1 research outputs found
Field sampling of cork value before extraction in Portuguese "montados"
The assessment of cork quality and the
estimation of cork value are very important to forest
landowners, for management purposes and for cork
commercialisation. The Forest Producers Associations
have been using a sampling scheme with the objective
of estimating cork value (price per unit of weight,
usually kg) before extraction, based on the sampling of
individual trees along a zigzag transect that covers the
entire stand. The sampling error is usually too high,
but, from a practical standpoint, it is difficult to
increase the sampling intensity if it would imply an
increase in sampling costs. The aim of this work was to
propose, from data collected in six stands representative
of the cork oak stands in Portugal, an alternative
sampling methodology with a more efficient precision/
cost ratio. Precision and costs of alternative sampling
designs based on clusters of different sizes, complemented
with analysis of the intracluster correlation
coefficient, were studied in order to propose the most
adequate sampling strategy. Single-stage cluster sampling
with clusters of 5–7 trees guarantees a reasonable
sampling error (10–15%) and can be conducted
without a large increase in cos