Several restoration practices are used to mitigate and compensate for the negative effects of large-scale forestry on biodiversity in temperate and boreal forests. A comprehensive synthesis of the benefits of these practices across taxa is missing. We conducted a systematic review and meta-analysis on this topic. We identified 93 relevant studies in which the effects of partial harvest, thinning, understory removal, prescribed burning, deadwood addition, or a combination of these were examined. Overall, restoration practices had a positive effect on richness and abundance of forest species, though effects varied among practices and taxa. The most consistent positive responses were found for plants and flying invertebrates. For other taxa, the response was not statistically significant, and in several cases, there were also negative responses. For instance, thinning and understory removal negatively affected birds, and prescribed burning had negative effects on bryophytes and lichens. Effects of restoration practices often became more positive over time, but 83% of data points were from within 10 years since the start of restoration, meaning the long-term impacts of restoration practices remain to be explored. Because different restoration practices benefit different taxa, promoting forest biodiversity requires a variety of restoration practices applied across forest landscapes. So far, evaluations have been done only at local scales, and evaluations of effects on landscape-scale biodiversity are needed.

Abstract Systematic reviews and meta‐analyses are key evidence synthesis methods for informing future research, interventions and policy. As the validity of their conclusions depends on the primary studies they synthesise, assessing the internal validity of the included studies is essential. In some fields, such as medicine, this is the norm and is commonly done using Risk of Bias assessment tools. Risk of Bias (RoB) assessment is however rare in ecology and evolutionary biology (EEB) even though several RoB tools have been developed in some ecological subfields and related fields. To identify potential reasons for a limited uptake, we conducted a survey of ecologists and evolutionary biologists with evidence synthesis experience and reviewed 275 journals that publish EEB research for guidelines on performing RoB or related assessments. Only 28 of 232 (12%) survey respondents had correct interpretation of the RoB concept, while 46 (40%) of 116 that had heard of RoB have confused RoB with publication bias. Just 10 (4%) had conducted a RoB assessment, most of whom found it challenging. Out of the 209 EEB journals that explicitly solicit evidence synthesis (N = 58) or reviews (N = 151), only five (2%) directly mentioned standards for conducting evidence synthesis, which include RoB or related (e.g. critical appraisal) assessments. An additional 45 (22%) journals indirectly linked to RoB or a related assessment via referring to the guidelines for reporting evidence synthesis (e.g. PRISMA), despite such reporting guidelines not providing information on how to conduct RoB assessments. To increase its uptake in EEB we recommend making RoB assessment: (1) known and recognised as an essential component of a reliable evidence synthesis by including it in training materials, and journals' and funders' guidelines and policies; (2) easy to perform by bringing the synthesis community together to determine the need for developing new or adjusting existing RoB tools; and (3) possible by further improving reporting standards for primary studies so that RoB assessment can be done on these studies. For those unfamiliar with the RoB assessment, we provide five key RoB questions that existing tools often cover. These questions can be considered to understand the basic composition of the evidence included in evidence synthesis.

Biodiversity generally enhances ecosystem productivity, but whether such effects persist or intensify during climate extremes is unclear. Here we synthesized data from 75 biodiversity experiments across grasslands and forests to assess how aridity and soil nutrients modulate plant diversity effects under drought and heat extremes. Biodiversity most strongly enhanced productivity under extreme drought in more arid grasslands but had limited effects in forests under such conditions. More arid grasslands showed enhanced complementarity effects under extreme drought, whereas less arid grasslands favoured selection effects driven by productive species. Heat extremes did not produce comparable context-dependent changes in plant diversity effects across ecosystem types or aridity gradients. Soil nutrients did not have any detectable influence under either drought or heat extremes, suggesting that as climatic stress intensifies, hydric limitations override edaphic constraints. Our synthesis identifies when and where plant diversity most strongly enhances productivity, showing that its effects are the greatest under extreme drought in more arid grasslands.

