Pollen limitation and a phenological climate inversion drive olive yield instability in North-East Italy

The northward expansion of olive ( Olea europaea L.) cultivation into marginal areas such as the Veneto region (northern Italy) exposes the crop to climatic and reproductive constraints that may enhance alternate bearing. To identify the primary drivers of this yield instability, we combined a decadal regional macro-climatic analysis with a localized field experiment. Regional time-series data (2015–2025) for production, airborne pollen and fruit set were related to temperature and precipitation anomalies, revealing airborne pollen load as the strongest predictor of annual production (R² = 0.76, p < 0.001). The analysis also identified a phenological “climate trap”: warmth and dryness favored pre-flowering and early flowering (April–mid-May) processes, whereas early-summer heat and water deficit triggered severe abscission during late flowering and fruit set (late May–June). Meteorological conditions during a two-year (2025–2026) field trial on cv. Arbequina closely mirrored this climate trap, offering a preliminary test of its consequences. Supplementary mechanical pollination sharply reduced fruit abscission compared to natural wind pollination, likely via improved fertilization rather than stress buffering, raising fruit set from 0.9% to 4.2% in 2025 and from 0.6% to 3.2% in 2026, and decreasing fruitless shoots (seven inflorescences each) from 63.3% to 23.3% and from 70.0% to 17.8%, respectively. Pollinated fruits were also more uniform in size in both years. These results suggest that pollen availability, not heat or drought per se, may constrain fruit set at this climatic margin, supporting compatible pollinizers as the structural remedy and mechanical pollination as an emergency alternative.