Can trees buffer the impact of climate change on pasture production and digestibility of Mediterranean dehesas?

Abstract

Sustainability of silvopastoral ecosystems under future scenarios of climate change remains poorly studied. Assessing the potential mitigation role of trees on biomass productivity and quality is timely to face the challenges associated with the increasing aridity forecasted for the Mediterranean region. We carried out a field experiment with increased temperature (+ 2-3 °C) and rainfall reduction (33 %) for three years to evaluate how biomass productivity and digestibility respond to climate-induced stress, and whether scattered trees can buffer the effects of higher aridity in silvopastoral ecosystems. Plant communities located beneath tree canopy were less productive (351 31 g) than those located in open grasslands (493 g) but they exhibited higher digestibility (44 % and 41 %, respectively), likely promoted by tree shade and the higher soil fertility of this habitat type. Both habitats exhibited a similar trend in terms of biomass productivity, with a 33 % increase under warming conditions and a 13 % decrease under reduced rainfall. An increase in temperature intensifies photosynthetic activity and favors plant growth, but the development of new organs is stopped by droughts. In contrast, biomass digestibility decreased significantly under increased temperatures (-38 7.5 %), likely because warming enhanced the fiber and lignin content and decreased the crude protein content. This warming-induced effect on biomass digestibility only appeared in grasslands, suggesting a buffering role of tree canopy in mitigating the impact of climate change on these ecosystem processes. Interestingly, warming did not only affect biomass productivity and digestibility in a direct way but also indirectly via changes in the functional composition of plant communities. Findings provided by this study could be applied to develop scientific strategies of controlling tree density, which could be used as a helpful tool in the management plans of agroforestry systems to cope with climate change.