Humans take control of fire-driven diversity changes in Mediterranean Iberia’s vegetation during the mid–late Holocene

Abstract

Fire regime changes are considered a major threat to future biodiversity in the Mediterranean Basin. Such predictions remain untested, however, given that fire regime changes and their ecological impacts occur over timescales that are too long for direct observation. Here we analyse centennial-3 and millennial-scale shifts in fire regimes and compositional turnover to track the consequences of fire regime shifts on Mediterranean vegetation diversity. We estimated rate-of-change, richness and compositional turnover (beta diversity) in 13 selected high-resolution palaeoecological records from Mediterranean Iberia and compared these to charcoal-inferred fire regime changes. Event sequence analysis showed fire regime shifts to be significantly temporally associated with compositional turnover, particularly during the last three millennia. We find that the timing and direction of fire and diversity change in Mediterranean Iberia are best explained by long-term human-environment interactions dating back perhaps 7500 years. Evidence suggests that Neolithic burning propagated a first wave of increasing vegetation openness and promoted woodland diversity around early farming settlements. Landscape transformation intensified around 5500-5000 cal. yr BP and accelerated during the last two millennia, as fire led to permanent transitions in ecosystem state. These fire episodes increased open vegetation diversity, decreased woodland diversity and significantly altered richness on a regional scale. Our study suggests that anthropogenic fires played a primary role in diversity changes in Mediterranean Iberia. Their millennia-long legacy in today's vegetation should be considered for biodiversity conservation and landscape management.

Sustainable Land Management, Wildfire Risk and the Role of Grazing in Mediterranean Urban-Rural Interfaces: A Regional Approach from Greece

“…Land abandonment in rural areas has been shown to stimulate biomass accumulation. Since vegetation is not used by animals or managed by humans, spatial heterogeneity of natural landscapes increases, leading to more unpredictable fire patterns [7,35]. In these regards, sustainable land management is fundamental to containing wildfires [1,33,34].…”

“…In the last century, the progressive decline of forests in advanced economies has been often linked with crop intensification [3]. While anthropogenic-driven fires have been historically used as a land management system in order to adapt natural settings to agricultural (or residential) use [4][5][6], wildfires combined with human activity have reinforced the development of fire-adapted forest ecosystems [7]. In Europe, biophysical and socioeconomic conditions supporting a dynamic balance between land-use allowed for keeping wildfires as a largely controlled phenomenon up to the 1950s [8].…”

“…Sustainable land management is fundamental in these circumstances [1,[30][31][32][33][34]. For instance, abandonment of forest and non-forest natural land including pastures, led to increased vegetation biomass which is no longer managed by humans or used by animals [7,35]. An excess of biomass leading to increased fuels in both forest and non-forest land has been considered to be a key driver of wildfire risk [22,23,36,37].…”

“…In other words, WUIs produce a spatial setting in which wildfires can easily spread from forest fuel to human settlements [58]. While requiring major investments, measures aimed at reducing the contact point between forests and settlements, e.g., creating buffers (or physical barriers) among buildings and vegetation, seem to be appropriate in such contexts [7,[59][60][61][62]. For instance, the European Commission invested more than 3.2 billion Euros per year in fire suppression with the aim of restraining the socioeconomic impact of wildfires [8,10].…”

“…Together with land-use change and farmland abandonment, a decline of livestock activities and grazing in peri-urban areas indirectly led to the accumulation of vegetation biomass in fringe natural land. Being strictly connected with the (increasing) urban market, animal husbandry around large cities has traditionally represented a natural control of vegetation, e.g., through nomadic sheep, goats, and cattle farming [7,[64][65][66][67][68][69]. Up to a sustainable carrying capacity, pasture and forest systems may support a high density of grazing animals.…”