Decision trees are perhaps the most useful decision/management tool for conservators. In any situation a number of actions are possible. These can be drawn as the first branches of the tree, not only the options of a number of actions (a), but also the options for not undertaking those actions (1-a). Each action will have a number of outcomes, these are often expressed as probabilities. Where all probabilities are described they should sum to 1. At the end of this process, and there can be several steps of action and outcome, you arrive at a final outcome. The actions within this decision tree will cost money to enact and the costs for undertaking a particular course of action can be calculated. If all the aspects of the process are described in monetary terms, the outcome is a simple series of potential profits or losses. The route with the greatest profit can be selected, and is referred to as the highest EMV (expected monetary value). Alternatively the route with the least risk or the greatest return for the least investment can be selected (Moore and Thomas 1976). The objectives for conservation are invariably more complex.