The thickness of cork oak trees varies highly, even when they are located in the same geographical location or stand. The objective was to research how climate variables affect different trees within the same site, for which precipitation and temperature variables were considered. The response variable was the cork growth index (cgi) – the cork thickness of the first eight complete growth years were measured after boiling. The differences between trees were characterised by nine different cork thickness quantiles, from lower (thinnest cork) to higher (thickest cork).
Impact of postponing cork extraction on the equivalent annual annuity stands, characterized by varying productivity and cork quality
The minimum interval between 2 successive cork extractions from the same tree is fixed by law as 9 years in Portugal. Postponing cork extraction to more than 9 years is an option that results (or not) in a variation of the cork price (for the same structure of cork prices). Site productivity, cork thickness and quality and discount rate contribute to the profitability of the farm, which may be evaluated, for example, by the equivalent annual annuity (EAA). The objective is to apply the SUBER model to evaluate the influence of the cork debarking rotation period (CDR) variation, from 9 to 11 years, on the EAA of different stands by analysing the opportunity to increase the market price of extracted cork.
- Evaluate the influence of tree size, stand characteristics, debarking coefficients and climatic variables on cork thickness and its evolution between consecutive cork extraction operations, i.e. between successive cork growth periods (cgp). Cork growth is assessed using the cgi, defined as the radial width of the first eight complete years of cork growth after stripping.
- Assess the impact of the increase in debarking intensity on cork growth. Debarking intensity is quantified by the cork debarking coefficient – the ratio of the vertical debarking height to the perimeter at breast height, measured over cork.