Mixture mitigates the effect of climate change on the provision of relevant ecosystem services in managed Pinus pinea L. forests

Forecasted scenarios of climate change are expected to result in a dramatic reduction in the provision of Ecosystem Services (ES) from forests. Increasing tree species diversity has been proposed as a measure for adapting forests and warrantee the provision of services, since mixed forests, if compared with monospecific forests, are expected to be more productive, resilient and stable facing disturbances. In the present work we use a modelling approach in order to quantify the provision of different ES under expected climate scenarios, comparing pure forests of Pinus pinea L. with mixed forests where the species grows accompanied by different Quercus and Juniperus species. To this aim we first adapted the existing individual tree level model PINEA2, originally constructed for pure even-aged stands of P. pinea, in order to consider the interspecific interactions acting in mixed forests. In a second step we used the so adapted model for forecasting and comparing the provision of different ES - focusing on stocking, growth, yield, CO2 fixation, economic income and structural diversity - under current climate and expected scenarios RCP 4.5 & 8.5. Our results indicate that although growth and allometry in P. pinea trees is enhanced in mixtures, this effect is currently counterbalanced by the expected reduction in growth in the species occupying the understorey, thus under current climate conditions little differences due to composition are observed in the provision of ES. On the other hand, our simulations point to a generalized decrease in the ES supply under more severe climate change scenarios, being this reduction mitigated - at least in part - in mixed P. pinea forests, which are more competitive under the most restrictive environmental conditions. As a consequence, the promotion of mixtures by under-planting and/or releasing of pre-existing advanced regeneration of complementary species may be postulated as a management concept for adapting these forests to climate change.

Automated summary

The study indicates that growth and allometry in P. pinea trees are enhanced in mixtures, but potential reduction in growth in understorey species may counterbalance this effect under current climate conditions, leading to little differences in ES provision due to composition. Simulations suggest a general decrease in ES supply under more severe climate change scenarios, with mixed P. pinea forests being more competitive under restrictive environmental conditions and potentially mitigating this reduction.