Assessment of Altered Fire Regimes as a Conservation Threat to Global Biodiversity
The degree to which altered fire regimes (roughly defined as too much, too little, or the wrong kind of fire) pose a major threat to the conservation of biological diversity and dependent human communities around the world is currently unknown. Ecosystems can generally be described as being fire-dependent (or fire-adapted), fire-sensitive (or fire-influenced) or fire-independent.
Since the majority of terrestrial as well as many aquatic ecosystems are influenced by fire, ecosystems can be described in terms of fire regimes (including the absence of fire) that operate within known or hypothesized ranges of variation in key characteristics, including frequency, severity, intensity, spatial scale, seasonality, and predominant ignition source. Thus, alteration can be defined as the extent to which key characteristics have (or are suspected to have) departed from natural, historical or ecologically acceptable patterns.
No one standard exists for determining “natural” or “historical.” Humans have been an important component of many fire regimes for centuries or millennia. “Ecologically acceptable” fire regimes may be influenced by people, while still acting to maintain the biota and ecological processes characteristic of a particular ecoregion or major habitat type.
For this assessment, altering one or more characteristic components of an ecologically acceptable fire regime is assumed to stress or degrade an ecosystem by significantly changing composition, structure, or function, which in turn establishes a trajectory toward a fundamentally different ecosystem type and fire regime. Degradation, in a biodiversity conservation context, is defined as creating current or near-term conditions that are likely to threaten the persistence of characteristic native plant and animal populations in the major habitat type or ecoregion at present or within the next 10 years. Characteristic fire regimes may include ignitions predominantly of natural origin (i.e., lightning) or a mix of human and natural.
The Global Fire Assessment is helping us to better understand fire regime status and trends and underlying causes of alteration by focusing on the human sources of alteration as well as maintenance of fire regimes. This assessment will provide the basis for developing effective strategies, allowing the Global Fire Partnership to better focus scarce resources on the most viable major habitat types and ecoregions, the most critical threats and most feasible actions. The scales of interest are major habitat types and ecoregions.
The assessment serves four broad purposes:
Fire Regime Types
1. Fire-Dependent Ecosystems - Fire is essential in maintaining predominant ecosystem composition, structure, function, and extent. If fire is removed, or if a fire regime is altered beyond its historical range of variability, the ecosystem changes to something else; dependent species and their habitats decline or disappear. Fire is not a disturbance but rather an essential process. Species composition is relatively stable and vegetation is fire-prone and highly flammable. Ecosystem structure and plant architecture facilitate fire spread.
2. Fire-Sensitive Ecosystems - Ecosystem structure and composition tend to inhibit ignition and fire spread. Thus, in most cases, fires tend to be infrequent and small in size. The majority of species generally lack adaptations to respond positively to or to rebound after fire. Fire can influence ecosystem structure, relative abundance of species, and/or limit ecosystem extent. Fire may create habitats for key species by creating gaps, regeneration niches, or by initiating or affecting succession. If fires are too frequent or too large, they can be damaging and cause ecosystem shifts to more fire-prone vegetation.
3. Fire-Independent Ecosystems – Fires characteristically would not occur because of a lack of fuel and/or ignition sources. Fire regimes can be altered by a change in fuels (e.g., invasive species) or ecologically- inappropriate human-caused ignitions.
Fire Regime Status and Trend
Three categories for the predominant fire regime status are used in this assessment, and are defined as follows:
1. Intact - Current fire regime substantially similar to ecologically acceptable state.
2. Degraded - Current fire regime departs substantially from ecologically acceptable state in one or more key characteristics, but those characteristics may be restorable to an ecologically acceptable state.
3. Very Degraded - Current fire regime departs substantially from ecologically acceptable in all key characteristics and may not be feasibly restorable to an ecologically acceptable state.
Fire regime trend can be described as either improving, relatively stable, or declining. Trend should be estimated as the direction of fire regime condition based on trends in sources of alteration expected over the next 10 years.
Overall Scientific Confidence
1. Very Good - The level of scientific agreement and/or consensus is high and amount of evidence and/or data is high.
2. Good - The level of scientific agreement/consensus and the amount of available evidence/data is moderate.
3. Fair - The level of scientific agreement/consensus moderate to high, but the amount of available evidence/data is low.
4. Poor - The level of scientific agreement/consensus and the amount of available evidence/data is low.