Anthropogenic pressures are pushing ecosystems towards collapse by disrupting their structure and functioning. Whilst ecological responses to climate and land cover changes are widely addressed at the global scale, a notable knowledge gap remains at the landscape level—a critical scale for translating science into action. To evaluate the impacts of anthropogenic pressures on ecosystem functioning at the landscape scale. Specifically, we assess the influence of climate trends and land cover changes on the spatial and temporal patterns of Normalized Difference Vegetation Index (NDVI) over a 30-year period (1995–2024). Using Sussex (UK) as a study area, we examined spatio-temporal patterns in climate trends and NDVI – used as a proxy for vegetation distribution and productivity—over three decades based on satellite imagery. We characterized the spatial heterogeneity of observed changes and evaluated the role of climate and land cover changes as drivers of long-term NDVI dynamics. We found an overall increase in NDVI across the study area and all land cover types (MK tau value = 0.605, p-value < 0.01, TS slope = 0.0044 ∆NDVI yr⁻1), marginally correlated with increasing average temperatures (ρ ≈ 0.34, p = 0.067). This increase in NDVI showed spatially heterogenous patterns with distinct hotspots of NDVI change (Local Moran’s I) linked to changes in land cover types. We detected rising temperatures in Sussex (annual average temperatures: Mann–Kendall (MK) tau value = 0.297, p-value = 0.022, Theil-Sen (TS) slope = 0.026 ℃ yr⁻1), but rainfall levels have not changed significantly (annual average rainfall: MK tau value = 0.21, p-value = 0.108, TS slope = 4.91 mm yr⁻1). These findings show a positive relationship between rising temperatures and vegetation greening, as reflected by NDVI gains with spatially heterogenous patterns associated with land cover changes and hotspots of NDVI change. Our study provides spatially explicit evidence to support effective landscape management strategies and inform policies by demonstrating the interaction between anthropogenic pressures at the landscape level. Because the landscape is a relevant scale at which environmental change and its outcomes are perceived, our results offer insights to address the effects of global and local changes.

Tree species diversity is known to affect tree growth and leaf traits, which in turn can influence various ecosystem processes. However, the reported direction of these tree diversity effects is inconsistent, indicating that their outcomes depend strongly on ecological context. Using the long-term Satakunta forest diversity experiment in Finland, we investigated how the effects of tree species diversity on growth and leaf traits vary with species identity, stand density, and spatial scale. By comparing the responses of light-demanding Scots pine Pinus sylvestris and shade-tolerant Norway spruce Picea abies, we show that the factors influencing diameter at breast height (DBH) and leaf traits differ between species with contrasting life-history strategies. Pine needle terpene concentrations were lowest in neighbourhoods dominated by conspecifics, while spruce needle terpenes were unaffected by tree species composition. Increasing canopy cover reduced spruce dry needle mass but had no effect on the dry needle mass of pines. Likewise, the factors that influenced tree growth differed between species; spruce DBH was lowest in thinned stands but was unaffected by tree species composition, whereas pine DBH did not vary significantly with plot density but was reduced in neighbourhoods containing silver birch Betula pendula. Our findings also indicate that diversity effects on leaf traits primarily operate at the local scale, as statistical models assessing the effect of immediate neighbours on pine terpenes yielded significant results, whereas models assessing diversity effects on a plot-level did not. In contrast, both pine and spruce DBH responded to plot and immediate-neighbour level factors, implying that tree growth is influenced by broader stand-level conditions, while leaf traits responses to diversity are more localised.

Expanding forest and woodland cover is a global strategy to mitigate and adapt to the climate crisis and reverse biodiversity decline. While most woodland in temperate regions is created through tree planting, natural colonisation has been advocated for as an alternative or complementary approach. However, there is limited understanding on how the structural attributes of woodlands created through these different approaches develop through time. To address this knowledge gap, we assessed a suite of structural metrics for 28 woodland sites (aged 13-43 years) that were established along a planted to natural colonisation continuum in England. We used an Uncrewed Aerial System to collect LiDAR data alongside field surveys and calculated metrics relating to above-ground biomass accumulation (canopy height and basal area) and metrics relating to structural complexity (the horizontal and vertical arrangement of canopy) as a proxy for biodiversity potential. Canopy height and basal area were higher in woodlands with larger proportions of planting. Additionally, woodlands with higher proportions of planting displayed greater vertical complexity (canopy stratification) whereas there was weak evidence that woodlands with higher proportions of natural colonisation develop greater horizontal complexity (gap fraction). This suggests that tree planting is the better option when biomass accumulation is the primary goal, whereas natural colonisation or hybrid approaches are likely to be beneficial when the focus is biodiversity or a mix of outcomes. Woodlands created through hybrid approaches that combine planting and natural colonisation offered intermediate values of biomass accumulation and structural complexity.

