European Atlantic deciduous forests are more resilient to fires than Pinus and Eucalyptus plantations

Abstract

In this study, we assess how ecosystem type affects the short-term post-fire resilience of fire-prone forests, which are the predominant ecosystems in South West (SW) Europe. For this purpose, we focused on three forest systems, widespread across the European Atlantic coast, which are highly susceptible to fires at their SW distribution boundary, namely the European thermophilous Atlantic deciduous forests, dominated by Quercus robur L., and two types of forest plantations widespread globally, Eucalyptus globulus Labill. and Pinus pinaster Aiton plantations. At the community structure level, resilience to fire was measured based on changes in cover of each vertical stratum. At the functional level, resilience to fire was measured based on replacements of (both morphological and regenerative) plant functional types in the overstory and understory layers. The study variables were vertical structure and abundance of plant functional types in both overstory and understory layers. Vertical structure was assessed by defining nine vertical strata and estimating the cover in each vegetation stratum. All species identified in the overstory and understory layers were functionally classified according to their morphological attributes and regenerative traits pertaining to fire. One year after fire, we observed considerable differences in the structure between the three forest communities studied, particularly in the overstory layer, because most of the vertical strata were well recovered in the oak forest, partially recovered in the E. globulus plantation, and completely lost in the P. pinaster plantation. In contrast to the Atlantic deciduous forest and eucalyptus plantation, the pine plantation displayed distinct changes in its distribution of plant functional types. The pine plantation showed extremely low resilience to fire because the overstory layer decreased considerably, and the understory layer experienced substantial changes in the distribution of morphological and regenerative plant functional types. Fire favoured certain species which prevailed over others and, while grasses, herbaceous and spiny shrubs increased, the abundance of most morphologically functional plant types disappeared or decreased. These changes in the structure of forest communities and in the distribution of plant functional types have important implications for ecosystem functioning and services provision. Therefore, this study may serve as a foundation for devising forest management measures aimed at increasing ecosystem resilience to fire.