Mechanical bending stress applied during dormancy and (or) growth stimulates stem diameter growth of Scots pine seedlings

Abstract

Five-year-old Scots pine (Pinus sylvestris L.) seedlings were given the following treatments: unbent control; bending during dormant period (frozen seedlings); bending during growth period; bending during both dormant and growth periods. Bending was executed manually to 30° from the vertical in four perpendicular directions. This was repeated on 9 occasions for the dormancy and growth treatments and on 18 occasions for the combined dormancy and growth treatment. There was increased xylem and bark production at the point of bending for all treatments. Growth response to bending during growth was of a higher magnitude than the response following bending during dormancy. Moreover, there was a tendency for bending during both dormant and growth phases to increase radial growth of xylem and bark more than the sum of each treatment administered singly. It is concluded that mechanical stress by wind and snow imposed during the dormant winter period could influence stem form.