Current issue: 55(5)
Under compilation: 56(1)
Strong wind is the major natural disturbance in European forests, that periodically causes tremendous damages to forestry. Yet, factors that affect the probability of wind damage for birch (Betula pendula Roth and B. pubescens Ehrh.), the most common deciduous tree species in hemiboreal forests, are studied scarcely. This study aimed to assess the effects of several tree- and stand-scale variables on the probability of wind damage to birch using data from the Latvian National Forest Inventory (2004–2018), and determine individual tree characteristics that affect the height of the stem breakage. The data analysis was done using the Bayesian binary logistic generalized linear mixed-effects model and a linear mixed-effects model. The probability of wind damage significantly increased by stand age, basal area, and slenderness ratio. Trees with prior damage had a significantly higher probability (odds ratio 4.32) for wind damage. For wind-damaged trees, the snapping height was significantly decreased by an increase in the slenderness ratio (p = 0.03) and prior damage (p = 0.003). Previously damaged trees were more frequently (73%) snapped in the lowest 40% of tree height than trees without prior damage (54%). The probability of wind damage is largely set by factors related to the selection of site, species composition, and rotation. The damage probability could be decreased by management measures that lower competition within the stand with particular regard to preserving intact remaining trees during these manipulations. Factors that reduce the probability of the damage simultaneously increase the snapping height, emphasizing their relevance for mitigation of the wind damages.
The effect of different kinds of injuries in the amount of merchantable timber was studied in 57 sample plots in the northernmost Finland. Without any injuries the yield of timber would have been 72.3% in Scots pine (Pinus sylverstris L.) and 89.9% in Norway spruce (Picea abies (L.) H. Karst.). Butting, and removal of parts of the stems due to Injuries decreased the volume by 10.4% in pine and 13.5% in spruce. The main cause for butting of pine was fire wounds, and butt rot in spruce. Also pine blister rust (Peridermium pini and Cronartium flaccidum) causes injuries in Scots pine. The better the forest site type, the smaller is the timber discarded due to injuries. In pine 54% and in spruce 53% of the trees and were healthy. The forests in the northernmost Finland are over-mature which increase the occurrence of fire wounds and decay. Thus, forest fire control and the felling or thinning of over-mature stands will improve the quality of the timber in the long run.
The PDF includes a summary in German.
The study material was collected from 10 localities in South Finland in 1971–72. The material comprised 816 damaged Norway spruce (Picea abies (L.) H. Karst.) trees with a total of 978 injuries.
Decay (discoloration) spread upward from the damaged point was about three times as fast as downward. The mean rate of advance upward was 21 cm/year. The decay spreading at the quickest rate started from above-ground root collar injuries. The size of the damaged area (surface area, width and depth) correlated positively with the rate of increase in decay initiated by the injury. For the first 10 years the decay advanced at the same rate after which the advance became slower though not ceasing. Damage produced in the early summer caused a faster spread of decay than that produced in the late summer or winter. The rate of advance was the greater the larger the stem involved. When decay started from trunk damage its rate of advance was greater the faster the growth of the trees. With a better soil type, the rate of advance in decay increased. Fertilization increased the rate of advance.
The widest stem injuries reduced tree growth by about one-third, and severed roots by nearly half of the growth of trees where the width of the injuries was 0–4 cm. Fomes annosus (Heterobasidion annosum) infected spruce injuries especially in the southern coastal district. The farthest tips of discoloration proved in most cases to be sterile. The most common fungus isolated from these sites was Stereum sanguinolentum.
The PDF includes a summary in Finnish.