Climate can vary spatially and temporally and is becoming increasingly unpredictable due to climate change. It can have a large impact on host-parasite interactions and investigating this effect is vital both for understanding current parasite distribution and epidemiology, and predicting how this will change in the future. Here, we conducted a meta-analysis to determine whether temperature and precipitation have an overall effect on parasite prevalence and infection intensity in terrestrial animals. This is a phylogenetically controlled quantitative synthesis to assess parasite prevalence and infection intensity in terrestrial animals across contrasting temperatures and precipitation. We found large variation in the effect of temperature on parasite prevalence, precipitation on parasite prevalence, and temperature on infection intensity. This provides robust quantitative evidence against the controversial "warmer sicker world" hypothesis. There was no effect of climate on parasitism, irrespective of whether the parasite was an endoparasite or ectoparasite, or across different parasite lifecycles. Although some host and parasite taxa were understudied, we found no consistent taxonomic patterns. Importantly, we revealed large gaps in the literature, including the relationship between humidity, prevalence, and infection intensity. Ectoparasites and reptile hosts were also very underrepresented, and deserve further study. Focusing future research on these gaps will help to confirm whether certain types of host-parasite interactions are more or less sensitive to changes in climate, with implications for conservation.

Trees growing in more diverse stands generally experience less herbivory than those in less diverse ones, potentially due to neighbourhood-mediated variations in traits which influence leaf palatability. While numerous studies have assessed leaf trait responses to species diversity, the influence of genotypic diversity on leaf traits, and subsequent effects on herbivory, remains poorly understood. We investigated two genotypes of silver birch (Betula pendula) growing in single-, 2-, 4- and 8-genotype mixture plots in the Satakunta birch clone diversity experiment in SW Finland. Our aim was to determine whether genotypic diversity causes leaf trait variation and whether these changes are linked to herbivory. We found no effect of genotypic diversity on specific leaf area (SLA) or concentrations of phenolic compounds, but increased canopy cover around the focal trees was associated with lower concentrations of some phenolics. Genotypic diversity had a significant effect on herbivory, with one of the genotypes suffering more herbivory in 2-genotype mixture plots than in single-genotype plots. Genotype identity was the strongest predictor of both leaf traits and herbivory. Two birch genotypes differed in concentrations of most phenolic compounds, SLA and herbivory. Leaf trait-herbivory relationships were also genotype specific, with only one of the two genotypes exhibiting a negative correlation between herbivory and phenolics. Our study demonstrates that genotypic diversity is a poor predictor of leaf traits and herbivory in silver birch and indicates the importance of genotype selection as a consideration when establishing herbivory-resilient forests.

Plants evolved alongside herbivores for over 400 million years and show remarkable plasticity in responses to attack by multiple herbivores. However, it is often debated which herbivore traits predict plant responses and it is poorly understood how plant life-history traits contribute to the variation observed in plant responses. We explored the role of ecological factors such as herbivore identity and plant life history by conducting a meta-analysis of 161 studies on the effects of sequential herbivory by arthropods, nematodes and mammals. We included herbivore performance and preference as measures of induced resistance and plant growth and damage as measures of plant performance. We uncovered that sequential herbivory reduced herbivore performance in most cases but did not consistently affect herbivore preference. Moreover, induced resistance was particularly observed in glasshouse experiments and in experiments on cultivated plant species. Plants managed to reduce plant damage but did not reduce biomass loss effectively. This study highlights that plants can effectively use induced responses to defend against sequential herbivore attack regardless of herbivore identity or plant life history. To elucidate the cost of multiherbivore attack and plant adaptations to these scenarios, there is a need to examine the consequences of the interactions on plant fitness.

