Ecosystems and extreme weather events

Conservation planners in the age of climate change attempt to model and predict the outcomes of mitigation strategies in the near and distant future. Global responses to the climate crisis have generally focused on how ecosystems will react to medium and long-term changes in global temperatures (warming oceans, rising sea levels and changing seasons). But short-term extreme weather and thermal events could challenge these best-laid plans, or even render them useless. According to a group of researchers from Australia and the United States, led by Sean L. Maxwell, “extreme weather and climate events…such as cyclones, floods, heat waves and droughts, have become more frequent and more intense in many parts of the world. a consequence of anthropogenic climate change. This pattern is likely to accelerate.

The group conducted extensive desk research to gather records of extreme weather and climate events – cyclones, droughts, cold spells, unseasonal floods and heat waves – that are rare in their statistical reference distribution at a particular location. Ultimately, they identified more than 500 peer-reviewed studies that documented the effects of extreme weather events on taxonomic groups including plants, birds, invertebrates, mammals, reptiles and amphibians.

Reactions to extreme weather conditions varied both by species and by environment. The team was able to sort the responses into nineteen categories: four positive; eight negatives; six ambiguous; and a neutral (no detectable response). On the positive On the other hand, some species increased in density or abundance after a weather event, mainly after cyclones or floods. For example, after a cyclone, bird species that preferred regenerating habitats increased in number, while some fish and invertebrate species increased in richness. On the negative Côté, the team found thirty-one cases of local disappearance. Eighteen of these cases were reassessed after a period of recovery; twelve of the cases reviewed were found to be persistent. In other words, the local extinction appeared permanent. The team found four cases of mammals becoming extinct after a flood and five cases of invertebrates rendered locally extinct after a cyclone.

Although the team found a larger number of positive or neutral responses to extreme events than expected, more than half of the impacts (57%) were negative and, more importantly, the majority continued well beyond of the single meteorological event. “Sixty percent of the studies in our review observed ecological responses for more than a year,” the team writes, “and of the studies that monitored species or ecosystem recovery after exposure to an extreme event, 38 % showed that species or ecosystems had not recovered to pre-disturbance levels.

Of the surviving flora and fauna, plants experienced the most weather-related negative reactions at 70%. From hurricane damage to repeated hot days, plant communities seemed to suffer evenly. And the team found few positive responses to cold spells. Perhaps unsurprisingly, cyclones – large-scale land and sea storms – have most often affected birds, fish, plants and reptiles. What may seem more surprising is that cyclones seem to have a particular impact on reptiles. In fact, the team found no positive reptilian response to an extreme event.

Notably, many of the studies reviewed lasted only one year. They did not take into account any subsequent recovery of injured species, nor did they consider the long-term effects of these short-term weather anomalies. But, as the researchers point out, a weather event can have catastrophic long-term impacts. For example, a single flood in Portal, Arizona is known to have “resulted in a rapid and wholesale reorganization of a desert rodent community.” At the same time, the study shows that it is possible that an extreme event could lead to an increase in species richness or composition, or allow species to occupy new habitats, which would be considered a positive effect.

The team’s findings had one glaring conclusion: extreme weather conditions will have extreme impacts. The authors conclude: “Integrating extreme events into climate change vulnerability assessments and adaptation plans will be challenging, but in doing so we have a greater chance of arriving at conservation interventions that genuinely address all the impacts of climate change. »

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Diversity and Distributions, Vol. 25, n° 4, Special issue: The biogeography of conservation in a changing climate (April 2019), pp. 613-625


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