Tree mortality, foliage recovery and top-kill in stands of Scots pine (Pinus sylvestris) subsequent to defoliation by the pine looper (Bupalus piniaria)

In 1996, the pine looper (Bupalus piniaria ) (L.) defoliated 7000 ha of Scots pine (Pinus sylvestris L.) forest at Hokensas, in southern Sweden. To study tree mortality, foliage recovery and top-kill, plots were laid out in stands with varying levels of defoliation in autumn 1997. Tree mortality peaked 2 yrs after defoliation, and amounted to 25% in stands suffering from 90-100% defoliation. Suppressed trees suffered higher mortality than intermediate and dominant trees. In stands suffering <90% defoliation, tree mortality did not exceed 8%. Foliage recovery in moderately and severely defoliated stands was not complete at the end of the 4 yr study period, whereas slightly defoliated stands had regained full foliage in 1998. Top-kill was most frequent in severely defoliated stands, and 50% of all trees in these stands suffered from top-kill at the end of the study period in spring 2001.