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Pyrodiversity and biodiversity: what do we know?

Date: March 09, 2022

Pyrodiversity begets biodiversity – or does it?

Multiple graphs showing support for pyrodiversity-biodiversity hypothesis
Support for pyrodiversity-biodiversity: (a) Across from top left - terrestrial mammals, bats, birds, reptiles, invertebrates, plant–pollinator interactions, and pollinators; (b) Across four broad ecosystem types
Multiple ecological hypotheses support the idea that ‘pyrodiversity begets biodiversity’ – that is, places with more variety in fire characteristics (e.g., severity, time-since-fire) will support more species of plants and animals. This is because greater variety in fire characteristics will presumably open up a host of ecological niches for different species to occupy. There is a growing body of literature testing this hypothesis, but results are mixed, and a synthesis of findings is lacking. 

We synthesized the existing literature and evaluated support for the pyrodiversity-biodiversity hypothesis. We reviewed 98 papers and recorded the geographic location, ecosystem type, taxa studied, whether a test of the pyrodiversity–biodiversity hypothesis appeared to have been performed and whether support for the hypothesis was inferred by the authors, how pyrodiversity was defined or conceptualized, and other key points and conclusions reached by the authors. The literature we reviewed spanned a period of 1992-2020 and covered five continents, seven taxonomic groups, and four ecosystem types.

In addition to summarizing the literature, we identified potential approaches for uncovering ecological mechanisms underlying pyrodiversity-biodiversity relationships. One such approach involves decomposing the effect from an aggregate impact of pyrodiversity on biodiversity, to a component effect of pyrodiversity on individual species. For example, does pyrodiversity benefit or harm/inhibit needs of individual species? We explored this idea using two species at opposite ends of the spectrum of fire affinity as a case study: the black-backed woodpecker (a “fire-reliant” species) and the spotted owl (an “old-growth” species).

Image of direct and indirect approaches to evaluate pyrodiversity-biodiversity
Direct and indirect approaches to evaluate pyrodiversity-biodiversity hypothesis. Direct approaches quantify variation in fire characteristics within sampling units (a & c). Indirect approaches quantify variation among sampling units (b & d).

Key Findings

  • We identified 41 tests of the pyrodiversity–biodiversity hypothesis, and we found that support was mixed (only 44% of studies supported the hypothesis), with no consistent patterns across taxonomic groups or ecosystem types.
  • Studies frequently define pyrodiversity in different ways, examine effects at different scales, and occur in ecosystems with different natural fire regimes, baseline levels of biodiversity, and evolutionary histories; these factors contribute to the inconsistent support for the pyrodiversity–biodiversity hypothesis.
  • Some studies we examined did not perform a direct test of the pyrodiversity-biodiversity hypothesis. This led us to define criteria for ‘direct’ and ‘indirect’ tests of the hypothesis, based on whether measurements of pyrodiversity occur within sampling units (‘direct’ test) or occur among them (‘indirect’ test).
  • We show that black-backed woodpeckers and spotted owls – two sympatric species that have long been seen to occupy distinct and largely non-overlapping habitats – both benefit from pyrodiversity. The mechanisms seem convergent: severe fire brings a boon of resources (nesting for the woodpecker, food for both the owl and woodpecker), but severe fire also brings danger (predation risk for the woodpecker and possibly the owl, and loss of limiting nesting habitat for the owl).

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Principal Investigators: 
Principal Investigators - External: 
Morgan Tingley - University of California - Los Angeles
Research Location: 
Global ecosystems