There are a series of general problems that can be encountered when monitoring vascular plants, not all of which will apply in every case. The type of plant being surveyed, the methods used and the recorders can all affect the results (Rich & Woodruff, 1990).

Defining an individual

Defining an individual plant can be a problem; opinions differ between botanists. With annuals or biennials there are rarely difficulties as their growth forms are generally simple. Perennials have more varied growth forms. If the species grows in dense clumps, the clumps might be composed of one or more individuals, and species spreading by stolons or rhizomes may form single or mixed patches of clones. Clonal perennials may also fragment, resulting in two or more parts of the original plant. Trees tend to be counted as individual trunks, although some trees such as Aspen Populus tremula spread by suckers.

Alternatively, proxy measures of abundance can be used such as the number of ramets or shoots, or percentage cover, rather than the number of individuals.

The method by which an individual is defined should be clearly stated at the outset of survey and monitoring, so that this can be followed subsequently.

Defining populations

The definition of the extent of a population varies between botanists. It is possible to delimit populations by compartment, habitat, site, ownership or other boundaries, distance to nearest neighbouring populations, or by 1 km square, etc.