• The development cycles of trees and forest stands are considerably longer than a foresters or forest scientists career and even longer than a human life.
• There are only a restricted number of possibilities to obtain reliable information on tree and forest growth other than long-term observations or experiments which provide data that can be used for scientific analyses and for modeling. The latter could then be a possibility to get more and faster information about forest development providing good and reliable data are available.
• To obtain this information, long-term forest research must be organized in such a way that a high degree of success is guaranteed:

1. First of all an institution with a long-term perspective of survival is needed and within such an institution a high level of continuity in internal organization and manpower is necessary
2. The research questions and as a consequence the research layout, should be chosen in such a way that the research can be adapted to possible changes of external factors such as politics, economics or environment without losses of scientific value.

The history of growth & yield research in Switzerland started 126 years ago. 12 research plots which where installed more than 100 years ago are still monitored today. Some of the original research question e.g. thinning methods and intensities in beech stands do not have any relevance today because on the basis of other experiments in Switzerland and else-where, better silvicultural methods were developed. These research plots still remain an invaluable source of data for scientific analyses of forest growth and climate which were not foreseen when the plots where installed.
Today the Growth & Yield Research Team takes care of a total of 450 plots (~150 ha) with an average size of 0.322 ha, some of them clustered. The smallest plot - part of a cluster in a provenance trial - measures 150 m², the largest plot with silvicultural treatment 5.01 ha, without treatment 11.0 ha. They are re-measured every 4th (young stands) to 12 (high elevation forests) years.
The database contains data from 1332 plots (346 ha) with an average size of 0.26 ha. The smallest plot - also here part of a cluster in a provenance trial - measures 25 m², the largest plot with silvicultural treatment 3.5 ha. They were measured between 1 and 19 times according to the research question.

Forests play a key role in the environment and to society, including provision of wood products, recreation, water, habitat, carbon sequestration and other environmental services. Forests are communities dominated by large long-lived trees that are less influenced by short-term perturbations than other organisms and are thus able to reflect long-term environmental trends.

Thus it is important to understand and monitor the functioning of forests, traditionally through permanent plots. Permanent plots have been proven to be a practical and cost-effective way to monitor forest growth, and are able to reveal unexpected long-term changes [1] indicative of forest health and tree vitality.

We recommend to maintain an adequate number of permanent plots [2] in each broad forest type [3]. Existing long-established plots [4] are of particular importance and should be continued.

[1] Book Growth trends in European Forests.
[2] Ideally, such plots should be representative and homogeneous (typically between 0.1 and 1 ha in area), should be subject to a standard documented management regime, and should be re-measured regularly including at the time of any management intervention. Measurement procedures should be well documented, and where possible follow standard international protocols.
[3] For example, Holdridge zones.
[4] In Europe, many plots were established over 100 years ago, and can reflect forest growth prior to the current escalation in atmospheric CO₂. Elsewhere, plots that are only a few decades old can indicate temporal trends that may otherwise remain unrecorded.

Jerry Vanclay, Australia, Valerie LeMay, Canada, Peter Marshall, Canada,
George Gertner, USA, Hubert Sterba, Austria, Markus Neumann, Austria,
Thomas Ledermann, Austria, Jürgen Nagel, Germany, Arne Nothdurft , Germany, Andreas Zingg, Switzerland, (Zermatt April 2009)