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Hello,
I am not sure these sentences are correct.
please, help you to check them
Thank you for your help.

The last decade few people in Taiwan have been over-harvesting trees, such as padauk and mangrove for the sake of earning their private profits that has resulted in downhill.

The last decade few people in Taiwan have been over-harvesting trees, such as padauk and mangrove for the sake of earning their private profits, resulting in downhill that killed many people.

In order to making private profits, few people in Taiwan have been over-harvesting trees, such as padauk and mangrove which have damaged tropical ecosystem.
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Comments  
Here are my suggestions

1st & 2nd Sentence
In the last decade a few people in Taiwan had over harvested trees, such as padauk and mangrove, for the sake of earning a private profit resulting in..............

3rd Sentence
In order to make a profit, a few people in Taiwan over harvested tree such as padauk and mangrove which eventualy damaged the tropical exosystem.

Hope this helps
 CalifJim's reply was promoted to an answer.