Situation of Armillaria spp. and Heterobasidion spp. in Slovenia

Abstract

Species of the genus Armillaria and Heterobasidion are among the most common causes of stem and root rot in Slovenia. Armillaria spp. infects deciduous and coniferous trees, while Heterobasidion spp. mainly threatens Norway spruce (Picea abies), pines (Pinus spp.), and silver fir (Abies alba). On the basis of the data about the sanitary felling of infected trees, we estimated the current state and calculated the proportions represented in total felling, total sanitary felling, total sanitary felling due to diseases, in wood stock, and in increments from 2013 to 2017. Since 2014, there has been a constant increase in the sanitary felling of deciduous and coniferous trees due to infections with Armillaria spp. In 2017, 32,849 m3 of timber were harvested due to Armillaria spp. Given the present situation, we assume that the amount of sanitary felling will continue to increase, but it will not account for large shares in wood stock or increment (< 1 %). In 2017, sanitary felling of infected conifers represented 27.6 % of all sanitary felling due to diseases. In the case of deciduous trees, the share was lower, i.e. 7.1 %. Armillaria spp. was the main cause of sanitary felling due to disease (51.9 %) in the Postojna forest management unit (FMU), while elsewhere shares of up to 10 % were recorded. With Heterobasidion spp., the amount of felling is decreasing over the years. In 2017, 33,922 m3 of wood, accounting for 15.7 % of the total sanitary felling due to disease, were felled due to Heterobasidion spp. A comparison of the felling of Norway spruce, silver fir, and Scots pine due to Heterobasidion spp. shows the different proportions of felling within the total sanitary felling due to the diseases. In Norway spruce, it is on average 79.5 %, in silver fir 12.9 %, and in Scots pine 34.3 %. We assume that the volume of timber harvested due to Heterobasidion spp. will gradually decrease over the years due to the lower wood stocks of Norway spruce, which has recently been hit by numerous natural disasters and infestation of bark beetles. However, the incidence will be higher due to climate change affects.