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Through a meta-analysis, Mupepele et al. (BMC Ecol Evol 21:1–193, 2021) assessed the effects of European agroforestry systems on biodiversity, estimated by species richness or species diversity. They showed that the effects of silvoarable and silvopastoral systems depend on the systems they are compared to and the taxa studied. Further, they found that only silvoarable systems increased species richness or diversity, compared to cropland. The authors conclude that agroforestry systems have weak effects on biodiversity and that landscape context or land-use history are probably more important than the practice of agroforestry in itself. However, we draw attention to important shortcomings in this meta-analysis, which downplay the potential of agroforestry for biodiversity conservation in agricultural landscapes. We hope that the meta-analysis by Mupepele et al. (BMC Ecol Evol 21:1–193, 2021), and our comments, will contribute to improving the quality of research on agroforestry systems and biodiversity conservation.

Au Maroc, les systèmes agroforestiers à base d’olivier sont très répandus et diversifiés. Ce travail vise à caractériser leur diversité et leurs performances dans la région de Moulay Driss Zerhoun, au Nord du Maroc. Pour ce faire, 72 enquêtes ont été réalisées auprès des agriculteurs. Pour chaque exploitation, les systèmes agroforestiers ont été comparés à des systèmes de culture pure et à des vergers d’oliviers purs. En condition pluviale, l’insertion des légumineuses et des céréales dans les oliveraies constitue la pratique dominante. Il y a des différences très significatives de rendements pour les cultures annuelles et pour les oliviers entre systèmes associés d’agroforesterie, témoins en cultures annuelles pures et témoins en verger d’olivier. Le Land Equivalent Ratio (surface équivalente assolée) des rendements et celui des marges brutes sont toujours supérieurs à 1 avec les céréales et les légumineuses en agroforesterie. Nos résultats suggèrent que les systèmes agroforestiers sont plus productifs, rentables et efficients que les cultures pures. L’agroforesterie constituerait donc une stratégie pour une production durable, mais il faudrait d’autres expérimentations pour mieux appréhender la productivité de ces systèmes et préciser leurs atouts et leurs limites. In Morocco, agroforestry systems based on olive trees are widespread and diverse. This work aims at characterizing their diversity and performance. To this end, 72 farmers surveys were conducted in the Moulay Driss Zerhoun region (Morocco). For each farm, agroforestry plots were compared to corresponding monocrops and pure olive orchards. Under rainfed conditions, the insertion of legumes and cereals in olive orchards is the dominant association. There are very significant differences in yields of annual crops and olive between agroforestry systems, and monocrops and pure orchards. The Land Equivalent Ratio of yields and gross margins is always greater than 1 with cereals and legumes in agroforestry. Our results suggest that agroforestry systems are more productive, profitable and land-efficient than monocrops. Therefore, agroforestry may constitute a relevant strategy for a sustainable production. Nevertheless, additional experiments are needed to better understand the productivity of these systems and their advantages and limits.

Summary Understanding the water‐use of plants is timely under increasing drought stress due to climate change. Despite the crucial role of roots in water uptake, relationships between water‐use and root traits are seldom considered. Combining a functional trait‐based approach with a water balance model, we tested whether root functional traits are related to spatial and temporal water‐use among 12 Mediterranean rangeland species grown in common garden monocultures. Soil water content was monitored for 10 months, and the dynamics of water uptake of each species was modelled at a daily time step. Root functional traits were measured at two soil depths (shallow and deep soil). Species with fast resource acquisition strategies in shallow soil, i.e. thin roots, maximised water uptake in a short period and consumed large amounts of water during periods of low water availability. Conversely, species with a more conservative root strategy, i.e. coarse roots, took up less water during the peak‐growing season, maintained water uptake over a longer period of time and consumed less water during periods of low water availability. Deep root traits are strongly related to species’ ability to take up water from deep soil. Deep roots with large diameters and low specific root length improve species’ ability to reach water from deep soil. Biomass investment in the deep soil layer was positively related to the amount of water consumed during periods of low water availability. Our results highlight that root functional traits influence a range of spatial and temporal water‐use among Mediterranean rangeland species. They account for the amount of water taken up during dry periods but not during the entire growing season. A lay summary is available for this article. Lay Summary

