The modern silviculture of Juglans regia L: A literature review

Juglans regia requires warmth during the growing season, with at least 6 months of an average temperature > 10 °C (BECQUEY, 1997). Juglans regia is sensitive to winter and late spring frosts, with the former being especially damaging for common walnut because the species often exhibits early initiation of vegetative activity (flushing) (BERNETTI, 1995). The timing of spring flushing can vary greatly between provenances, as demonstrated by various authors (FADY et al., 2003), therefore provenance choice could affect propensity to frost damage (HEMERY et al., 2005b). In The Netherlands cold-tolerant cultivars have been developed in the north of the country (OOSTERBAAN et al., 2006). With good quality plant material it still remains important to avoid cold sites or areas where cold air can accumulate (BECQUEY, 1997), even within an overall good site (e.g. valley bottoms or hollows). Young shoots and flowers are easily damaged by spring frosts of –1 °C in Britain where these frequently cause failure of the nut crop (SAVILL, 1991). Late spring frosts affect both leaf and flower buds; whilst early frosts in autumn can affect shoots not yet lignified ŞOFLETEA and CURTU, 2007).