An Ode to Evergreens
A story by Bob Buring. This article is also featured in the January 25, 2023, edition of Now in Nature.
As winter focuses attention on cone-bearing evergreens, or “conifers,” curious individuals might ask why there are generally two types of trees worldwide.
While plants were evolving on the planet, conifers were roughly 150 million years earlier than hardwood trees. These seed and cone-bearing plants, called gymnosperms, are initially found in the geologic record beginning in the Carboniferous Period, about 300 million years ago.
Their ability to thrive in variable conditions with climatic changes in temperature, sunlight, and water was suited to the evolving earth at that time.
The hardwoods, which are thought of by most as deciduous broad-leafed trees, appeared much later—in the early Cretaceous Period, about 150 million years ago. This era is most famous for the dinosaurs.
These trees with flat, green leaves are angiosperms or flowering plants that produce fruits.
Studying the evolution of these very different giant plants presents us with two approaches to success.
For the evergreen gymnosperms, the ability to retain green leaves throughout the winter extends their photosynthetic season, while the small waxy needles retain water and resist freezing. They are very slow growing and can survive harsh climates.
The trade-off is a less efficient temperate season production efficiency, simply due to less surface area to collect sunlight and slower water transport.
In contrast, angiosperms lose their leaves when scarce sunlight and water would be problematic. Since leaves are a significant conduit for water loss, the plant saves this precious liquid for spring, when their photosynthetic activity resumes and outpaces that of the gymnosperms.
It is postulated that flower and fruit-bearing plants evolved to be more adaptable to various habitats. They mature more quickly, produce greater numbers of seeds, and move water within the tree more efficiently.
As we are seeing all plants and animals as a snapshot in evolutionary time, these two tree types appear to be static.
In reality, living species change with time. Can you predict which of these tree types will be favored by a global temperature increase or the return of glaciers?