Coppicing is an old technique of cutting plants hard back, almost to ground level, to encourage vigorous new growth. Historically, hazels were coppiced and resultant stems harvested at different ages to meet different needs, for example fencing, hop posts, building materials or firewood.
Pollarding is a similar process that takes plants back to an established branch framework. Usually this is close to ground level though with some plants, e.g. basket willows, it may be on a taller stem.
The advantage of both these techniques is that your plant will respond with vigorous new growth, often producing particularly long and beautiful new stems.
Coppiced foliage plants, e.g. Cotinus coggygria and its many cultivars such as 'Royal Purple' or 'Grace', respond by producing very vigorous stems covered with young foliage. Many eucalypts can be pollarded in a similar way, to a low frame of branches, to ensure production of the very beautiful and frequently silver young leaves.
Coppiced plants develop more numerous young stems. Frequently it is these young stems that are of real beauty. If left to grow on a mature plant they appear at the end of large branches but coppicing brings them to lower levels where they can be enjoyed.
The dogwoods, Cornus Alba and Cornus stolonifera and some of the coloured stemmed willows are ideal for this.
Plants that produce early spring flowers should be coppiced after flowering. Prunus glandulosus, for example, can be coppiced a few centimetres above ground level. It will respond by producing masses of stems - better for autumn colour, better for next season's flowers.
Many shrubs that flower in late summer and grow quickly can also be coppiced. Iochromas, buddleias, Clerodendrum ugandense will all respond to this treatment, growing back with great enthusiasm to give a prolific flowering display in the second half of the summer.