Stem hydraulic properties and growth in lodgepole pine stands following thinning and sway treatment

Abstract

The objective of this study was to explore the effects of wind-caused sway on the growth and stem hydraulic properties of fire-origin juvenile lodgepole pine (Pinus contorta Dougl. ex Loud.) stands after thinning. Nine plots were thinned and trees were treated to suppress or exacerbate sway from the wind: thinned and supported with a pole (TP), thinned with an added sail (TS), thinned control (TC), and unthinned control (UC). Terminal leader growth, radial increment, and earlywood and latewood widths at breast height were measured for the last six growing seasons. The specific hydraulic conductivity of stems was measured. The results showed that thinning increased diameter growth and reduced height growth and slenderness coefficient (particularly for trees with added sails) compared with the unthinned control. Trees from thinned stands had reduced specific conductivity compared with the trees from unthinned controls, suggesting that tree bending caused functional damage to sapwood. Specific conductivity was 1.36 × 10–5, 1.06 × 10–5, 0.96 × 10–5, and 0.83 × 10–5 m·s–1 in UC, TP, TC, and TS treatments, respectively. Trees from thinned stands, however, increased their total leaf area in the years following thinning.