Abstract Assessing the extent of genotypic and phenotypic trait variation within a genetically diversified species is crucial to understanding how plants cope with environmental differences. We examine these components in Olea europaea L. europaea, one of the most widespread and diverse tree crops cultivated in the Mediterranean Basin, a region facing rapid climatic shifts with increasing summer drought. We compared trait values of 83 olive varieties from different Mediterranean countries, grown in two ex situ varietal collections with contrasting environments: subhumid and semi-arid climates. Ten leaf-, stem- and branch traits related to resource and water use were compared across 50 varieties within each site, and phenotypic plasticity was assessed for the 17 varieties common to them. Trait plasticity was assessed with the phenotypic dissimilarity index while varietal plasticity was assessed in multidimensional trait space with the multivariate plasticity index. Our results showed considerable phenotypic variability within (up to 59.54%) and between (up to 39.17%) sites. Varieties grown in semi-arid conditions were more conservative, showing denser leaves and wood, and thicker bark. Common varieties exhibited contrasting degrees of plasticity across traits, demonstrating that high plasticity for some traits does not necessarily imply overall plasticity. Additionally, varieties with conservative trait values were not less plastic than more acquisitive varieties. Varieties showed distinct phenotypic adjustments across sites, with trait variations indicating acclimation strategies to reduce water loss in the arid environment. Our results also suggest that acclimation to different environments occurs through the adjustment of multiple traits, complicating plasticity comparisons across varieties. This study explores how cultivated olive trees adjust their leaf, stem, and branch traits across two contrasting environments. By examining 17 varieties in subhumid and semi-arid sites, we reveal substantial phenotypic variation and trait-specific plasticity. Some traits are highly plastic while others remain stable, showing that plant acclimation involves coordinated adjustments across multiple traits, highlighting the interplay of genetic background and environment in shaping adaptive strategies.

Summary The interactions between hydrological and ecological processes are key issues to improve our predictions of ecosystem responses to increasing droughts. However, predicting the dynamics and the impacts of vegetation water stress remains challenging because of complex ecohydrological feedbacks. The ecohydrological optimality approach proposes that functional adjustments within plant communities may buffer the increase in vegetation water stress despite local water shortage. This study aimed to test whether vegetation water stress may be invariant across contrasting plant communities, reflecting possible optimality processes. We addressed the following question: does a lower soil water storage capacity under the same climate generate greater vegetation water stress over time? We hypothesized that vegetation water stress would be buffered around a low and constant level through the adjustment of vegetation biomass productivity net primary productivity (NPP), evapotranspiration (ET) and/or water‐use efficiency (WUE) in relation with local soil water storage capacity. We monitored 12 native plant communities distributed along a gradient of soil water storage capacity (ranging from 20 mm to 120 mm) during five successive years. Net primary productivity, ET, WUE as well as soil water dynamics were assessed and modelled for each plant community throughout the 5 years of study. Vegetation water stress was determined for each plant community as the deviation of between actual ET and their maximum ETm rate achieved under non‐limiting conditions. We found that NPP and ET were together proportionally related to local soil water storage capacity across the 5 years of study while WUE did not differ between plant communities. Vegetation water stress was found quite similar for all plant communities whatever the soil water storage capacity. These results suggested that vegetation water stress was strongly buffered by the community‐level plant growth rates and total water use along the soil gradient, but not by WUE. Our results suggest that stressful environments rarely exist for plant communities. A dynamic scaling relationship between NPP and ET may underpin the control of vegetation water stress over seasonal and pluriannual time‐scales. Such results could contribute to better understanding processes associated with ecohydrological optimality and improve the predictions of vegetation dynamics under increasing droughts. A lay summary is available for this article. Lay Summary

Duru et al. (Agron Sustain Dev 35:1259-1281, 2015) highlighted a missing tool for studying and improving the performance of cropping systems in the transition to highly diversified agriculture. In response, this paper proposes a concept for designing, modeling, monitoring, and auditing desired ecosystem services, in intercropping and agroforestry systems. We have labelled this concept ESSU (Ecosystem Services functional Spatial Unit). It delimits the smallest spatial unit encompassing all the interacting species and other functional components (e.g., crops, trees, livestock, spontaneous vegetation, semi-natural habitats such as hedges, ditches, forest patches, and animals) that together provide a specified set of ecosystem services. The novel ESSU concept allows representation of an entire diversified agroecosystem by the repetition of the spatial unit that provides the same sets of targeted ecosystem services as the agroecosystem it represents. It can then be used for various activities, such as the (i) design of more efficient agroecological systems according to the targeted ecosystem services; (ii) rapid audit of farming practices for biodiversity/resilience across large tracts of farmland as part of achieving Sustainable Development Goal 2 targets of sustainable food systems; and (iii) modeling such diversified agroecosystems using a motif adapted to represent the targeted ecosystem services and the species spacing design. We demonstrate that the ESSU concept is highly flexible and applicable to a wide range of diversified agroecosystems, like arable intercropping, crop-tree intercropping, tree-tree agroforestry, and agro-pastoralism. We also show its relevance and suitability for representing temporal changes over 1 year, across several years, and over decades, indicating its generalizability and flexibility. We argue that ESSU could open new theoretical and practical research avenues for the study of diversified agroecosystems. Considered with all the knowledge available on practices, biodiversity, and ecosystem services, ESSU might provide a learning-support tool to fill the knowledge gap about relationships among practices, biodiversity, and associated ecosystem services.

