Abstract

Phenological records of apple and pear trees, including flowering, harvest and leaf drop, and concomitant weather records at Klein-Altendorf (50° N) near Bonn, Germany were correlated using two approaches: (a) linear curve fitting and (b) comparison of mean values of the first 30 years (1956–1988) versus the recent 30 years of climate change (1989–2017). The annual air temperature increased by 1.7 °C from 8.6 °C in 1958 to 10.3 °C in 2017 over the last 60 years and similarly in the vegetation period (1 April–30 October) from 13.7 °C in 1958 to 15.2 °C in 2017 by 1.5 °C. The combination of stronger increase in winter temperatures (by +1.2 °C) than in the summer (air +1.0 °C) with advanced bud break and −0.3 °C lower minimum temperatures in April during flowering resulted a continued risk of a late frost, as experienced in 2017. The strongest climate change effect, i.e., 11–14 days advanced flowering (in apple and pear) highly correlated (R2 −0.7) with the March/April temperature. Fruit ontogeny was 4 days shorter in cv. ‘Lucas’ pear, but 5 days longer in cv. ‘Cox’ and 10 days longer in cv. ‘Boskoop’, but remained unchanged in cv. ‘Golden Delicious’, irrespective of early or late ripening variety and contradictory climate effects, fruit matured 4–12 days earlier indicating its sole dependency on variety. Climate data and (earlier) harvest date closely correlated (R2: 0.6–0.7). The lowest correlation was between canopy duration (bloom to leaf fall), which was consistently extended by 6–10 days and the leaf drop stage beginning 2–4 days earlier. The correlations indicated that the Meckenheim fruit growing region is strongly affected by climate change and the comparison between two equally-balanced 30-year phases gave more realistic results than linear curve fitting.

Highlights

  • Publisher’s Note: MDPI stays neutralFor the interpretation of climate change effects on fruit crops, long-term data sets are required but are scarce [1,2]

  • The lowest correlation was between canopy duration, which was consistently extended by 6–10 days and the leaf drop stage beginning 2–4 days earlier

  • The calculated temperature rise of 1.7 ◦ C in the last 60 years resembles the nationwide average of 1.7 ◦ C in the 45 years between 1955 und 2000 [7,8]) and is in the same order with the temperature increase of 0.2 ◦ C/decade reported by Hansen et al (2006 [10])

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Summary

Introduction

For the interpretation of climate change effects on fruit crops, long-term data sets are required but are scarce [1,2]. This contribution represents the ideal scientific situation with 30 years before and 30 years during climate change to achieve equal weighing of both periods. The data presented here are the oldest/longest historic combined data sets of complete pome fruit phenology (flowering, frost and harvest leaf fall) and weather data at the same site, without change of variety or record site, followed by Angers (Britany, since 1963) and Forli The objective of the present work was to use this rich source of information to elaborate the effects of recent climate change using a unique combination of 60 years of phenological with regard to jurisdictional claims in published maps and institutional affiliations

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