Most native woodland species will be tolerant of the cold temperatures that typically occur over winter in British conditions and introduced tree species will have been selected on appropriate tolerance for typical past climate conditions. However, the warming climate has already reduced the frequency and severity of frosts and increased the length of the frost-free season in many areas, and this trend is projected to increase. 

Trees are particularly vulnerable to cold temperature episodes if they occur outside the period that trees are dormant or hardened. Milder winters may delay or prevent full dormancy, increasing the risk of damage or mortality from autumn frosts, severe frosts and periods of extreme cold. Milder springs may lead to bud-break, flushing and growth earlier in the season, increase the risk of damage from late frosts. 

Impact of frost

• Extreme cold periods can damage plant tissues and lead to die-back or tree death. The increase in stress may affect tree growth or make trees more susceptible to disease.
• Frosts may cause damage to sensitive new growth or de-hardened shoots in spring or early summer (late frosts), or to the current year’s leaves in autumn (early frosts) before leaf fall or shoot hardening.

Risk factors

• Frost risk tends to be highest inland and lower in coastal areas.
• Frost pockets or hollows and north-facing slopes are at higher risk, this can be exacerbated if there are light, sandy soils where the surface cools more rapidly.