The picture above shows the border between Haiti and the Dominican Republic. As you can tell the right side has much more vegetation covering the land. While the left side, which is Haiti, is barren of trees and plants that are responsible for holding in the soil. Without these plants the land is susceptible to erosion and flooding. The widespread deforestation is due to decades of mono-cropping and charcoal harvesting that have not only ruined the quality of the soil but no longer allows the soil to be held into place. The loose soil allows rainstorms to become major threats to the overall safety of the people. When storms hit the area, the loose soil is taken with the water and can cause major mudslides that, in many cases, can be deadly.
This problem stems from the need to clear land to make way for more room for agriculture. One of Haiti's main exports is coffee, and so much of the land that was cleared was to make way for coffee plants that helped slightly improve Haiti's struggling economy. This created a mono-cropping culture, that over time, depleted all nutrients from the soil, and eventually will lead to a decrease in production, unless the use of expensive fertilizers is implemented, such as the United States does with corn production.
Land was not only cleared for cash crops, but also for crops that would be responsible for feeding the county's population, and as Haiti's population grows, the amount of land that needs to be farmed grows as well. This cycle only accelerated deforestation. Both of these ineffective farming practices are responsible for the depletion of the soil's nutrient supply that plants need to thrive. Not only are Haitian's mono-cropping, but they are planting crops on the sides of mountains and other terrain that is not meant for these crops and it has only lead to further erosion.
Therefore, in order to counteract the problems with their agriculture system and the dangerous side-effects that follow (flooding and mudslides), it is important to plant trees and other vegetation that will allow the soil to stay held in place.