Trees often display green, fuzzy, or crusty growths on their trunks and branches. These growths blend into the bark, sometimes appearing as soft carpets or intricate, flaky patterns. This article explores the nature of these organisms, how they interact with trees, and what their presence signifies for tree health.
Understanding Epiphytes on Trees
The growths observed on trees are known as epiphytes, organisms that grow on another plant but do not derive nutrients from it. The most common types seen on tree bark are mosses and lichens, distinct biological entities often confused due to their similar appearance.
Mosses are small, soft, green plants that create a fuzzy or sponge-like texture, often forming dense mats on the bark. They are true plants with tiny leaf-like structures and stems, lacking the complex root systems of vascular plants. Mosses thrive in damp, shady conditions, absorbing water and nutrients directly from the air and surface moisture.
Lichens, in contrast, are not single organisms but a symbiotic partnership between a fungus and an alga or cyanobacterium. This unique arrangement allows them to appear in diverse forms and colors, including flat, crusty patches, leafy structures, or upright, branching growths. Lichens can range in color from green and gray to yellow, white, or orange.
How Moss and Lichen Thrive on Trees
Mosses and lichens establish themselves on trees without drawing sustenance from the host plant itself. They are non-parasitic, meaning they do not invade the tree’s tissues or extract its sap. The tree merely serves as a stable anchor point, providing a surface for these organisms to grow.
These epiphytes obtain all their necessary moisture and nutrients from the environment. They absorb water from rain, dew, and atmospheric humidity, and gather nutrients from airborne dust, decaying organic matter on the bark, and dissolved minerals in precipitation. Mosses use root-like structures called rhizoids primarily for attachment to the tree’s surface, rather than for absorbing water or nutrients from the tree itself. Lichens similarly adhere to the bark through various fungal structures, utilizing the tree as a substrate for their growth.
Impact on Tree Health
For most trees, the presence of moss and lichen is generally harmless. These epiphytes use the tree as physical support and do not tap into its vascular system to steal water or nutrients. Their growth does not cause disease or decline in healthy, established trees.
In rare instances, extremely dense growths of moss might retain moisture against the bark, potentially creating a microclimate that slows its drying. However, for a robust, mature tree, this effect is negligible and does not lead to significant harm. While a thick layer of epiphytes might slightly shade the bark, this rarely impedes the tree’s overall health. These growths also contribute to the ecosystem by providing microhabitats for small insects and other invertebrates, supporting local biodiversity.
Managing Tree Epiphytes
Given that moss and lichen are largely benign to tree health, their removal is typically unnecessary. Their presence is a natural part of a tree’s ecosystem, often indicating good air quality and consistent moisture. Many find their aesthetic contribution to the tree’s character appealing, adding to its natural beauty.
There are rare situations where one might consider removal, such as for purely aesthetic reasons or if an extremely dense accumulation occurs on a very young or already stressed tree. If removal is desired, gentle methods, like lightly brushing the growths off with a soft brush, can be employed for small areas, taking care not to damage the tree’s bark. For the majority of trees, however, these growths are a natural and harmless component of their environment, requiring no intervention.