Tree biomass and the diversity relationship in mixed forest have an impact on forest ecosystem services provisions. Tree biomass yield is driven by several aspects such as species identity, site condition, stand density, tree age and tree diversity expressed as species mingling and structural diversity. By comparing diverse degrees of tree mixtures in natural forests, we can gain insight into the ecosystem services provision level and dynamic. Two monitoring sites in the Castilian Northern Plateau (Spain) have been analyzed to disentangle the relationships between biodiversity levels and tree biomass yield. Two permanent one hectare (ha) squared plots were established at Llano de San Marugán and Valdepoza. In each plot, all individual trees were measured (diameter and height), georeferenced and its species identity defined. Tree species in the two sites were Pinus sylvestris, Pinus nigra, Pinus pinea, Quercus pyrenaica, Quercus ilex, Quercus faginea and Juniperus thurifera. From these datasets, ten diversity indices that fall in three categories (species richness indices, species compositional/mingling indices and vertical structural indices) were used as predictor variables to fit several candidate models. By merging the trees by site (without considering the species identity) selected models include individual tree basal area as an explanatory variable combining by addition or interaction with diversity indices. When species are analyzed independently, structural diversity impacts on biomass yield in combination (additive or multiplicative) with tree size is negative for Pinus nigra and positive for the other species.

Tree biomass and diversity relationship in mixed forest impacts on forest ecosystem services provisions. Tree biomass yield is driven by several aspects such as species identity, site condition, stand density, tree age as well as tree diversity expressed as species mingling and structural diversity. By comparing diverse degrees of tree mixture in natural forests we can insight on the ecosystem services provision level and dynamic. Two monitoring sites in the Castilian Northern Plateau (Spain) have been analyzed to disentangle the relationships between biodiversity levels and tree biomass yield. Two permanent one ha squared plots were established at Llano de San Marugan and Valdepoza. In each plot all individual trees were measured (diameter and height), georeferenced and its species identity defined. Tree species in the two sites were Pinus sylvestris, Pinus nigra, Pinus pinea, Quercus pyrenaica, Quercus ilex, Quercus faginea and Juniperus thurifera. From these datasets ten diversity indices that fall in three categories (species richness indices, species compositional/mingling indices and vertical structural indices) were used as predictor variables to fit several candidate models. By merging the trees by site (without considering the species identity) selected models include individual tree basal area as explanatory variable combining by addition or interaction with diversity indices. When species are analyzed independently structural diversity impacts on biomass yield in combination (additive or multiplicative) with tree size is negative Pinus nigra and positive for the other species.

<p>Forest ecosystems are known to be vulnerable to climate change. Climate extremes, such as drought<br>events, are expected to increase in duration and frequency in many areas across the globe. Unexpected<br>and prolonged drought events already caused forests dieback all over the world in the last decades,<br>leading to dramatic consequences, such as biodiversity loss, ecosystem services alteration and reduction<br>of carbon sequestration potential. Indeed, in Central Europe, monocultures consisting mostly of <br>secondary conifer forests, showed low resistance to such events, and their viability is further threatened<br>by the interaction with other biotic and abiotic factors. In this context, the need of a deeper understanding<br>of the physiological mechanisms behind the tree response to extreme drought eventsis fundamental. The<br>present study, developed under the network of the CARE4C Project (Carbon smart forestry under climate<br>change GA 778322), aims at investigating Pinus sylvestris xylem plasticity in response to extreme drought.<br>We selected P. sylvestris pure forests in contrasting climatic zones of Europe, i.e. continental (Poland) and<br>Mediterranean (Spain), to study P. sylvestris xylem plasticity to extreme drought events under different<br>climatic conditions. Contemporarily, this study aims at comparing the xylem plasticity of P. sylvestris in<br>mono-specific and mixed forests. In the latter, the admixture is with Quercus petraea and Quercus<br>pyrenaica, in Poland and Spain respectively. The responses of P. sylvestris wood anatomical traits, such as<br>tracheid lumen area, cell wall thickness and parenchyma ray area, will be quantified along the entire treering chronologies. Short-term and legacy effects of extreme drought on P. sylvestris wood anatomical<br>traits will be evaluated in order to provide insights about the vulnerability of this speciesin a future climate<br>scenario. Locally, the comparison between P. sylvestris wood anatomical traitsin mono-specific and mixed<br>forests will highlight whether the mixing of species with different ecological needs can affect P. sylvestris<br>performance, ameliorating the resilience of this species to extreme drought events.</p>

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