Deforestation: A Lesson from the Permian Extinction

Satellite photo of Amazon fires. Credit: NASA

The recent fires at Amazonas, Gran Canaria (Spain), Australia, and Indonesia sparked international outcry. Climate change makes forests hotter and drier, thus more likely to sustain uncontrolled fires. But fires are also linked with deforestation. Almost 1 million km2 of Amazon forest has already been deforested, and a recent study indicates that the number of active fires in this August was actually three times higher than 2018. Deforestation is a threat to biodiversity and ecosystems stability. It also leads to the loss of cultural diversity, the alteration of the hydrological cycle and climate systems.

The geological records show that large and rapid global warming events occurred repeatedly during the course of Earth history. The End-Permian extinction event (EPE) serves as a powerful deep-time analogue for modern deforestation and diversity loss, with as much as 95% of the marine animal species and a similarly high proportion of terrestrial plants and animals going extinct . This great crisis ocurred about 252 million years ago (Ma) during an episode of global warming. A recent study focussed on the Sydney Basin, Australia, shows how the typical Permian temperate forest communities disappeared abruptly, followed by a short ‘dead zone’ characterized only by charcoal, wood fragments, and fungi, signatures of an interval of wildfire and saprotrophic breakdown of organic matter.

Global paleogeographic map for the Permian-Triassic transition showing the location of the Siberian Traps Large Igneous Province. From Vajda et al., 2019

Two palynological events marked the end-Permian Event: the ‘algal/fungal/acritarch event’ (a bloom of Reduviasporonites, and of acritarchs in marine environments); and the ‘spore-spike event’. The first event in post-extinction continental deposits has contributed to a continuing debate as to whether the EPE interval was marked by eustatic sea-level rise. The ‘spore-spike event’ indicates that many plant groups survived in regional refugia, possibly at higher altitudes, or in coastal settings where conditions were consistently cooler or wetter. Some of those survivors constituted the pioneer vegetation during the Early Triassic.

During the EPE the woody gymnosperm vegetation (cordaitaleans and glossopterids) were replaced by spore-producing plants (mainly lycophytes) before the typical Mesozoic woody vegetation evolved. Glossopterids were the prime contributors of biomass to the vast Permian coal deposits of Gondwana, therefore their disappearance had major implications for ecosystem structure. The very rapid appearance of drought-tolerant plant associations (dominated by conifers and the seed fern Lepidopteris) in the macroflora of the Sydney Basin, may represent immigration of drought-adapted biota from other regions of Pangea.

Spores and pollen identified in the post-extinction mudstone at the Frazer Beach section. From Vajda et al., 2019

The palynological record suggests that wooded terrestrial ecosystems took four to five million years to reform stable ecosystems, while spore-producing lycopsids had an important ecological role in the post-extinction interval. The disappearance of the Glossopteris that dominated the cool Permian wetland forest of Gondwana, had  enormous consequences for landscape coverage, ecosystem structure, food webs, and caused substantial perturbations to the hydrological and carbon cycles of the entire biosphere.

Since the industrial revolution, the wave of animal and plant extinctions that began with the late Quaternary has accelerated. Australia has lost almost 40 percent of its forests, and almost 20% of the Amazon has disappeared in last five decades.Calculations suggest that the current rates of extinction are 100–1000 times above normal, or background levels. If we want to stop the degradation of our planet, we need to act now.

 

References:

V. Vajda et al. (2020), End-Permian(252Mya) deforestation, wildfires and flooding—An ancient biotic crisis with lessons for the present, Earth and Planetary Science Letters 529 (2020) 115875 https://doi.org/10.1016/j.epsl.2019.115875

Jos Barlow et al, Clarifying Amazonia’s burning crisis, Global Change Biology (2019). DOI: 10.1111/gcb.14872

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