Like many other animals the black lemurs are in danger due to human deforestation for agricultural purposes and timber production. Lemurs are also hunted for food by humans.
Unfortunately we have found that deforestation for agriculture often does not produced very fertile land in the long term. Many deforested lands become barren because of over farming and a washing away of the nutrient rich soils which were protected from weathering by the existing forestry ecosystems.
Human intervention into many of these lands has had many unintented consequences.