Pentti Niemistö, Harri Kilpeläinen, Henrik Heräjärvi. (2019). Effect of pruning season and tool on knot occlusion and stem discolouration in Betula pendula – situation five years after pruning. Silva Fennica vol. 53 no. 1 article id 10052. https://doi.org/10.14214/sf.10052

Keywords: silver birch; pruning saw; discolouration; healing-over; secateurs; stick pruning

Highlights: The occlusion was the fastest in the case of small living branches of fast growing trees pruned in springtime; Occlusion was quicker after saw pruning than after secateurs pruning, due to shorter knot stubs; Branches that were pruned in living state occluded faster than the ones pruned as dead; Dead branches hit down with a stick occluded slowly.

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This paper investigates and models the effects of pruning season and tool on wound occlusion with varying tree and branch characteristics of silver birch (Betula pendula Roth) stems at the pruning height of 0−4 metres. Dates of eight secateurs prunings, three saw prunings and two sticks prunings as well as unpruned control were tested in permanent plots on four sites. Knot occlusion and discolouration in stemwood were measured from about 1600 studied knots of 112 sample trees felled five to six years after pruning in 2010. Knot occlusion rate was modelled according to pruning tool, date, tree growth, and branch characteristics. The occlusion was the fastest in trees pruned in spring or early summer, and the slowest in trees pruned in autumn. Stubs of living branches occluded faster than the dead ones with the same diameter. Saw pruning resulted in clearly better occlusion rates than secateurs pruning, caused by the shorter knot stubs after saw pruning. Hitting dead branches away with a stick resulted in the worst occlusion status. The colour defects spread more often upward from the knot than downward. Discolouration in stemwood was detected more frequently near to the pruned branches than the unpruned ones, and more widely near to the stubs of dead branches than the living ones. Most saw and secateurs pruned branches were completely occluded during the experiment, so these prunings were suitable for all branches under 20 mm in diameter, and for living branches even up to 30 mm in fast-growing trees.

Niemistö, Natural Resources Institute Finland (Luke), Natural resources, Kampusranta 9 C, FI-60320 Seinäjoki, Finland E-mail: pentti.niemisto@luke.fi
Kilpeläinen, Natural Resources Institute Finland (Luke), Production systems, Yliopistokatu 6 B, FI-80100 Joensuu, Finland E-mail: harri.kilpelainen@luke.fi
Heräjärvi, Natural Resources Institute Finland (Luke), Production systems, Yliopistokatu 6 B, FI-80100 Joensuu, Finland E-mail: henrik.herajarvi@luke.fi

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