The Mechanisms Through Which Fire Drives Population Change in Terrestrial Biota

Abstract

Global fire regime change is threatening terrestrial biodiversity. Understanding how these changes affect biota is essential to protect biodiversity now and into the future. A targeted examination of the mechanisms through which fire influences populations will help achieve this by enabling comparisons and connections across taxa. Here, we develop a cross-taxa framework that identifies mechanisms through which fire regimes influence terrestrial species populations over different time scales, and traits on which those mechanisms depend. We focus on amphibians, birds, fungi, insects, mammals, plants, and reptiles. First, we identify key mechanisms through which fire regimes influence species populations across different taxonomic groups. Second, we link these mechanisms to functional traits that influence the relevance to different species. Third, we identify traits that shape the vulnerability-or conversely, resilience-of species populations to frequent, high-intensity, and large wildfires that are emerging as a threat in many parts of the world. Finally, we highlight how this integrative framework can be useful for understanding and identifying fire-related threats common to different taxa across the globe and for guiding future research on fire-related population change.

Keywords: fire regimes; fire‐related mechanisms; fire‐related threats; fire‐related traits; functional traits; population change; population viability; species extinction.

FIGURE 1

A proposed framework for the generalized mechanisms through which fire influences terrestrial populations. We show eight proposed key mechanisms through which fire influences population change in terrestrial biota via impacts on individuals' birth, death, and movement (emigrations and immigrations). The four direct individual‐based mechanisms in the top row have a direct influence on demographic processes and thus population outcomes and operate during, soon after, or several years after fire. The indirect, community‐mediated mechanisms (middle row) influence on population outcomes (bottom row) are mediated by fire's direct influence (top row) on other components of the community and operate during fire or from days, to weeks to centuries after fire, depending on community structure and characteristics of ecosystems. Population outcomes related to births are colored in green, deaths in red, and movements (emigrations and immigrations) in blue. Examples of important fire regime attributes that commonly influence each direct, individual‐based mechanism are shown next to each mechanism. The timescales at which each mechanism and population outcome can occur over is represented by a gradient scale, where the darker colours indicate it applies at such a timescale. The timescale movies from during the fire, to days to weeks after the fire, to months to years after the fire, to decades to centuries after the fire, in equal quarters of the scale.

FIGURE 2

Examples of groups of functional traits that determine the mechanisms of fire‐related change. The columns represent the key mechanisms of population change, and the rows relate the 12 groups of functional traits. The value and expression of these functional traits determine individuals' responses to fire and thus produce the mechanism of change in species populations. Study taxa are represented as colored icons, where the mechanism and associated trait group apply to at least one species in the taxon, according to evidence. The MPPE type demonstrates the kinds of traits—morphological (M), physiological (P), phenological (Ph), and ecological (E) performance traits—that make up the groups of functional traits.

FIGURE 3

Traits associated with vulnerability and resilience to frequent, high‐intensity, and spatially uniform wildfires. The 12 trait groupings that determine the key mechanisms through which fire influences species populations are expressed with examples of vulnerability (red) or resilience (blue) to high frequency, high‐intensity wildfires with limited patchiness. Four example species from two taxonomic groups (plants, mammals) are displayed, demonstrating how various combinations of these traits may contribute to species' vulnerability or resilience to a specific fire regime. Photo of Nycticebus menagensis by Dixon Lau, photo of Eucalyptus regnans by David Clode on Unsplash, photo of Tadarida brasilensis by USFWS/Ann Froschauer on Wikimedia Commons, photo of Chamaenerion angustifolium by H. Zell on Wikimedia Commons.

FIGURE 4

Examples of interactions between other threatening processes and fire‐related mechanisms and traits. (a) Perrier's sifaka, a species threatened by fire due to interactions with habitat loss. Photo by Thomas Martin. (b) A landscape with complex disturbances, Oregon, USA. Photo by Ella Plumanns‐Pouton. (c) Post‐fire traits such as resprouting are also influenced by climate‐driven precipitation and temperature. Photo by Ella Plumanns‐Pouton.