Permanent sample plot
A marked field plot measured repeatedly over time so that growth, mortality and disturbance can be tracked on the same trees.
A permanent sample plot is physically demarcated and measured on a repeating schedule. Every stem above a defined diameter is tagged, so the same individuals are re-measured rather than a new sample being drawn each time.
This design yields something a one-off survey cannot: change. Increment, recruitment, mortality and harvested volume all become directly observable, and measurement error is separable from real growth because the same stems are compared with themselves.
Carbon projects depend on this for crediting. Removals are the difference between two stock measurements, and only a permanent plot network can attribute that difference to biological growth rather than to a different set of trees being sampled by chance.
Frequently asked questions
How often are permanent plots re-measured?
Commonly every one to five years depending on growth rates, programme rules and the risk profile of the project.
Why not just re-sample randomly each cycle?
Random re-sampling confounds growth with sampling variation, making change estimates far noisier for the same field effort.