Diversifying planted forests to reduce the risks associated with large scale disturbances, such as pathogens, is a major aim of sustainable forest management. Previous meta-analyses have shown that insect pest damage is lower in mixed forest stands compared to monocultures, but the same has not been shown for pathogens. Here, we provide the first systematic review and meta-analysis specifically testing the effects of tree species diversity on pathogen damage. Relevant studies were retrieved using bibliographic databases and internet searches, as well as previously unpublished data sets contributed by stakeholders. We found that more diverse forest stands overall had significantly lower pathogen damage, and that this result was most pronounced in temperate forests for which the most studies were available. Although in some cases tree diversity had a strong effect, this was not universal and was influenced neither by pathogen specialism, nor by the presence of alternative hosts in stands. Several studies reported specific effects of tree neighbours in mixed stands, including impacts on the microclimate of stands. Future work should focus on mechanistic explanations that could underpin neighbour identity effects in mixed forests. We suggest the use of the disease triangle as a tool for considering the multiple factors that can influence pathogen damage in mixed forest stands.

Mixed-species forests have emerged as a promising approach to mitigate climate change impacts through enhanced carbon (C) sequestration while maintaining productivity, biodiversity, and other ecosystem services. However, we still have a poor understanding of the context-dependency of soil C sequestration in tree mixtures, particularly how it is influenced by plant-soil-microbe interactions and environmental conditions.Using soil samples collected from nine European sites within the global network of tree diversity experiments, TreeDivNet, we examined how tree species richness is associated with topsoil C stocks, fungal community composition and diversity, and their interactions. We further investigated the influence of biotic, edaphic, and climatic factors on the relationship between tree richness and topsoil C stocks. We hypothesised that increased tree species richness leads to increased topsoil C stocks and fungal diversity, and that this effect is modulated by site-specific interactions between biotic and abiotic factors.Overall, we found topsoil C stocks in stands with high tree diversity to be greater than in monocultures across the study sites. Lower soil fertility, cooler mean annual temperatures, and lower interannual variability of temperature and precipitation were found to correlate with positive effects of tree diversity on soil C stocks. While tree diversity did not directly influence fungal diversity, topsoil C stocks were positively correlated to fungal species richness. In addition, fungal richness showed a positive correlation with the net diversity effect of tree mixtures on topsoil C, suggesting that fungal diversity may be one of several factors contributing to the context-dependency of tree diversity effects on soil C stocks.Our study shows that tree species diversity can increase topsoil C storage across Europe, influenced both directly and indirectly by fungal diversity and environmental conditions. The mediation of direct and indirect linkages between tree diversity, fungal diversity and topsoil C stocks by local abiotic context highlights the need to improve our mechanistic understanding for site-specific management of soil C sequestration in tree mixtures to promote climate change mitigation in European forests.

Assisted migration is a tree-planting method where tree species or populations are translocated with the aim of establishing more climate-resilient forests. However, this might potentially increase the susceptibility of translocated trees to herbivory. Stand diversification through planting trees in species or genotypic mixtures may reduce the amount of damage by insect pests, but its effectiveness in mitigation of excess herbivory on climate-matched trees has seldom been explored. Using the Climate Match Experiment which manipulates both tree climatic provenance and stand diversity, we compared growth, insect herbivory and leaf traits of pedunculate oaks (Quercus robur) of local and Italian provenances in monocultures, provenance mixtures or species mixtures. Additionally, we investigated whether tree apparency and light availability cause variation in leaf traits and herbivory and tested whether these factors were influenced by stand diversity. We found that Italian oaks were subject to greater herbivore damage than those of local English provenance regardless of stand diversity and that insect herbivory in Italian oaks was higher on more apparent trees. Italian oaks also had lower concentrations of hydrolysable tannins than English oaks, but tannin concentrations were poor predictors of herbivory. Additionally, we show that leaf trait variation is strongly associated with differences in light availability.

