F53D23008220001

Plant traits of native and invasive species in fire ecosystems across the world (WiFIn)

 

Descrizione

Fire is an important ecosystem disturbance, having significant socio-economic consequences on the one hand, while fulfilling a vital ecological role on the other. Across fire-prone ecosystems, different fire regimes can be found, reflecting a combination of climatic factors and of different plant species characteristics. Ecosystem flammability and fuel load are the most evident and well-studied aspects of plant interactions with fire regimes. Only recently, has there been a major focus on how other plant traits, and especially fire responses, shape the fire regime. For example, invasive alien species with highly competitive traits, when introduced by humans into novel ranges, can have dramatic impact on the local fire regimes. The aim of this research is to determine the role that plant traits have in driving fire regimes in different ecosystems across the world and for various climates, including also the role played by invasive species. The main hypothesis is that plant traits of native and invasive species, especially those determining fire responses, are an important factor in determining whether an ecosystem might tip into an alternative ecosystem state, driven by differences in how traits determine fire regimes and in relation to competition between plant species. The key objectives of this research are: 1) to identify how plant traits co-vary in fire-prone ecosystems at a global scale; 2) to assess for which regions and under which conditions plant trait syndromes are fundamental in determining fire regimes and the occurrence of different plant communities under the same climatic conditions 3) to determine how fire-related plant traits allow alien species to successfully invade established communities and potentially lead to ecosystem shifts. Based on a combination of statistical and mathematical, mechanistic modelling, using existing and available, extensive datasets, this research has the potential to improve the ability to predict fire regimes in the future at a global scale, given climate change and its influence on ecosystem dynamics. Namely, broader societal and scientific impacts will be: improving the definition of plant functional types for fire used in global vegetation models, which would lead also to improvements in Earth System Models for climate prediction; improved understanding of the role of plants on fire regime in the future, to assist in fire management prevention efforts, related to both native and invasive species; providing guidance on plant-fire responses in relation to ecosystem restoration / change (i.e. afforestation) projects.

Finalità

Identifying how plant traits co-vary in fire-prone ecosystems at a global scale and determining how fire-related plant traits allow alien species to successfully invade established communities and potentially lead to ecosystem shifts

Specific research questions (RQs) are: Given the local climate in ecosystems across the world,

• Are there relationships between Fire, Growth and Competition (FGC) traits in plant species that can be quantitatively identified across taxa and climatic regimes, and, if so, how do they relate with different fire regimes?
• Are there FGC plant traits which, alone or in combination, allow certain invasive plant species to thrive in fire ecosystems?
• Do the (combinations of) FGC plant traits that influence fire regimes predict the possible emergence of alternative ecosystem states (AES)?
• Can invasive species contribute to ecosystem loss of resilience and possible tipping, by influencing their fire regimes and post-fire recovery?

 

Risultati attesi 

We will address our research questions by analysing large datasets and by developing mathematical models in two main work packages. We hypothesise that results will show that fire response generally increases with flammability. More specifically, we expect to find that plants with low flammability can display a broad range of fire responses, while highly flammable plants have different fire responses depending on their growth rate (and thus also taxa): slow growers (such as trees) always have strong fire responses, while fast growers (such as grasses) can display medium to strong fire responses. At community level, we expect that the post-fire response of the dominant species is key to the existence of AES, and thus we expect to be able to classify the resilience of various fire ecosystems worldwide from their FGC traits. Finally we expect to find that high flammability in conjunction with some fire adaptation is expected to be important for the success of invasive species, as seen for invasive grasses, and might determine their ability to tip the ecosystem.

Stato dell’arte

Fire is generally seen as a destructive force, especially given its increasing social and economic impacts (e.g. California, Australia; Mediterranean). Yet, vital ecological processes also depend on fire. For example, biodiversity is generally positively impacted by fires, which also maintain ecosystems, e.g. savannas. Climate and vegetation are the most important drivers of fire activity. Climate can influence fires via fire prone weather conditions (wind, low humidity and high temperatures), which are becoming more and more common because of climate change. Also, temperature and moisture control fuel drying. However, fire regimes are also determined by biological feedbacks, whereby plants and fire are strongly interrelated. Plants influence fires primarily in terms of the availability and flammability of fuel. In the past, the evolution of new plant properties or the shift of plant community composition led to changes in fire regime. Similarly, invasive alien species, introduced by humans outside their native range, can have dramatic impact on fire regimes. For example, over the last decades invasive grasses led to increased fire frequencies and altered fire intensities around the globe. In turn, fire regimes influenced the development of plant fire adaptations, where individuals quickly re-sprout following intense fire events, or can withstand low intensity fires by means of a thick bark. Fire regimes thus influence plant composition, and this in turn influences ecosystem flammability. This positive vegetation-fire feedback has been proposed to drive alternative ecosystem states (AES) in boreal and temperate forests, and in the widely studied tropical forests and savannas. Here, flammable savanna C4 grasses maintain frequent fires that suppress fire-intolerant tropical forest trees; conversely, forest trees shade grasses and reduce the chances of fires by creating a moist understory. Climate and plant effects on fires are not disconnected. Increased aridity enhances fuel flammability, while at the same time decreasing fuel continuity, thus potentially acting as either a limitation or an enhancer of fire activity. In addition, but less widely studied, the influence of aridity on fire responses (e.g., resprouting) and on plant growth has been shown to determine fundamentally the type of fire regime and ecosystem, with the combination of climate change and fire leading to a loss of resilience of Mediterranean forests. To describe the role of plants within the plant-fire-climate nexus, we need to analyse how fire-prone plant communities form: given a certain environment, communities are shaped by assembly dynamics, e.g. competition, but also by fire responses and adaptations. Plant characteristics, i.e., functional traits, determine all these processes. For a given species, plant trait values reflect the trade-off between strategies, with for example “competitive” species maximizing growth in productive systems at the expense of resilience. Plant traits also determine invasion dynamics by alien species introduced by humans into novel ranges, with traits associated to fast growth rates, fast dispersal and competitive ability (e.g., tall plants with large fleshy leaves and small seeds) typically favouring invasions. To allow a species to survive within a particular environment, traits are often correlated, giving rise to trait “syndromes”. Fire-adapted plant communities include species whose traits are shaped by coping with fire (‘fire responses’). Plant individuals that survive fire may have thicker bark39 or resprout after fires due to large below-ground carbohydrate reserves40. Species that survive fires at population level generally have elements of their life cycle closely tied to fire, including germination caused by combustion, post-fire seed release in crown systems (serotiny) or enhanced flammability to increase the frequency and intensity of fires to the detriment of non-resprouting competitors. Finally, fire-intolerant species have few adaptations to fire and are generally found in areas where fires are infrequent. These strategies help to fundamentally determine the plant community compositions in fire-prone environments, together with classically studied assembly processes such as competition for resources. At present, the interactions between plant traits associated with growth and competition, and those associated with fire, for both native and invading species, have not been comprehensively investigated across the world, nor in their relationships with the emerging fire regimes and the stability and resilience of the ecosystems involved. Similarly, despite growing recognition of the prevalence and importance of invasion-fire cycles, the plant traits of invasive species that may contribute to successful invasion and subsequent ecosystem tipping under different fire regimes have not been studied yet.

 

Riferimento: PRIN 2022 PNRR – Codice progetto: PRIN PNRR P2022NRLF2 – CUP: F53D23008220001

Investimento totale del progetto: 236.736  €

Partner/proponente: Centro Nazionale delle Ricerche (Coordinatore), Università degli Studi Roma Tre

Coordinatore dell’UdR Università degli Studi Roma Tre:  Marta Carboni