Analysis of cork quality and cork tree health in stands of western Spain

Abstract

Good knowledge of the factors that influence cork quality and the health of forests is essential when making decisions regarding the management of productive cork oak forests. The quality of cork planks depends on: plank thickness, plank porosity and the presence of anomalies. So far, no studies have evaluated cork quality based on cork anomalies, partly due to the difficulty of obtaining adequate data. In 1985, it was developed the first Cork Quality Field Assessment Plan (CQFAP) to provide information about the quality of harvested cork by collecting data of very high quality. This work analyzes the anomalies present in 2049 cork sampling units collected from ten stands under the CQFAP for the period 1986–2012 in three consecutive cork stripping cycles. Data on diseases, pests and stripping damages are also analyzed in the 654 trees where cork sampling units were collected in the third stripping cycle. Additionally, mean monthly temperature and precipitation values for the 35 years covering the three stripping periods were calculated. A progressive deterioration of cork quality was observed in the sampled cork oak stands. It was found a positive relationship between cork thickness and temperature indicating that the cork growing period could be extended when temperatures are moderate. Sampled cork oaks were more affected by Cerambycidae attacks and Coraebus undatus indicating their prevalent nature. The presence of Coraebus undatus were higher in stands with good health status. The studied diseases were Biscogniauxia mediterranea, Phytophthora sp. and fungi of the family Botryosphaeriaceae, finding a not previously reported correlation between the presence of Crematogaster scutellaris and the three studied diseases. Stripping damages increase with smaller cork thickness but climate is not a decisive factor for a proper stripping. Although having room for improvement, the CQFAP is proving to be an effective tool for assessing the quality of cork, the health status of cork oak forests and the evolution of these forests over time. The information provided could be also used to identify places worthy of further studying. The main recommendation for improving the CQFAP would be to monitor the same trees in each consecutive sampling for properly monitoring cork thickness and the presence of defects to be used as a proxy for tree health. Regarding forest management, the main recommendations would be to extend the length of stripping cycles to enhance cork production, and to use the new tools and systems for cork stripping to reduce damage.