Pathways for resilience in Mediterranean cork oak land use systems

Abstract

Context Loss of woodlands and degradation of vegetation and soil have been described for all Mediterranean-type ecosystems worldwide. In the Western Iberian Peninsula, overexploitation of evergreen cork oak land use systems has led to soil erosion, failures in oak recruitment, and loss of forests. Degraded and dry sites are quickly colonised by pioneer heathland rockrose (Cistus spp.) shrubs forming highly persistent patches. Aims Although traditionally shrublands have been considered as a transient successional state, we present evidence that they can represent persistent alternative states to former cork oak forests. Review trends and conclusions We first describe how Mediterranean vegetation evolved in the Iberian Peninsula and the role of fire and long-term human management as main disturbances. We then discuss alternative pathways through state-and-transition models indicating the ecological and land use variables that halt cork oak regeneration and recruitment and drive vegetation transitions towards persistent shrublands. Unless concerted management actions and restoration programmes are undertaken, the cork oak land use systems will not be sustainable.

Cork Oak Landscapes, Promised or Compromised Lands? A Case Study of a Traditional Cultural Landscape in Southern Spain

“…The sharp decline in the population, coupled with the increased cost of labor, led to a swift decline in the daily activities in the dehesa, notably the gradual disappearance of goats, regarded by interviewees as key in controlling understory growth of shrubs and hampering tree regeneration by grazing on oak saplings. Similar trends linking rural depopulation and declining dehesa/montado activities have been described in other areas of Spain and Portugal (Acácio and Holmgren 2014;Domínguez et al 2006). While the dehesa system was in sharp decline, demand for wood and cellulose for the expanding national industry increased, leading to a rapid expansion of eucalyptus, and to a lesser extent pine, plantations on private lands in Berrocal in the 1960s and 1970s.…”

“…Acácio and Holmgren (2014) describe a continuum of oak landscapes ranging from savannah-like open systems known as dehesas (Spain) or montados (Portugal), to densely covered cork oak woodlands. Mean annual precipitation is proposed as a major factor determining tree density, where long-term adjustments have led to an optimal functional hydrological equilibrium (Joffre et al 1999).…”

Long-term sustainability of cork oak agro-forests in the Iberian Peninsula: A model-based approach aimed at supporting the best management options for the montado conservation

“…Droughts contribute to cork oak population losses as it hampers regeneration and increases tree mortality (Acácio and Holmgren, 2014). Considering the historical trends of droughts in mainland Portugal from 1976(INAG, 2007, the drought effects per year were considered as direct constrains over seedlings and saplings viability, the more vulnerable classes to this environmental factor.…”

“…We considered as stressors the lack of cork oak health and the low natural regeneration rates. Tree health has been affected by intensive pruning, exaggerated cork harvesting and the influence of pests and diseases (Camilo-Alves et al, 2013;Acácio and Holmgren, 2014). The limitations to natural regeneration have been attributed to various causes, including: a) poor dispersal and shortage of viable acorns (Branco et al, 2002;Pulido and Díaz, 2005;Acácio et al, 2007); b) high post-dispersive acorn losses associated with seedling mortality due to over-grazing by livestock and wild animals (Herrera, 1995;Plieninger et al, 2004;Acácio et al, 2007;Pulido et al, 2013); c) low seedling survival to summer drought (Gimeno et al, 2009;Smit et al, 2009).…”

Leaf decomposition of cork oak under three different land uses within a montado of southern Portugal

“…This ecosystem is a protected habitat within the EU Habitats Directive (92/43/EEC, http://ec.europa.eu/environment/nature/legislation/ habitatsdirective/index_en.htm, verified 12 September 2016) but the long-term persistence of cork oak in montados is a subject of serious concern among the public and the scientific community. The main causes of degradation are poor cork oak phytosanitary conditions and low natural regeneration rates (Díaz et al 1997;Pulido and Díaz 2005;Acácio et al 2007;Camilo-Alves et al 2013;Acácio and Holmgren 2014;Arosa et al 2015).…”