An important aspect of the science of plant ecology is the
determination of the nature and causes of variation in vegetation.
Reflecting the controlling influence of the physical environment, this
variation is continuous both in space and in time. The most rewarding
means of unravelling the intricate relationships between vegetation and
habitat is through the detection and analysis of pattern.
In an ecological context, pattern may be defined as the non-random
distribution of vegetation units within a defined area. This means in
effect, that the distribution is either more contagious or more regular
than could be expected, if chance was the only factor which influenced
the distribution. Greig-Smith (1964) described a random distribution as
one in which the presence of one individual (unit) does not either raise
or lower the probability of another occurring nearby.
The existence of pattern in vegetation is apparently a universal
phenomenom. It may be manifest on a very wide range of scales and
intensities; from broad global-wide belts of vegetation, down to the
variable performance of a single species over a small are.. Causes of
pattern may be either intrinsic, (e.g. method of dispersion, competitive
ability) or extrinsic, (e.g. variations in the effective physical
environment). [From Introduction]