Mixed-species forests are proposed to enhance tree resistance and resilience to drought. However, growing evidence shows that tree species richness does not consistently improve tree growth responses to drought. The underlying mechanisms remain uncertain, especially under unprecedented multiyear droughts. We used a network of planted tree diversity experiments to investigate how neighborhood tree diversity and species' functional traits influence individual tree responses to drought. We analyzed tree cores (948 trees across 16 species) from nine young experiments across Europe featuring tree species richness gradients (1-6 species), which experienced recent severe droughts. Radial growth response to drought was quantified as tree-ring biomass increment using X-ray computed tomography. We applied hydraulic trait-based growth models to analyze single-year drought responses across all sites and site-specific responses during consecutive drought years. Growth responses to a single-year drought were partially explained by the focal species' hydraulic safety margin (representing species' drought tolerance) and drought intensity, but were independent of neighborhood species richness. The effects of neighborhood functional diversity on growth responses shifted from positive to negative with increasing drought duration during a single growing season. Tree diversity effects on growth responses strengthened during consecutive drought years and were site-specific with contrasting directions (both positive and negative). This indicates opposing diversity effects pathways under consecutive drought events, possibly resulting from competitive release or greater water consumption in diverse mixtures. We conclude that tree diversity effects on growth under single-year droughts may differ considerably from responses to consecutive drought years. Our study highlights the need to consider trait-based approaches (specifically, hydraulic traits) and neighborhood scale processes to understand the multifaceted responses of tree mixtures under prolonged drought stress. This experimental approach provides a robust framework to test biodiversity-ecosystem functioning (BEF) relationships relevant for young, planted forests under increased drought stress.

Plant diversity is known to influence ecosystem functioning, but the strength and direction of this relationship vary considerably among studies, most of which have a short duration. In communities with long‐lived species, such as forests, traits of individual trees change from seedlings to maturity, and the environment in which trees grow also continually changes through stand development and forest succession. We argue that interactions between these individual and community‐level effects over time will alter biodiversity‐ecosystem functioning (BEF) relationships, likely explaining at least part of the reported variation in BEF effects among studies. We outline a series of mechanisms through which temporal changes at the tree and stand levels can alter BEF relationships and illustrate these processes using data from the long‐term Satakunta forest diversity experiments in Finland. We argue that long‐term forest diversity experiments are essential to robustly characterize temporal dynamics emerging from the complex interplay between plant functional traits and environmental conditions over time. These experiments can provide critical insights for predicting the consequences of biodiversity loss on ecosystem functioning and service provisioning over time.

1.Creating woodlands through natural processes, as opposed to traditional tree planting, is expected to result in more structurally diverse, locally adapted woodlands that enhance the resilience of existing treescapes. However, the outcomes of natural colonisation can be variable, and there is still considerable uncertainty around the ecological processes involved. 2.To address knowledge gaps and guide a future research and policy agenda, we synthesise current knowledge of the ecology of natural colonisation in Great Britain. We combine expertise from 31 practitioners and researchers spanning varied British contexts, including insights from 15 case studies and an expert survey on the relative importance of ecological factors influencing natural colonisation. 3.The most important determinants of successful natural colonisation, identified by practitioners and researchers, were the availability of seed sources and low levels of herbivory. However, key knowledge gaps remain around the timeframe and trajectory of woodland development and appropriate management practices. Natural colonisation and tree planting can be combined to meet diverse woodland objectives, but this has been little explored to date. 4.Solutions. Land managers and advisors face uncertainty and many knowledge gaps when creating woodland through natural processes. Site monitoring and adaptive management can help meet site objectives that, in turn, can be supported by policies reflecting uncertainties in the process. Collaboration between researchers and land managers to monitor woodland development, use experimental approaches and share knowledge will help further applied ecological understanding, supporting informed decision-making by land managers.

Plant diversity effects on community productivity often increase over time. Whether the strengthening of diversity effects is caused by temporal shifts in species-level overyielding (i.e., higher species-level productivity in diverse communities compared with monocultures) remains unclear. Here, using data from 65 grassland and forest biodiversity experiments, we show that the temporal strength of diversity effects at the community scale is underpinned by temporal changes in the species that yield. These temporal trends of species-level overyielding are shaped by plant ecological strategies, which can be quantitatively delimited by functional traits. In grasslands, the temporal strengthening of biodiversity effects on community productivity was associated with increasing biomass overyielding of resource-conservative species increasing over time, and with overyielding of species characterized by fast resource acquisition either decreasing or increasing. In forests, temporal trends in species overyielding differ when considering above- versus belowground resource acquisition strategies. Overyielding in stem growth decreased for species with high light capture capacity but increased for those with high soil resource acquisition capacity. Our results imply that a diversity of species with different, and potentially complementary, ecological strategies is beneficial for maintaining community productivity over time in both grassland and forest ecosystems.

