On one hand, you might think it would slow it down, however, in a hypothetical situation, not everything is thought of. The effect depends on the environment before planting begins...
- If you are someone being encouraged out of the favellas in Brazil with enticing offers of fertile land and a little money to kick-start your new life, the actual effect of you planting your crops does not particularly slow erosion down: if you actually cared about the environment (which, if you were them, you wouldn't), you would have left the rainforest standing as the ancient rainforest does hold the soil together: your puny crops, aligned in rows etc. do not. Basically: if the vegetation you're talking about is crops, the answer is not much at all.
- Another situation is whereby someone has decided to build themselves a hotel in Kenya; in the middle of the rainforest. Deforestation takes place, and you've also decided to build a driveway and plaza, perhaps also to clear a space for a swimming pool while you're at it: more deforestation. Now that your hotel is finished, you thought you'd give something back to the environment, so you've bought a large plant pot with a tree in it, and put an orchid seed in it. The problem is that your little orchid isn't holding any soil together, and the ground on which your hotel is build is still being eroded. In summary: planting vegetation in a pot does nothing to erosion.
- Now let's consider something a little more farcical: someone actually doing something to prevent soil erosion...by planting vegetation! Brilliant, why didn't they do it before? It's less profitable than destroying the Earth's resources, in fact it's not profitable at all. This group has decided to plant natural, local, indigenous vegetation. As a result, the land is held together, and the soil is not washed away.
From three situations above, two very real, the other hypothetical, you can gather how vegetation may affect erosion: crops, especially those arranged in systematic rows, do not bind the soil together very well, and are not permanent, so when they're removed, the soil is totally exposed. Furthermore, vegetation in a pot does nothing to stop erosion: the soil in the pot will never be eroded as it is contained completely. When people plant vegetation in soil, and the plants are not planted for commercial purposes and are allowed to grow properly and more densely than is seen elsewhere in the world, the soil is bound firmly, and erosion is vastly slowed down.
I hope this has answered your question.
