Field sampling of cork value before extraction in Portuguese ‘montados’

Abstract

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 cost.

Predicting site index from climate and soil variables for cork oak (Quercus suber L.) stands in Portugal

“…Data from 100 plots established in 42 even-aged cork oak stands of known age were used for this study. Due to the low density of trees typical in adult cork oak stands, the characterization of several stand variables demands the measurement of plots with areas larger than the ones typically used in forest inventories (Almeida and Tomé 2010;Tomé 2005). For this reason, plots with an area of 2827 m 2 were defined, either circular with 30 m of radius or rectangular with 53.2 m 9 53.2 m. This set of plots was obtained from two different sources: 40 permanent research plots from ForChange research group established during several research projects, and 60 plots established for this research.…”

Assessing the impact of understory vegetation cut on soil epigeic macrofauna from a cork-oak Montado in South Portugal

“…This system has an inherent economic value, due to cork production-one of Portugal's main economic products-and cattle rising (Almeida and Tomé 2009;Pinto-Correia and Mascarenhas 1999). Besides, ''Montados'' also have an ecological importance, since they support a high biological diversity (Pinto-Correia 1993;ScarasciaMugnozza et al 2000).…”

Quassia amara L. diameter and total height under different light conditions: implications for the management of agroecosystems

“…This feature is also encountered in other species producers of NWFP more extensively researched and found in tropical agroforestry landscapes such as Coffea arabica, Camellia sinensis L. and Theobroma cacao (Tscharntke et al 2011). This evidences the importance of defining sustainable management plans for natural forests where NWFP are being extracted on the basis of reliable data collected with differentiated inventory methodologies and sampling schemes from forest inventories (e.g., Wong et al 2001;Almeida and Tomé 2010). The inventories should not only allow the quantification of the species abundance and carbon stock but also of the natural regeneration, seed availability and characterization of light conditions.…”