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Doctoral thesis2000Open access

Effects of release cutting and soil scarification on natural regeneration in Pinus sylvestris shelterwoods

Karlsson, Christer


The objective of this thesis was to evaluate different methods of improving seed production, seed germination, seedling survival and seedling growth when using natural regeneration with Scots pine (Pinus sylvestris L.) seed trees and shelterwoods. Two experiments and a survey study were used to evaluate effects of (i) shelterwood density and seedling height at release on survival, damage and height growth of advance growth seedlings of Norway spruce (Picea abies (L.) Karst.), (ii) release cutting on seed production, seed quality and needle nutrient contents in seed trees, (iii) weather and seed tree size on seed production, (iv) correlation between needle nutrient contents and seed production and seed weight, and (v) scarification in relation to seed fall. For all advance growth seedling sizes, growth was highest at shelterwood densities of 80-160 stems ha⁻¹, whereas the optimum density for survival was about 160 stems ha⁻¹. Height, top-shoot length and top-shoot diameter in seedlings the year before release cutting showed significant positive correlations with both survival and height growth. A majority of the small seedlings (<20 cm) wilted the spring after overstorey release cutting, probably as a combined effect of drought in the humus and “light shock”. The only identified damaging agent causing significant mortality was pine weevil (Hylobius abietis L.). Cone and seed production were about five times higher in seed trees that had been released for 4-5 years, compared to control trees in the unreleased forest. Seed trees released for less than three years had about the same level of cone production as the controls. After release, the number of cones increased more in the lower part of the tree crowns than in the uppermost two metres. The concentration of nitrogen, potassium, and phosphorus in needles and mean needle dry weight was significantly higher in released trees compared to unreleased control trees. N, P and K concentrations in needles were significantly positively correlated to numbers of conelets as well as to mean 1000-seed weight. In 1996, there were about eight times more cones than in 1995, probably because summer temperatures were higher in 1994 than in 1993, the years when the respective flower buds were initiated. Trees with a diameter at breast height of 400 mm produced twice as many cones as trees with a diameter of 300 mm. By timing soil scarification in relation to a rich seed fall twice as many seedlings were established compared to scarification immediately after release cutting. Unscarified plots showed poorest result according number of seedlings, and number of plots without seedlings (0-plots). Height growth was significantly improved by scarification.


Advance-growth seedlings; cone production; conelet production; frost injury; Hylobius abietis; nitrogen; phosphorus; potassium; seed production; seed quality; seedling establishment; seedling growth; seedling mortality; soil preparation

Published in

Acta Universitatis Agriculturae Sueciae. Silvestria
2000, number: 137
ISBN: 91-576-5871-4
Publisher: Southern Swedish Forest Research Centre, Swedish University of Agricultural Sciences