Societal Impact Statement Reducing herbicide use and preparing agroecosystems for climate change are two top priorities on the global policy agenda. Here, we explore whether these two challenges can be tackled simultaneously. While weeds are generally considered a threat to crop production, we show that weeds can help overcome climate change challenges in agroecosystems. However, crop–weed interactions need to be carefully managed. Options for this were found to be greater in perennial than in annual systems. These findings provide a new perspective on weeds and call for more research on the appreciation of weeds as service plants, which ultimately may create new avenues for weed management and agricultural policy. Summary Sustainable agricultural production is at risk due to climate change, the increasing herbicide resistance of weeds and pressures to minimise herbicide use. Rather than solely considering weeds as part of the problem, we see this as an opportunity to investigate whether weeds can help overcome climate change challenges in agroecosystems. Using both ecological and agronomic perspectives, we assessed to what extent weeds can support the ecosystem functions water and climate regulation and whether their potential role as service plants would interfere with crop production. Based on ecological trait‐based analyses, we demonstrate that weeds are excellent candidates to support the delivery of water and climate regulation. Despite climate change‐induced shifts in weed communities, weeds continue to support these ecosystem functions. However, weed trait values that promote the ecosystem processes underlying water and climate regulation also tend to increase competition with crops. We show that confining weed–crop interactions is key to allow weeds to operate as service plants and that the spatial and temporal opportunities to manage these interactions vary among annual and perennial cropping systems. Overall, diversified management is recommended in both systems to avoid the selection of weed communities composed of just a few highly competitive weed species. We conclude that weeds could act as service plants in a changing climate rather than being considered a threat to agroecosystems. Weed management and research should thus prioritise the investigation and implementation of this new perspective.

Through a meta-analysis, Mupepele et al. (BMC Ecol Evol 21:1–193, 2021) assessed the effects of European agroforestry systems on biodiversity, estimated by species richness or species diversity. They showed that the effects of silvoarable and silvopastoral systems depend on the systems they are compared to and the taxa studied. Further, they found that only silvoarable systems increased species richness or diversity, compared to cropland. The authors conclude that agroforestry systems have weak effects on biodiversity and that landscape context or land-use history are probably more important than the practice of agroforestry in itself. However, we draw attention to important shortcomings in this meta-analysis, which downplay the potential of agroforestry for biodiversity conservation in agricultural landscapes. We hope that the meta-analysis by Mupepele et al. (BMC Ecol Evol 21:1–193, 2021), and our comments, will contribute to improving the quality of research on agroforestry systems and biodiversity conservation.

Quantifying species relative abundances in plant communities remains a key issue for the assessment of community functional structure. This is particularly challenging when non-destructive estimates are required over time. We tested whether the point intercept method (PIM), originally developed for low-diverse communities, is relevant for assessing the aboveground biomass and functional structure of highly diverse, low-productive Mediterranean grasslands. We sampled 18 communities with the PIM along a gradient of soil depth and texture, twice over the growing season. After each sampling period, we harvested the aboveground biomass in order to measure species biomass and to assess species richness and community functional structure with plant height, leaf area and leaf dry matter content (LDMC). We investigated the relationship between point intercept measurements and aboveground biomass at three hierarchical levels (species, growth-form and community) to find generalizable calibration equations for estimating community biomass and tested for sensitivity of estimates to community structure. We then compared the community weighted mean (CWM) and variance (CWV) of LDMC, calculated with and without calibration. Differences in species growth strategy and phenology strongly impacted biomass estimates at both the species and the community level. These differences were, however, successfully accounted for by growth-form specific calibrations, which provided accurate estimates without any influence of community structure. Lack of calibration may have dramatic consequences on functional structure assessment by inducing errors in estimates of CWV up to 80 %, depending on growth-form proportions. This work contributes to a better understanding of the possible methodological biases induced during sampling with the PIM, when quantifying species relative abundances for functional structure assessment in complex communities.

1. Understanding the water-use of plants is timely under increasing drought stress due to climate change. Despite the crucial role of roots in water uptake, relationships between water-use and root traits are seldom considered. 2. Combining a functional trait-based approach with a water balance model, we tested whether root functional traits are related to spatial and temporal water-use among 12 Mediterranean rangeland species grown in common garden monocultures. Soil water content was monitored for 10 months, and the dynamics of water uptake of each species was modelled at a daily time step. Root functional traits were measured at two soil depths (shallow and deep soil). 3. Species with fast resource acquisition strategies in shallow soil, i.e. thin roots, maximised water uptake in a short period and consumed large amounts of water during periods of low water availability. Conversely, species with a more conservative root strategy, i.e. coarse roots, took up less water during the peak-growing season, maintained water uptake over a longer period of time and consumed less water during periods of low water availability. Deep root traits are strongly related to species' ability to take up water from deep soil. Deep roots with large diameters and low specific root length improve species' ability to reach water from deep soil. Biomass investment in the deep soil layer was positively related to the amount of water consumed during periods of low water availability. 4. Our results highlight that root functional traits influence a range of spatial and temporal water-use among Mediterranean rangeland species. They account for the amount of water taken up during dry periods but not during the entire growing season.