Trees are one of the longest living artifacts of life we know of, but they’ve manifested numerous ways since archeologists began resurfacing their past. Functionally, trees tell stories of their past through connections to varying climates, environments, and geographic histories.
One of the most prevailing ways trees carry the past into the present is through their rings. A tree’s rings can tell us how lush an environment was, how much sunlight a tree was given, and which seasons produced the most growth during any point in the tree’s life.
But these rings we’re just used to show growth rates. Archeologists use ring measurements to reconstruct past climates and determine responses to environmental stresses.
To understand where tree artifacts came from, we’ll need to explore how archeologists discovered the ‘modern tree.’
The modern tree didn’t emerge until around 370 million years ago but was essential for creating the first developing forests. Once plants could support additional weight, they began building rings, protective bark, supportive collars around the base of branches, and internal layers of wood that prompted greater height and weight.
But this evolutionary process took more than 100 million years and didn’t come to fruition until Archaeopteris, a now extinct tree in the Devonian period, surfaced as the first modern tree.
For years, archeologists couldn’t piece together the history of the modern tree, but recent discoveries in Morocco helped fill in the gaps.
Up to three feet wide and 60 to 90 feet tall, Archaeopteris made up 90% of forests while other tree species became extinct.
After looking at numerous Archaeopteris fossils, Stephen Scheckler, a biology professor, proposed it to be the earliest modern tree. Scheckler attributes Archaeopteris with the same attachment of branches, swelling of the branch base, and collars containing internal layers of wood as the modern tree.
Within Devonian’s developing forests, Archaeopteris extended its branches and canopies to nourish life in the rivers and streams. At the same time, freshwater fish exploded in varieties and numbers—helping to expedite the evolution of other marine ecosystems.
Decaying trunks, branches, and leaves altered oxygen and CO2 levels for a good while producing a vast root system that impacted soil chemistry and ecosystems at the ground level. According to Sheckler, Archaeopteris carried ecosystems well into the modern era and are the reason trees look as they do today.
Today, evolved tree species comprise millions of square miles of land around the globe. In fact, trees make up roughly a third of the earth’s total land area, 70% of global organic carbon, and 80% of the world’s terrestrial biodiversity.
Broadly speaking, the global tree population is divided into three distinct forests, each with its own climates, ecologies, and geographical locations.
Located near the equator, Central America, Southeast Asia, and Sub-Saharan Africa, tropical rainforests house roughly 50% of the earth’s plants and animals. These forests are often characterized by warm climates, vast biodiversity, and lush plant life.
Expansive tree canopies allow little light to reach the forest floor and force trees to grow shallow roots, sometimes more than 100 feet long to stabilize and grip the ground. Rainforests are so biodiverse that over 100 species, including insects, mammals, bromeliads, ferns, and vines, can thrive within a single square kilometer.
The largest rainforest on earth is the Amazon rainforest, but tropical mangrove forests, seasonal rainforests, temperate rainforests, semi-evergreen forests, and deciduous forests make up the world’s rainforests.
Spanning Western and central Europe, the coast of Eastern North America, and Northeastern Asia, temperate forests support wildlife such as deer, birds, wolves, foxes, black bears, and squirrels. These forests are characterized by modern climates broken up into four distinct seasons that limit growth between 140-200 days per year.
Because temperate forests experience long winters, wildlife species migrate or hibernate during the winter and colder months. Unlike rainforests, temperate forests host deciduous trees whose leaves drop annually, and canopies allow ample light to come through.
Common trees among temperate forests include hickory, beech, maple, elm, willow, hemlock, and basswood tree species. However, these trees span numerous temperate forest subcategories such as dry conifer forests, Mediterranean forests, temperate broad-leaved rainforests, and temperate coniferous forests.
Characterized by short summers and long winters, boreal forests span Eurasia and North America and comprise the earth’s largest terrestrial biome. These forests reach temperatures as cold as -65°F and are primarily found in Siberia, Alaska, Scandinavia, and Canada.
Because of the extreme cold, species that can survive are deciduous trees and evergreens like spruce, pine, and fir. Dense canopies limit understory life, but that hasn’t stopped biodiverse life from adapting and thriving in these conditions.
Moose, foxes, wolves, deer, woodpeckers, hawks, lynx, bear, and bats are all animal species who’ve found solace in boreal forests—many of whom migrate or hibernate during the winters to survive.
The evolution of different tree species has given way to some of the lushest and biodiverse places on earth, but these forests do not exist independently. More than half the earth’s tropical forests have been destroyed or cleared for fuel, agricultural expansion, or lumber.
Temperate forests are often cleared because of their rich soils and moderate climates for human settlements, and boreal forests are constantly threatened by deforestation due to logging.
Archaeopteris once made up over 90% of forests around the globe, but now there are thousands of tree species humans will need to protect to allow trees to evolve further.