Increasing resistance and resilience of Mediterranean conifer forests: the experience of Spain and France and their implications for management

Management strategies, using thinning combined or not combined with underplanting, have been tested
in experimental forests of Spain and southern France to promote growth, recruitment and increase their
resilience.
In dry and fire-prone areas of southern Spain and France, Pinus halepensis forests were thinned at
different levels and hardwood species were introduced under pine canopy and in opened areas. Thinning
activities increased light, modified microclimate and soil moisture availability. Growth was improved in
all sites but survival showed a more contrasted response. In mountainous areas, thinning treatments
applied on Abies alba forests of southern France and Pinus nigra forests of central Spain were tested.
Thinned silver fir stands showed higher tree growth than the control stands. In black pine forests,
maximal seedling emergence was found for high basal area values whereas survival and growth were
the highest for lower values.
Despite strong site differences, thinning to a basal area around 15-20 m2/ha appeared to be a good
compromise to promote growth of the residual stand and recruitment. In fire-prone areas, thinning, alone
or combined thinning with the introduction of resprouting hardwood species, is an efficient technique
but has to be adapted to site conditions and species under focus. Finally, we discussed usual thinning
limitations and options of remediation in the light of the new opportunity opened by the increasing
demand in forest biomass.