Planning, Monitoring and Evaluation - Afforestation, Reforestation and Forest Restoration in Arid and Semi-arid Tropics - page 214

A project is broken up into discrete self-contained tasks or activities (Table 9.1 ).
The time it takes to complete each activity is firmed up and noted down. The activi-
ties are then listed in their technical order, and this order is represented in form of a
network, wherein nodes represent the activities and the arrows indicate precedence
relationships. An activity preceding another activity is its 'predecessor' and the one
following it is its 'successor'. An immediate predecessor of an activity is the activ-
ity that must be completed before starting the activity in question. If activity a is
immediate predecessor of activity b , then b is said to be the immediate successor
of a .
In a network diagram a node contains a letter indicating an activity, and its dura-
tion. Above this node are recorded the early start and early finish times of the activity.
Early start time of an activity is the early finish time of its immediate predecessor,
and the early finish time of an activity is its early start time plus the time it takes
to complete the activity. Thus, in a forward pass of computation the early start and
early finish times of all the activities are recorded. The early finish time of the last
activity gives the project completion time.
On the other hand, if one starts at the project finish time on the last node, and
subtracts from it the time it takes to complete an immediate predecessor, one gets the
late start time of an activity. The late finish time of an activity is the late start time
of its successor. From this the duration of the activity is subtracted to arrive at its
late start time. In this manner—in a backward pass—one can compute the late start
and the late finish times of the activities in a project. These times are the ones which
cannot be missed or else the project will be adversely affected (Fig. 9.2 ).
It will be seen that there are certain activities that have identical early start and
late start times. These are called 'critical activities' and a delay in these activities
will delay the project and thus lead to project failure if such delays are significant.
A path that runs through critical activities is a 'critical path'.
By superimposing the network on a calendar of dates it is possible to arrive at a
schedule or a calendar of activities in a tabular form that may be more accessible
to the field personnel. Thus network analysis can be seen as a means to deriving a
calendar and delineating the structure of the project.

9.1.2.1 Managing with Schedules and Calendars

Extensive use of schedules can greatly help in planning activities, and communicating
such plans to various levels in the organisation. Calendars (e.g. the nursery calendar)
and schedules (e.g. watering schedule) are methods of recording the time dependence
of activities and sequencing them in a simple manner so that the field workers can
understand and take appropriate action in time.
Calendars can be said to be the schedules that are more or less static, uniform
and repeat themselves periodically. They record cyclic patterns of activities and their
associated timings. Since every afforestation project is set in its own climatological,
seasonal, and socio-economic patterns, a given calendar may not be suitable for all
places and for all times (Table 9.3 ).