Effects of Invasive Alien Plants on Fire Regimes
Summarized by Emily Cline
The scientific summaries team chose to summarize this article as it emphasizes the importance of native plants in coexistence with fire regimes, an especially topical study with the raging wildfire season California is experiencing. Since the Ecological Restoration Association values reintroducing native species and removing invasive species, this scientific paper combines our passion with what is timely. We hope you enjoy learning more about how invasive species contribute to fire regimes!
Introduction
In the article the authors discuss the impact of non-native plants on fire patterns in an ecosystem and present a management plan to lessen their potentially harmful effects. “Invasive alien plants”, also known as simply invasive plants, are non-native plant species that have spread onto land which they do not naturally grow on, taking up space and nutrients from native species. “Fire regime” is used frequently in the article and can be loosely defined as a description of the broad fire patterns in a particular ecosystem over time. It is characterized by five main features: frequency, intensity, extent, type, and seasonality.
Fuel properties and their effects on fire regimes
This article focuses primarily on fuel sources and their impacts on fire behavior. There are many different ways that fuel sources and their effects may be categorized. The two most important categories are a fuel source’s intrinsic and extrinsic properties. Intrinsic properties relate to the characteristics of the plant itself: for example, its moisture content or its relative flammability. Extrinsic properties, on the other hand, refer to “external properties” and indicate the way that a plant is arranged across a landscape.
Effects of plant invasions on intrinsic fuel properties and fire regimes
Invasive plants make the greatest immediate impact on an ecosystem’s fire regime by changing potential fire fuel sources. One way this may occur is through its intrinsic properties. Two areas these changes typically occur in are the plant’s moisture content or its fuel chemistry.
Effects of plant invasions on extrinsic fuel properties and fire regimes
Typically, invasive plants make the greatest impact by changing the extrinsic properties of fuel sources. Plant invasions may impact the “fuel load” or the amount of fuel available in an environment. They may also impact fuel continuity by, for example, growing in interspaces where native plants typically could not survive. Finally, plant invasions can also impact fuel packing ratio, amount of fuel per unit area, due to differences in plant distribution and density. In certain scenarios, these fuel alterations can eventually lead to changes in broader fire patterns.
The invasive plant-fire regime cycle
Invasive species can completely shift an environment’s fire regime to the point of creating a more ideal ecosystem for themselves, thus perpetuating their own survival at the expense of native systems. There are four phases of this “invasive plant-fire regime cycle”, describing exactly how an invasive plant can change the fire regime of an ecosystem it has taken over.
Phase 1 refers to the pre-invasion state. It outlines the plant’s existing adaptations to its native habitat, particularly in regards to its native fire regime, and thus acts as a measure of the plant’s ability to persist within and alter a new environment.
Phase 2 indicates the ability of the plant species to overcome geographic barriers in order to disperse and spread across multiple regions. At this point, the species has officially become invasive by effectively “invading” a new region.
Phase 3 has been reached when the plant has spread to a sufficient enough point to impact native populations. The fire regime cycle itself has not yet been altered, but the invasive species has begun to alter the landscape.
The final phase 4 occurs when the impacts of the invasive species have altered the ecosystem’s fire regime. This typically becomes permanent when the effect of this altered fire regime also provides a benefit to the invasive species, resulting in a self-perpetuating cycle.
The costs and probabilities of successful prevention or mitigation efforts
Finally, the authors address how we can use this knowledge to create a more effective system of invasive plant control. There are 4 basic stages of this process, each one corresponding to the 4 phases of the plant-fire regime cycle.
The ideal option is to work at phase 1 by identifying which plants pose the greatest danger and create a set of pre-screening criteria to prevent introduction in the first place. Unfortunately, current US standards do not consider this and primarily look at exclusion criteria relevant to species defined as “noxious weeds”.
During phase 2, we must look at invasive species which have not yet spread far enough to cause a significant ecological impact. Those which have high potential to take over the environmental landscape should be studied and prioritized for control.
For species that have reached phase 3, we must investigate plants’ likelihood of altering fuel or fire regime patterns, and also work on the restoration of depleted native species populations.
Once a new fire regime has been established in the final phase, we must begin to examine the extent of the regime’s negative impacts on local human communities. Oftentimes, it is too late to restore the native plant species by the time this stage has been reached. It is most efficient for us to develop better exclusion criteria to prevent these problems from occurring in the first place. The later we identify harmful invasive plant species, the more expensive solutions become and the less likely it becomes that we are able to conserve fragile native ecosystems.
Matthew L. Brooks, Carla M. D'Antonio, David M. Richardson, James B. Grace, Jon E. Keeley, Joseph M. DiTomaso, Richard J. Hobbs, Mike Pellant, David Pyke, Effects of Invasive Alien Plants on Fire Regimes, BioScience, Volume 54, Issue 7, July 2004, Pages 677–688, https://doi.org/10.1641/0006-3568(2004)054[0677:EOIAPO]2.0.CO;2