1. Plant fire syndromes are usually defined as combinations of fire response traits, the most common being resprouting (R) and seeding (S). Plant flammability (F), on the other hand, refers to a plant’s effects on communities and ecosystems. Despite its important ecological and evolutionary implications, F has rarely been considered to define plant fire syndromes and, if so, usually separated from response syndromes.

2. We propose a three-dimensional model that combines R, S and F, encapsulating both plant response to fire regimes and the capacity to promote them. Each axis is divided into three possible standardized categories, reflecting low, medium and high values of each variable, with a total of 27 possible combinations of R, S and F.

3. We hypothesized that different fire histories should be reflected in the position of species within the three-dimensional space and that this should help assess the importance of fire as an evolutionary force in determining R-S-F syndromes.

4. To illustrate our approach we compiled information on the fire syndromes of 24 dominant species of different growth forms from the Chaco seasonally-dry forest of central Argentina, and we compared them to 33 species from different Mediterranean-type climate ecosystems (MTCEs) of the world.

5. Chaco and MTCEs species differed in the range (seven syndromes vs. thirteen syndromes, respectively) and proportion of extreme syndromes (i.e. species with extreme values of R, S and/or F) representing 29% of species in the Chaco vs. 45% in the MTCEs.

6. Additionally, we explored the patterns of R, S and F of 4032 species from seven regions with contrasting fire histories, and found significantly higher frequencies of extreme values (predominantly high) of all three variables in MTCEs compared to the other regions, where intermediate and low values predominated, broadly supporting our general hypothesis.

7. The proposed three-dimensional approach should help standardize comparisons of fire syndromes across taxa, growth forms and regions with different fire histories. This will contribute to the understanding of the role of fire in the evolution of plant traits and assist vegetation modelling in the face of changes in fire regimes.

Data collection for Chaco species

From previous studies, we compiled data on post-fire resprouting (R) (Jaureguiberry 2012; Jaureguibery et al. 2020), germination capacity after heat shock treatments (S) (Jaureguiberry & Díaz) and flammability (F) (Jaureguiberry et al. 2011) of 24 dominant species of the seasonally-dry Chaco forest of central Argentina (hereafter Chaco). We then transformed the original data from the mentioned studies into three possible categorical ordinal values: 1, 2 or 3, indicating low, medium and high values of each variable, respectively. To do so, we used the following criteria:

1) For R data: we focused on the survival percentage recorded for each species (Jaureguiberry et al., 2020) as a proxy for resprouting capacity (Pérez-Harguindeguy et al., 2013). This was because this variable is widely used in fire studies and has a standard scale and range of values, therefore facilitating comparisons between species from different regions. Survival percentages were assigned to one of three possible intervals: 0 to 33 %; 34 to 66 % and from 67 to 100%, and then each interval was assigned the value 1, 2 or 3 respectively, indicating low, medium and high values of resprouting capacity.

2) For S data: based on germination response to heat shock treatments we classified species as heat-sensitive (germination lower than the control), heat-tolerant (germination similar to the control) or heat-stimulated (germination higher than the control) (see details in Jaureguiberry and Díaz 2015). Each of these categories was respectively assigned a value of 1, 2 or 3.

3) For F data: while original measurements included burning rate, maximum temperature and biomass consumed (see details in Jaureguiberry et al. 2011), with the purpose of comparing Chaco species with species from other regions, and considering that burning rate is rarely reported, data of the two latter variables were collected from studies that followed Jaureguiberry et al. (2011). A PCA followed by cluster analysis allowed classifying species into the following categories: 1=low flammability; 2=moderate flammability; and 3=high flammability.

Data collection for other regions

We performed an unstructured literature review of fire-related traits relevant to our model. Whenever possible, we searched for the same or similar variables to those used for the Chaco, namely survival percentage, germination response to heat shock, and variables related to flammability (e.g. maximum temperature, biomass consumed and burning rate), as proxies for R, S and F, respectively.

Classification into different R intervals was based either on quantitative data on survival percentage, or on qualitative information from major databases. For example, resprouting capacity reported as “low”, or “high” (e.g. Tavşanoğlu & Pausas, 2018) were assigned R values of 1 and 3, respectively. For Southern Australian species, those reported as “fire killed” and “weak resprouting” (Falster et al., 2021) were assigned a value of 1, while those reported as “intermediate resprouting” and “strong resprouting” were assigned values of 2 and 3, respectively. The vast majority of records in our dataset refer to resprouting of individuals one growing season after the fire. Flammability data for most of the species were based on quantitative measurements that have used the method of Jaureguiberry et al. (2011), which was standardised following the criteria explained earlier. However, for some species, classification was based either on other quantitative measures that followed other methodologies (e.g. measures based on plant parts such as twigs or leaves, or fuel beds) or on qualitative classifications reported in the literature (most of which are in turn based on reviews of quantitative measurements from previous studies). We standardised the original data collected for the other regions following the same approach as for the Chaco. We then built contingency tables to analyse each region and to compare between regions.

The curated total number of records from our literature review was 4411 (records for R, S and F, were 3399, 678 and 334, respectively) for 4,032 species (many species had information on two variables, and very few on the three variables). The database covers a wide taxonomic range, encompassing species from approximately 1,250 genera and 180 botanical families, belonging to ten different growth forms, and coming from seven major regions with a wide range of evolutionary histories of fire, from long and intense (Mediterranean-Type Climate Ecosystems) to very recent (New Zealand).

The provided files operate with Excel.

File 1

Data file with full list of records: File containing a full list of records of standardised values of resprouting (R), seeding (S) and flammability (F) obtained for species from different regions, through an unstructured literature review. Ordinal categorical values 1, 2 and 3 indicate low, intermediate and high values of the corresponding variable. Cells with "N/A" indicate data not available. Total number of records = 4,411; total number of species = 4,032. References for the "Source" column are provided as a separate file. 

File 2

List of references used to compile the database: File containing the list of references with full citations for the "Source" column of the data file.