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Economic Botany

, Volume 69, Issue 2, pp 171–184 | Cite as

Insights into the Responsiveness of Cork Oak (Quercus suber L.) to Bark Harvesting

  • Augusta CostaEmail author
  • Luís Catela Nunes
  • Heinrich Spiecker
  • José Graça
Article

Insights into the Responsiveness of Cork Oak ( Quercus suber L.) to Bark Harvesting

The cork oak (Quercus suber L.) is harvested for its bark (cork), a highly valuable non-timber forest product. Recurrent cork harvesting is practiced over the lifetime of the tree and constitutes a stressful action that, while artificially promoting cork growth, may severely deplete tree vigor after an exploitation time span. To date, few long-term studies have been conducted regarding the effect of recurrent cork harvests on cork growth rates, and there is a complete lack of knowledge on the effect of the stress, induced by cork harvesting, on the vigor of the cork oak. In this study we propose to address the resilience of the cork oak to cork harvesting, using cork-ring width as an indicator of tree vigor. We use dendrochronological methods to develop an extended cork-ring width series that was analyzed by autoregressive integrated moving average modeling with an intervention analysis approach. We show that cork harvesting represents a human-induced loss of tree resilience only after six consecutive harvests, and that only after a single stochastic cork-harvesting event may trigger a sudden collapse in cork oak vigor. Our results also suggest that the tree (optimum) exploitation period of 110–120 years, which includes more than nine consecutive harvests, extends more than 35 years beyond the tree vigor breakpoint (occurring at the sixth consecutive harvest). Within this time frame, the tree is producing cork instinctively to survive, and its vulnerability to other (a)biotic stresses may increase, leading to untimely cork oak decline. These results suggest that there is a great potential in the time-series analysis of cork-ring widths for the development of tools that may enhance typical cork oak management planning by addressing both economic and ecological objectives.

Key Words

Non-timber forest product cork-rings ARIMA modeling Mediterranean evergreen cork oak woodlands dendrochronology 

Compreender a capacidade de resposta do sobreiro ( Quercus suber L.) ao descortiçamento

O sobreiro (Quercus suber L.) distingue-se das outras árvores pelas características singulares da sua espessa casca suberosa, a cortiça. Atualmente, a cortiça é considerada um importante produto não-lenhoso da floresta da região Mediterrânica, com elevado valor comercial. A extração da cortiça (descortiçamento) é feita periodicamente ao longo da vida da árvore, em sucessivos ciclos de produção de cortiça. Após um descortiçamento, a camada geradora de cortiça (felogene) morre e a árvore tem a capacidade de regenerar uma nova que, quase imediatamente, começa a formar novas camadas de cortiça. A longo prazo, os sucessivos descortiçamentos, do mesmo modo que “forçam” a árvore a produzir novas camadas de cortiça, afetam decisivamente os processos fisiológicos da árvore. Apesar de bem estudadas, as reações fisiológicas imediatas do sobreiro ao descortiçamento e a curva crescimento de cortiça num ciclo de produção, nada se sabe sobre como a árvore reage a sucessivos descortiçamentos, ao longo da sua vida.

Neste estudo, apresenta-se uma abordagem inovadora para obter informação sobre a variação da resiliência do sobreiro ao descortiçamento. Assume-se que a largura do anel de crescimento da cortiça é um indicador do vigor vegetativo da árvore e efetuou-se uma análise dendrocronológica de séries temporais extensas da largura dos anéis para modelar o crescimento da cortiça. Os resultados obtidos mostraram que a resposta da árvore ao descortiçamento é diferente ao longo da sua vida. A partir de determinado descortiçamento, a árvore tem um colapso da sua resiliência ao descortiçamento, reduzindo drasticamente a largura do seu anel de crescimento da cortiça. A explorabilidade económica da árvore estende-se muito para além deste colapso na sua resiliência ao descortiçamento, a partir do qual poderá aumentar a vulnerabilidade da árvore a outros agentes nocivos (a)bióticos e a promover a sua morte prematura.

Notes

Acknowledgments

This research was partially supported by the IsoCork project (Climate effects on cork growth assessed by isotope fingerprinting) (EXPL/AGR/FOR/1220/2012) funded by FCT-MCTES. Augusta Costa’s contribution was funded by the Foundation for Science and Technology of the Portuguese Ministry of Education and Science (FCT-MEC). The authors acknowledge comments on the manuscript from two anonymous reviewers and final text editing from the Economic Botany editor.

Supplementary material

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Copyright information

© The New York Botanical Garden 2015

Authors and Affiliations

  • Augusta Costa
    • 1
    • 2
    Email author
  • Luís Catela Nunes
    • 3
  • Heinrich Spiecker
    • 4
  • José Graça
    • 5
  1. 1.Center for Environmental and Sustainability Research (CENSE), Faculdade de Ciências e TecnologiaUniversidade Nova de LisboaCaparicaPortugal
  2. 2.Instituto Nacional de Investigação Agrária e Veterinária, I.P.OeirasPortugal
  3. 3.Nova School of Business and EconomicsUniversidade Nova de LisboaLisboaPortugal
  4. 4.Chair of Forest GrowthAlbert-Ludwigs-University FreiburgFreiburgGermany
  5. 5.Instituto Superior de AgronomiaUniversidade de Lisboa, Centro de Estudos FlorestaisLisboaPortugal

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