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Why does moss only grow on the north side of trees? Also why is its texture fuzzy?
Question Date: 2004-05-11
Answer 1:

Your observation that moss only grows on the north side of trees tells me you haven't looked for moss near trees in the southern hemisphere. Moss is a simple plant and likes to grow in shady locations so it does not dry out.It is pretty simple to picture why this is the north side of trees here and the south side of trees in Australia for example. The sun's rays strike the earth's surface nearly perpendicular close to the equator.

As you move away from the tropics, the suns rays intersect the earth at an angle. Here in Santa Barbara, California, the sun is not directly overhead, but to the south, so the south side of any object will get more sunlight than the north. This is why moss likes the north side of trees.

The fuzzy texture and shade-loving characteristics of moss are in part due to it being a non-vascular plant. Mosses belong to a group of plants called Bryophytes. These plants do not have roots, or the xylem and phloem of vascular plants, but rather have rhizomes that hold the moss in place and collect water and nutrients the moss requires.

The "fuzzy" texture you mention helps to keep the plant from drying out and also helps diffuse the light used for photosynthesis.

Answer 2:

Good question! Actually, moss doesn't only grow on the north side of trees,it just MOSTLY grows on the north side. Also, that rule only applies in the northern hemisphere--in the southern hemisphere, moss mostly grows on the south sides of trees. The reason is that in the northern hemisphere, because of the tilt of the Earth on its axis, the sun almost always appears to be a little south of directly overhead. That's why rooms with windows facing south are brighter than rooms with windows facing north. This is important for the mosses because the north sides of trees (in the northern hemisphere)are shadier and therefore moister. The south sides of trees get more sunlight, so water evaporates faster there.

Mosses need a lot of water for two reasons. One is that they're not"vascular" plants --that means that they don't have the plant version of a circulatory system, and they can't move water around inside their bodies. All cells in a moss's body need to have easy access to water from the environment.

The second reason they need water is because their male reproductive cells can only survive by swimming in droplets of water. The only way these cells can get from one plant to another is to hope that a raindrop will cause the water they're swimming in to be splashed onto a neighboring plant. If the surface that they live on (like a tree trunk)dries out, the moss will be unable to reproduce, and it will dry out. That's much more likely to happen on the sunnier side of a tree trunk than on the shadier side.

The same rule applies to rocks, fallen logs, or anything else that mosses might grown on. If it has a sunny side and a shady side, the moss will mostly grow on the shady side. In the northern hemisphere, that's usually the northern side, and in the southern hemisphere, it's usually the southern side. If you look closely enough, though, you'll see exceptions.

The texture of mosses is usually (but not always!) fuzzy because their leaves have many little projections on them, like the finger-like projections on a maple leaf. The moss leaves and their projections are so small, though, that they seem fuzzy to us. These projections are probably to help the moss cells deep inside the leaves to be as close as possible to external water sources.

Keep asking great questions!

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