If you are a non-resident of the US and the only business you have in the U.S. are investments, you are subject to the following tax guidelines.

Profits made from selling your stocks are called capital gains.

Your profits on Bamboo are not subject to U.S. capital gains tax and you don’t have to pay capital gains tax on them in Nigeria. However, if you pay taxes elsewhere, you will likely have to declare this income and pay tax in your home country. 

If a U.S. company pays you a dividend, there is a 30% tax on the dividend amount. 

This 30% tax will be deducted before you receive the dividend, so you do not have to worry about it.

Any dividends you receive are all yours.