Are drought and wildfires turning Mediterranean cork oak forests into persistent shrublands?

Abstract

In the Iberian Peninsula Mediterranean oak forests have been transformed into a mosaic landscape of four main patch-types: forests, savannas, shrublands and grasslands. We used aerial photographs over a period of 45 years to quantify the persistence and rates of transitions between vegetation patch-types in southern Portugal, where cork oak is the dominant tree species. We used logistic regression to relate vegetation changes with topographical features and wildfire history. Over the 45 years, shrublands have been the most persistent patch-type (59%), and have been expanding; forests are also persistent (55%) but have been decreasing since 1985; savannas and grasslands were less persistent (33% and 15%, respectively). Shrublands persistence was significantly correlated with wildfire occurrence, particularly on southern exposures after 1995. In contrast, forest persistence decreased with wildfire occurrence, and forests were more likely to change into shrublands where wildfire had occurred after 1995.

Landscape – wildfire interactions in southern Europe: Implications for landscape management

“…As was mentioned in the previous section, one first explanatory mechanism for this increased fire recurrence is the low resilience of some forest types which prevents auto-succession, and favours the establishment of more fire-prone fuel types (Acácio et al, 2009;Lloret et al, 2002Lloret et al, , 2003Pérez and Moreno, 1998) (Fig. 3).…”

Wildfire frequency varies with the size and shape of fuel types in southeastern France: Implications for environmental management

“…Cork oak (Q. suber) forests of the MAUR area burned more frequently due to the expansion of surrounding maquis. As stated by Acácio et al (2009) in Portugal, this protected habitat tends to shift towards shrublands due to a combination of droughts, fires and plant competition .…”

“…Both have flammable live fuels and dead fuels . A positive feedback likely exists between fire and shrubs abundance since most areas burned recurrently turn into flammable shrublands Moreira et al, 2011;Mouillot et al, 2003;Diaz-Delgado et al, 2004) due to the predominance of auto-succession (Trabaud 1998;Lloret, 2002;Acácio et al, 2009). In contrast, the hazard of burning tends to decrease over time in the AIXM area.…”

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

“…Besides, the development of farm mechanization, including the generalised use of wide plows, disc harrows, and scarifiers destroys young trees and may damage roots and weaken established trees, creating more susceptibility to the attack of pests and diseases (Branco and Ramos, 2009;Arosa et al, 2015). The fire frequency detected in the last few decades in this ecosystem (Pausas and Vallejo, 1999) has also become an additional obstacle to cork oak survival and recruitment (Acácio et al, 2009(Acácio et al, , 2010. Although cork oak is able to exhibit fire-resistance characteristics due to the bark insulation and to the mechanism of resprouting afterwards, frequent or intense wildfires may kill adult trees, especially if these events occur immediately after cork extraction (Moreira et al, 2007).…”