Based on observations for the beginning of the flowering stage of Malus domestica (apple) and Pyrus communis (pear) for the 1950–2018 period, phenological trends in north-eastern Belgium were investigated in function of temperatures during dormancy. Moreover, two different phenological models were adapted and evaluated. Median flowering dates of apple were on average 9.5 days earlier following warm dormancy periods, and 11.5 days for pear, but the relationship between bloom date and temperature was found not to be linear, suggesting delayed fulfilment of dormancy requirements due to increased temperatures during the chilling period. After warm chilling periods, an average delay of 5.0 and 10.6 days in the occurrence date of dormancy break was predicted by the phenological models while the PLSR reveals mixed signals regarding the beginning of flowering. Our results suggest overlapping chilling and forcing processes in a transition phase. Regarding the beginning of flowering, a dynamic chill model coupled to a growing degree days estimation yielded significantly lower prediction errors (on average 5.0 days) than a continuous chill-forcing model (6.0 days), at 99% confidence level. Model performance was sensitive to the applied parametrization method and limitations for the application of both models outside the past temperature ranges became apparent.

Background: Spring frosts pose an important threat to orchard productivity in temperate zones and projections do not exclude damaging events in the future. However, there is no up-to-date and systematic comparison of the effectiveness and conditionality of the existing passive and active damage prevention strategies. This systematic review seeks to answer the questions “How do the performances of spring frost damage reduction strategies in temperate fruit orchards compare?” and “How do environmental conditions affect the effectiveness of frost damage reduction strategies in temperate fruit orchards?”. Methods: This review covers a large range of on-field strategies for the protection of flowering orchards against damage inflicted by late spring frost. All major temperate fruit tree crops and grapevines were included, provided that the performance of frost damage reduction was compared against a control in terms of bud and flower survival, yield and delays in flowering time, or ambient temperature change. Articles and reports were collected between June and October 2021 from the Web of Science Core Collection and regional indexes and from the databases Scopus, FAO AGRIS, USDA Agricola, CAB Abstracts and the Groenekennis database of the University of Wageningen, the Netherlands, as well as from relevant institutional websites and the Chinese scholarly search engine ‘Baidu’. Biases resulting from inadequate randomisation, incomplete reporting or deficient study designs were reported. Temporal and spatial research trends and gaps were mapped based on 104 selected studies (from 8970 identified studies). Data was extracted for every experiment that an article reported on, leading to 971 data points. Groups of frost protection methods were compared in terms of effectiveness whereby environmental factors were examined to explain the variation of the effectiveness by means of mixed linear models. Review findings: Most included studies originate from the United States and Europe more than from the temperate fruit production regions in Asia. An increase over time in the research on foliar applications, including growth regulation hormones was observed. Apple, peach and more recently grapevine were the most researched fruit types, followed by cherry and pear. The validity of the selected studies was generally low as measures of variability were reported only occasionally. Therefore, only descriptive comparisons of effectiveness were undertaken between intervention classes by fruit types. Sprinkler systems were found to perform best for most studied outcomes, while the emerging biochemical solutions revealed mixed results. The performances of resource-intensive heating systems did not outperform low-resource techniques such as tunnels or coverings of individual buds. The lack of reporting standards did not allow extensive correlations with ambient factors and reduced the transferability of the review’s findings. A need for standard protocols for experiments and reporting is therefore apparent. Conclusions: In this field, strong shortcomings in the documentation of experimental setups and reporting standards were exposed. Implications for policy making are limited while for research recommendations to reduce bias and increase comparability are put forward.

Background: Spring frosts pose an important threat to orchard productivity in temperate zones and predictions of future occurrences do not exclude damaging events. However, there is no up-to-date and systematic comparison of the effectiveness and conditionality of the existing passive and active damage prevention strategies. This review seeks to answer the questions “How do the performances of spring frost damage reduction strategies in temperate fruit orchards compare?” and “How do environmental conditions affect frost damage reduction strategies in temperate fruit orchards?”. Methods and output: The review covers on-site frost damage prevention mechanisms and interventions for the most important temperate pome, stone and citrus fruit trees as well as grapevine. Searches include the core collection and regional databases on the Web of Science platform, Scopus, as well as specialized libraries like Agris, Agricola, CAB Abstracts, Groenekennis and selected institutional websites. Included studies report on the effectiveness of at least one intervention in reducing spring frost damage or increasing temperatures in the field. The validity of the studies will be evaluated based on their risk of general research bias and on topic-specific, stakeholder co-designed validity criteria. Data will be extracted regarding the study setup (study design, location, characteristics of frosts) and the resulting temperature increase, crop development alteration and/or damage reductions. The effectiveness of interventions will be evaluated in terms of yields, damage to flowers, ambient temperature and/or crop development. An Evidence Atlas will identify general and geographic research gaps, as well as research trends. Meta-regression of effectiveness on environmental conditions will be attempted.

Apples and pears represent an important share of Belgium’s horticultural production but the sector has been subjected to a range of challenging meteorological conditions over the past decade. The most disastrous event was the extraordinarily severe frost night happening during peak flowering of commercially grown apple cultivars, in April 2017. This research aims at investigating how meteorological hazards in Belgium will evolve in space and time with changing climate and at challenging the claim of the insurance sector that the hazards are spatially invariant. It features the assessment of the probability and severity of frosts during the flowering period throughout the 21st century, using a set of regional climate model realizations from the CORDEX ensemble. To this end, the apple and pear tree phenology is modelled using the strong relation between air temperature during winter/early spring and dormancy break and consequently flowering. Local observations since 1950 of the phenology of major cultivars indeed confirm a shift in phenological stages in relation to warmer winters as an effect of climate change. Preliminary results from sequential phenological models, running on future daily mean temperatures, suggest that both the onset of flowering and the last frost event in spring are likely to occur earlier in the year, so that the challenge is to determine which trend is dominant and how the return periods of severe frost nights (< -2◦C) during sensitive stages evolve. Thereby, differences between cultivars and between orchard locations within Belgium are taken into consideration. Furthermore, the potential impact of shifting temperature regimes on the pollinator activity during the blossom period is taken into account, knowing that the most commonly commercially employed bee species are sensitive to colder and more variable temperatures. The distinct resulting hazard maps can be used to support decision making regarding adaptation and prevention measures at the field, farm and regional scales. Further downscaling will be possible by considering local pedologic and topographic conditions, while for validation, data about damage compensation claims will be used.

Commercial apple production relies on managed honey bees for pollination, and on intensive management for pest control. Previous studies revealed the detrimental effects of these factors on wild bee diversity in agroecosystems, and the pollination services they provide. However, the extent to which honey bee dominance and management interact under field-realistic conditions to shape wild communities has never been investigated. We measured the species richness and functional and phylogenetic diversity of wild bees associated with apple blossoms, in 46 organic and non-organic orchards, and along a climatic gradient across Western Europe and Morocco. Our results consistently show a strong and negative association between honey bee dominance and all diversity indices, regardless of local practices and surrounding landscape cover. Collectively, we show that wild bee diversity decreases with increasing honey bee density, with alternative management practices (i.e., organic) having no significant influence on wild bee communities in commercial apple orchards.