Drivers for Annual Cork Growth under Two Understory Management Alternatives on a Podzolic Cork Oak Stand

Sónia P Faias,Margarida Tomé,Paulo N Firmino,Joana A Paulo

doi:10.3390/f10020133

Abstract

Understory management practices and stand density characteristics allow one to distinguish a cork oak traditional silvopastoral system (known as a montado) from a cork oak forest system. Although understanding the manner in which different management practices affect cork growth is imperative, there are still only a few outputs from experimental research that contribute to this knowledge. The effect of potential drivers on annual cork growth was analyzed using a linear mixed model approach. Two dimensions of drivers were considered: intraspecific competition, assessed by tree level distance-dependent indices; and interspecific competition, assessed by variables characterizing understory management. The present dataset was collected from an experimental trial established on a cork oak stand in Podzolic soil on the Tagus river basin, covering two different cork growth cycles over the period from 2003 to 2015. The adjusted models considered two understory management alternatives: spontaneous shrubs maintenance and forage application. In both models, annual precipitation displayed a positive effect on annual cork growth, as expected. However, no significant effect of intraspecific competition was found. Additionally, there was a positive effect on annual cork growth associated with the spontaneous shrubs growth and a negative effect associated with lupine presence; both effects linked to different cork ring ages’ thresholds. The study main contributions are the following: (i) the introduction of the interaction between cork growth cycle stage and understory management practices, only possible with cork sample collections from different cork rotation cycles; (ii) the finding that there was no significant effect of intraspecific competition on cork growth.

Highlights

Cork oak (Quercus suber L.) is an important species in the Mediterranean forest, as it is provides raw material suitable for cork stoppers and other high value manufactured products
Linear models developed in this study were used to contribute to the knowledge about the effect of intra- and interspecific drivers, such as distance-dependent competition indices or understory management operations, on annual cork growth
The analyses undertaken do not show any impact of intraspecific competition on cork growth, expressed through a set of competition indices

Summary

Introduction

Cork oak (Quercus suber L.) is an important species in the Mediterranean forest, as it is provides raw material suitable for cork stoppers and other high value manufactured products. This species mainly occurs in a traditional silvopastoral system called a montado, characterized by low density and sparse trees. The Portuguese National Forest Inventory characterizes cork oak stands by an average density of around 66 trees per hectare [1], making no distinction between these two systems: montado and cork oak forest. Since there is no clear definition of a tree density threshold to differentiate between these two systems, they can only be distinguished by their management practices and production aims: the first is oriented for cork production, crop production and/or grazing; the second focuses mainly on cork production.

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Conclusion