In Indonesia, jungles were converted into very productive palm oil plantations. Orangutan habitat was sacrificed. In Brazil, jungles are harvested of their valuable hardwoods, then the brush is burned and productive farms are developed. Habitat to the native species is lost. The environmentalists have done a great job of making it sound like it is a terrible waste of resources. There is, no doubt, a short period of deficit as far as photosynthesis goes, and if it is your home that is lost it is tragic, but the land generally becomes more productive. There are exceptions, but wise management can make land more productive.

Areas have been reclaimed from desertification by wise use of grazing animals (see link).

It's pretty well known that rainforest doesn't grow back with the same diversity, if it indeed grows back at all, after it's used as farmland. It's a terrible waste of resources, because the land isn't much food for farming anyway. The topsoil usually washes away fairly quickly. The farmland produces more co2 than the rainforest. It's very sad when you think about it.

Well I wish Jim and Harold Harold are right but they are not, that is a hypothesis which in some case is correct, and some cases wrong.

There are now farms in the Amazon basin that are successfully producing crops year after year, the erosion and washout of minerals can be prevented.

Soil can be enriched with carbon (google Terra Petra) and remain fertile for thousands of years.

However I am against rainforest use because of the loss of diversity and more importantly rainforests recycle water, the rainfall that occurs far in the Amazon basin originates from the Atlantic ocean and is recycle inland many many times.

Grassland is best used for cattle, if proper rotation is used grassland can support huge numbers of cattle (in fact grassland is a co evolved habitat by herbivores and grasses) google Alan Savory.

The Dakotas are a great example of the grassland. Once they were mostly devoid of trees and were rapidly becoming bad lands. Man stepped in and now the Eastern portion is productive farmland.

As for rainforests, the con artists had to change the name. When I was young we called them jungles. Everyone knows that jungles are not the best for the earth and so the greenies renamed them 'rainforests'. This appeals to one's emotions and makes it an emotional issue rather than a scientific.

Tropical rainforests typically make very poor farmland. The soil is known as a laterite and is devoid of many minerals. It is often so depleted in other minerals that is literally iron and / or aluminum ore. After one crop, the soil is so depleted it is often abandoned and then it may no longer be suitable for rainforest reclamation. If only a small portion is used, the rainforest can recover but it becomes much more problematic if large swaths are removed for farmland.

It becomes farmland.