The Enduring Myth
The belief that moss grows exclusively on the north side of trees is a widespread myth, often used for wilderness navigation. This idea suggests moss growth indicates north. However, this simplification can lead to misdirection.
Moss does not solely colonize the north side of trees. While it may appear predominantly on one side, this is not a dependable rule for determining cardinal direction. Relying on this myth for navigation increases the risk of getting lost.
Key Factors for Moss Growth
Mosses are simple, non-vascular plants, meaning they lack true roots and a complex internal system for transporting water. They absorb moisture and minerals directly from their environment. This makes moisture availability the most important factor for their growth and survival. Mosses require consistent moisture, whether from rainfall, dew, or high humidity, to thrive and reproduce.
Shade is another important environmental condition for mosses. Most prefer shaded or semi-shaded conditions, though some varieties can tolerate partial sun. Direct sunlight quickly dries out moss, causing browning or even death, as their leaves are highly susceptible to desiccation. Shade helps reduce evaporation, allowing moss to retain needed moisture.
Humidity also plays a significant role. Mosses generally prefer high humidity levels, ideally above 70-80%. In humid environments, moss can absorb moisture directly from the air, which is vital for their metabolic activities and growth. Consistent humidity prevents moss from drying out, even during periods without direct rainfall.
The type of substrate on which moss grows also influences its presence. Mosses can grow on various surfaces, including tree bark, rocks, soil, and man-made structures. Tree bark, particularly, offers an excellent surface because its grooves and crevices provide suitable spots for moss spores to establish and for moisture to collect. The texture and composition of the substrate can affect how well it retains moisture and provides a stable anchor for the moss. Additionally, moss often prefers slightly acidic soil, a common characteristic of woodland areas.
Finally, local microclimates significantly impact where moss grows. These are small-scale climate variations influenced by factors like topography, proximity to water sources, and the density of overhead canopy. For example, a depression in the ground, a sheltered side of a rock, or an area where water consistently drips can create a localized pocket of ideal conditions for moss, regardless of its cardinal direction.
The Nuance Behind the Myth
The myth that moss grows exclusively on the north side of trees stems from a kernel of truth applicable under specific circumstances. In the Northern Hemisphere, the sun generally tracks across the southern sky. As a result, the north side of a tree or object typically receives less direct sunlight throughout the day. This reduced sun exposure means the north side tends to be cooler and retains moisture longer due to slower evaporation.
These shadier, more consistently damp conditions on the north side can indeed be more favorable for moss growth in certain environments. In some temperate forests of the Northern Hemisphere, moss might appear more prevalent or robust on the northern aspects of trees. This observation likely contributed to the development of the directional myth.
However, this is not a universal rule and is often overridden by other localized conditions. Factors such as a dense forest canopy can create shade on all sides of a tree, allowing moss to grow uniformly. Water runoff patterns, the presence of nearby streams, or even the angle of a slope can create microclimates that promote moss growth on any side. For instance, in areas with high humidity, like the Pacific Northwest, moss can grow on all sides of trees and other surfaces due to the consistently moist environment. Ultimately, specific environmental factors of shade and moisture, not cardinal direction, determine where moss thrives.