Catalonia and California share solutions to protect biodiversity from drought, heatwaves and fires

The Department of Territory, Housing and Ecological Transition of the Catalan autonomous government has presented, within the framework of the COP17 on Biodiversity, in Yerevan (Armenia), the first study on the impact of climate change on the biodiversity of the Mediterranean bioregions that Catalonia is developing jointly with California within the framework of the MCAP (Mediterranean Climate Action Partnership). The study, that has been commissioned from CREAF, compares the two regions and seeks shared solutions. The Secretary of Ecological Transition, Jordi Sargatal, explained that “the study's objective led by Catalonia and California is to analyze the effects of climate change on natural systems and society, such as species displacements, hydrological changes or the loss of ecosystem growth. This will allow us to share and advance in providing more effective responses to the challenges posed by extreme climate phenomena and provide models that can be replicated in the rest of the countries and regions that share our climate”.

The work confirms that the two regions are experiencing a progressive loss of native species - especially in freshwater systems -, as well as an increase in phenomena such as large fires, prolonged droughts that cause serious impacts on the forest mass and marine heat waves that can irreversibly alter marine ecosystems. The expert organizations in the two regions agree that protecting biodiversity in the new climate context involves creating refuges so that species can withstand extreme episodes, favoring more diverse ecosystems, acting on problems that aggravate the situation (such as overexploitation of aquifers or overfishing) and strengthening monitoring to understand what is changing and be able to act in time.

In this report, CREAF has carried out a bibliographic review and has consulted with experts who have proposed new articles, questions and knowledge that could be relevant. In total, 4 experts from Catalonia and 4from California have participated, including Mireia Banqué from CREAF, Núria Bonada from the University of Barcelona and Mark Carr and Jennifer Caselle, from the University of California, among others.

The freshwater aquatic systems of California and Catalonia share severe drought episodes combined with increasingly extreme rainfall patterns. This directly impacts the fauna and flora of the rivers, where native fish are the ones suffering the most from the climate effects in both regions. Regarding Catalonia, the State of Nature already warned that the populations of species in rivers, lakes and wetlands decreased by 54% between 2002 and 2019, while in California, it is estimated that 82% of native fish are very vulnerable to climate change. Furthermore, in both places climate change does not act alone, the overexploitation of aquifers, pollution and the presence of invasive species are also added. To solve this, the two regions are aware that the key action is the creation of aquatic refuges.

If there were to be a priority action to recover the life of rivers in the two Mediterranean regions, it would be to identify, protect and guarantee the connectivity of a network of water refuges spread across the territory. We are talking about ponds, springs and habitats fed by groundwater where species can live when the river dries up and thus be able to recolonize the rivers after a drought.

The general director of Environmental Policies and the Natural Environment of the Catalan government, Marc Vilahur, explained in this regard that "this study allows us to identify how similar the trends of the different Mediterranean territories are towards the dual problem of climate change and biodiversity loss. The impacts are severe and the transformation of the strategies to be developed will have to be profound if this trend of increasing temperatures is not reversed. We will have to adapt to a drier climate and at the biodiversity level this means prioritizing recovering water points where possible".

Regarding forests, Catalonia and California have reached a similar problem by different paths. In Catalonia, rural abandonment and the end of intensive exploitation have led to the growth of young, dense and structurally homogeneous forests, with a high demand of water. In California, on the other hand, decades of fire suppression have also produced dense forests vulnerable to drought, pests and fires. In fact, in Catalonia, in 2023 drought affected 66,482 hectares of forest. In California between 2012 and 2016, drought was responsible for the death of more than 129 million trees. However, the report highlights that in both regions, drought has also served to regulate forest density, reduce competition for water among survivors, open clearings and generate dead wood, favoring species that depend on these habitats. Despite these local dynamics, dense and poorly managed forests remain exposed to combined climate risks, with mortality from drought and loss of carbon sink capacity.

As for solutions, although both regions have forest management instruments, the report proposes prescribing forest management that is closer to nature, taking into account elements such as dead wood, trees of different ages or micro-refugees. Likewise, forest management should help reduce competition for water, favor drought-resistant native species, recover meadows and open spaces and plan at a landscape scale.

