In this module we examine one criterion, the maintenance of soil and water resources. While the Montreal Process deals with these two attributes in a single criterion, they are both so important that they have been given a module to themselves. Soil and water are two of the fundamental resources essential for forests. While it is possible to find occasional trees, particularly pines, seemingly growing out of solid rock, a healthy forest requires soil. Without soil, there is no rooting medium for the trees, and even in those cases where a tree apparently grows out of rock, there is always a crack or fissure that the trees roots have anchored into, and within this, there are some of the basic elements of a soil. Many different soil types exist, and while we will not examine every type, we will look at some of the basic processes resulting in the formation of soils, and some of the processes that can lead to their degradation and removal. In the first topic, you will learn how forest soils develop, and also how they can be lost. The second topic deals with the roles that soils play in controlling the fertility of a site, a subject that is also examined in Module 4 in the context of forest productivity.
In the third and fourth topics, you will look at water, another critical element of a forest. Without water in some form, no life is possible. Forests require freshwater, although a specialized form of forest known as a mangrove is found below the high and low water marks in some parts of the world (tropical, sub-tropical and some temperate areas). The availability of water is one of the primary determinants of forest types. However, water can also be a force of destruction, washing away soils and, in some circumstances, flooding and drowning forests. However, more often than not, it is a shortage of water that causes problems for forests, and this is an issue of growing concern in the light of disturbances to weather patterns associated with climate change. There are also concerns about the interactions between forests and water. For example, does having a forested catchment mitigate the size of floods coming from that catchment? Does afforestation result in a reduction in water from a catchment? Questions such as these are important, and you will learn some of the answers in this module.