Loss of which habitat has had the greatest impact on the earth's biodiversity

Tropical rainforest

Explanation:

The tropical rainforest forms the major biodiversity on earth. It is because this habitat is located in the tropical region, where there is a high amount of sunlight and rainfall every year. The most essential nutrients are received by the organisms (both plants and animals) living in this habitat. Due to this reason, it supports a large number of living species in this region.  

The plants and trees also play an important role by providing the highest amount of oxygen from this region which is distributed globally.

So, this tropical rainforest is the most important habitat. The loss of this habitat will directly have a great impact on the earth's total biodiversity.