"We are promoting several projects to test solutions along these lines, such as the LIFE RedBosques_Clima project that has been developed in the Els Ports Natural Park (Catalonia) to promote mature forests and promote forest biodiversity or boosting mosaic landscapes in protected natural spaces such as Cap de Creus (North East Catalonia)", Marc Vilahur highlighted.

According to the scientific evidence collected by the report, both Catalonia and California are in a situation known as the extinction trap. This trap or paradox occurs when policies focused exclusively on fire suppression reduce fires in the short term, but increase their risk in the long term. Since most resources and investments are allocated to emergency suppression, structural prevention efforts are relegated, and this allows biomass to accumulate dangerously. This situation occurs in both Catalonia and California. "The more efficient we are in extinguishing all fires, prevention takes a back seat and more fuel accumulates", according to Alicia Pérez-Porro. "And when drought, heat and extreme weather conditions coincide, fires appear that can exceed the extinguishing capacity".

It is particularly interesting because Catalonia and California have arrived at this same trap through different social trajectories. In Catalonia the responsible factor has been mainly rural abandonment and the disappearance of agricultural and pastoral uses in forests. In California, the key factors have been institutional fire suppression (decades of official policy of extinguishing all fires, eliminating fire as an ecological process) and the displacement of indigenous peoples, which has led to the loss of traditional burning practices.

However, the report introduces an important nuance from a biodiversity point of view, fire is not always the enemy. In fact, the solution shared between the two regions proposes prescribed burns (or small controlled fires) to build heterogeneous landscapes, open clearings and generate mosaics of open habitats, spaces in retreat in the two regions that are key habitats for many species in decline. Thus, it also proposes combining it with specific forest management plans, extensive livestock farming and pastoralism, a set of practices that require coordinating owners and administrations and integrating forest policy, biodiversity and rural development.

Without a doubt, the Mediterranean sea is the habitat where climate change is having the strongest impact. In fact, the recurring marine heat waves that the Mediterranean has experienced have caused episodes of mass mortality of more than 50 species (including corals, gorgonians and sponges) and a constant decrease in the habitat of Posidona oceanica . One of the problems of this sea is that its closed geography means that species adapted to the cold can only move north to a certain point, becoming a kind of biogeographic cul-de-sac, at first they are climate refuges but, if warming continues, they eventually end up being extinction traps. In the case of the Pacific Ocean, California experienced a very important change in the state of the ecosystem during and after a marine heat wave dubbed 'The Blob', between 2014 and 2016, when forests of a macroalgae called kelp ( Nereocystis luetkeana ) decreased by more than 95% in some stretches of the northern coast of California, due to the combined effect of the heat wave, a starfish disease and the proliferation of sea urchins.

Despite being very different seas and oceans, the report considers that both regions face the risk of suffering almost irreversible changes in the status of species that create key habitats: Posidonia in the Mediterranean and kelp in California. And the effects are not only ecological. In Catalonia, temperatures above 28 °C can cause up to 100% mortality of mussel seed in the Ebro Delta, while the models included in the report project a 20% reduction in total fish catches in 2051–2060.

The shared solution in this case is resounding, the report makes it clear that we have marine protected areas designed to conserve biodiversity in a climate that no longer exists. Marine protected areas of the future must also be designed and assessed based on their climate resilience. This means effectively protecting food webs, identifying and protecting marine thermal refuges, such as cooler areas, and connecting heatwave warning systems with management protocols that are activated when there are mass mortalities. At the same time, before establishing any new marine areas or restoring any other habitat, it will be necessary to reduce the pressures that are affecting marine life, overfishing, pollution and eutrophication.

"In the face of a changing climate, protecting biodiversity no longer means just conserving what we have, but helping ecosystems to resist, recover and adapt to new conditions. Sharing what works and what doesn't between Mediterranean regions is precisely one of the objectives of the MCAP and this report", concludes Alicia Pérez-Porro.