The fossil record preserves the same fragmented leaf litter. Comparison of the shapes of thousands of epidermal cells with the leaf area index we measured revealed a remarkably strong relationship: The longer the cells, the denser the forest canopy above them.
This relationship allowed us to reconstruct the structure of Wyoming’s forests millions of years ago and show how they changed over time.
One of the most surprising discoveries was that the forests did not reach the Paleocene-Eocene thermal maximum in decline.
Just before rapid warming began, the forest canopy reached its greatest density in hundreds of thousands of years, likely due to favorable growing conditions as atmospheric carbon dioxide increases began. A leading theory for the source Of this, the proportion of carbon dioxide comes from volcanic eruptions.
However, this blooming forest did not last. As temperatures rose, heat and drought offset the benefits of higher carbon dioxide levels. The canopy was rapidly thinned as the trees diedand it remained much thinner for over 100,000 years.
The forests functioned very differently in this diminished state, and this also affected the surrounding environment. Ancient soils gave way to coarser fluvial deposits, suggesting that tree canopy loss altered the movement of water and sediment through the basin.
Climate change changed the forest and the forest changed the landscape.
Lessons for today
This sequence contains an important lesson for today.
Higher carbon dioxide levels as the world is experiencing it now can stimulate plant growth, but only as long as temperatures and water remain within the limits that trees will tolerate.
Beyond these limits, heat, drought, insects, pathogens, and wildfires can negate any fertilizing effect that would promote growth.
Many all over the world Forests are already showing signs of decline As temperatures rise, deforestation for timber, crops and pasture occurs in addition to deforestation, further reducing their resilience.
The forests recovered, but it took over 100,000 years
The history of the ancient forests 56 million years ago does not end with collapse.
Over time, in warmer climates, rocks become increasingly broken down, known as weathering Carbon pulled out of the airand stores it in marine sediments. This cooled the climate and made water more available.
The forest canopy recovered and eventually became even denser than before warming began. As forests expanded, they likely restored their ability to stabilize soils, regulate the water cycle, and pull carbon from the atmosphere, helping to reduce the greenhouse effect and promote the planet’s long-term recovery.
Our study shows that carbon dioxide emissions have increased Forests used to exceed their physiological limitswhich triggers changes that impact from vegetation to rivers and entire landscapes. It also shows that forests are remarkably resilient when given time to recover, but what counts as time is much longer than a human’s lifespan – it requires thousands of generations. Today it is human-caused carbon emissions and warming unfolds much more quickly than during the PETM. The fossil record reminds us that forests can recover, but only if humanity avoids pushing them beyond thresholds from which recovery takes tens of thousands of years. Regan E Dunnassistant curator at La Brea Tar Pits and Museum; Associate Professor of Geosciences, USC Dornsife College of Letters, Arts and Sciences This article was republished by The conversation under a Creative Commons license. Read that Original article.
