Frost damage to planted Norway spruce seedlings - influence of site preparation and seedling type

Damage to Norway spruce (Plcea abies (L.) Karst.) seedlings by summer frost was monitored on 10 clear-cuttings of various ages to which slash removal and foul types of site preparation had been applied. The clear-cuttings wer e established on two sites (5 on each) in southern Sweden from 1989 through 1993 and planted each year from the pear of cutting until 1993. In total, 7680 seedlings were analysed for frost injuries during the first three year s following planting. The site preparation methods evaluated were: applicat ion of herbicide to ground vegetation; mowing of ground vegetation; scarifi cation (mounding); and control. Two seedling types, bare-rooted and contain erised seedlings, were evaluated. Periods of frost susceptibility were calculated using data on bud and shoot development during 1997 together with weather data fur each of the studied years and sites. The date of hushing was well correlated to the air temper ature sum (+5 degreesC threshold value) in spring. Frost damage varied cons iderably between sites and study years. The lowest measured minimum air tem perature and the frost-day sum during the frost-susceptible: period were co rrelated to the frequency of frost damage. Soil scarification reduced frost damage in the first growing season. Bare-rooted seedlings had a considerab ly lower frequency of frost injury compared with containerised ones, possib ly because Rushing of the former was delayed. There was no statistically si gnificant effect of herbicide application, mowing or slash removal on the f requency of frost damage. Seedling growth was significantly reduced by fros t injury, especially in cases where injuries were sustained during several years. Survival was only slightly affected by frost damage. (C) 2001 Elsevi er Science B.V. All rights reserved.