Understanding and modelling wildfire regimes: an ecological perspective

Recent extreme wildfire seasons in several regions have been associated with exceptionally hot, dry conditions, made more probable by climate change. Much research has focused on extreme fire weather and its drivers, but natural wildfire regimes – and their interactions with human activities – are far from being comprehensively understood. There is a lack of clarity about the ‘causes’ of wildfire, and about how ecosystems could be managed for the co-existence of wildfire and people. We present evidence supporting an ecosystem-centred framework for improved understanding and modelling of wildfire. Wildfire has a long geological history and is a pervasive natural process in contemporary plant communities. In some biomes, wildfire would be more frequent without human settlement; in others they would be unchanged or less frequent. A world without fire would have greater forest cover, especially in present-day savannas. Many species would be missing, because fire regimes have co-evolved with plant traits that resist, adapt to or promote wildfire. Certain plant traits are favoured by different fire frequencies, and may be missing in ecosystems that are normally fire-free. For example, post-fire resprouting is more common among woody plants in high-frequency fire regimes than where fire is infrequent. The impact of habitat fragmentation on wildfire crucially depends on whether the ecosystem is fire-adapted. In normally fire-free ecosystems, fragmentation facilitates wildfire starts and is detrimental to biodiversity. In fire-adapted ecosystems, fragmentation inhibits fires from spreading and fire suppression is detrimental to biodiversity. This interpretation explains observed, counterintuitive patterns of spatial correlation between wildfire and potential ignition sources. Lightning correlates positively with burnt area only in open ecosystems with frequent fire. Human population correlates positively with burnt area only in densely forested regions. Models for vegetation-fire interactions must be informed by insights from fire ecology to make credible future projections in a changing climate.

Fire in African Landscapes

Fires have burned in African landscapes for more than a hundred million years, long before vertebrate herbivores trod the earth and modified vegetation and fire regimes. Hominin use of lightning fires is apparent c.1.5 million years ago, becoming deliberate and habitual from c. 400 thousand years ago (kya). The emergence of modern humans c. 195 kya was marked by widespread and deliberate use of fire, for hunting and gathering through to agricultural and pastoral use, with farming and copper and iron smelting spreading across sub-Saharan Africa with the Bantu migrations from 4–2.5 kya. Europeans provided detailed reports of Africans’ fire use from 1652 in South Africa and the 1700s in West Africa. They regarded indigenous fire use as destructive, an agent of desiccation and destruction of forests, with ecological theories cementing this in the European imagination from the 1800s. The late 1800s and early 1900s were characterized by colonial authorities’ attempts to suppress fires, informed by mistaken scientific ideas and management principles imported from temperate Europe and colonial forestry management elsewhere. This was often ignored by African and settler farmers. In the 1900s, the concerns of colonial foresters and fears about desiccation and soil erosion fueled by the American Dust Bowl experience informed anti-fire views until mid-century. However, enough time had elapsed for colonial and settler scientists and managers to have observed fires and indigenous burning practices and their effects, and to begin to question received wisdom on their destructiveness. Following World War II, during a phase of colonial cooperation and expert-led attempts to develop African landscapes, a more nuanced understanding of fire in African landscapes emerged, alongside greater pragmatism about what was achievable in managing wildfires and fire use. Although colonial restrictions on burning fueled some independence struggles, postcolonial environmental managers appear on the whole to have adopted their former oppressors’ attitudes to fire and burning. Important breakthroughs in fire ecology were made in the 1970s and 1980s, influenced by a movement away from equilibrium-based ecosystems concepts where fires were damaging disturbances to ecosystems, to an understanding of fires as important drivers of biodiversity integral to the functioning of many African landscapes. Notably from the 1990s, anthropologists influenced by related developments in rangeland ecology combined ecological studies with studies of indigenous land use practices to assess their impacts over time, challenging existing narratives of degradation in West African forests and East African savannas. Attempts were made to integrate communities (and, to a lesser extent, indigenous knowledge) into fire management plans and approaches. In the 2000s, anthropologists, archeologists, geographers, historians, and political ecologists have contributed studies telling more complex stories about human fire use. Together with detailed histories of landscape change offered by remote sensing and analysis of charcoal and pollen deposits, these approaches to the intertwined human and ecological dimensions of fire in African landscapes offer the prospect of integrated histories that can inform our understanding of the past and guide our policies and management in the future.

