Our forests do not like extreme weather
The forest health inventory is part of the international Level 1 ICP Forests programme. In 2021, we monitored the health status of 1473 trees at 75 measurement points. The main measure is the leaf loss score. Trees with more than 25% leaf loss are considered damaged. We also checked each tree for symptoms of infestation or damage by fungi, insects or other factors. In 2021, one tree in five was damaged (19.9%). Quercus robur scored worst, with more than a quarter of trees damaged (27.4%). The average leaf loss of all species together was 22.7%.
Compared to 2020 we observed a positive evolution across all tree species. There was no significant improvement for oak and Scots pine, but the crown condition did improve significantly for beech, Corsican pine and a group of 'other deciduous tree species'. This is a group including chestnut, birch, alder, maple and poplar.
The summers of 2018, 2019 and 2020 were characterised by heat waves and prolonged droughts. In 2021 we observed no discolouration, leaf deformation or early leaf fall caused by drought. This shows that many tree species prefer a typical Belgian summer, without drought and heat.
Not every negative evolution is due to weather extremes or a changing climate. Air pollution, site characteristics and inappropriate management can also have a negative impact on health. In addition, the introduction of new infectious diseases or insects worries forest managers. The false ash canker is an invasive fungus that has been affecting ash trees for more than a decade. Between 2014 and 2021, 252 ash trees were monitored and in the meantime 24.2% of these trees died.
Geert Sioen, Pieter Verschelde
Read more: Sioen, G., Verschelde, P., & Roskams, P. (2022). Bosvitaliteitsinventaris 2021. Resultaten uit het bosvitaliteitsmeetnet (Level 1). (Rapporten van het Instituut voor Natuur- en Bosonderzoek; Nr. 7). Instituut voor Natuur- en Bosonderzoek. https://doi.org/10.21436/inbor.71783042