The Science Behind Birch’s Bark
A young Downy Birch on Cloudforest Five
Birch trees, including our native Irish species Silver Birch (Betula pendula) and Downy Birch (Betula pubescens), are known for their distinctive bark and significant ecological roles.
While young tree stems are often a reddish-brown, the bark of older Downy Birch and Silver Birch is rich in betulin. Betulin is a white, water-repellent substance giving the bark its characteristic silvery-white colour and peeling texture. This substance protects the tree from herbivores, insects, and pathogens, while also reflecting sunlight to help regulate the tree's temperature.
The bark also features horizontal lines called lenticels, which are pores that facilitate gas exchange. These lenticels are more prominent on Silver Birch, often seen in Irish landscapes. As the tree grows, the outer layers of bark peel off in papery strips, revealing fresh, white bark underneath. This peeling process helps shed old, damaged tissue and deters mosses and lichens, which grow quickly in Ireland's damp climate.
While both species share the white bark characteristic, there are subtle differences. Silver Birch bark is smoother and peels more distinctly, with a brighter white colour and more prominent, darker lenticels. Its branchlets are slender and often drooping.
In contrast, Downy Birch bark is less peeling and often rougher, especially at the base, with a darker grey, black or brownish tint and less prominent lenticels. Its branchlets are more upright and hairy when young.
Ecological Benefits
Birch trees play crucial roles in various ecosystems. Both Silver Birch and Downy Birch are pioneer species, meaning they are among the first to colonise disturbed or barren land, helping to stabilize soil and create conditions for other plants to grow.
They also provide food and shelter for numerous species; their seeds are eaten by birds, their bark is a food source for insects and mammals, and their canopy offers nesting sites and protection. Additionally, birch trees form symbiotic relationships with mycorrhizal fungi, which help them absorb nutrients and water from the soil, benefiting both the trees and the fungi.
Birch trees also contribute to soil health in several ways. The fallen leaves of birch trees decompose relatively quickly, adding organic matter to the soil and improving its fertility. They also help cycle nutrients by absorbing them from the soil and returning them through leaf litter and decomposition. Their root systems help prevent soil erosion, particularly in disturbed areas.
Like all trees, birch trees play a role in carbon sequestration. They absorb carbon dioxide from the atmosphere during photosynthesis, helping to mitigate climate change, and store the carbon in their biomass, including trunks, branches, and roots, as well as in the soil.
Photo by Vladyslav Rusenchyk (@vlad-orient)
