Pedro Jaureguiberry: Plants from regions with different fire histories respond to fire and burn differently

In this new post Pedro Jaureguiberry—Adjunct Researcher at IMBIV (CONICET-UNC)—Argentina, presents his last work ‘A three-dimensional approach to general plant fire syndromes’. He highlights the importance of effect traits for fire ecology, hypothesizes plant traits based on regional fire history, and shows his interest in the connections between humans and nature. 

Una versión en Español de esta publicación está disponible aquí!

About the paper

Fire has shaped many ecosystems for millions of years. With environmental change currently affecting fire patterns in many regions of the world, there is renewed interest in understanding its ecological and evolutionary role. This includes a focus on which plant traits are recurrently associated with fire in different floras, either in isolation or combined in trait syndromes. The focus has usually been on the response to fire, that is, what recurrent combinations of traits give the plant the ability to maintain or increase its fitness when facing fire. One of the most widely used classifications distinguishes two fire response syndromes: resprouting (R) and seeding (S) which, respectively, rely on the regeneration of vegetative tissues that survived fire, or on the recruitment of new individuals from seeds.

Much less common have been studies of traits or trait syndromes that determine a plant’s flammability, broadly defined as the propensity of living or dead plant material to ignite and sustain combustion. Flammability determines a plant’s individual contribution to a landscape’s fire regime. However, flammability has rarely been considered to define fire syndromes, and if so, it is usually separated from response syndromes. This hampers global modeling efforts for vegetation responses to, and effects on, changing fire regimes.

Some woody species burn intensely under dry and hot conditions typical of the late winter/early spring season in the Chaco seasonally-dry woodlands of central Argentina (credit: Gustavo A. Bertone)

We set out to combine both aspects, that is on what the plant “does” both to a fire regime and in response to it. We present a three-dimensional model that explicitly combines fire-related specific response (resprouting, R, and seeding, S) and effect (flammability, F) functions, allowing the detection of fire syndromes. Each of these three major axes is divided into three possible standardized categories, giving rise to a total of 27 possible fire syndromes. These simple and integrated fire syndromes are applicable across floras and growth forms, and therefore can contribute to ongoing global efforts in comparative ecology.

We hypothesize that environmental factors at the ecosystem level, specifically fire, limit the occurrence of certain syndromes, and facilitate others. Therefore, the species in a given region should not include all possible combinations of R, S and F values, but rather reflect its fire history. In regions with a long and intense history of fire such as Mediterranean-type climate ecosystems (MTCE), high values of R, S and F, which increase the performance of the plants in the face of recurrent fires, should be relatively common. In regions with moderate fire history, such as the South American Chaco, intermediate values of R and S should prevail, although some species could have high resprouting or seeding as a strategy against other common disturbances, such as herbivory and extreme drought; combined with intermediate values of flammability (usually associated with growth form). In regions with only recent fire history, fire-sensitive and non-flammable species should be more common.

About the research

To illustrate our approach, we assessed the fire syndromes of 24 species that are common in the seasonally dry Chaco Forest of central Argentina, and compared them to 33 species from MTCE. Supporting our hypothesis, we found that MTCE species had more variety of syndromes than Chaco species (13 vs. 7, respectively), and higher frequency of species with extreme values of R, S and F (16 vs. 7 species, respectively).

The dry Chaco region is composed of a mosaic of woodlands, shrublands and grasslands, many of which are highly fire-prone (credit: Pedro Jaureguiberry)

In addition, we conducted a literature review and collected information on R, S and F for over 4000 species, covering approximately 1250 genera and 180 botanical families, belonging to 10 different growth forms, and from 7 major regions with a wide range of fire histories, from long and intense (MTCE) to very recent (New Zealand). Supporting our hypothesis, MTCE species (except South Africa) had predominantly high or low R values, and very few had intermediate values. In contrast, most New Zealand species had low R values, with only a few showing intermediate values. For the S-axis, high values predominated in two of the MTCE (South Africa and South Australia), and intermediate values were the most frequent in the remaining regions, but the proportions differed. Finally, the F axis showed a clear predominance of high values in MTCE, while the low—and intermediate values to a lesser extent—predominated in the Brazilian Cerrado, the Chaco, and New Zealand.

Our model, based on resprouting, seeding and flammability, is a step forward from previous classifications because it incorporates not only specific response, but also specific effect functions of plants with respect to fire. This model is of special interest in ecosystems prone to disturbances (such as fire, herbivory and extreme drought), where the stability of the system depends on feedback between plant response and the marked influence on their own environment through effect traits. In such ecosystems, R, S, and F are more likely to be correlated, rather than independent.

Post-fire regeneration in the Chaco woodlands one growing season after a fire. The spaces generated after the fire can be quickly colonized by different species (top and bottom left), either by recruiting individuals from seeds (for example many annual forbs and grasses), resprouting vigorously from the base as Prosopis flexuosa (bottom right), and/or from root suckers such as Parkinsonia praecox and Celtis ehrenbergiana (top right) (credits: Pedro Jaureguiberry)

Our model represents a greater synthesis effort than previous works in three ways: (a) it is more sensitive to capture variations of fire syndromes across regions with contrasting fire regimes, broadening the scope of previous models; (b) it is not limited to particular growth forms or taxa; (c) it focuses on the performance of the plant in relation to the three proposed axes or functions, regardless of the particular underlying traits that determine them.

Giant sequoias (Sequoiadendron giganteum) rely on periodic low-severity fires for cones to release their seeds and recruit new individuals (credit: Pedro Jaureguiberry)

The expansion of this database, including more species and regions, will help produce a more comprehensive picture, and will allow exploring patterns at finer scales. We hope to stimulate colleagues around the world to join this effort.

About the author

Pedro Jaureguiberry hiking in the Córdoba mountains, Argentina

From a very young age, I was interested in natural sciences, and the relationship between humans with nature. From my early years of college, I was drawn to macrobiology, particularly ecology at the level of communities and ecosystems, and how these are shaped by different disturbances. When I arrived at the IMBIV Research Group, on my first field trips I became interested in fire because it is a factor of growing socio-ecological relevance, not only in the Chaco but worldwide, and is relatively little studied. Fire attracted me because it is both a natural factor and has been a tool for human beings throughout history. This allows me to focus on both ecological aspects—for example in relation to disturbances as factors shaping the evolution of species—and in aspects that involve humans as agents of change over natural fire regimes, thereby changing the role of fire across the world (by promoting or suppressing fire) with major impacts.

Today, the sustainable coexistence between fire and human beings is a great challenge in many regions of the world. That is why I am interested in studying how plants respond to fire, but also how they affect the ecosystem through their flammability; and how these two aspects combine in general whole-plant strategies. I hope my work will help not only to advance knowledge of the dynamics of ecosystems, but also to facilitate integrated fire management in fire-prone regions and also in places where fires are becoming increasingly common.

Enjoyed the blogpost? Read the research here!

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