Weeds and pests in forestry
Invasive species and control – from hogweed to cherry laurel
Introduction
According to the education's competence objectives, you must be able to plan and carry out control of weeds and pests within forestry, including identifying the most common weed species and other pests and choosing optimal treatment methods. This requires you to know the species — and know which method actually works.
What are invasive species?
Invasive species are plants or animals that spread aggressively in nature and threaten the original, native biodiversity. In Denmark these include giant hogweed, Japanese knotweed, giant knotweed, Canadian goldenrod, Japanese rose and black cherry, which are designated as problematic and must be kept down. Japanese knotweed, giant knotweed and Bohemian knotweed have also been on the EU list of invasive species since 7-8-2025 (Implementing Regulation (EU) 2025/1422).
Giant hogweed — dangerous to touch
Glossy-leaved privet and other woody invasive species
Glossy-leaved privet is an invasive, woody species that tolerates both strong wind and drought and therefore spreads easily and threatens heaths, grassland and plantations. It is typically controlled by felling combined with milling, excavation or root removal — often over several years, because the species is hardy and readily regrows from roots.
Selection of control method
| Method | Usually used for |
|---|---|
| Manual excavation/root removal | Smaller populations, sensitive nature types |
| Mowing | Preventing seed setting, repeated continuously |
| Felling combined with milling | Tree-like species such as cherry laurel |
| Grazing | Large, open areas over time |
The choice of method depends on the species, how far it has spread, and what considerations there are for the location's other nature. Prevention and early action are usually both cheaper and more effective than waiting until a population is well established.
Damaging agents on the trees themselves
Beyond invasive plants, you also encounter pests that attack the trees themselves — insects and fungi that under the right conditions can weaken or kill forests. Being able to recognise the early signs and react quickly is an important part of daily forest monitoring.
“The best control is the one you deploy before the problem becomes big.”