Enhancing tree diversity may be important to fostering resilience to drought-related climate extremes. So far, little attention has been given to whether tree diversity can increase the survival of trees and reduce its variability in young forest plantations. We conducted an analysis of seedling and sapling survival from 34 globally distributed tree diversity experiments (363,167 trees, 168 species, 3744 plots, 7 biomes) to answer two questions: (1) Do drought and tree diversity alter the mean and variability in plot-level tree survival, with higher and less variable survival as diversity increases? and (2) Do species that survive poorly in monocultures survive better in mixtures and do specific functional traits explain monoculture survival? Tree species richness reduced variability in plot-level survival, while functional diversity (Rao's Q entropy) increased survival and also reduced its variability. Importantly, the reduction in survival variability became stronger as drought severity increased. We found that species with low survival in monocultures survived comparatively better in mixtures when under drought. Species survival in monoculture was positively associated with drought resistance (indicated by hydraulic traits such as turgor loss point), plant height and conservative resource-acquisition traits (e.g. low leaf nitrogen concentration and small leaf size). Synthesis. The findings highlight: (1) The effectiveness of tree diversity for decreasing the variability in seedling and sapling survival under drought; and (2) the importance of drought resistance and associated traits to explain altered tree species survival in response to tree diversity and drought. From an ecological perspective, we recommend mixing be considered to stabilize tree survival, particularly when functionally diverse forests with drought-resistant species also promote high survival of drought-sensitive species. Rising climate extremes, such as drought, can cause major uncertainty in the survival of young trees. Tree diversity can reduce survival variability and stabilize tree survival. Functionally diverse communities with drought-tolerant species can promote the survival of drought-sensitive species.image

Outcomes of meta-analyses are increasingly used to inform evidence-based decision making in various research fields. However, a number of recent studies have reported rapid temporal changes in magnitude and significance of the reported effects which could make policy-relevant recommendations from meta-analyses to quickly go out of date. We assessed the extent and patterns of temporal trends in magnitude and statistical significance of the cumulative effects in meta-analyses in applied ecology and conservation published between 2004 and 2018. Of the 121 meta-analyses analysed, 93% showed a temporal trend in cumulative effect magnitude or significance with 27% of the datasets exhibiting temporal trends in both. The most common trend was the early study effect when at least one of the first 5 years effect size estimates exhibited more than 50% magnitude difference to the subsequent estimate. The observed temporal trends persisted in majority of datasets once moderators were accounted for. Only 5 datasets showed significant changes in sample size over time which could potentially explain the observed temporal change in the cumulative effects. Year of publication of meta-analysis had no significant effect on presence of temporal trends in cumulative effects. Our results show that temporal changes in magnitude and statistical significance in applied ecology are widespread and represent a serious potential threat to use of meta-analyses for decision-making in conservation and environmental management. We recommend use of cumulative meta-analyses and call for more studies exploring the causes of the temporal effects.

Tree diversity can promote both predator abundance and diversity. However, whether this translates into increased predation and top-down control of herbivores across predator taxonomic groups and contrasting environmental conditions remains unresolved. We used a global network of tree diversity experiments (TreeDivNet) spread across three continents and three biomes to test the effects of tree species richness on predation across varying climatic conditions of temperature and precipitation. We recorded bird and arthropod predation attempts on plasticine caterpillars in monocultures and tree species mixtures. Both tree species richness and temperature increased predation by birds but not by arthropods. Furthermore, the effects of tree species richness on predation were consistent across the studied climatic gradient. Our findings provide evidence that tree diversity strengthens top-down control of insect herbivores by birds, underscoring the need to implement conservation strategies that safeguard tree diversity to sustain ecosystem services provided by natural enemies in forests.