

Researchers have concluded that the best way to maximize biodiversity is to have a balance between two extremes of no fire and frequent fire. For example, one hypothesis, titled the intermediate disturbance hypothesis, argues that biodiversity in local communities is at its highest when disturbances like fires are neither too infrequent nor too frequent. This is because few species can survive in habitats with extreme disturbance, but many also cannot survive in a habitat with no disturbance. 

For example, a 2016 study in Yosemite’s Illilouette Basin found that diversity in fire frequency, size and severity increases biodiversity of plants and pollinators. A 5% increase in pyrodiversity (the amount of diversity in fire size, severity and frequency) led to gaining one pollinator and one flowering plant species. While this may sound small, this represents a significant increase in biodiversity. 

The study also found that ecosystems with variable fire characteristics led to increased spatial heterogeneity of plants and pollinators, or the existence of “patchy” communities in which different species live in different areas. Patchily distributed communities means that each community of plants and animals is competing for different resources, rather than all competing for the same ones, leading to increased species richness overall. This study highlights the fact that a balance of fire characteristics, rather than extremely frequent or extremely infrequent fires, is best for increasing biodiversity.

Because of the varied effects of wildfire on biodiversity, the exact “right amount” or “right intensity” of fires to maximize diversity is still unknown. In fact, the academic journal Fire is in the process of creating a 2022 Special Issue on the effects of wildfire on biodiversity. The editors’ goal is to answer the question:

How do we identify where and when, and at what scale, wildfires are too rare or too frequent [to support biodiversity?]

Fire, Editors Note for 2022 Special Edition

As fire size and frequency continue to increase around the world, this will likely become an increasingly important question to answer in order to preserve global biodiversity.

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