FellowshipS Seminar 2016

Poster ABSTRACTS
Stability of Sitka spruce in relation to thinning
type, intensity and timing
Gonzalo González-Fernández, Niall Farrelly¹, Áine Ní Dhubháin²
1 Rural Economy & Development Centre, Teagasc, Mellows Campus, Athenry, Co. Galway
2 School of Agriculture and Food Science, University College Dublin, Belfield, Dublin 4
Windthrow, i.e. the overturning of trees, is common worldwide, especially in areas that experience winter storms. Ireland
is one such area, where windthrow is a continuous cause of economic loss in forestry plantations. This project seeks to
determine how thinning by differing intensity and timing can affect the stability of Sitka spruce stands. Tree pulling tests
were conducted on a surface water gley forest in Frenchpark, Co. Roscommon, where five different thinning treatments
were replicated three times. The thinning treatments differed according to the basal area removed (light, medium,
heavy, no thin and a medium thin performed three years delay). Four trees representing the average tree in each plot
were tested until failure of the roots to calculate the trees’ maximum overturning moments. Results indicate that trees
from thinned plots have greater overturning moments than trees in unthinned plots, with the heavy thinned trees
being the most stable. Additionally, heavy thinned trees had the largest root plates and crowns as a result of the new
environmental conditions created by thinning. A positive relationship between the root and the crown spread was found.
Further, the depth of the root plate was found to be influenced by the water table depth at the beginning of the growing
season in the plot and not by the thinning treatment applied. The results of the tested trees in the delayed thinning
suggest that timing of thinning is a determinant factor in crop stability, as trees react quicker when they are released in
early stages.
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