The practice of agriculture for thousands of years in the New Guinea highlands led long ago to significant problems of deforestation in the more heavily populated areas. According to Collapse, how has the casuarina tree proved to be an important part of their efforts to deal with this problem? What are its advantages?
The answer to this can be found in Chapter 9 of Collapse. Since I only have this book on Kindle, I cannot give you a page number. However, Amazon’s searchable copy says that the relevant discussion begins on p. 282. On that page and following pages, Diamond lists a number of benefits that casuarina trees have.
First of all, the seedlings of these trees grow naturally in New Guinea along stream banks. They can be transplanted to other places and still thrive. Next, this kind of tree grows very fast. This means that it can produce a lot of wood in a relatively short period of time. Its wood can be used for building and for burning. Third, the tree has structures on its roots that fix nitrogen in the soil. It also has many leaves that fall from the trees. Both of these factors mean that it helps to make soil more fertile. Casuarina trees can help keep gardens fertile and can help to rehabilitate areas that have already been farmed and are not very fertile anymore. Fourth, the trees can grow on steep slopes and help reduce erosion. Fifth, they are believed to repel beetles that would otherwise infest taro plants. Finally, the highlanders of New Guinea simply like the aesthetics of these trees because they like the sound of the wind blowing through the trees’ needles.
In all of these ways, casuarina trees have advantages that allow them to help highland New Guineans deal with the fact that they cut down the original forests in the regions where they live.