Multispecies tree planting has long been applied in forestry and landscape restoration in the hope of providing better timber production and ecosystem services; however, a systematic assessment of its effectiveness is lacking. We compiled a global dataset of matched single-species and multispecies plantations to evaluate the impact of multispecies planting on stand growth. Average tree height, diameter at breast height, and aboveground biomass were 5.4, 6.8, and 25.5% higher, respectively, in multispecies stands compared with single-species stands. These positive effects were mainly the result of interspecific complementarity and were modulated by differences in leaf morphology and leaf life span, stand age, planting density, and temperature. Our results have implications for designing afforestation and reforestation strategies and bridging experimental studies of biodiversity–ecosystem functioning relationships with real-world practices.

When tree‐species mixtures are more productive than monocultures, higher light absorption is often suggested as a cause. However, few studies have quantified this effect and even fewer have examined which light‐related interactions are most important, such as the effects of species interactions on tree allometric relationships and crown architecture, differences in vertical or horizontal canopy structure, phenology of deciduous species or the mixing effects on tree size and stand density. In this study, measurements of tree sizes and stand structures were combined with a detailed tree‐level light model (Maestra) to examine the contribution of each light‐related interaction on tree‐ and stand‐level light absorption at 21 sites, each of which contained a triplet of plots including a mixture and monocultures ofFagus sylvaticaandPinus sylvestris(63 plots). These sites were distributed across the current distribution of these species within Europe. Averaged across all sites, the light absorption of mixtures was 14% higher than the mean of the monocultures. At the whole community level, this positive effect of mixing on light absorption increased as canopy volume or site productivity increased, but was unrelated to climate. At the species population or individual tree levels, the mixing effect on light absorption resulted from light‐related interactions involving vertical canopy structure, stand density, the presence of a deciduous species (F. sylvatica), as well as the effects of mixing on tree size and allometric relationships between diameter and height, crown diameter and crown length. The mixing effects on light absorption were only correlated with the mixing effects on growth forP. sylvestris, suggesting that the mixing effects on this species were driven by the light‐related interactions, whereas mixing effects onF. sylvaticaor whole community growth were probably driven by non‐light‐related interactions. Synthesis. The overall positive effect of mixing on light absorption was the result of a range of light‐related interactions. However, the relative importance of these interactions varied between sites and is likely to vary between other species combinations and as stands develop.

Mixtures can be more productive than monocultures and may therefore use more water, which may make them more susceptible to droughts. The species interactions that influence growth, transpiration and water-use efficiency (WUE, tree growth per unit transpiration) within a given mixture vary with intra- and inter-annual climatic variability, stand density and tree size, but these effects remain poorly quantified. These relationships were examined in mixtures and monocultures of Eucalyptus globulus Labill. and Acacia mearnsii de Wildeman. Growth and transpiration were measured between ages 14 and 15 years. All E. globulus trees in mixture that were growing faster than similar sized trees in monocultures had higher WUE, while trees with similar growth rates had similar WUE. By the age of 14 years A. mearnsii trees were beginning to senesce and there were no longer any relationships between tree size and growth or WUE. The relationship between transpiration and tree size did not differ between treatments for either species, so stand-level increases in transpiration simply reflected the larger mean tree size in mixtures. Increasing neighbourhood basal area increased the complementarity effect on E. globulus growth and transpiration. The complementarity effect also varied throughout the year, but this was not related to the climatic seasonality. This study shows that stand-level responses can be the net effect of a much wider range of individual tree-level responses, but at both levels, if growth has not increased for a given species, it appears unlikely that there will be differences in transpiration or WUE for that species. Growth data may provide a useful initial indication of whether mixtures have higher transpiration or WUE, and which species and tree sizes contribute to this effect.

Extreme droughts are expected to increase in frequency and severity in many regions of the world, threatening multiple ecosystem services provided by forests. Effective strategies to adapt forests to such droughts require comprehensive information on the effects and importance of the factors influencing forest resistance and resilience. We used a unique combination of inventory and dendrochronological data from a long‐term (>30 years) silvicultural experiment in mixed silver fir and Norway spruce mountain forests along a temperature and precipitation gradient in southwestern Germany. We aimed at examining the mechanisms and forest stand characteristics underpinning the resistance and resilience to past mild and severe droughts. We found that (i) fir benefited from mild droughts and showed higher resistance (i.e., lower growth loss during drought) and resilience (i.e., faster return to pre‐drought growth levels) than spruce to all droughts; (ii) species identity determined mild drought responses while species interactions and management‐related factors strongly influenced the responses to severe droughts; (iii) intraspecific and interspecific interactions had contrasting effects on the two species, with spruce being less resistant to severe droughts when exposed to interaction with fir and beech; (iv) higher values of residual stand basal area following thinning were associated with lower resistance and resilience to severe droughts; and (v) larger trees were resilient to mild drought events but highly vulnerable to severe droughts. Our study provides an analytical approach for examining the effects of different factors on individual tree‐ and stand‐level drought response. The forests investigated here were to a certain extent resilient to mild droughts, and even benefited from such conditions, but were strongly affected by severe droughts. Lastly, negative effects of severe droughts can be reduced through modifying species composition, tree size distribution and stand density in mixed silver fir‐Norway spruce forests.