AUTHOR=Gazol Antonio , Camarero J. Julio , Sangüesa-Barreda Gabriel , Vicente-Serrano Sergio M. 

TITLE=Post-drought Resilience After Forest Die-Off: Shifts in Regeneration, Composition, Growth and Productivity

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 9 - 2018

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.01546

DOI=10.3389/fpls.2018.01546

ISSN=1664-462X

ABSTRACT=A better understanding on the consequences of drought on forests can be reached by paying special attention to their resilience capacity, i.e. the ability to return to a state similar to pre-drought conditions. Nevertheless, extreme droughts may surpass the threshold for the resilience capacity triggering die-off and causing multiple changes at varying spatial scales. We evaluated the changes in the abundance, regeneration capacity (seedling abundance), radial growth (annual tree rings) of the main tree species, as well as in productivity (remote sensing imagery; Normalized Difference Vegetation Index, NDVI) of two coniferous forests which displayed drought-induced die-off during the last decades: a Scots pine (Pinus sylvestris) forest under continental Mediterranean conditions and a Silver fir (Abies alba) forest under more temperate conditions. We found a strong negative impact of a recent severe drought (2012) on Scots pine growth, whereas the coexisting Juniperus thurifera showed positive trends in basal area increment (0.02 ± 0.003 cm2 yr-1). No Scots pine recruitment was observed in sites with intense die-off, but J. thurifera and Quercus ilex recruited. The 2012 drought event translated into a strong NDVI reduction (32% lower than the 1982-2014 average). In Silver fir we found a negative impact of the 2012 drought on short-term radial growth, whilst long-term growth of Silver fir and the coexisting Fagus sylvatica showed positive trends. Growth rates were higher in F. sylvatica (0.04 ± 0.003 cm2 yr-1) than in A. alba (0.02 ± 0.004 cm2 yr-1). These two species recruited beneath declining and non-declining Silver-fir trees. The 2012 drought translated into a strong NDVI reduction which lasted until 2013. The results presented here suggest two different post-drought vegetation pathways. In the Scots pine forest, the higher growth and recruitment rates of J. thurifera correspond to a vegetation shift where Scots pine is being replaced by the drought-tolerant juniper. Conversely, in the Silver-fir forest there is an increase of F. sylvatica growth and abundance but no local extinction of the Silver-fir. Further research is required to monitor the evolution of these forests in the forthcoming years to illustrate the cumulative impacts of drought on successional dynamics.