© 1987 by Institute of Chartered Foresters
Effect of Desiccation on Water Status and Forest Performance of Bare-rooted Sitka Spruce and Douglas Fir Transplants
Forestry Commission, Northern Research Station Roslin, Midlothian, Scotland EH25 9SY
Sitka spruce transplants which had been exposed to drying conditions were assessed for shoot water potential (
), shoot moisture content (MC), water saturation deficit (WSD) and root moisture content (RMC) before forest planting. Exposure for 1 hour 44 minutes had no effect on subsequent survival or growth, but exposure for 3 hours 18 minutes reduced survival to 68 per cent after two years and significantly reduced height growth. The damaged plants were clearly distinguished at the time of planting by and RMC but not by MC or WSD.
After a range of desiccation treatments, survival was high in Sitka spruce unless RMC had fallen below 180 per cent but survival was reduced in Douglas fir with smaller reductions in RMC or . During the desiccation treatment, Douglas fir started with and maintained a higher RMC than Sitka spruce and reached low levels of less rapidly. The poor performance of desiccated Douglas fir was therefore not the result of an inability to conserve water.
After rewetting for one hour in the dark RMC was restored but not , and there was no significant effect on survival or growth in either species.
It may be possible to devise a method to establish when plants are in poor condition by direct or indirect measurement of RMC, but high levels of RMC can be misleading if rewetting has occurred.
Handling systems which involve brief periods of exposure are tolerable for Sitka spruce but not for Douglas fir, and special measures are justified to ensure that the latter species is never subjected to root desiccation during handling.