Meta-analysis using a Lehmann classifier of obligate seeding species germination in fire-prone Mediterranean Type environments

The generalization that specific seed traits such as dormancy, longevity, or heat-triggered germination of plant species expanding in pyrogenic environments where stochastically but recurrently fire disturbance occurs is a fitness increasing adaptation of obligate seeders dates from the early 20th century. During the last few decades, this hypothesis, qualified as a pyrophytic strategy, is re-evaluated under the lenses of conservation biology and climate change research. The validity of pyrophytism as an equilibrium response to fire vs. the interpretation that the obligate seeding strategy is instead an opportunistic or generalist response to the multitude of abiotic and biotic factors determining the variability and heterogeneity of fire-prone environments such as the Mediterranean Type Ecosystems is indirectly examined and narratively promoted in the renewed fire ecology literature. In this paper, I suggest a need for a typified meta-analysis of the abundant but disparate wealth of research protocols and data to achieve a quantitatively strict understanding of the limits of the contrasting hypotheses. I develop a meta-analytic classifier and test its feasibility and applicability across taxonomic, biologic, and ecological levels of organization, i.e., from the intra-population or inter-individual local level progressively to inter-genus and intra-family levels, across the Mediterranean Basin. Cistaceae species, emblems of the Mediterranean shrublands, are the model for this research. The results of this exercise support the feasibility and flexibility of the Lehmann-type classifier developed. Although Cistus species do respond positively to heat-shocks at the local level, significant variability is uncovered among higher taxa levels and furthermost as the environmental variability increases. The germination variability complicates generalizations when climatic variability and change come into play, questioning long-standing ‘certitudes’ and Mediterranean forest managers and conservation planners' practices.

Vegetation ecology with anthropic drivers and consequences

Current research on vegetation makes a difference in people’s lives. Plant community classification is a backbone of land management, plant communities are changing in response to anthropogenic drivers, and the processes of change have impacts on ecosystem services. In the following progress report, we summarize the status of classification and recent research on vegetation responses to pollution, especially nitrogen deposition, invasive species, climate change, and land use and direct exploitation. Two areas with human feedbacks are underscored: fire ecology and urban ecology. Prominent questions at the current research frontier are highlighted with attention to new perspectives.

How Do Plants Respond Biochemically to Fire? The Role of Photosynthetic Pigments and Secondary Metabolites in the Post-Fire Resprouting Response

Resprouting is one of the main regeneration strategies in woody plants that allows post-fire vegetation recovery. However, the stress produced by fires promotes the biosynthesis of compounds which could affect the post-fire resprouting, and this approach has been poorly evaluated in fire ecology. In this study, we evaluate the changes in the concentration of chlorophylls, carotenoids, phenolic compounds, and tannins as a result of experimental burns (EB). We asked whether this biochemical response to fire could influence the resprouting responses. For that, we conducted three EB in three successive years in three different experimental units. Specifically, we selected six woody species from the Chaco region, and we analyzed their biochemical responses to EB. We used spectrophotometric methods to quantify the metabolites, and morphological variables to estimate the resprouting responses. Applying a multivariate analysis, we built an index to estimate the biochemical response to fire to EB per each species. Our results demonstrate that photosynthetic pigment concentration did not vary significantly in burnt plants that resprout in response to EB, whereas concentrations of secondary metabolites (phenolic compounds and tannins) increased up to two years after EB. Our main results showed that phenolic compounds could play a significant role in the resprouting responses, while photosynthetic pigments seem to have a minor but significant role. Such results were reaffirmed by the significant correlation between the biochemical response to fire and both resprouting capacity and resprouting growth. However, we observed that the biochemical response effect on resprouting was lower in tree species than in shrubby species. Our study contributes to the understanding of the biochemical responses that are involved in the post-fire vegetation recovery.